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Versions: (draft-rajeshkumar-mmusic-sdp-atm) 00 01 02 03 04 RFC 3108

Internet Engineering Task Force
Internet Draft                                               Rajesh Kumar
Document: draft-ietf-mmusic-sdp-atm-04.txt                Mohamed Mostafa
January 9, 2001                                             Cisco Systems
Expires: July 9, 2001


     Conventions for the use of the Session Description Protocol (SDP)
                         for ATM Bearer Connections


STATUS OF THIS DOCUMENT


   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Drafts.

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   at any time.  It is inappropriate to use Internet- Drafts as
   reference material or to cite them other than as work in progress.

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

Abstract

   This document describes conventions for using the Session Description
   Protocol (SDP) described in RFC2327  [1] for controlling ATM Bearer
   Connections, and any associated ATM Adaptation Layer (AAL). The AALs
   addressed are Type 1, Type 2 and Type 5. This list of conventions is
   meant to be exhaustive. Individual applications can use subsets of
   these conventions. Further, these conventions are meant to comply
   strictly with the SDP syntax as defined in rfc2327.

1. Introduction...............................................................3
2. Representation of Certain Fields within SDP description lines..............4
 2.1  Representation of Extension Attributes.................................4
 2.2  Representation of Parameter Values.....................................5
 2.3  Directionality Convention..............................................5
 2.4 Case convention.........................................................7
 2.5 Use of special characters in SDP parameter values.......................7
3.  Capabilities Provided by SDP conventions..................................7



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4. Format of the ATM Session Description......................................9
5.  Structure of the Session Description Lines...............................11
 5.1 The Origin Line........................................................11
 5.2 The Session Name Line..................................................12
 5.3 The Connection Information Line........................................12
 5.4 The Timestamp Line.....................................................14
 5.5 Media Information Line for ATM connections.............................15
   5.5.1  The Virtual Connection ID.........................................15
   5.5.2  The Transport Parameter...........................................17
   5.5.3  The Format List for AAL1 and AAL5 applications....................19
   5.5.4  The Format List for AAL2 applications.............................19
   5.5.5  Media information line construction...............................19
 5.6 The Media Attribute Lines..............................................24
   5.6.1  ATM bearer connection attributes..................................25
   5.6.1.1  The 'eecid' attribute...........................................27
   5.6.1.2  The 'aalType' attribute.........................................28
   5.6.1.3  The 'capability' attribute......................................29
   5.6.1.4  The 'qosClass' attribute........................................30
   5.6.1.5  The 'bcob' attribute............................................30
   5.6.1.6  The 'stc' attribute.............................................31
   5.6.1.7  The 'upcc' attribute............................................31
   5.6.1.8  The 'atmQOSfparms' and 'atmQOSbparms' attributes................32
   5.6.1.9  The 'atmFtrfcDesc' and 'atmBtrfcDesc' attributes................33
   5.6.1.10 The 'abrFparms' and 'abrBparms' attributes......................35
   5.6.1.11 The 'abrSetup' attribute........................................36
   5.6.1.12 The 'bearerType' attribute......................................37
   5.6.1.13 The 'lij' attribute.............................................38
   5.6.1.14 The 'anycast' attribute.........................................38
   5.6.1.15 The 'cache' attribute...........................................39
   5.6.1.16 The 'bearerSigIE' attribute.....................................39
   5.6.2  ATM Adaptation Layer (AAL) attributes.............................40
   5.6.2.1  The 'aalApp' attribute..........................................41
   5.6.2.2  The 'cbrRate' attribute.........................................43
   5.6.2.3  The 'sbc' attribute.............................................44
   5.6.2.4  The 'clkrec' attribute..........................................45
   5.6.2.5  The 'fec' attribute.............................................46
   5.6.2.6  The 'prtfl' attribute...........................................46
   5.6.2.7  The 'structure' attribute.......................................47
   5.6.2.8  The 'fcpsSDUsize' and 'bcpsSDUsize' attributes..................47
   5.6.2.9  The 'aal2CPS' attribute.........................................48
   5.6.2.10 The 'aal2CPSSDUrate' attribute..................................48
   5.6.2.11 The 'aal2sscs3661unassured' attribute...........................48
   5.6.2.12 The 'aal2sscs3661assured' attribute.............................49
   5.6.2.13 The 'aal2sscs3662' attribute....................................50
   5.6.2.14 The 'aal5sscop' attribute.......................................52
   5.6.3  Service attributes................................................52
   5.6.3.1  The 'atmmap' attribute..........................................53
   5.6.3.2  The 'silenceSupp' attribute.....................................58
   5.6.3.3  The 'ecanf' and 'ecanb' attributes..............................59
   5.6.3.4  The 'gcf' and 'gcb' attributes..................................60
   5.6.3.5  The 'profileDesc' attribute.....................................60
   5.6.3.6  The 'vsel' attribute............................................62



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   5.6.3.7  The 'dsel' attribute............................................63
   5.6.3.8  The 'fsel' attribute............................................64
   5.6.3.9  The 'codecconfig' attribute.....................................66
   5.6.3.10 The 'isup_usi' attribute........................................66
   5.6.4   Miscellaneous media attributes...................................67
   5.6.4.1 The 'chain' attribute............................................67
   5.6.5   Use of the second media-level part in H.323 Annex C applications.68
   5.6.6   Use of the eecid media attribute in call establishment procedures 68
6.0   List of Parameters with  Representations...............................73
7.0   Examples of ATM session descriptions using SDP.........................82
8.0 Security Considerations..................................................83
 8.1  Bearer Security.......................................................83
 8.2  Security of the SDP description.......................................83
9.0  ATM SDP Grammar.........................................................84

1. Introduction

   SDP will be used in conjunction with a connection handling /device
   control protocol such as Megaco (H.248) [26], SIP [18] or  MGCP [25] to
   communicate the information  needed to set up ATM  and AAL2 bearer
   connections. These  connections include voice connections, voiceband data
   connections, clear channel circuit emulation connections, video connections
   and baseband data  connections (such as fax relay, modem relay, SSCOP,
   frame relay etc.).

   These conventions use standard SDP syntax as defined in rfc2327
   to describe the ATM-level and AAL-level connections, addresses and
   other parameters. In general, parameters associated with layers
   higher than the ATM adaptation layer are included only if they are
   tightly coupled to the ATM or AAL layers. Since the syntax conforms to
   rfc2327, standard SDP parsers should react in a well-defined and safe
   manner on receiving session descriptions based on the SDP conventions
   in this document. This is done by extending the values of fields  defined in
   rfc2327 rather than by defining new fields. This is true for all SDP lines
   except the of the media attribute  lines, in which case new
   attributes are defined. The SDP protocol allows the definition
   of new attributes in the media attribute  lines which are free-form.
   For the remaining lines, the fact that the <networkType> field in
   an  SDP descriptor is set to "ATM" should preclude the misinterpretation of
   extended parameter values by rfc2327-compliant SDP parsers.

   These conventions are meant to address the following ATM applications:

       1. Applications in which a new SVC is set-up for each service
          connection. These SVCs could be AAL1 or AAL5 SVCs or
          single-CID AAL2 SVCs.

       2. Applications in which existing  path  resources are assigned
          to service connections. These resources could be:

          *  AAL1/AAL5 PVCs, SPVCs or cached SVCs,
          *  AAL2 single-CID PVCs, SPVCs or cached SVCs,



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          *  CIDs within AAL2 SVCs/PVCs/SPVCs that multiplex multiple
             CIDs.

  Note that the  difference between PVCs and SPVCs is  in the way the bearer
  virtual circuit connection is set up. SPVCs are a class of PVCs that use
  bearer signaling, as opposed to node-by-node provisioning,  for connection
  establishment.

  This document is limited to the case when the network type is ATM.
  This includes raw RTP encapsulation [45] or voice sample encapsulation
  [46] over AAL5 with no intervening IP layer. It does not address SDP usage
  for IP, with or without ATM as a lower layer.

  In some cases, IP connection set-up is independent of lower layers, which
  are configured prior to it. For example, AAL5  PVCs that connect IP routers
  can be used for VoIP calls. In other cases,  VoIP call set-up is  closely
  tied to ATM-level  connection set-up. This might require a chaining of IP and
  ATM descriptors, as  described in section 5.6.4.1.

  This document makes no assumptions on who constructs the session
  descriptions (media gateway, intermediate ATM/AAL2 switch, media
  gateway controller etc.). This will be different in different
  applications. Further, it allows the use of one session description
  for both directions of a connection (as in SIP and MGCP applications)
  or the use of separate session descriptions for different directions. It
  also addresses the ATM multicast and anycast capabilities.

  This document makes no assumptions about how the SDP description will
  be coded. Although the descriptions shown here are encoded as text,
  alternate codings are possible:

  - Binary encoding such as ASN.1. This is an option (in addition to
    text encoding) in the Megaco context.

  - Use of extended ISUP parameters [36] to encode the information in
    SDP descriptors, with conversion to/from binary/text-based  SDP
    encoding when needed.

2. Representation of Certain Fields within SDP description lines

   This document conforms to the syntactic conventions of standard SDP as
   defined in RFC2327 [1].

2.1  Representation of Extension Attributes

   The SDP protocol [1] requires that non-standard attributes and codec
   names use an "X-" prefix.

   In this internet draft, the "X-" prefix is used consistently for
   codec names (Table 2) that have not been registered with the IANA.
   The IANA-registered codec names listed in [31] do not
   use this prefix, regardless of  whether they are statically or



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   dynamically assigned payload types.

   However, this prefix is not used for the extension SDP attributes
   defined in this document.  This has been done to enhance legibility.

   This document suggests that parsers be flexible in the use of the
   "X-" prefix convention. They  should accept codec names and attribute
   names with or without the "X-" prefix.

2.2  Representation of Parameter Values

    Depending on the format of their representation in SDP, the
    parameters defined in this document fall into the following
    classes:

    (1) Parameters always represented in a decimal format.
    (2) Parameters always represented in a hexadecimal format.
    (3) Parameters always represented as character strings.
    (4) Parameters that can be represented in either decimal or
        hexadecimal format.

    No prefixes are needed for classes 1 - 3, since the format is
    fixed.  For class 4, a "0x" prefix shall always be used to
    differentiate the hexadecimal from the decimal format.

    For both decimal and hex representations,  if the underlying bit field
    is smaller or larger than the binary equivalent of the SDP representation,
    then leading 0 bits should be added or removed as needed. Thus, 3 and
    0x3 translate  into the following five-bit pattern: 0 0011. The SDP
    representations 0x12 and 18 translate  into the following five-bit
    pattern: 1 0010.

    Leading 0 digits shall not be used in decimal representations.
    Generally, these are also not used in hexadecimal
    representations. Exceptions are when an exact number of hex digits
    is expected, as in the case of NSAP addresses. Parsers shall not
    reject leading zeros in hex values.

    Both single-character and multi-character string values are enclosed in
    double quotes (i.e. "). By contrast, single quotes (i.e. ') are used for
    emphasizing keywords rather than to refer to characters or strings.

    In the text representation of decimal and hex numbers, digits to the
    left are more significant than digits to the right.

2.3  Directionality Convention

    This section defined the meaning of the terms 'forward' and
    'backward' as used in this document. This is specially applicable
    to parameters that have a specific direction associated with them.

    In this document, 'forward' refers to the direction away from the



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    ATM node under consideration, while 'backward' refers to the direction
    towards the ATM node. This convention must be used in all SDP-based
    session descriptions regardless of whether underlying bearer is an SVC, a
    dynamically allocated PVC/SPVC or a dynamically allocated CID. This
    is regardless of which side originates the service connection. If ATM
    SVC or AAL2 Q.2630.1 signaling is used, the directionality convention
    is independent of which side originates the SVC or AAL2 connection.

    This provides a simple way of identifying the direction in which a
    parameter is applicable, in a manner that is independent of the
    underlying ATM or AAL2 bearer. This simplicity comes at a price,
    described below.

    The convention used by all ATM/AAL2 signaling specifications (e.g. Q.2931
    Section 1.3.3 and Q.2630.1) mandates that  forward direction is from the
    end initiating setup/establishment via bearer signaling towards the end
    receiving  the setup/establishment  request. The backward direction is in
    the opposite direction.  In some  cases, the 'forward' and 'backward'
    directions of the ATM signaling  convention might be the exact opposite of
    the SDP convention described  above, requiring the media gateway to perform
    the necessary translation. An example case in which this is needed is
    described below.

    Consider an SDP description sent by a media gateway  controller to the
    gateway originating a service-level call. In the backward SVC call set-up
    model, this gateway terminates (rather than originates) an SVC call. The
    media gateway refers to the traffic descriptor (and hence the PCR) in the
    direction  away from this gateway as the forward  traffic descriptor and
    forward PCR. Clearly, this is at odds with ATM SVC signaling which refers
    to this very PCR as the backward PCR. The gateway needs to be able to
    perform the required swap of directions. In this  example, the media
    gateway terminating the service level call (and hence originating the SVC
    call) does not need to perform this swap.

    Certain attributes are defined exclusively for the forward or  backward
    directions. Examples are the atmQOSfparms, atmFtrfcDesc, abrFparms and
    fcpsSDUsize for the forward direction, and atmQOSbparms, atmBtrfcDesc,
    abrBparms and  bcpsSDUsize for the backward direction. Certain parameters
    within attributes are defined exclusively for the forward or  backward
    directions. Examples for the forward direction are the <fsssar>
    subparameter within the 'aal2sscs3661unassured' media attribute line,
    the <fsssar>, <fsscopsdu> and <fsscopuu> subparameters within the
    'aal2sscs3661assured' media attribute line, the <fsscopsdu> and
    <fsscopuu> subparameters within the 'aal5sscop' media attribute line,
    and the <fmaxFrame> parameter within the 'aal2sscs3662' media attribute
    line. Examples for the backward direction are the <bsssar>
    subparameter within the 'aal2sscs3661unassured' media attribute line,
    the <bsssar>, <bsscopsdu> and <bsscopuu> subparameters within the
    'aal2sscs3661assured' media attribute line, the <bsscopsdu> and
    <bsscopuu> subparameters within the 'aal5sscop' media attribute line,
    and the <bmaxFrame> parameter within the 'aal2sscs3662' media attribute
    line.



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    For applications such as SIP, both the forward and backward attributes,
    and the forward and backward subparameters within attributes can be
    placed within the same SDP descriptor. In other applications
    (such as Megaco-based applications), the appropriate place for the
    forward attributes and subparameters within attributes is the remote
    descriptor, while the appropriate place for the backward
    attributes and subparameters within attributes is the local
    descriptor.

2.4 Case convention

    As defined in RFC2327 [1], SDP syntax is case-sensitive.  Since these ATM
    conventions conform strictly with SDP syntax, they are case-sensitive. SDP
    line types (e.g. "c", "m", "o", "a") and fields in the SDP lines should be
    built according to the case conventions in [1] and in this document. It is
    suggested, but not required, that SDP parsers for ATM applications be case-
    tolerant where ignoring case does not result in ambiguity.

2.5 Use of special characters in SDP parameter values

    In general, rfc2327-conformant string values of SDP parameters[1] do
    not include special characters that are neither alphabets nor
    digits. An exception is the "/"  character used in the value "RTP/AVP"
    of transport sub-field of the 'm' line.

    String values used in SDP descriptions of ATM connections retain this
    convention, while allowing the use of the special character "/" in a manner
    commensurate with [1]. In addition, the special characters "$" and "-" are
    used in the following manner. A "$" value is a wildcard that allows the
    recipient of the SDP description to select any permitted value of the
    parameter. A "-" value indicates that it is not necessary to specify the
    value of the parameter in the SDP description because this parameter is
    irrelevant for this application, or because its value can be
    known from another source such as provisioning, defaults, another
    protocol, another SDP descriptor or another part of the same SDP
    descriptor. If the use of these special characters is construed as a
    violation of rfc2327 [1] syntax, then reserved string values can be used.
    The string "CHOOSE" can be used in lieu of "$". The string "OMIT" can be
    used in lieu of "-" for an omitted parameter. A decision to use special
    characters or reserved keywords will be made before this internet draft
    is upgraded to an rfc.

3.  Capabilities Provided by SDP conventions

    To support the applications listed in section 1, the SDP conventions in
    this document provide the following session control capabilities:

        * Identification of the underlying bearer network type as ATM.

        * Identification by an ATM network element of its own address,
          in one of several possible formats. A connection peer can



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          initiate SVC set-up to this address. A call agent or connection
          peer can select an pre-established bearer path to this address.

        * Identification of the ATM bearer connection that is to be
          bound to the service-level connection. This is either
          a VCC in AAL1/AAL2/AAL5  applications or a channel (identified by
          a CID) in AAL2 applications.

        * Identification of media type: audio, video, data.

        * In AAL1/AAL5  applications, declaration of a set of payload
          types that can be bound to the ATM bearer connection.
          The encoding names and payload types defined for use in
          the RTP context [31] are  re-used for AAL1 and AAL5,
          if applicable.

        * In AAL2 applications, declaration of a set of profiles that
          can be bound to the ATM bearer connection. A mechanism for
          dynamically defining custom profiles within the SDP session
          description is included. This allows the use of custom
          profiles for connections that span multi-network interfaces.

        * A means of correlating service-level connections with
          underlying ATM bearer connections. The backbone network
          connection identifier or bnc-id specified in ITU Q.1901 [36]
          standardization work is used for this purpose. In order to
          provide a common SDP base for applications based on
          Q.1901 and SIP/SIP+, the neutral term 'eecid' is used
          in lieu of 'bnc-id' in the SDP session descriptor.

        * A means of  mapping codec types and packetization periods into
          service types (voice, voiceband data and facsimile). This is
          useful in determining the encoding to use when the connection is
          upspeeded in response to modem or facsimile tones.

        * A means of describing the adaptation type, QoS class, ATM transfer
          capability/service category, broadband bearer class, traffic
          parameters, CPS parameters and SSCS parameters related the underlying
          bearer connection.

       *  Means for enabling or describing special functions such as leaf-
          initiated-join, anycast and SVC caching.

       *  For H.323 Annex C applications, a  means of specifying the IP address
          and port number on which the node will receive RTCP messages.

       *  A means of chaining consecutive SDP descriptors so that they refer to
          different layers of the same connection.







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4. Format of the ATM Session Description

  The sequence of lines in the session descriptions in this document
  conforms to rfc2327 [1]. In general, a session description consists of
  a  session-level part followed by zero or more media-level parts. ATM
  session descriptions consist of a session-level part followed by one
  or two media-level parts. The only two media applicable are the ATM
  bearer medium and RTCP control (where applicable).


   The session level part consists of the following lines:

   v=  (protocol version, zero or one line)
   o=  (origin, zero or one line)
   s=  (session name, zero or one line)
   c=  (connection information, one line)
   b=  (bandwidth, zero or more lines)
   t=  (timestamp, zero or one line)
   k=  (encryption key, zero or one line)

   In ATM session descriptions, there are no media attribute lines in the
   session level part. These are present in the media-level parts.

   The media level part for the ATM bearer consists of the following
   lines:

   m=  (media information and transport address, one line)
   b=  (bandwidth, zero or more lines)
   k=  (encryption key, zero or more lines)
   a=  (media attribute, zero or more lines)

   The media level part for RTCP control consists of the following
   lines:

   m=  (media information and transport address, one line)
   c=  (connection information for control only, one line)

   In general, the 'v', 'o', 's', and 't' lines are mandatory.
   However, in the Megaco [26] context, these lines have been made optional.
   The 'o', 's', and 't' lines are omitted in most MGCP [25] applications.

   Note that SDP session descriptors for ATM can contain bandwidth (b=) and
   encryption key (k=) lines. Like all other lines, these lines should
   strictly conform to the SDP standard [1].

   The bandwidth (b=) line is not necessarily redundant in the ATM context
   since, in some applications, it can be used to convey application-level
   information which does not map directly into the atmFtrfcDesc and
   atmBtrfcDesc media attribute lines. For instance, the 'b' line can be used



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   in SDP descriptors in RTSP commands to describe content bandwidth.

   The   encryption key line (k=) can be used
   to indicate an encryption key for the bearer, and a method to
   obtain the key. At present, the encryption of ATM and AAL2 bearers
   has not been conventionalized, unlike the encryption of RTP payloads.
   Nor has the authentication or encryption of ATM or AAL2 bearer signaling.
   In the ATM and AAL2 contexts, the term 'bearer' can include 'bearer
   signaling'  as well as 'bearer payloads'.

   The order of lines in an ATM session description is exactly in the
   rfc2327-conformant order depicted above. However, there is no order
   of the media attribute ('a') lines with respect to other 'a' lines.

   The SDP protocol version for session descriptions using these
   conventions is 0. In conformance with standard SDP, it  is strongly
   recommended that the 'v' line be included at the beginning of each
   SDP session description. In some contexts such as Megaco, the
   'v' line is optional and may be omitted unless several session
   descriptions are provided in sequence, in which case the
   'v' line serves as a delimiter. Depending on the application,
   sequences of session descriptions might refer to:
   -  Different connections or sessions.
   -  Alternate ways of realizing the same connection or session.
   -  Different layers of the same session (section 5.6.4.1).

   The 'o', 's' and 't' lines are included for strict conformance with
   RFC2327. It is possible that these lines might not carry useful
   information in some ATM-based applications.
   Therefore, some applications might omit these lines, although
   it is recommended that they not do so.  For maximum
   interoperability, it is preferable that SDP parsers  not
   reject session descriptions that do not contain these lines.






















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5.  Structure of the Session Description Lines

5.1 The Origin Line

   The origin line for an ATM-based session is structured as follows:

         o=<username> <sessionID> <version> <networkType>
           <addressType> <address>

   The <username> is set to "-".

   The <sessionID> can be  set to one of the following:

      *   an NTP timestamp referring to the moment when the SDP session
          descriptor was created.
      *   a Call ID, connection ID or context ID that uniquely
          identifies the session within the scope of the ATM node.
          Since calls can comprise multiple connections (sessions),
          call IDs are generally not suitable for this purpose.

   NTP time stamps can be represented as decimal or hex integers.
   The part of the NTP timestamp that refers to an integer number
   of seconds is sufficient.  This is a 32-bit field

   On the other hand, call IDs, connection IDs and context IDs can be
   can be 32 hex digits long.

   The <sessionID> field is represented as a decimal or hex number of
   up to 32 digits. A "0x" prefix is used before the hex representation.

   The <version> refers to the version of the SDP session descriptor
   (not that of the SDP protocol). This is can be set to one of the
   following:

      * 0.
      * an NTP timestamp referring to the moment when the SDP session
        descriptor was modified. If the SDP session descriptor has not
        been modified by an intermediate entity (such as an MGC),
        then the <version> timestamp will be the same as the <sessionId>
        timestamp, if any. As with the <sessionId>, only the integer part
        of the NTP timestamp is used.

   When equated to the integer part of an NTP timestamp, the <version> field
   is 10 digits wide. This is more restricted than [1], which allows unlimited
   size. As in [1], the most significant digit is non-zero when an NTP
   timestamp is used.

   The <networkType> in  SDP  session descriptions for ATM applications
   should be assigned the string value "ATM" or wildcarded to a "$" or "-".

   The <addressType> and <address>  parameters are identical to
   those for the connection information ('c') line (Section 5.3). Each of



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   these parameters can be wildcarded per the conventions described
   for the 'c' line in Section 5.3. These parameters should not me omitted
   since this would violate SDP syntax [1].

   As with the 'c' line, SDP parsers are not expected to check the consistency
   of <networkType> with <addressType>, <address> pairs. The <addressType>
   and <address> need to be consistent with each other.
 5.2 The Session Name Line

   In general, the session name line  is structured as follows:

        s=<sessionName>

   For ATM-based  sessions, the <sessionName> parameter  is set to a   "-".
   The resulting line is:

        s=-

5.3 The Connection Information Line

   In general, the connection information line [1] is structured as follows:

        c=<networkType> <addressType> <address>

   For ATM networks, additional values of <networkType>, <addressType>
   and <address> are defined, over and above those listed in [1]. The
   ABNF syntax (Section 9) for ATM SDP does not limit the ways in which
   <networkType> can be combined with <addressType>,  <address> pairs.
   However, some combinations will not be valid in
   certain applications, while others will never be valid. Invalid
   combinations should be rejected by application-specific functions, and
   not by generic parsers. The ABNF syntax does limit the ways in which
   <addressType> and <address> can be paired.

   For ATM networks, the value of <networkType> should be set to "ATM".
   Further, this may be wildcarded to "$" or "-". If this is done, an
   node using ATM as the basic transport mechanism will select a
   value of "ATM". A node that interfaces with multiple network types
   ("IN", "ATM" etc.) that include ATM can also choose a value of "ATM".

   When the SDP description is built by a  node such as a media gateway,
   the <address> refers to the address of the node building the SDP
   description. When this description is forwarded to another node, it still
   contains the original node's address. When the media gateway
   controller builds part or all of the SDP description, the local descriptor
   contains the address of the local node, while the
   remote descriptor contains the address of the remote node.
   If the <address> and/or <addressType>  are irrelevant or are
   known by other means, they can be set to a "$" or a "-", as described
   below.

   Additionally, in all contexts, the 'm' line can have an ATM address in the



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   <virtualConnectionId> subparameter which, if present, is the
   remote address if  the 'c' line address is local, and vice versa.

   For ATM networks, the <addressType>  can be NSAP, E164 or GWID (ALIAS).
   For ATM networks, the <address>  syntax depends on the syntax of
   the <addressType>. SDP parsers should  check the consistency
   of <addressType> with <address>.

   NSAP: If the addressType is NSAP, the address is expressed in
   the standard dotted hex form. This is a string of 40 hex digits,
   with dots after the 2nd, 6th, 10th, 14th, 18th, 22nd, 26th, 30th,
   34th and 38th digits. The last octet of the NSAP address is the
   'selector' field that is available for non-standard use.  An example
   of a æcÆ line with an NSAP address is:

        c=ATM NSAP 47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00

   A "0x" prefix shall not be used in this case since this is always in
   hexadecimal format.

   E164: If the addressType is E164, the address is expressed as
   a decimal number  with up to 15 digits. For example:


        c=ATM E164 9738294382

  The use of E.164 numbers in the B-ISDN context is defined in ITU E.191.
  There is a disparity between the ATM forum and the ITU
  in the use of E.164 numbers for ATM addressing. The ATM forum (e.g. UNI
  Signaling 4.0) allows only International Format E.164 numbers, while
  the ITU (e.g. Q.2931) allows private numbering plans. Since the goal
  of this SDP specification is to interoperate with all bearer signaling
  protocols, it allows the use of numbers that do not conform to the
  E.164 International Format. However, to maximize overall consistency,
  network administrators can restrict the provisioning of numbers to the
  E.164 International Format.

   GWID (ALIAS): If the addressType is GWID meaning that the address is a
   Gateway Identifier or Node Alias. This may or may not be globally unique.
   In this case, the  address is expressed as alphanumeric string
   ("A"-"Z", "a"-"z", "0" - "9",".","-","_"). For example:

        c=ATM GWID officeABCmgx101vism12

   Since these SDP conventions can be used for more than gateways, the
   string "ALIAS" can be used instead of "GWID" in the 'c' line. Thus,
   the example above is equivalent to:

        c=ATM ALIAS officeABCmgx101vism12

   An example of a GWID (ALIAS)is the CLLI code used for telecom
   equipment. For all practical purposes, it should be adequate for the



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   GWID (ALIAS) to be a variable length string with a maximum size of 32
   characters.

   The connection information line is always present in an SDP session
   descriptor. However, each of the parameters on this line can be wildcarded
   to a "$" or a "-", independently of whether other parameters on this line
   are wildcarded or not. Not all syntactically legal wildcard combinations
   are meaningful in a particular application.

   Examples of meaningful wildcard combinations in the ATM context are:

        c=- - -
        c=$ $ $
        c=ATM - -
        c=ATM $ $
        c=ATM <addressType> -
        c=ATM <addressType> $

   Specifying the ATM address type without specifying the ATM address
   is useful when the recipient is asked to select an ATM address of
   a certain type (NSAP, E.164 etc.).

   Examples of syntactically legal wildcard combinations of dubious utility
   are:

        c=- $ -
        c=- $ $
        c=- <addressType> -
        c=$ <addressType> $
        c=- <addressType> <address>
        c=$ <addressType> <address>

   Note that <addressType> and/or  <address> should not omitted
   without being set to  a "-" or "$" since this would violate basic
   SDP syntax [1].

5.4 The Timestamp Line

   The timestamp line for an SDP session descriptor is structured as
   follows:

        t= <startTime> <stopTime>

   Per Ref. [49], NTP time stamps use  a 32 bit unsigned
   representation of seconds, and a 32 bit unsigned representation of
   fractional seconds. For ATM-based sessions, the  <startTime>parameter can
   be made equal to the NTP timestamp referring to the moment when
   the SDP session descriptor was created. It can also be set to 0
   indicating its irrelevance. If it made equal to the NTP
   timestamp in seconds, the fractional part of the NTP timestamp is omitted.
   When equated to the integer part of an NTP timestamp, the <startTime>
   field is 10 digits wide. This is more restricted than [1], which



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   allows unlimited size. As in [1], the most significant digit is
   non-zero when an NTP timestamp is used.

   The <stopTime> parameter is set to 0 for ATM-based SDP descriptors.

5.5 Media Information Line for ATM connections

    The general format of the media information line adapted for AAL1
    and AAL5 applications is:

    m=<media> <virtualConnectionId> <transport> <format list>

    The general format of the media information line adapted for AAL2
    applications is:

    m=<media> <virtualConnectionId> <transport#1> <format list#1>
              <transport#2> <format list#2> ... <transport#M> <format list#M>

    Note that <virtualConnectionId> is equivalent to  <port> in [1].

    The subparameter <media> can take on all the values defined in [1].
    These are: "audio", "video", "application", "data" and "control".

    When the <transport> parameter has more than one value in the 'm'
    line, the <transport> <format list> pairs can be arranged in
    preferential order.

5.5.1  The Virtual Connection ID

   The <virtualConnectionId> in AAL1 and AAL5  applications can be in
   one of the following formats:

        * <ex_vcci>
        * <addressType>-<address>/<ex_vcci>
        * <address>/<ex_vcci>
        * <ex_bcg>/<ex_vcci>
        * <ex_portId>/<ex_vpi>/<ex_vci>
        * <ex_bcg>/<ex_vpi>/<ex_vci>
        * <ex_vpci>/<ex_vci>
        * <addressType>-<address>/<ex_vpci>/<ex_vci>
        * <address>/<ex_vpci>/<ex_vci>

   The <virtualConnectionId> in AAL2  applications can be in one of the
   following formats:

        * <ex_vcci>/<ex_cid>
        * <addressType>-<address>/<ex_vcci>/<ex_cid>
        * <address>/<ex_vcci>/<ex_cid>
        * <ex_bcg>/<ex_vcci>/<ex_cid>
        * <ex_portId>/<ex_vpi>/<ex_vci>/<ex_cid>
        * <ex_bcg>/<ex_vpi>/<ex_vci>/<ex_cid>
        * <ex_vpci>/<ex_vci>/<ex_cid>



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        * <addressType>-<address>/<ex_vpci>/<ex_vci>/<ex_cid>
        * <address>/<ex_vpci>/<ex_vci>/<ex_cid>

   Here,
          <ex_vcci> = VCCI-<vcci>
          <ex_vpci> = VPCI-<vpci>
          <ex_bcg> = BCG-<bcg>
          <ex_portId> = PORT-<portId>
          <ex_vpi> = VPI-<vpi>
          <ex_vci> = VCI-<vci>
          <ex_cid> = CID-<cid>

   The <vcci>,  <vpi>, <vci>, <vpci> and <cid> are decimal numbers
   or hexadecimal numbers. An "0x" prefix is used before their values
   when they are in the hex format.

   The <portId> is always a hexadecimal number. An "0x" prefix is not used
   with it.

   The <addressType> and <address> are identical
   to their definitions above for the connection information line with
   the difference that this address refers to the remote peer in the
   media information line. Since the <virtualConnectionId>, as defined
   here, is meant for use in ATM networks, the values of <addressType>
   and <address> in the <virtualConnectionId> are limited to ATM-specific
   values.

   The <vpi>, <vci> and <cid> have their usual ATM connotation. The
   <vpi> is an 8 or 12 bit field. The <vci> is a 16-bit field. The <cid>
   is an 8-bit field.

   The <vpci> is a 16-bit field defined in Section 4.5.16 of ITU
   Q.2931 [Ref. 15]. The <vpci> is similar to the <vpi>,except for its
   width and the fact that it retains  its value across VP crossconnects.
   In some applications, the size of the <vpci>  is the same as the size of
   the <vpi> (8 or 12 bits). In this case, the most significant 8 or 4 bits
   are ignored.

   The <vcci> is a 16-bit field defined in ITU Recommendation Q.2941.2 [32].
   The <vcci> is similar to the <vci>, except for the fact that it retains
   its value across VC crossconnects.

   Since <vpci> and  <vcci> values are  unique between  a  pair of nodes, they
   need to be qualified, at any node, by the ATM address of the remote  node.
   These parameters can be pre-provisioned or signaled. When signaled, the
   <vpci> is encapsulated in the connection identifier information element of
   SVC signaling messages. The <vcci> is encapsulated in the Generic
   Information Transport (GIT) information element of  SVC signaling messages.
   In an ATM node pair, either node can assign <vcci> values and signal it to
   the other end via SVC signaling. A glare avoidance scheme is defined in [32]
   and [44].This mechanism works in SVC applications. A different glare
   avoidance technique is needed when a pool of existing PVCs/SPVCs is



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   dynamically assigned to calls. One such scheme for glare reduction is the
   assignment of <vcci> values from different ends of the <vcci> range, using
   the lowest or highest available value as applicable.

   When <vpci> and <vcci> values are pre-provisioned, administrations have the
   option of provisioning them uniquely in a network or in a subnet. In this
   case, the ATM address of the far end is not needed to qualify these
   parameters.

   In the AAL2 context, the definition of a VCC implies that there is no
   CID-level switching between its ends. If either end can assign <cid>
   values, then a glare reduction mechanism is needed. One such scheme for
   glare reduction is the assignment of <cid> values from different ends
   of the <cid> range, using the lowest or highest available value as
   applicable.

   The <portId> parameter is used to identify the physical trunk port
   on an  ATM module. It can be represented as a hexadecimal number of
   up to 32 hex digits.

   In some applications, it is meaningful to bundle  a set of connections
   between a pair of ATM nodes into a bearer connection group. The <bcg>
   subparameter is an eight bit field that allows the bundling of up
   to 255 VPCs or VCCs.

   In some applications, it is necessary to wildcard the <virtualConnectionId>
   parameter, or some elements of this parameter. The "$" wildcard character
   can be substituted for the entire <virtualConnectionId> parameter, or some
   of its terms. In the latter case, the constant strings that
   qualify the terms in the <virtualConnectionId> are retained. The
   concatenation <addressType>-<address> can be wildcarded in the
   following ways:
        * The entire concatenation, <addressType>-<address>, is
          replaced with a "$".
        * <address> is replaced with a "$", but <addressType> is
          not.

    Examples of wildcarding the <virtualConnectionId> in the AAL1 and AAL5
    contexts are: $, VCCI-$, BCG-100/VPI-20/VCI-$. Examples of
    wildcarding the <virtualConnectionId> in the AAL2 context are: $,
    VCCI-40/CID-$, BCG-100/VPI-20/VCI-120/CID-$, NSAP-$/VCCI-$/CID-$,
    $/VCCI-$/CID-$.

    It is also permissible to set the entire <virtualConnectionId> parameter
    to a "-" indicating its irrelevance.

5.5.2  The Transport Parameter

    The <transport> parameter indicates the method used to encapsulate the
    service payload. These methods are not defined in this document, which
    refers to existing ATMF and ITU-T standards, which, in turn, might
    refer to other standards. For ATM applications, the following



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    <transport> values are defined:

Table 1: List of Transport Parameter values used in SDP in the ATM context
   +---------------------------------------------------------------------+
   |                        |       Controlling Document for             |
   |   Transport            |    Encapsulation of Service Payload        |
   +------------------------+--------------------------------------------+
   |    AAL1/ATMF           |          af-vtoa-0078.000 [7]              |
   +------------------------+--------------------------------------------+
   |    AAL1/ITU            |          ITU-T H.222.1 [51]                |
   +------------------------+--------------------------------------------+
   |    AAL5/ATMF           |          af-vtoa-0083.000 [46]             |
   +------------------------+--------------------------------------------+
   |    AAL5/ITU            |          ITU-T H.222.1 [51]                |
   +------------------------+--------------------------------------------+
   |    AAL2/ATMF           |          af-vtoa-0113.000 [44]  and        |
   |                        |          af-vmoa-0145.000 [52]             |
   +------------------------+--------------------------------------------+
   |    AAL2/ITU            |          ITU-T I.366.2 [13]                |
   +------------------------+--------------------------------------------+
   |    AAL1/custom         |         Corporate document or              |
   |    AAL2/custom         |   application-specific interoperability    |
   |    AAL5/custom         |              statement.                    |
   +------------------------+--------------------------------------------+
   |  AAL1/<corporateName>  |                                            |
   |  AAL2/<corporateName>  |                                            |
   |  AAL5/<corporateName>  |                                            |
   |  AAL1/IEEE:<oui>       |          Corporate document                |
   |  AAL2/IEEE:<oui>       |                                            |
   |  AAL5/IEEE:<oui>       |                                            |
   +------------------------+--------------------------------------------+
   |     RTP/AVP            |          Annex C of H.323 [45]             |
   +------------------------+--------------------------------------------+

    In H.323 Annex C applications [45], the <transport> parameter has a
    value of "RTP/AVP". This is because these applications use the RTP
    protocol [2] and audio/video profile [3]. The fact that RTP is carried
    directly over AAL5 per [45] can be indicated explicitly via the aalApp
    media attribute.

    A value of "AAL1/custom", "AAL2/custom" or "AAL5/custom"  for the
    <transport> parameter can indicate non-standard or semi-standard
    encapsulation schemes defined by a corporation or a multi-vendor
    agreement. Since there is no standard administration of this
    convention, care should be taken to preclude inconsistencies
    within the scope of a deployment.

    The use of <transport> values "AAL1/<corporateName>",
    "AAL2/<corporateName>", "AAL5/<corporateName>", "AAL1/IEEE:<oui>",
    "AAL2/IEEE:<oui>" and "AAL5/IEEE:<oui>" is similar. These indicate
    non-standard transport mechanisms or AAL2 profiles which should
    be used consistently within the scope of an application or deployment.



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    The parameter <corporateName> is the registered, globally unique name
    of a corporation(e.g. Cisco, Telcordia etc.). The parameter <oui>
    is the hex representation of a three-octet field identical to the OUI
    maintained by the IEEE. Since this is always represented in hex,  the "0x"
    prefix shall not be used. Leading zeros can be omitted. For
    example, "IEEE:00000C" and "IEEE:C" both refer to
    Cisco Systems, Inc.

5.5.3  The Format List for AAL1 and AAL5 applications

    In the AAL1 and AAL5 contexts, the <format list> is a list of payload
    types:

        <payloadType#1> <payloadType#2>...<payloadType#n>

   In most AAL1 and AAL5  applications, the ordering  of payload types
   implies a preference (preferred payload types before less favored
   ones).  The payload type can be statically assigned  or dynamically
   mapped. Although the transport is not the same, SDP in the ATM
   context leverages the encoding names and payload types registered
   with IANA [31] for RTP. Encoding names not listed in [31] use a "X-"
   prefix. Encodings that are not statically mapped to payload types in
   [31] are to be dynamically mapped at the time of connection
   establishment to  payload types in the decimal  range 96-127.
   The SDP 'atmmap' attribute (similar to 'rtpmap') is used for this
   purpose.

   In addition to listing the IANA-registered encoding names and
   payload types found in [31], Table 2 defines a few
   non-standard encoding names(with "X-" prefixes).

5.5.4  The Format List for AAL2 applications

    In the AAL2 context, the <format list> is a list of AAL2 profile
    types:

        <profile#1> <profile#2>...<profile#n>

   In most applications, the ordering  of profiles implies
   a preference (preferred profiles before less favored ones).
   The <profile> parameter is expressed as a decimal number in the
   range 1-255.

5.5.5  Media information line construction

   Using the parameter definitions above, the 'm' for AAL1-based audio
   media can be constructed as follows:

      m=audio <virtualConnectionId> AAL1/ATMF  <payloadType#1>
                <payloadType#2>...<payloadType #n>





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    Note that only those payload types, whether statically mapped or
    dynamically assigned, that are consistent with af-vtoa-78 [7] can be used
    in this construction.

    Backwards compatibility note: The transport value  "AAL1/AVP" used in
    previous versions of this document should be considered equivalent to
    the value "AAL1/ATMF" defined above. "AAL1/AVP" is unsuitable because
    the AVP profile is closely tied to RTP.

    An example 'm' line use for audio media over AAL1 is:

        m=audio VCCI-27 AAL1/ATMF 0

    This indicates the use of an AAL1 VCC with VCCI=24  to carry PCMU audio
    that is encapsulated according to ATMF's af-vtoa-78 [7].

    Another example of the use of the 'm' line use for audio media over AAL1
    is:

         m=audio $  AAL1/ATMF 0 8

   This indicates that any AAL1 VCC may be used. If it exists already, then
   its selection is subject to glare rules.  The audio media on this VCC
   is encapsulated according to ATMF's af-vtoa-78 [7]. The encodings to be
   used are either PCMU or PCMA, in preferential order.

   The 'm' for AAL5-based audio media can be constructed as
   follows:

      m=audio <virtualConnectionId> AAL5/ATMF  <payloadType#1>
                <payloadType#2>...<payloadType #n>

    An example 'm' line use for audio media over AAL5  is:

            m=audio PORT-2/VPI-6/$  AAL5/ITU  9  15

   implies that any VCI on VPI= 6 of trunk port #2 may be used. The identities
   of the terms in the virtual connection ID are implicit in the application
   context. The audio media on this VCC is encapsulated according to ITU-T
   H.222.1 [51]. The encodings to be  used are either ITU-T G.722  or ITU-T
   G.728 (LD-CELP), in preferential order.

   The 'm' for AAL5-based H.323 Annex C audio [45] can be constructed as
   follows:

     m=audio <virtualConnectionId> RTP/AVP <payloadType#1>
                   <payloadType#2>...<payloadType #n>
    For example:

          m=audio PORT-9/VPI-3/VCI-$  RTP/AVP 2 96
          a=rtpmap:96 X-G727-32
          a=aalType:AAL5



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          a=aalApp:itu_h323c - -

   implies that any VCI on VPI= 3 of trunk port #9 may be used. This VC
   encapsulates RTP packets directly on AAL5 per [45]. The 'rtpmap' (rather
   than the 'atmmap') attribute is used to dynamically map the payload type
   of 96 into the codec name X-G727-32 (Table 2). This name represents 32
   kbps EADPCM.

   The 'm' line for AAL5-based video media can be constructed as follows:

      m=video <virtualConnectionId> AAL5/ITU  <payloadType#1>
                <payloadType#2>...<payloadType #n>

    In this case, the use of AAL5/ITU as the transport points to H.222.1
    as the controlling standard [51]. An example 'm' line use for video media
    is:

              m=video PORT-9/VPI-3/VCI-$  AAL5/ITU  33

    This indicates that any VCI on VPI= 3 of trunk port #9 may be used.
    The video media on this VCC is encapsulated according to ITU-T
    H.222.1 [51]. The encoding scheme is an MPEG 2 transport stream ("MP2T"
    in Table 1). This is  statically  mapped per [31] to a payload type of 33.

   Using the parameter definitions in the previous subsections, the media
   information line for AAL2-based audio media can be constructed as follows:

      m=<media> <virtualConnectionId> <transport#1> <format list#1>
              <transport#2> <format list#2> ... <transport#M> <format list#M>

      where <format list#i> has the form <profile#i_1>...<profile#i_N>


   Unlike the 'm' line for AAL1 or AAL5 applications, the 'm' line for AAL2
   applications can have multiple <transport> parameters, each followed by
   a <format list>. This is because it is possible to consider definitions
   from multiple sources (ATMF, ITU and non-standard documents) when selecting
   AAL2 profile to be bound to a connection.

   In most applications, the ordering  of profiles implies a preference
   (preferred profiles before less favored ones). Therefore, there can be
   multiple instances of the same <transport> value in the same 'm' line.

   An example 'm' line use for audio media over AAL2  is:

        m=audio VCCI-27/CID-19 AAL2/ITU 7 AAL2/custom 100 AAL2/ITU 1

   This indicates the use of CID #19 on VCCI #27 to carry audio. It provides
   a preferential list of profiles for this connection: profile  AAL2/ITU 7
   defined in [13], AAL2/custom 100 defined in an application-specific or
   interoperability document and profile AAL2/ITU 1 defined in [13].




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   Another example of the use of the 'm' line use for audio media over AAL2
   is:

         m=audio VCCI-$/CID-$  AAL2/ATMF 6 8

   This indicates that any AAL2 CID  may be used, subject to any applicable
   glare avoidance/reduction rules. The profiles that can be bound to this
   connection are AAL2/ATMF 6 defined in af-vtoa-0113.000 [44] and AAL2/ATMF 8
   defined in af-vmoa-0145.000 [52]. These sources use non-overlapping
   profile number ranges. The profiles they define fall under the <transport>
   category "AAL2/ATMF". This application does not order profiles
   preferentially. This rule is known a priori. It is not embedded in the 'm'
   line.

   Another example of the use of the 'm' line use for audio media over AAL2
   is:

         m=audio VCCI-20/CID-$  AAL2/xyzCorporation 11

   AAL2 VCCs in this application are single-CID VCCs. Therefore, it is possible
   to wildcard the CID. The single-CID VCC with VCCI=20 is selected. The AAL2
   profile to be used is AAL2/xyzCorporation 11 defined by xyzCorporation.

   In some applications, an "-" can be used in lieu of:
   - <format list>
   - <transport> and <format list>

   This implies that these parameters are irrelevant or are known by
   other means (such as defaults). For example:

         m=audio VCCI-234 - -
         a=aalType:AAL1

   indicates the use of VCCI=234 with AAL1 adaptation and unspecified encoding.

   In another example application, the'aal2sscs3662' attribute  can indicate
   <faxDemod> = "on" and any other competing options as "off", and the
   <aalType> attribute can indicate AAL2. Thus:

      m=audio VCCI-123/CID-5 - -
      a=aalType:AAL2
      a=aal2sscs3662:audio off off on off on off off off - - -

   Besides indicating an audio medium, a VCCI of 123 and a CID of 5,
   the 'm' line indicates an unspecified profile.  The media attribute lines
   indicate an adaptation layer of AAL2, and the use of the audio SAP [13]
   to carry demodulated facsimile.

   The media information line for "data" media has one of the following
   the following formats:

     m=data <virtualConnectionId> - -



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     m=data - - -

   The data could be circuit emulation data carried over AAL1 or AAL2,
   or packet data carried over AAL5. Media attribute lines, rather  than
   the 'm' line, are used to indicate the adaptation type for the data
   media. Examples of the representation of data media are listed below.

        m=data  PORT-7/VPI-6/VCI-$  - -
        a=aalApp:AAL5_SSCOP-                             -

   implies that any VCI on VPI= 6 of trunk port #7 may be used. This VC
   uses SSCOP on AAL5 to transport data.

        m=data  PORT-7/VPI-6/VCI-50  - -
        a=aalType:AAL1_SDT
        a=sbc:6

   implies that VCI 50 on VPI 6 on port 7 uses structured AAL1 to transfer
   6 x 64 kbps circuit emulation data. This may be alternately represented
   as:

        m=data  PORT-7/VPI-6/VCI-50  - -
        b=AS:384
        a=aalType:AAL1_SDT

   The following lines:

      m=data VCCI-123/CID-5 - -
      a=aalType:AAL2
      a=sbc:2

   imply that CID 5 of VCCI 123 is used to transfer 2 x 64 kbps
   circuit emulation data.

   In the AAL1 context, it is also permissible to represent circuit
   mode data as an "audio" codec. If this is done, the codec types used
   are X-CCD or  X-CCD-CAS. These encoding names are dynamically
   mapped into payload types through the 'atmmap' attribute. For example:

              m=audio VCCI-27 AAL1/AVP 98
              a=atmmap:98 X-CCD
              a=sbc:6

   implies that AAL1 VCCI=27 is used for 6 x 64 transmission.

   In the AAL2 context,   the X-CCD codec  can  be assigned a profile
   type  and number. Even though it is not possible to construct
   a profile table  as described in ITU I.366.2  for this "codec",
   it is preferable to adopt the common AAL2 profile convention in its
   case. An example AAL2 profile mapping  for the X-CCD codec could
   be as follows:




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        PROFILE TYPE         PROFILE NUMBER        "CODEC" (ONLY ONE)
          "custom"                200                     X-CCD


   The profile does not identify the number of subchannels ('n' in nx64).
   This is known by other means such as the 'sbc' media attribute line.

   For example, the media information line:
          m=audio $ AAL2/custom 200
          a=sbc:6

   implies 384 kbps circuit emulation using AAL2 adaptation.

   It is not necessary to define a profile with the X-CCD-CAS codec, since
   this method of CAS transport [7] is not used in AAL2 applications.

5.6 The Media Attribute Lines

   In an SDP  line sequence, the media information line 'm'  is
   followed by one or more media attribute or 'a'  lines. Media
   attribute lines are per the format below:

       a=<attribute>:<value>

   or

       a=<value>

   In general, media attribute lines are optional except when needed to
   qualify the media information line. This qualification is necessary
   when the "m" line for an AAL1 or AAL5 session specifies a payload
   type that needs to be dynamically mapped. The 'atmmap' media
   attribute line defined below is used for this purpose.

   In attribute lines, subparameters that are meant to be left
   unspecified are set to a "-". These are generally inapplicable or, if
   applicable, are known by other means such as provisioning. In some
   cases, a media attribute line with all parameters set to "-" carries
   no information and should be preferably omitted. In other cases,
   such as the 'lij' media attribute line, the very presence of the
   media attribute line conveys meaning.

   There are no restrictions placed by rfc2327 [1] regarding the order
   of 'a' lines with respect to other 'a' lines. However, these lines
   must not contradict each other or the other SDP lines. Inconsistencies
   are not to be ignored and should be flagged as errors. Repeated media
   attribute lines can carry additional information.  These should not
   be inconsistent with each other.

   Applications will selectively use the optional media attribute
   lines listed below. This is meant to be an exhaustive list for
   describing the general attributes of ATM bearer networks.



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  The base specification for SDP, rfc2327 [1], allows the definition
  of new attributes. In keeping with this spirit, some of the attributes
  defined in this document can also be used in SDP descriptions of IP
  and other non-ATM sessions. For example, the 'vsel', 'dsel' and 'fsel'
  attributes defined below refer generically to codecs. These can be
  used for service-specific codec negotiation and assignment in non-ATM
  as well as ATM applications.

   SDP media  attributes defined in this document for use in the ATM
   context are classified as:

      * ATM bearer connection attributes (Section 5.6.1)
      * AAL attributes (Section 5.6.2)
      * Service attributes (Section 5.6.3).
      * Miscellaneous media attributes, that cannot be classified as
        ATM, AAL or service attributes (Section 5.6.4).

  In addition to these,  the SDP attributes defined in [1] can also
  be used in the ATM context. Examples are:

        * The attributes defined in RFC2327 which allow indication of
          the direction in which a session is active. These are
          a=sendonly, a=recvonly, a=sendrecv, a=inactive.

        * The 'Ptime' attribute defined in RFC2327. It indicates the
          packet period. It is not recommended that this attribute be used
          in ATM applications since packet period information is provided with
          other parameters e.g. the profile type and number in the 'm' line,
          and the 'vsel', 'dsel' and 'fsel' attributes. Also, for AAL1
          applications, 'ptime' is not applicable and should be flagged as an
          error. If used in AAL2 and AAL5 applications, 'ptime' should be
          consistent with the rest of the SDP description.

        * The 'fmtp'  attribute used to designate format-specific
          parameters.

  5.6.1  ATM bearer connection attributes

   The following is a summary list of the SDP media attributes that can
   be used to describe ATM bearer connections. These are detailed in
   subsequent subsections.

        * The 'eecid' attribute. This stands for 'end-to-end connection
          identifier'. It provides a  means of  correlating service-level
          connections with underlying ATM bearer connections.
          In the Q.1901 [36] context, the eecid is synonymous with the
          bnc-id (backbone network connection identifier).

        * The 'aalType' attribute. This is used to indicate the nature
          of the ATM adaptation layer (AAL).




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        * The 'capability' attribute, which indicates the ATM transfer
          capability (ITU nomenclature), synonymous with the ATM Service
          Category (ATMF nomenclature).

        * The 'qosClass' attribute, which indicates the QoS class of the
          ATM bearer connection.

        * The 'bcob' attribute, which indicates the broadband connection
          oriented bearer class, and whether end-to-end timing is
          required.

        * The   'stc' attribute, which indicates susceptibility to
          clipping.

        * The   'upcc' attribute, which indicates the  user plane connection
          configuration.

        * The 'atmQOSfparms' and 'atmQOSbparms' attributes, which are
          used to describe certain key ATM QoS parameters in the forward
          and backward directions respectively.

        * The 'atmFtrfcDesc' and 'atmBtrfcDesc' attributes, which are
          used to describe  ATM traffic descriptor parameters in the
          forward and backward directions respectively.

        * The 'abrFparms' and 'abrBparms' attributes, which are
          used to describe  ABR-specific parameters in the
          forward and backward directions respectively. These parameters
          are per the UNI 4.0 signaling  specification [5].

        * The 'abrSetup' attribute, which is used to indicate the
          ABR parameters needed during call/connection establishment.

        * The 'bearerType' attribute, which is used to indicate
          whether the underlying bearer is an ATM PVC/SPVC, an ATM SVC,
          or an AAL2 CID connection within an existing ATM SVC/PVC/SPVC.

        * The 'lij' attribute, which is used to indicate the
          presence of a connection that uses the Leaf-initiated-join
          capability described in UNI 4.0 [5], and to optionally
          describe parameters associated with this capability.

        * The 'anycast' attribute, which is used to
          indicate the applicability of the anycast function described
          in UNI 4.0 [5], and to optionally qualify it with certain
          parameters.

        * The 'cache' attribute, which is used to enable
          SVC caching and to specify an inactivity timer for SVC release.

        * The 'bearerSigIE' attribute, which can be used to represent
          ITU Q-series information elements in bit-map form. This is useful



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          in describing parameters that are not closely coupled to the
          ATM and AAL layers. Examples are the B-HLI and B-LLI IEs specified
          in ITU Q.2931 [15], and the user-to-user information
          element described in ITU Q.2957 [48].

5.6.1.1  The 'eecid' attribute

   The 'eecid' attribute is synonymous with the 4-byte'bnc-id'
   parameter used  by T1SI, the ATM forum and the ITU (Q.1901)
   standardization effort. The term 'eecid' stands for 'end-to-end
   connection identifier', while 'bnc-id' stands for 'backbone network
   connection identifier'.  The name "backbone" is slightly misleading
   since it refers to the entire ATM network including the ATM edge and
   ATM core networks. In   Q.1901 terminology, an ATM "backbone"
   connects TDM or analog edges.

   While the term 'bnc-id' might be used in the bearer signaling plane
   and in an ISUP (Q.1901) call control plane,   SDP session descriptors
   use the neutral term 'eecid'. This provides a common SDP baseline
   for applications that use ISUP (Q.1901) and applications that use
   SIP/SIP+.

   Section 5.6.6 depicts the use of the eecid in call establishment
   procedures. In these procedures, the eecid is used to correlate
   service-level calls with SVC set-up requests.

   In the  forward SVC establishment model, the call-terminating gateway
   selects an eecid and transmits it via SDP to the call-originating
   gateway. The call originating gateway transmits this eecid to the
   call terminating gateway via the bearer set-up message (SVC set-up
   or Q.2630.1 establish request).

   In the  backward SVC establishment model, the call-originating gateway
   selects an eecid and transmits it via SDP to the call-terminating
   gateway. The call terminating gateway transmits this eecid to the
   call originating gateway via the bearer set-up message (SVC set-up
   or Q.2630.1 establish request).

   The value of the eecid attribute  values needs to be unique within
   the node terminating the SVC set-up but not across multiple
   nodes.  Hence, the SVC-terminating gateway has complete control
   over using and releasing values of this  parameter. The eecid
   attribute is used to  correlate, one-to-one, received bearer set-up
   requests with service-level call control signaling.

   Within an SDP session description, the eecid attribute is used as
   follows:

            a=eecid:<eecid>


  where <eecid> consists of up to 8 hex digits (equivalent to 4



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  octets). Since this is always represented in hex,  the "0x"
  prefix shall  not be used.

  Within the text representation of the <eecid> parameter, hex digits
  to the left are more significant than hex digits to the right
  (Section 2.2).

  This SDP document does not specify how the eecid (synonymous
  with bnc-id) is to be communicated through bearer signaling
  (Q.931, UNI, PNNI, AINI, IISP, proprietary signaling equivalent,
  Q.2630.1). This is a task of these bearer signaling protocols.
  However, the following informative statements are made to
  convey a sense of the interoperability that is a goal of
  current standardization efforts:

  -  ITU Q.2941.3 and the ATMF each recommend the use of the
     GIT IE for carrying the eecid (synonymous with bnc-id)
     in the set-up message of  ATM signaling protocols (Q.2931,
     UNI 4.0, PNNI, AINI, IISP). The coding for carrying the eecid (bnc-id)
     in the GIT IE is defined in ITU Q.2941.3 and accepted by the ATM forum.

 -   Another alternate method is to use the called party
     subaddress IE. In some networks, this might be considered
     a protocol violation and is not the recommended means of carrying
     the eecid (bnc-id). The GIT IE is the preferred method of
     transporting the eecid (bnc-id) in ATM signaling messages.

-    The establish request (ERQ) message of the Q.2630.1 [37]
     signaling protocol can use the  SUGR (Served User Generated
     Reference)  IE to transport the eecid (bnc-id).

   The node assigning the eecid can release and re-use it when it
   receives a Q.2931 [15] set-up  message or a Q.2630.1 [37]
   establish request message containing the eecid.

   However, in both cases (backward and forward models),
   it is recommended that this eecid be retained until the connection
   terminates. Since the eecid space is large enough, it is not
   necessary to release it as soon as possible.

5.6.1.2  The 'aalType' attribute

   When present, the 'aalType' attribute is used to indicate
   the ATM adaptation layer. If  this information is redundant
   with the 'm' line, it can be omitted. The format of the
   'aalType' media attribute line is as follows:

   a=aalType: <aalType>

   Here, <aalType> can take on the following string values:
   "AAL1", "AAL1_SDT", "AAL1_UDT", "AAL2", "AAL3/4", "AAL5"
   and "USER_DEFINED_AAL". Note that "AAL3/4" and "USER DEFINED AAL"



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   are not addressed in this document.

5.6.1.3  The 'capability' attribute

   When present, the 'capability' attribute indicates the ATM Transfer
   Capability described in ITU I.371 [28], equivalent to the ATM Service
   Category described in the UNI 4.1 Traffic Management specification [6].

   The  'capability' media attribute line is structured in one of
   the following ways:

       a=capability:<asc> <subtype>

       a=capability:<atc> <subtype>

   Possible values of the <asc> are enumerated below:

       "CBR", "nrt-VBR", "rt-VBR", "UBR", "ABR", "GFR"

   Possible values of the <atc> are enumerated below:

       "DBR","SBR","ABT/IT","ABT/DT","ABR"

   Some applications might use non-standard <atc> and <asc> values not
   listed above. Equipment designers will need to agree on the meaning and
   implications of non-standard transfer capabilities / service capabilities.

   The <subtype> field essentially serves as a subscript to the <asc>
   and <atc> fields. In general, it can take on any integer value, or the
   "-" value indicating that it does not apply or that the underlying data is
   to be known  by other means, such as provisioning.

   For an <asc> value of CBR and an <atc> value of DBR, the <subtype>
   field can be assigned values from Table 4-6 of ITU Q.2931 [15]. These are:

    <asc>/<atc>    <subtype>   Meaning

     "CBR"/"DBR"      1        Voiceband signal transport
                               (ITU G.711, G.722, I.363)
     "CBR"/"DBR"      2        Circuit transport (ITU I.363)
     "CBR"/"DBR"      4        High-quality audio signal transport
                               (ITU I.363)
     "CBR"/"DBR"      5        Video signal transport (ITU I.363)

   Note that [15] does not define a <subtype> value of 3.

   For other values of the <asc> and <atc> parameters, the following
   values can be assigned to the <subtype> field, based on [6] and [28].







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            <asc>/<atc>              <subtype>     Meaning

              nrt-VBR                   1          nrt-VBR.1
              nrt-VBR                   2          nrt-VBR.2
              nrt-VBR                   3          nrt-VBR.3
              rt-VBR                    1          rt-VBR.1
              rt-VBR                    2          rt-VBR.2
              rt-VBR                    3          rt-VBR.3
              UBR                       1          UBR.1
              UBR                       2          UBR.2
              GFR                       1          GFR.1
              GFR                       2          GRR.2
              SBR                       1          SBR1
              SBR                       2          SBR2
              SBR                       3          SBR3

   It is beyond the scope of this specification to examine the
   equivalence of some of the ATMF and ITU definitions. These need to
   be recognized from the ATMF and ITU source specifications and exploited,
   as much as possible, to simplify ATM node design.

   When the bearer connection is a single AAL2 CID connection within a
   multiplexed AAL2 VC, the 'capability' attribute does not apply.


5.6.1.4  The 'qosClass' attribute

   When present, the   'qosClass' attribute indicates the QoS class
   specified in ITU I.2965.1 [34].

   The  'qosClass' media attribute line is structured as follows:

       a=qosClass:<qosClass>

   Here, <qosClass> is an integer in the range 0 - 5.

      <qosClass>      Meaning

           0            Default QoS
           1            Stringent
           2            Tolerant
           3            Bi-level
           4            Unbounded
           5            Stringent bi-level

5.6.1.5  The 'bcob' attribute

   When present, the   'bcob' attribute represents the broadband
   connection oriented bearer class defined in [5], [15]
   and [33]. It can also be used to indicate whether end-to-end
   timing is required.




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   The 'bcob' media attribute line is structured as follows:

       a=bcob:<bcob> <eetim>

   Here, <bcob> is the decimal or hex representation of a 5-bit field.
   Currently, all values are unused and reserved with the following
   exceptions:

        <bcob>          Meaning

        0x01             BCOB-A
        0x03             BCOB-C
        0x05             Frame relaying bearer service
        0x10             BCOB-X
        0x18             BCOB-VP (transparent VP service)



   The <eetim> parameter can be assigned a value of "on" or "off"
   depending on whether end-to-end timing is required or not (Table
   4-8 of [15]).

   Either of these parameters can be left unspecified by setting it
   to a "-". A 'bcob' media attribute line with all parameters set to
   "-" carries no information and should be omitted.

5.6.1.6  The 'stc' attribute

   When present, the   'stc' attribute represents susceptibility
   to clipping. The 'stc' media attribute line is structured as
   follows:

       a=stc:<stc>

   Here, <stc> is the decimal equivalent of a 2-bit field. Currently,
   all values are  unused and reserved with the following exceptions:

      <stc> value      Binary Equivalent     Meaning

           0                   00            Not susceptible to clipping
           1                   01            Susceptible to clipping

5.6.1.7  The 'upcc' attribute

   When present, the   'upcc' attribute represents the user plane
   connection configuration. The 'upcc' media attribute line is
   structured as follows:

       a=upcc:<upcc>

   Here, <upcc> is the decimal equivalent of a 2-bit field. Currently,
   all values are  unused and reserved with the following exceptions:



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      <upcc> value     Binary Equivalent    Meaning

           0                 00             Point to point
           1                 01             Point to multipoint


5.6.1.8  The 'atmQOSfparms' and 'atmQOSbparms' attributes

   When present, the 'atmQOSfparms' and 'atmQOSbparms'
   attributes are  used to describe certain key ATM QoS parameters
   in the forward and backward directions respectively. See Section
   2.3 for a definition of the terms 'forward' and 'backward'.

   The 'atmQOSfparms' and 'atmQOSbparms' media attribute lines
   are structured as follows:

   a=atmQOSfparms: <cdvType><acdv><ccdv><eetd><cmtd><aclr>
   a=atmQOSbparms: <cdvType><acdv><ccdv><eetd><cmtd><aclr>

   The <cdvType> parameter can take on the string values of
   "PP" and "2P". These refer to the peak-to-peak and two-point
   CDV as defined in UNI 4.0 [5] and ITU Q.2965.2 [35] respectively.

   The CDV parameters, <acdv> and <ccdv>, refer to  the acceptable
   and cumulative  CDVs respectively. These are expressed in units
   of microseconds and represented as the decimal  equivalent
   of a 24-bit field.  These use the cell loss ratio, <aclr>, as the
   "alpha" quantiles defined in the ATMF TM 4.1 specification [6]
   and in ITU I.356 [47].

   The transit delay  parameters, <eetd> and <cmtd>,  refer to the
   end-to-end and cumulative  transit delays respectively in
   milliseconds. These are represented as the decimal equivalents
   of  16-bit fields. These parameters are defined in Q.2965.2 [35],
   UNI 4.0 [5] and Q.2931 [15].

   The <aclr> parameter refers to  forward and backward acceptable
   cell loss ratios. This is the ratio between the number of cells
   lost and the number of cells transmitted. It is expressed as the decimal
   equivalent of an 8-bit field. This field expresses an order of
   magnitude n, where n is an integer in the range 1-15. The Cell Loss
   Ratio takes on the value 10 raised to the power of minus n.

   If any of these parameters is not specified, is inapplicable or is
   implied, then it is set to   "-".

   An example use of these  attributes for an  rt-VBR, single-CID AAL2
   voice VC is:

        a=atmQOSfparms:pp  8125 3455 32000 -  11
        a=atmQOSbparms:pp  4675 2155 18000 -  12



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   This implies a forward acceptable peak-to-peak CDV of 8.125 ms, a
   backward acceptable peak-to-peak CDV of 4.675 ms, forward
   cumulative peak-to-peak CDV of 3.455 ms, a backward cumulative
   peak-to-peak CDV of 2.155 ms, a forward end-to-end
   transit delay of 32  ms, a backward end-to-end
   transit delay of 18  ms, an unspecified forward cumulative
   transit delay, an unspecified backward cumulative transit
   delay, a forward cell loss ratio of 10 raised to  minus 11 and a
   backward cell loss ratio of 10 to the minus 12.

5.6.1.9  The 'atmFtrfcDesc' and 'atmBtrfcDesc' attributes

   When present, the 'atmFtrfcDesc' and 'atmBtrfcDesc' attributes
   are  used to indicate ATM traffic descriptor parameters in the
   forward and backward directions respectively. See Section 2.3 for a
   definition of the terms 'forward' and 'backward'.

   The  'atmFtrfcDesc' and 'atmBtrfcDesc' media attribute lines
   are structured as follows:

      a=atmFtrfcDesc:<clpLvl> <pcr><scr><mbs><cdvt><mcr><mfs><fd><te>
      a=atmBtrfcDesc:<clpLvl> <pcr><scr><mbs><cdvt><mcr><mfs><fd><te>

   If any of these parameters in these media attribute lines is not
   specified, is inapplicable or is implied, then it is set to "-".

   The <clpLvl> (CLP level) parameter indicates whether the rates and
   bursts described in these media attribute lines apply to CLP
   values of 0 or  (0+1). It can take on the following string values:
   "0", "0+1" and "-". If rates and bursts for both <clpLvl> values are to
   be described, then it is necessary to use two separate
   media attribute lines for each direction in the same session
   descriptor.  If the <clpLvl> parameter is set to "-", then it
   implies that the CLP parameter is known by other means such as default,
   MIB provisioning etc.

   The meaning, units and applicability of the remaining parameters
   are per [6] and [28]:
















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   PARAMETER      MEANING       UNITS         APPLICABILITY

   <pcr>          PCR           Cells/        CBR, rt-VBR, nrt-VBR,
                                second        ABR, UBR, GFR;
                                              CLP=0,0+1

   <scr>          SCR           Cells/        rt-VBR, nrt-VBR;
                                second        CLP=0,0+1

   <mbs>          MBS           Cells         rt-VBR, nrt-VBR,
                                              GFR;
                                              CLP=0,0+1

   <cdvt>        CDVT           Microsec.     CBR, rt-VBR, nrt-VBR,
                                              ABR, UBR, GFR;
                                              CLP=0,0+1

   <mcr>         MCR            Cells/         ABR,GFR;
                                second         CLP=0+1


   <mfs>         MFS            Cells          GFR;
                                               CLP=0,0+1


   <fd>         Frame          "on"/"off"      CBR, rt-VBR, nrt-VBR,
                Discard                        ABR, UBR, GFR;
                Allowed                        CLP=0+1


   <te>         CLP            "on"/"off"      CBR, rt-VBR, nrt-VBR,
                tagging                        ABR, UBR, GFR;
                Enabled                        CLP=0


   <fd> indicates that frame discard is permitted. It can take on the string
   values of "on" or "off". Note that, in the GFR case, frame discard
   is always enabled. Hence, this subparameter can be set to "-" in
   the case of GFR. Since the <fd>   parameter is  independent
   of CLP, it  is meaningful in the case when <clpLvl> = "0+1".
   It  should be set to "-" for the case when <clpLvl> = "0".

   <te> (tag enable)   indicates that CLP tagging is allowed.
   These can take on the string values of "on" or "off".
   Since the <te>   parameter applies only to cells with
   a CLP of 0, it  is  meaningful in the case when <clpLvl> = "0".
   It should be set to "-" for the case when <clpLvl> = "0+1".

   An example use of these media attribute lines for an  rt-VBR,
   single-CID AAL2 voice VC is:





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     a=atmFtrfcDesc:0+1 200   100  20   - - - on  -
     a=atmFtrfcDesc:0   200   80   15   - - - -  off
     a=atmBtrfcDesc:0+1 200   100  20   - - - on -
     a=atmBtrfcDesc:0   200   80   15   - - - -  off

   This implies a forward and backward PCR of 200 cells per second
   all cells regardless of CLP,  forward and backward PCR of 200 cells
   per second for cells with CLP=0, a forward and backward SCR of 100
   cells per second for all cells regardless of CLP, a forward and
   backward SCR of 80 cells per second for cells with CLP=0,
   a forward and backward MBS of 20 cells  for all cells regardless
   of CLP, a forward and backward MBS of 15 cells for cells with
   CLP=0,  an unspecified CDVT which can be known by other means,
   and an  MCR and MFS which are unspecified because they are
   inapplicable. Frame discard is enabled in both the forward and
   backward directions. Tagging is not enabled in either direction.

   The <pcr>, <scr>, <mbs>, <cdvt>, <mcr> and <mfs> are represented as
   decimal integers, with range as defined in Section 6. See section 2.2
   regarding the omission of leading zeros in decimal representations.

5.6.1.10 The 'abrFparms' and 'abrBparms' attributes

   When present, the 'abrFparms' and 'abrBparms' attributes
   are used to indicate the 'additional' ABR parameters specified
   in the UNI 4.0 signaling specification [5]. These refer to the
   forward and backward directions respectively. See Section
   2.3 for a definition of the terms 'forward' and 'backward'.

   The 'abrFparms' and 'abrBparms' media attribute lines are structured
   as follows:

   a=abrFparms:<nrm><trm><cdf><adtf>
   a=abrBparms:<nrm><trm><cdf><adtf>

   These parameters are mapped into the ABR service parameters in
   [6] in the manner described below. These parameters can be
   represented in SDP as decimal integers, with fractions permitted
   for some. Details of the meaning, units and applicability of
   these parameters are in [5] and [6].

   If any of these parameters in the 'abrFparms' or 'abrBparms' media
   attribute  lines is not specified, is inapplicable or is implied,
   then it is set to   "-".

   In SDP, these parameters are represented as the decimal or hex
   equivalent of the binary fields mentioned below.








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  +-----------+----------------------------------+-----------------------+
  | PARAMETER |            MEANING               | FIELD SIZE            |
  +-----------+----------------------------------+-----------------------+
  | <nrm>     | Maximum number of cells per      |    3 bits             |
  |           | forward Resource Management cell |                       |
  +-----------+----------------------------------+-----------------------+
  | <trm>     | Maximum time between             |    3 bits             |
  |           | forward Resource Management cells|                       |
  +-----------+----------------------------------+-----------------------+
  | <cdf>     | Cutoff Decrease Factor           |    3 bits             |
  +-----------+----------------------------------+-----------------------+
  | <adtf>    | Allowed Cell Rate Decrease       |    10 bits            |
  |           | Time Factor                      |                       |
  +-----------+----------------------------------+-----------------------+

5.6.1.11 The 'abrSetup' attribute

   When present, the 'abrSetup' attribute is used to indicate the
   ABR parameters needed during call/connection establishment (Section
   10.1.2.2 of the UNI 4.0 signaling specification [5]). This line
   is structured as follows:

   a=abrSetup:<ficr><bicr><ftbe><btbe><crmrtt><frif><brif><frdf><brdf>

   These parameters are defined as follows:






























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  +-----------+----------------------------------+-----------------------+
  | PARAMETER |            MEANING               | REPRESENTATION        |
  +-----------+----------------------------------+-----------------------+
  | <ficr>    | Forward Initial Cell Rate        | Decimal equivalent    |
  |           | (Cells per second)               | of 24-bit field       |
  +-----------+----------------------------------+-----------------------+
  | <bicr>    | Backward Initial Cell Rate       | Decimal equivalent    |
  |           | (Cells per second)               | of 24-bit field       |
  +-----------+----------------------------------+-----------------------+
  | <ftbe>    | Forward transient buffer         | Decimal equivalent    |
  |           | exposure (Cells)                 | of 24-bit field       |
  +-----------+----------------------------------+-----------------------+
  | <btbe>    | Backward transient buffer        | Decimal equivalent    |
  |           | exposure (Cells)                 | of 24-bit field       |
  +-----------+----------------------------------+-----------------------+
  | <crmrtt>  | Cumulative RM round-trip time    | Decimal equivalent    |
  |           | (Microseconds)                   | of 24-bit field       |
  +-----------+----------------------------------+-----------------------+
  | <frif>    | Forward rate increase factor     | Decimal integer       |
  |           | (used to derive cell count)      | 0 -15                 |
  +-----------+----------------------------------+-----------------------+
  | <brif>    | Backward rate increase factor    | Decimal integer       |
  |           | (used to derive cell count)      | 0 -15                 |
  +-----------+----------------------------------+-----------------------+
  | <frdf>    | Forward rate decrease factor     | Decimal integer       |
  |           | (used to derive cell count)      | 0 -15                 |
  +-----------+----------------------------------+-----------------------+
  | <brdf>    | Backward rate decrease factor    | Decimal integer       |
  |           | (used to derive cell count)      | 0 -15                 |
  +-----------+----------------------------------+-----------------------+

   See Section 2.3 for a definition of the terms 'forward' and 'backward'.

   If any of these parameters in the 'abrSetup' media attribute  line
   is not specified, is inapplicable or is implied, then it is set to
   "-".

5.6.1.12 The 'bearerType' attribute

   When present, the 'bearerType' attribute is used to indicate
   whether the underlying bearer is an ATM PVC/SPVC, an ATM SVC,
   or an AAL2 CID connection within an existing ATM PVC/SPVC.
   Additionally, for ATM SVCs and AAL2 CID connections, the
   'bearerType' attribute can be used to indicate whether the
   media gateway initiates connection set-up via bearer signaling
   (Q.2931-based or Q.2630.1 based). The format of the 'bearerType'
   media attribute line is as follows:

   a=bearerType: <bearerType> <localInitiation>

   The <bearerType> field can take on the following string values:



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   "PVC", "SVC", "CID", with semantics as defined above. Here, "PVC"
   includes both the PVC and SPVC cases.

   In the case when the underlying bearer is a PVC/SPVC, or a CID
   assigned by the MGC rather than through bearer signaling, the
   <localInitiation> flag can be omitted or set to "-". In the
   case when bearer signaling is used, this flag can be omitted
   when it is known by default  or by other means whether the media
   gateway initiates the connection set-up via bearer signaling. Only
   when this is to be indicated explicitly that the <localInitiation>
   flag takes on the values of "on" or "off". An "on" value indicates
   that the media gateway is responsible for initiating connection set-up
   via bearer signaling (SVC signaling or Q.2630.1 signaling),
   an "off" value indicates otherwise.


5.6.1.13 The 'lij' attribute

   When present, the 'lij' attribute is used to indicate
   the presence of a connection that uses the Leaf-initiated-join
   capability described in UNI 4.0 [5], and to optionally describe
   parameters associated with this capability.  The format of the
   'lij' media attribute line is as follows:

   a=lij: <sci><lsn>

   The <sci> (screening indication) is a 4-bit field expressed as a
   decimal or hex integer. It is defined in the UNI 4.0 signaling
   specification [5]. It is possible that the values of this field will
   be defined later by the ATMF and/or ITU. Currently, all values are
   reserved with the exception of 0, which indicates a 'Network Join
   without Root Notification'.

   The <lsn> (leaf sequence number) is a 32-bit field expressed as a
   decimal or hex integer. Per the UNI 4.0 signaling specification [5], it
   is used by a joining leaf to associate messages and responses during
   LIJ (leaf initiated join) procedures.

   Each of these fields can be set to a "-" when the intention
   is to not specify them in an SDP descriptor.

 5.6.1.14 The 'anycast' attribute

   When present, the 'anycast' attribute line is used to indicate
   the applicability of the anycast function described in UNI
   4.0 [5]. Optional parameters to  qualify this function are
   provided. The format of the 'anycast' attribute is:

   a=anycast: <atmGroupAddress> <cdStd> <conScpTyp> <conScpSel>

   The <atmGroupAddress> is per Annex 5 of UNI 4.0 [5]. Within
   an SDP descriptor, it can be represented in one of the formats



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   (NSAP, E.164, GWID/ALIAS) described elsewhere in this document.

   The remaining subparameters mirror the connection scope selection
   information element in UNI 4.0 [5]. Their meaning and representation
   is as shown below:

   PARAMETER     MEANING                                  REPRESENTATION
   <cdStd>       Coding standard for the                  Decimal or hex
                 connection scope selection IE            equivalent of
                 Definition: UNI 4.0 [5]                  2 bits

  <conScpTyp>    Type of connection scope                 Decimal or hex
                 Definition: UNI 4.0 [5]                  equivalent of
                                                          4 bits

  <conScpSel>    Connection scope selection               Decimal or hex
                 Definition: UNI 4.0 [5]                  equivalent of
                                                          8 bits

 Currently, all values of <cdStd> and   <conScpTyp> are reserved with
 the exception of <cdStd> = 3 (ATMF coding standard) and <conScpTyp> = 1
 (connection scope type of 'organizational').

  Each of these fields can be set to a "-" when the intention
  is to not specify them in an SDP descriptor.

 5.6.1.15 The 'cache' attribute

    This attribute is used  to enable SVC caching. This attribute
    has the following format:

        a=cache:<cacheEnable><cacheTimer>

   The <cacheEnable> flag indicates whether caching is enabled or
   not, corresponding to the string values of "on" and "off"
   respectively.

  The <cacheTimer> indicates the period of inactivity following which
  the SVC is to be released by sending an SVC release message into
  the network. This is specified as the decimal or hex equivalent of
  a 32-bit field, indicating the timeout in seconds. As usual, leading
  zeros can be omitted. For instance,

    a=cache:on 7200

  implies that the cached SVC is to be deleted if it is idle for 2 hours.

  The <cacheTimer> can be set to "-" if it is inapplicable or implied.

5.6.1.16 The 'bearerSigIE' attribute

ATM signaling standards provide 'escape mechanisms' to



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represent, signal and negotiate higher-layer parameters. Examples
are the B-HLI and B-LLI IEs specified in ITU Q.2931 [15], and
the user-to-user information element described in ITU Q.2957 [48].

The 'bearerSigIE'(bearer signaling information element) attribute is
defined to allow  a similar escape mechanism that can be used with
these ATM SDP conventions. The format of this media attribute line
is as follows:

   a=bearerSigIE: <bearerSigIEType> <bearerSigIELng> <bearerSigIEVal>

When an  'bearerSigIE' media attribute line is present, all its
subparameters are mandatory. The "0x" prefix is not used since these are
always represented in hex.

The <bearerSigIEType> is represented as exactly 2 hex digits. It is the
unique IE identifier as defined in the ITU Q-series standards. Leading
zeros are not omitted. Some pertinent values are 7E (User-user IE
per ITU Q.2957 [48]), 5F (B-LLI IE) and 5D (B-HLI IE). B-LLI and B-HLI,
which stand for Broadband Low-layer Information and Broadband
High-layer Information respectively, are defined in ITU Q.2931 [15].
Both of these refer to layers above the ATM adaptation layer.

The <bearerSigIELng> consists of 1-4 hex digits. It is the length of
the information element in octets. Leading zeros may be omitted.

The <bearerSigIEVal> is the value of the information element, represented
as a hexadecimal bit map. Although the size of this bit map is network/
service dependent, setting an upper bound of 256 octets (512 hex digits)
is adequate. Since this a bit map, leading zeros should not be
omitted. The number of hex digits in this bit map is even.

5.6.2  ATM Adaptation Layer (AAL) attributes

   The following is a summary list of the SDP media attributes that can
   be used to describe the ATM Adaptation Layer (AAL). These are detailed in
   subsequent subsections.

        * The 'aalApp' attribute, which is used to point to the
          controlling standard for an application layer above the ATM
          adaptation layer.

        * The 'cbrRate' attribute, which represents
          the CBR rate octet defined in Table 4-6 of ITU Q.2931  [15].

        * The 'sbc' attribute, which denotes the
          subchannel count in the case of  n x 64 clear channel
          communication.

        * The 'clkrec' attribute, which indicates the clock recovery
          method for AAL1 unstructured data transfer (UDT).




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        * The 'fec' attribute, which indicates the use of
          forward error correction.

        * The 'prtfl' attribute, which indicates indicate the fill
          level of partially filled cells.

        * The 'structure' attribute, which is used to indicate
          the presence or absence of AAL1 structured data transfer (SDT),
          and the size of the SDT blocks.

        * The 'fcpsSDUsize' and 'bcpsSDUsize'
          attributes, which are used to  indicate the maximum size of the
          CPCS SDU payload in the forward and backward directions.

        * The 'aal2CPS' attribute, which is used to
          indicate that an AAL2 CPS sublayer as defined in
          ITU I.363.2 [13] is associated with the VCC referred to in the
          'm' line. Optionally, it can be used to indicate selected
          CPS options and parameter values for this VCC.

        * The 'aal2CPSSDUrate' attribute, which is used to place
          an upper bound on the SDU bit rate for an AAL2 CID.

        * The 'aal2sscs3661unassured' attribute, which is used
          to indicate the presence of an AAL2 SSCS sublayer with
          unassured transmission as defined in ITU I.366.1 [12].
          Optionally, it can be used to indicate selected options and
          parameter values for this SSCS.

        * The 'aal2sscs3661assured' attribute, which is used
          to indicate the presence of an AAL2 SSCS sublayer with
          assured transmission as defined in ITU I.366.1 [12].
          Optionally, it can be used to indicate selected options and
          parameter values for this SSCS.

        * The 'aal2sscs3662' attribute, which is used to
          indicate the presence of an AAL2 SSCS sublayer as defined
          in ITU I.366.2. Optionally, it can be used to indicate
          selected options and parameter values for this SSCS.

        * The 'aal5sscop' attribute, which is used to
          indicate the existence of an SSCOP protocol layer over
          an AAL5 CPS layer, and the parameters which pertain to
          this SSCOP layer.

5.6.2.1  The 'aalApp' attribute

   When present, the 'aalApp' attribute is used to  point to the
   controlling standard for an application layer above the ATM adaptation
   layer. The format of the 'aalApp' media attribute line is as follows:

   a=aalApp: <appClass> <oui> <appId>



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   If any  of the subparameters, <appClass>,  <oui> or <appId>, is meant
   to be left, unspecified, it is set to "-". However, an 'aalApp' attribute
   line with all subparameters set to "-" carries no information and
   should be omitted.

   The <appClass>, or application class,  field can take on the
   string values listed below.

   This list is not exhaustive. An "X-" prefix should be used with
   <appClass>  values not listed here.

           <appClass>           Meaning

        "itu_h323c"           Annex C of H.323 which specifies direct
                              RTP on AAL5 [45].

         "af83"               af-vtoa-0083.001, which specifies
                              variable size AAL5 PDUs with PCM voice
                              and a null SSCS [46].

        "AAL5_SSCOP"          SSCOP as defined in ITU Q.2110 [43]
                              running over an AAL5 CPS [21].
                              No information is provided regarding
                              any layers above SSCOP such as Service
                              Specific Coordination Function  (SSCF)
                              layers.

      "itu_i3661_unassured"   SSCS with unassured transmission,
                              per ITU I.366.1 [12].

      "itu_i3661_assured"     SSCS with assured transmission,
                              per ITU I.366.1 [12]. This uses SSCOP [43].

         "itu_i3662"          SSCS per ITU I.366.2 [13].

         "itu_i3651"          Frame relay SSCS per ITU I.365.1 [39].

         "itu_i3652"          Service-specific coordination function,
                              as defined in ITU I.365.2, for Connection
                              Oriented Network Service (SSCF-CONS) [40].
                              This uses SSCOP [43].

         "itu_i3653"          Service-specific coordination function,
                              as defined in ITU I.365.3, for Connection
                              Oriented Transport Service (SSCF-COTS) [41].
                              This uses SSCOP [43].

         "itu_i3654"          HDLC Service-specific coordination function,
                              as defined in ITU I.365.4 [42].

         "FRF5"               Use of the FRF.5 frame relay standard [53],



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                              which references ITU I.365.1 [39].

         "FRF8"               Use of the FRF.8.1 frame relay standard [54].
                              This implies a null SSCS and the mapping of
                              the frame relay header into the ATM header.

         "FRF11"              Use of the FRF.11 frame relay standard [55].

         "itu_h2221"          Use of the ITU standard H.222.1 for audiovisual
                              communication over AAL5 [51].

The <oui>, or Organizationally Unique Identifier, refers to the organization
responsible for defining the <appId>, or Application Identifier. The <oui> is
maintained by the IEEE. One of its uses is in 802 MAC addresses. It is a three-
octet field represented as one to  six hex digits. Since this is always
represented in hex,  the "0x" prefix is not used. Leading zeros may be omitted.

The <appId> subparameter refers to the application ID, a hex number consisting
of up to 8 digits. Leading zeros may  be omitted. The "0x" prefix is not used,
since  the  representation  is  always  hexadecimal.  Currently,  the  only
organization that has defined applicable application identifiers is the ATM
forum (Section 5 of [61]). These can be used with <appClass> = itu_i3662. The
<oui> value for the ATM forum is 0x00A03E.

In the following example, the aalApp media attribute line is used to
indicate 'Loop Emulation Service using CAS (POTS only) without the
Emulated Loop Control Protocol (ELCP) [52]. The Application ID is defined
by the ATM forum [61]. The SSCS used is per ITU I.366.2 [13].

    a=aalApp:itu_i3662 A03E A

If leading zeros are not dropped, this can be represented as:

    a=aalApp:itu_i3662 00A03E 0000000A

5.6.2.2  The 'cbrRate' attribute

   When present, the 'cbrRate' attribute is used to represent the CBR
   rate octet defined in Table 4-6 of ITU Q.2931  [15]. The format
   of this media attribute line is:

     a=cbrRate: <cbrRate>

   Here, <cbrRate> is represented as exactly two hex digits. The "0x"
   prefix is omitted since this parameter is always represented in
   hex. Values currently defined by the ITU are:









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        +------------+-----------------------------------------------+
        |  VALUE     |             MEANING                           |
        +------------+-----------------------------------------------+
        |   0x01     |  64 kbps                                      |
        +------------+-----------------------------------------------+
        |   0x04     |  1544 kbps                                    |
        +------------+-----------------------------------------------+
        |   0x05     |  6312 kbps                                    |
        +------------+-----------------------------------------------+
        |   0x06     |  32064 kbps                                   |
        +------------+-----------------------------------------------+
        |   0x07     |  44736 kbps                                   |
        +------------+-----------------------------------------------+
        |   0x08     |  97728 kbps                                   |
        +------------+-----------------------------------------------+
        |   0x10     |  2048 kbps                                    |
        +------------+-----------------------------------------------+
        |   0x11     |  8448 kbps                                    |
        +------------+-----------------------------------------------+
        |   0x12     |  34368 kbps                                   |
        +------------+-----------------------------------------------+
        |   0x13     |  139264 kbps                                  |
        +------------+-----------------------------------------------+
        |   0x40     |  n x 64  kbps                                 |
        +------------+-----------------------------------------------+
        |   0x41     |  n x 8 kbps                                   |
        +------------+-----------------------------------------------+

   It is preferable that the cbrRate attribute be omitted rather
   than set to an unspecified value of "-", since it conveys no
   information in the latter case.

5.6.2.3  The 'sbc' attribute

   The 'sbc' media attribute line denotes the subchannel count and
   is meaningful only in the case of  n x 64 clear channel communication.
   A clear n x 64 channel can use AAL1 (ATM forum af-vtoa-78) or AAL2
   adaptation (ITU I.366.2). Although no such standard definition exists,
   it is also possible to use AAL5 for this purpose. An  n x 64 clear channel
   is represented by the encoding names of  "X-CCD" and "X-CCD-CAS" in
   Table 2.

   The format of the 'sbc' media attribute line is as follows:

     a=sbc:<sbc>

   Here, <sbc> can be expressed as a decimal or hex integer. This
   attribute indicates the number of DS0s in a T1 or E1 frame that are
   aggregated for transmitting  clear channel data. For T1-based
   applications, it can take on integral values in the inclusive range
   [1...24]. For E1-based applications, it can take on integral values in
   the inclusive range [1...31]. When omitted, other means are to be used



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   to determine the subchannel count.

   Use of the 'sbc' attribute provides a direct way to indicate the
   number of 64 kbps subchannels bundled into an n x 64  clear
   channel. An alternate mechanism to indicate this exists within
   the SDP bandwidth information, or 'b',  line [1]. In this case,
   instead of specifying the number of subchannels, the aggregate
   bandwidth in kbps is specified. The syntax of the 'b' line, copied
   verbatim from [1], is as follows:

      b=<modifier>:<bandwidth-value>

   In the case of n x 64 clear channels, the <modifier> is assigned a
   text string value of "AS", indicating that the 'b' line is application-
   specific. The <bandwidth-value> parameter, which is a decimal number
   indicating the bandwidth in kbps, is limited to one of the
   following values in the n x 64 clear channel application context:

      64, 128, 192, 256, 320, 384, 448, 512, 576, 640, 704, 768, 832,
      896, 960, 1024, 1088, 1152, 1216, 1280, 1344, 1408, 1472, 1600,
      1664, 1728, 1792, 1856, 1920, 1984

    Thus, for n x 64 circuit mode data service,

      a=sbc:6

    is equivalent to

      b=AS:384

   The media attribute line

      a=sbc:2

    is equivalent to

      b=AS:128

5.6.2.4  The 'clkrec' attribute

   When present, the 'clkrec' attribute is used to indicate
   the clock recovery method. This attribute is meaningful in the
   case of AAL1 unstructured data transfer (UDT). The format of the
   'clkrec' media attribute line is as follows:

   a=clkrec:<clkrec>

   The <clkrec> field can take on the following string values: "NULL",
   "SRTS" or "ADAPTIVE". SRTS and adaptive clock recovery  are defined in
   ITU I.363.1 [10]. "NULL" indicates   that the stream (e.g. T1/E1)
   encapsulated in ATM is synchronous to  the ATM network or is retimed,
   before AAL1 encapsulation, via slip buffers.



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5.6.2.5  The 'fec' attribute

   When present, the 'fec' attribute is used to indicate the use of
   forward error correction. Currently, there exists a forward error
   correction method defined for AAL1 in ITU I.363.1 [10]. The format of the
   'fec' media attribute line is as follows:

   a=fec:<fecEnable>

   The <fecEnable> flag indicates the presence of absence of Forward
   Error Correction. It can take on the string values of "NULL",
   "LOSS_SENSITIVE" and "DELAY_SENSITIVE". An "NULL" value implies disabling
   this capability. FEC can be enabled differently for delay-sensitive
   and loss-sensitive connections.

5.6.2.6  The 'prtfl' attribute

   When present, the 'prtfl' attribute is used to indicate the fill
   level of cells. When this attribute is absent, then
   other means (such as provisionable defaults) are used to determine
   the presence and level of partial fill.

   This attribute indicates the number of non-pad payload
   octets, not including any AAL SAR or convergence sublayer octets. For
   example, in some AAL1 applications that use partially filled cells with
   padding at the end, this attribute indicates the number of leading
   payload octets not including any AAL overhead.

   The format of the 'prtfl' media attribute line is as follows:

      a=prtfl:<partialFill>

   Here, <partialFill> can be expressed as a decimal or a hex integer.
   In general, permitted values are integers in  the range 1 - 48
   inclusive. However, this upper bound is  different for different
   adaptations since the AAL overhead, if any, is different. If the specified
   partial fill is greater than or equal to the maximum fill,  then complete
   fill is used. Using a 'partial' fill of 48 always disables partial fill.

   In the AAL1 context, this media attribute line applies uniformly to
   both P and non-P cells. In AAL1 applications that do not distinguish
   between P and non-P cells, a value of 47 indicates complete fill (i.e. the
   absence of partial fill). In AAL1 applications that distinguish between P
   and non-P cells, a value of 46 indicates no padding in P-cells and a
   padding of one in non-P cells.

   If partial fill is enabled (i.e there is padding in at least some
   cells), then AAL1 structures must not be split across cell boundaries.
   These shall fit in any cell. Hence,
   their size shall be less than or equal to the partial fill
   size. Further, the partial fill size is preferably



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   an integer multiple of the structure size. If not, then the
   partial fill size stated in the SDP description shall be
   truncated to an integer multiple (e.g. a partial fill size of
   40 is truncated to 36 to support six 6 x 64 channels).

5.6.2.7  The 'structure' attribute

   This attribute applies to AAL1 connections only. When present,
   the 'structure' attribute is used to indicate the presence or
   absence of structured data transfer (SDT), and the size in octets
   of the SDT blocks. The format of the 'structure' media attribute line
   is as follows:

   a=structure: <structureEnable> <blksz>

   where the <structureEnable> flag indicates the presence of absence of SDT.
   It can take on the values of "on" or "off". An "on" value implies
   AAL1 structured data transfer (SDT), while an "off" value implies
   AAL1 unstructured data transfer (UDT).

   The block size field, <blksz>,  is an optional 16-bit field (Q.2931)
   that can be represented in decimal or hex. It is set to
   a "-" when not applicable, as in the case of unstructured data transfer
   (UDT). For SDT, it can   be set to a "-" when <blksz> is known
   by other means. For instance, af-vtoa-78 [7] fixes the structure size for
   n x 64 service, with or without CAS. The theoretical maximum value  of
   <blksz> is 65,535, although most services  use much less.


5.6.2.8  The 'fcpsSDUsize' and 'bcpsSDUsize' attributes

   When present, the 'fcpsSDUsize' and 'bcpsSDUsize' attributes are used to
   indicate the maximum size of the CPCS SDU payload in the forward and
   backward directions respectively. See section 2.3 for a definition of the
   terms 'forward' and 'backward'. The format of these media attribute lines is
   as follows:

     a=fcpsSDUsize: <cpcs>
     a=bcpsSDUsize: <cpcs>

   The <cpcs>  fields is a 16-bit integer that can be represented in
   decimal  or in hex.
   The meaning and  values of these fields are as follows:

   Application    Field      Meaning                         Values

   AAL5           <cpcs>    Maximum CPCS-SDU size           1- 65,535


   AAL2           <cpcs>    Maximum CPCS-SDU size           45 or 64





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5.6.2.9  The 'aal2CPS' attribute

   When present, the 'aal2CPS' attribute is used to describe
   parameters associated with the AAL2 CPS layer.

   The format of the 'aal2CPS' media attribute line is as follows:
   a=aal2CPS:<cidLowerLimit><cidUpperLimit><timerCU> <simplifiedCPS>

   Each of these fields can be set to a "-" when the intention is to not
   specify them in an SDP descriptor.

   The <cidLowerLimit> and <cidUpperLimit> can be assigned integer
   values between 8 and 255 [11], with the limitation that <cidUpperLimit>
   be greater than or equal to <cidLowerLimit>. For instance, for POTS
   applications based on [52], <cidLowerLimit> and <cidUpperLimit>
   can have values of 16 and 223 respectively.

   The <timerCU> integer represents the "combined use" timerCU defined in
   ITU I.363.2. This timer is represented as an integer number of microseconds.

   The <simplifiedCPS> parameter can be assigned the values "on" or "off". When
   it is "on", the AAL2 CPS simplification described in [52] is adopted. Under
   this simplification, each ATM cell contains exactly on AAL2 packet. If
   necessary, octets at the end of the cell are padded with zeros. Since the
   <timerCU> value in this context is always 0, it can be omitted.

5.6.2.10 The 'aal2CPSSDUrate' attribute

   When present, the 'aal2CPSSDUrate' attribute is used to place an upper
   bound on the SDU bit rate for an AAL2 CID. This is useful for
   limiting the bandwidth used by a CID, specially if the CID is used
   for frame mode data defined in [13], or with the SSSAR defined in
   [12]. The format of this media attribute line is as follows:

         a=aal2CPSSDUrate: <fSDUrate><bSDUrate>

   The fSDUrate and bSDUrate are the maximum forward and backward SDU
   rates in bits/second. These are represented as
   decimal integers, with range as defined in Section 6. If any
   of these parameters in these media attribute lines is not
   specified, is inapplicable or is implied, then it is set to "-".

5.6.2.11 The 'aal2sscs3661unassured' attribute

   When present, the 'aal2sscs3661unassured' attribute is used to indicate
   the options that pertain to the unassured transmission SSCS defined
   in ITU I.366.1 [12]. This SSCS can be selected via the aalApp
   attribute defined below, or by virtue of the presence of the
   'aal2sscs3661unassured' attribute. The format of this
   media attribute line is as follows:

   a=aal2sscs3661unassured: <ted> <rastimer> <fsssar> <bsssar>



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   Each of these fields can be set to a "-" when the intention is to not
   specify them in an SDP descriptor.

   The <ted> flag indicates the presence or absence of transmission
   error detection as defined in I.366.1. It can be assigned  the
   values of "on" or  "off". An "on" value indicates presence of
   the capability.

   The <rastimer> subparameter indicates the SSSAR reassembly timer
   in microseconds. It is represented as the decimal equivalent of
   32 bits.

   The  <fsssar> and  <bsssar> fields are 24-bit integers  that
   can be represented in decimal or in hex. The meaning and  values of
   the  <fsssar> and  <bsssar> fields are as follows:

   Field      Meaning                         Values

   <fsssar>   Maximum SSSAR-SDU size           1- 65,568
              forward direction

   <bsssar>   Maximum SSSAR-SDU size           1- 65,568
              backward direction


  If present, the SSTED (Service-Specific Transmission Error
  Detection) sublayer is above the SSSAR (Service-Specific Segmentation
  and Reassembly) sublayer [12]. Since the maximum size  of the
  SSTED-SDUs can be derived from the maximum SSSAR-SDU size, it need
  not be specified separately.

5.6.2.12 The 'aal2sscs3661assured' attribute

   When present, the 'aal2sscs3661assured' attribute is used to indicate
   the options that pertain to the assured transmission SSCS defined
   in ITU I.366.1 [12] on the basis of ITU Q.2110 [43]. This SSCS can be
   selected via the  aalApp attribute defined below, or by virtue
   of the presence of the 'aal2sscs3661assured' attribute. The format of
   this media attribute line is as follows:

   a=aal2sscs3661assured: <rastimer> <fsssar> <bsssar> <fsscopsdu>
                          <bsscopsdu><fsscopuu> <bsscopuu>

   Each of these fields can be set to a "-" when the intention is to not
   specify them in an SDP descriptor.

   The <rastimer> subparameter indicates the SSSAR reassembly timer
   in microseconds. It is represented as the decimal equivalent of
   32 bits.

   The  <fsssar> and  <bsssar> fields are 24-bit integers  that



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   can be represented in decimal or in hex. The <fsscopsdu>,
   <bsscopsdu>, <fsscopuu> and <bsscopuu> fields are 16-bit integers
   that can be represented in decimal or in hex. The meaning and  values
   of these fields is as follows:

    Field      Meaning                          Values

   <fsssar>    Maximum SSSAR-SDU size           1- 65,568
               forward direction

   <bsssar>    Maximum SSSAR-SDU size           1- 65,568
               backward direction

   <fsscopsdu> Maximum SSCOP-SDU size           1- 65,528
               forward direction

   <bsscopsdu> Maximum SSCOP-SDU size           1- 65,528
               backward direction

   <fsscopuu>  Maximum SSCOP-UU field           1- 65,524
               size, forward direction

   <bsscopuu>  Maximum SSCOP-UU field           1- 65,524
               size, backward direction


  The SSTED (Service-Specific Transmission Error Detection) sublayer
  is above the SSSAR (Service-Specific Segmentation and Reassembly)
  sublayer [12]. The SSADT (Service-Specific Assured Data Transfer)
  sublayer is above  the SSTED sublayer.  Since the maximum size  of
  the SSTED-SDUs and SSADT-SDUs can be derived from the maximum
  SSSAR-SDU size, they need not be specified separately.

  The SSCOP protocol defined in [43] is used by the Assured Data
  Transfer service defined in [12]. In the context of the ITU I.366.1
  SSCS, it is possible to use the 'aal2sscs3661assured' attribute to limit
  the maximum sizes of the SSCOP SDUs and UU (user-to-user) fields in
  either direction. Note that it is necessary for the parameters on the
  'aal2sscs3661assured' media attribute line to be consistent with each
  other.

5.6.2.13 The 'aal2sscs3662' attribute

   When present, the 'aal2sscs3662' attribute is used to indicate
   the options that pertain to the SSCS defined  in ITU I.366.2 [13].
   This SSCS can be selected via the aalApp attribute defined below,
   or by the presence of  the 'aal2sscs3662' attribute.

The format of this media attribute line is as follows:






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   a=aal2sscs3662: <sap> <circuitMode> <frameMode> <faxDemod>
                   <cas> <dtmf> <mfall> <mfr1> <mfr2>
                   <PCMencoding> <fmaxFrame> <bmaxFrame>

   Each of these fields can be set to a "-" when the intention
   is to not specify them in an SDP descriptor. Additionally, the values
   of these fields need to be consistent with each other. Inconsistencies
   should be flagged as errors.

   The <sap> field can take on the following string values: "AUDIO"
   and "MULTIRATE". These correspond to the audio and multirate
   Service Access Points (SAPs) defined in ITU I.366.2.

   For the multirate SAP, the following parameters on the aal2sscs3662
   attribute line do not apply: <faxDemod>,<cas>, <dtmf>, <mfall>,
   <mfr1>,  <mfr2> and <PCMencoding>. These are set to "-" for the
   multirate SAP.

   The <circuitMode> flag indicates whether the transport of circuit
   mode data is enabled or disabled, corresponding to the string
   values of "on" and "off" respectively. For the multirate SAP, it
   cannot have a value of "off". For the audio SAP, it can be assigned
   a value of "on", "off" or "-". Note that the <sbc> attribute, defined
   elsewhere in this document, can be used to specify the number of
   64 kbps subchannels bundled into a circuit mode data channel.

   The <frameMode> flag indicates whether the transport of frame
   mode data is enabled or disabled, corresponding to the string
   values of "on" and "off" respectively.

   The <faxDemod> flag indicates whether facsimile demodulation
   and remodulation are enabled or disabled, corresponding to the
   string values of "on" and "off" respectively.

   The <cas> flag indicates whether the transport of Channel
   Associated Signaling (CAS) bits in AAL2 type 3 packets is enabled
   or disabled, corresponding to the string values of "on" and "off"
   respectively.

   The <dtmf> flag indicates whether the transport of DTMF dialled
   digits in AAL2 type 3 packets is enabled or disabled, corresponding
   to the string values of "on" and "off" respectively.

   The <mfall> flag indicates whether the transport of MF dialled
   digits in AAL2 type 3 packets is enabled or disabled, corresponding
   to the string values of "on" and "off" respectively. This flag
   enables  MF dialled digits in a generic manner, without specifying
   type (e.g. R1, R2 etc.).

   The <mfr1> flag indicates whether the transport,  in AAL2 type 3
   packets, of MF dialled digits for signaling system R1 is enabled
   or disabled, corresponding to the string values of "on" and "off"



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   respectively.

   The <mfr2> flag indicates whether the transport,  in AAL2 type 3
   packets, of MF dialled digits for signaling system R2 is enabled
   or disabled, corresponding to the string values of "on" and "off"
   respectively.

   The <PCMencoding> field indicates whether  PCM encoding, if used,
   is based on the A-law or the Mu-law. This can be used to qualify
   the 'generic PCM' codec stated in some of the AAL2 profiles. The
   <PCMencoding> field can take on the string values of "PCMA"
   and "PCMU".

   The  <fmaxFrame> and  <bmaxFrame> fields are 16-bit integers  that
   can be represented in decimal  or in hex. The meaning and  values of
   the  <fmaxFrame> and  <bmaxFrame> fields are as follows:

   Field         Meaning                         Values

   <fmaxFrame>   Maximum length of a             1- 65,535
                 frame mode data unit,
                 forward direction

   <bmaxFrame>   Maximum length of a             1- 65,535
                 frame mode data unit,
                 backward direction

5.6.2.14 The 'aal5sscop' attribute

   When present, the 'aal5sscop' attribute is used to indicate the
   existence of an SSCOP [43] protocol layer over an AAL5 CPS
   layer [21], and the parameters which pertain to this SSCOP layer.
   SSCOP over AAL5 can also be selected via the  aalApp attribute
   defined below. The format of the 'aal5sscop' media attribute
   line is as follows:

   a=aal5sscop: <fsscopsdu> <bsscopsdu> <fsscopuu> <bsscopuu>

   Each of these fields can be set to a "-" when the intention is to not
   specify them in an SDP descriptor.

   The representation, meaning and values of the <fsscopsdu>, <bsscopsdu>,
   <fsscopuu> and <bsscopuu> fields are identical to those for the
   'aal2sscs3661assured' media attribute line (Section 5.6.2.12). Note that it
   is necessary for the parameters on the 'aal5sscop' media attribute
   line to be consistent with each other.

5.6.3  Service attributes

   The following is a summary list of the SDP media attributes that can
   be used to describe the services that use the  ATM Adaptation Layer (AAL).
   These attributes are detailed in  subsequent subsections.



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        * The 'atmmap' attribute. In the AAL1 and AAL5 contexts, this is
          used to dynamically map payload types into codec strings.

        * The 'silenceSupp' attribute, used to indicate the use of
          of voice activity detection for silence suppression, and to
          optionally parameterize the silence suppression function.

        * The 'ecanf' and 'ecanb' attributes, used to indicate the use of
          of echo cancellation, and to parameterize the this function.

        * The 'gcf' and 'gcb' attributes, used to indicate the use of
          of gain control, and to parameterize the this function.

        * The 'profileDesc' attribute, which can be used to describe
          AAL2 profiles. Although any AAL2 profile can be so described,
          this attribute is useful for describing, at connection
          establishment time,  custom profiles that might not be known
          to the far end. This attribute applies in the AAL2 context
          only.

        * The 'vsel' attribute, which indicates a prioritized list of
          3-tuples for voice service. Each 3-tuple indicates a codec,
          an optional packet length and an optional packetization
          period. This complements the 'm' line information and should
          be consistent with it.

        * The 'dsel' attribute, which indicates a prioritized list of
          3-tuples for voiceband data service. Each 3-tuple indicates a
          codec, an optional packet length and an optional packetization
          period. This complements the 'm' line information and should
          be consistent with it.

        * The 'fsel' attribute, which indicates a prioritized list of
          3-tuples for facsimile service. Each 3-tuple indicates a
          codec, an optional packet length and an optional packetization
          period. This complements the 'm' line information and should
          be consistent with it.

        * The 'codecconfig' attribute, which is used to represent the
          contents of the single codec information element (IE) defined
          in ITU Q.765.5 [57].

        * The 'isup_usi' attribute, which is used to represent
          the 'User Information Layer 1 protocol' field within the
          bearer capability information element defined in Section
          4.5.5 of ITU Q.931 [59].

5.6.3.1  The 'atmmap' attribute

  The 'atmmap' attribute is defined on the basis of the 'rtpmap'
  attribute used in RFC2327.



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        a=atmmap:<payloadType> <encodingName>

   The 'atmmap' attribute is used to dynamically map encoding names
   into payload types. This is necessary for those encoding names which
   have not been assigned a static payload type through IANA [31]. Payload
   types and encoding techniques that have been registered with IANA
   for RTP are retained for AAL1 and AAL5.

   The range of statically defined payload types is in the range
   0-95. All static assignments of payload types to codecs are
   listed in [31]. The range of payload types defined dynamically
   via the 'atmmap' attribute is 96-127.

   In addition to reiterating the payload types and encoding
   names in [31], Table 2 defines non-standard encoding names
   (with "X-" prefixes). Note that [31], rather than Table 2,
   is the authoritative list of standard codec names and payload
   types in the ATM context.




































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               Table 2: Encoding Names and Payload Types
      |---------------------|--------------|---------------------------|
      | Encoding Technique  | Encoding Name|    Payload type           |
      |---------------------|--------------|---------------------------|
      | PCM - Mu law        | "PCMU"       |    0 (Statically Mapped)  |
      |---------------------|--------------|---------------------------|
      | 32 kbps ADPCM       | "G726-32"    |    2 (Statically Mapped)  |
      |---------------------|--------------|---------------------------|
      |Dual rate 5.3/6.3kbps| "G723"       |    4 (Statically Mapped)  |
      |---------------------|--------------|---------------------------|
      | PCM- A law          | "PCMA"       |    8 (Statically Mapped)  |
      |---------------------|--------------|---------------------------|
      | 7 KHz audio coding  | "G722"       |    9 (Statically Mapped)  |
      | within 64 kbps      |              |                           |
      |---------------------|--------------|---------------------------|
      | LD-CELP             | "G728"       |    15 (Statically Mapped) |
      |---------------------|--------------|---------------------------|
      | CS-ACELP            | "G729"       |    18 (Statically Mapped) |
      |(normal/low-complexity)             |                           |
      |---------------------|--------------|---------------------------|
      | Low-complexity      | "X-G729a"    |    None, map dynamically  |
      | CS-ACELP            |              |                           |
      |---------------------|--------------|---------------------------|
      |Normal               | "X-G729b"    |    None, map dynamically  |
      |CS-ACELP w/ ITU      |              |                           |
      |defined silence      |              |                           |
      |suppression          |              |                           |
      +---------------------+--------------+---------------------------+
      |Low-complexity       | "X-G729ab"   |    None, map dynamically  |
      |CS-ACELP w/ ITU      |              |                           |
      |defined silence      |              |                           |
      |suppression          |              |                           |
      |---------------------|--------------|---------------------------|
      | 16 kbps ADPCM       | "X-G726-16"  |    None, map dynamically  |
      |---------------------|--------------|---------------------------|
      | 24 kbps ADPCM       | "X-G726-24"  |    None, map dynamically  |
      |---------------------|--------------|---------------------------|
      | 40 kbps ADPCM       | "X-G726-40"  |    None, map dynamically  |
      |---------------------|--------------|---------------------------|
      | Dual rate 5.3/6.3   |"X-G7231-H"   |    None, map dynamically  |
      | kbps - high rate    |              |                           |
      |---------------------|--------------|---------------------------|
      | Dual rate 5.3/6.3   |"X-G7231-L"   |   None, map dynamically   |
      | kbps - low rate     |              |                           |
      |---------------------|--------------|---------------------------|
      | Dual rate 5.3/6.3   |"X-G7231a-H"  |   None, map dynamically   |
      | kbps - high rate w/ |              |                           |
      | ITU-defined silence |              |                           |
      | suppression         |              |                           |
      |----------------------------------------------------------------|





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      +---------------------+--------------+---------------------------+
      | Dual rate 5.3/6.3   |"X-G7231a-L"  |   None, map dynamically   |
      | kbps - high rate w/ |              |                           |
      | ITU-defined silence |              |                           |
      | suppression         |              |                           |
      |---------------------|--------------|---------------------------|
      | 16 kbps EADPCM      | "X-G727-16"  |    None, map dynamically  |
      |---------------------|--------------|---------------------------|
      | 24 kbps EADPCM      | "X-G727-24"  |    None, map dynamically  |
      |---------------------|--------------|---------------------------|
      | 32 kbps EADPCM      | "X-G727-32"  |    None, map dynamically  |
      |---------------------|--------------|---------------------------|
      |n x 64 kbps Clear    | "X-CCD"      |    None, map dynamically  |
      |Channel without CAS  |              |                           |
      |per af-vtoa-78 [7]   |              |                           |
      |---------------------|--------------|---------------------------|
      |n x 64 kbps Clear    | "X-CCD-CAS"  |    None, map dynamically  |
      |Channel with CAS     |              |                           |
      |per af-vtoa-78 [7]   |              |                           |
      |---------------------|--------------|---------------------------|
      |GSM Full Rate        | "GSM"        |    3 (Statically Mapped)  |
      |---------------------|--------------|---------------------------|
      |GSM Half Rate        |    "GSM-HR"  |    None, map dynamically  |
      |---------------------|--------------|---------------------------|
      |GSM-Enhanced Full Rate    "GSM-EFR" |    None, map dynamically  |
      |---------------------|--------------|---------------------------|
      |GSM-Enhanced Half Rate  "GSM-EHR"   |    None, map dynamically  |
      |---------------------|--------------|---------------------------|
      |Group 3 fax demod.     "X-FXDMOD-3" |    None, map dynamically  |
      |---------------------|--------------|---------------------------|
      | Federal Standard    |    "1016"    |   1 (Statically Mapped)   |
      | FED-STD 1016 CELP   |              |                           |
      |---------------------|--------------|---------------------------|
      | DVI4, 8 KHz [3]     |    "DVI4"    |   5 (Statically Mapped)   |
      |---------------------|--------------|---------------------------|
      | DVI4, 16 KHz [3]    |    "DVI4"    |   6 (Statically Mapped)   |
      |---------------------|--------------|---------------------------|
      | LPC [3], Linear     |    "LPC"     |   7 (Statically Mapped)   |
      | Predictive Coding   |              |                           |
      |---------------------|--------------|---------------------------|
      | L16 [3], Sixteen    |    "L16"     |   10 (Statically Mapped)  |
      | Bit Linear PCM,     |              |                           |
      | Double channel      |              |                           |
      |---------------------|--------------|---------------------------|
      | L16 [3], Sixteen    |    "L16"     |   11 (Statically Mapped)  |
      | Bit Linear PCM,     |              |                           |
      | Single channel      |              |                           |
      |---------------------|--------------|---------------------------|
      | QCELP [3]           |    "QCELP"   |   12 (Statically Mapped)  |
      |---------------------|--------------|---------------------------|
      | MPEG1/MPEG2 audio   |    "MPA"     |   14 (Statically Mapped)  |
      |---------------------|--------------|---------------------------|



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      +---------------------+--------------+---------------------------+
      | DVI4, 11.025 KHz[3] |    "DVI4"    |   16 (Statically Mapped)  |
      |---------------------|--------------|---------------------------|
      | DVI4, 22.05 KHz [3] |    "DVI4"    |   17 (Statically Mapped)  |
      |---------------------|--------------|---------------------------|
      | MPEG1/MPEG2 video   |    "MPV"     |   32 (Statically Mapped)  |
      |---------------------|--------------|---------------------------|
      | MPEG 2 audio/video  |    "MP2T"    |   33 (Statically Mapped)  |
      | transport stream    |              |                           |
      |---------------------|--------------|---------------------------|
      | ITU H.261 video     |    "H261"    |   31 (Statically Mapped)  |
      |---------------------|--------------|---------------------------|
      | ITU H.263 video     |    "H263"    |   33 (Statically Mapped)  |
      |---------------------|--------------|---------------------------|
      | ITU H.263 video     |"H263-1998"   | None, map dynamically     |
      | 1998 version        |              |                           |
      |---------------------|--------------|---------------------------|
      |MPEG 1 system stream |    "MP1S"    | None, map dynamically     |
      |---------------------|--------------|---------------------------|
      |MPEG 2 program stream|    "MP2P"    | None, map dynamically     |
      |---------------------|--------------|---------------------------|
      |Redundancy           |    "RED"     | None, map dynamically     |
      |---------------------|--------------|---------------------------|
      |Variable rate DVI4   |    "VDVI"    | None, map dynamically     |
      |---------------------|--------------|---------------------------|
      |Cell-B               |    "CelB"    | 25                        |
      |---------------------|--------------|---------------------------|
      |JPEG                 |    "JPEG"    | 26                        |
      |---------------------|--------------|---------------------------|
      |nv                   |    "nv"      | 28                        |
      |---------------------|--------------|---------------------------|
      |L8, Eight Bit Linear |    "L8"      | None, map dynamically     |
      |PCM                  |              |                           |
      |---------------------|--------------|---------------------------|
      | ITU-R Recommendation|   "BT656"    | None, map dynamically     |
      | BT.656-3 for        |              |                           |
      | digital video       |              |                           |
      |---------------------|--------------|---------------------------|
      | Adaptive Multirate  |   "FR-AMR"   | None, map dynamically     |
      |-Full Rate (3GPP)[58]|              |                           |
      |---------------------|--------------|---------------------------|
      | Adaptive Multirate  |   "HR-AMR"   | None, map dynamically     |
      |-Half Rate (3GPP)[58]|              |                           |
      |---------------------|--------------|---------------------------|
      | Adaptive Multirate  |   "HR-UMTS"  | None, map dynamically     |
      |- UMTS(3GPP)  [58]   |              |                           |
      |---------------------|--------------|---------------------------|







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5.6.3.2  The 'silenceSupp' attribute

   When present, the 'silenceSupp' attribute is used to indicate
   the use or non-use of  silence suppression.
   The format of the 'silenceSupp' media attribute line is
   as follows:

   a=silenceSupp: <silenceSuppEnable> <silenceTimer> <suppPref> <sidUse>
                   <fxnslevel>

   If any of the parameters in the silenceSupp media attribute line
   is not specified, is inapplicable or is implied, then it is set to
   "-".

   The <silenceSuppEnable> can take on values of "on" or "off". If it
   is "on", then silence suppression is enabled.

   The <silenceTimer> is a 16-bit field which can be represented in
   decimal or hex. Each increment (tick) of this timer represents
   a millisecond. The maximum value of this timer is between 1 and 3
   minutes. This timer represents the time-lag before silence
   suppression kicks in. Even though this can, theoretically, be
   as low as 1 ms, most DSP algorithms take more than that to
   detect silence. Setting <silenceTimer> to a large value (say
   1 minute> is equivalent to disabling silence suppression
   within a call. However, idle channel suppression between calls
   on the basis of silence suppression is still operative in
   non-switched, trunking applications if <silenceSuppEnable> = "on"
   and <silenceTimer> is a large value.

   The <suppPref> specifies the preferred silence suppression
   method that is preferred or already selected.  It can
   take on the string values of "standard" and "custom". If
   its value is "standard", then a standard method (e.g. ITU-defined)
   is preferred to custom methods if such a standard
   is defined. Otherwise, a custom method may be used. If
   <suppPref> is set to "custom", then a custom method, if
   available, is preferred to the standard method.

  The <sidUse> indicates whether SIDs (Silence Insertion
  Descriptors) are to be used, and whether they use fixed comfort
  noise or sampled background noise. It can take on the
  string values of "No SID", "Fixed Noise", "Sampled Noise".

  If the value of <sidUse> is "Fixed Noise", then  <fxnslevel>
  provides its level. It can take on integer values in the range
  0-127, as follows:








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     +-----------------------+---------------------+
     | <fxnslevel> value     |         Meaning     |
     +-----------------------+---------------------+
     |  0-29                 |          Reserved   |
     |   30                  |          -30 dBm0   |
     |   31                  |          -31 dBm0   |
     |   . . .               |           . . .     |
     |   77                  |          -77 dBm0   |
     |   78                  |          -78 dBm0   |
     |  79-126               |          reserved   |
     |   127                 | Idle Code (no noise)|
     +-----------------------+---------------------+

   In addition to the decimal representation of <fxnslevel>, a
   hex representation, preceded by a "0x" prefix, is also allowed.

5.6.3.3  The 'ecanf' and 'ecanb' attributes

   When present, the 'ecanf' and 'ecanb' attributes are used to indicate
   the use or non-use of  echo cancellation in the forward
   and backward directions respectively. See Section
   2.3 for a definition of the terms 'forward' and 'backward'.

   The format of the 'ecanf' and 'ecanb' media attribute lines is
   as follows:

   a=ecanf: <ecanEnable> <ecanType>
   a=ecanb: <ecanEnable> <ecanType>

   If any of the parameters in the ecanf and ecanb media attribute lines
   is not specified, is inapplicable or is implied, then it is set to
   "-".

   If the 'ecanf' or 'ecanb' media attribute lines is not present,
   then means other than the SDP descriptor must be used to determine
   the applicability and nature of echo cancellation in that direction.
   Examples of such means are MIB provisioning, the local connection options
   structure in MGCP etc.

   The <ecanEnable> parameter can take on values of "on" or "off". If it
   is "on", then echo cancellation is enabled. If it is "off",
   then echo cancellation is disabled.

   The <ecanType> parameter can take on the string values "G165" and "G168"
   respectively.

   When SDP is used with some media gateway control protocols such as MGCP
   and Megaco [26], there exist means outside SDP descriptions to specify
   the echo cancellation properties of a connection. Nevertheless, this
   media attribute line is included for completeness.  As a result, the
   SDP can be used for describing echo cancellation in applications
   where alternate means for this are unavailable.



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5.6.3.4  The 'gcf' and 'gcb' attributes

   When present, the 'gcf' and 'gcb' attributes are used to indicate
   the use or non-use of  gain control in the forward and backward
   directions respectively. See Section 2.3 for a definition of the
   terms 'forward' and 'backward'.

   The format of the 'gcf' and 'gcb' media attribute lines is as
   follows:

   a=gcf: <gcEnable> <gcLvl>
   a=gcb: <gcEnable> <gcLvl>

   If any of the parameters in the gcf and gcb media attribute lines
   is not specified, is inapplicable or is implied, then it is set to
   "-". If the 'gcf' or 'gcb' media attribute line is  not present,
   then means other than the SDP descriptor must be used to determine the
   applicability and nature of gain control in that direction. Examples of such
   means are MIB provisioning, the local connection options structure in MGCP
   etc.

   The <gcEnable> parameter can take on values of "on" or "off". If it
   is "on", then gain control is enabled. If it is "off", then
   gain control is disabled.

   The <gcLvl> parameter is represented as the decimal or hex
   equivalent of a  16-bit binary field. A value of 0xFFFF implies
   automatic gain control. Otherwise, this number indicates the
   number of decibels of inserted loss. The upper bound, 65,535 dB
   (0xFFFE) of inserted loss,  is an absurdly large  number and is a
   carryover from Megaco [26]. In practical applications, the inserted loss
   is much lower.

   When SDP is used with some media gateway control protocols such as MGCP
   and Megaco [26], there exist means outside SDP descriptions to specify
   the gain control properties of a connection. Nevertheless, this
   media attribute line is included for completeness.  As a result, the
   SDP can be used for describing gain control in applications
   where alternate means for this are unavailable.

5.6.3.5  The 'profileDesc' attribute

   There is one  'profileDesc' media attribute line  for each AAL2
   profile that is intended to be described.  The 'profileDesc' media
   attribute line  is  structured  as follows:

     a=profileDesc: <aal2transport> <profile>  <uuiCodeRange#1>
       <encodingName#1> <packetLength#1> <packetTime#1>
       <uuiCodeRange#2> <encodingName#2> <packetLength#2>
       <packetTime#2>... <uuiCodeRange#N> <encodingName#N>
        <packetLength#N> <packetTime#N>



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   Here, <aal2transport> can have those values of <transport> (Table 1) that
   pertain to AAL2. These are:

             AAL2/ATMF
             AAL2/ITU
             AAL2/custom
             AAL2/<corporateName>
             AAL2/IEEE:<oui>

   The parameter <profile> is identical to its definition for the 'm'
   line (Section 5.5.4).

   The profile elements (rows in the profile tables of  ITU I.366.2 or
   AF-VTOA-0113) are represented as four-tuples following the <profile>
   parameter in the 'profileDesc' media attribute line. If a member of
   one of these four-tuples is not specified or is implied, then it is
   set to   "-".

   The <uuiCodeRange> parameter is represented by D1-D2, where D1 and
   D2 are decimal integers in the range 0 through 15.

   The <encodingName> parameter can take one of the values in column 2
   of Table 2. Additionally, it can take on the following descriptor
   strings:  "PCMG", "SIDG" and "SID729".  These stand for generic PCM,
   generic SID and G.729 SID respectively.

   The <packetLength> is a decimal integer representation of the AAL2
   packet length in octets.

   The <packetTime> is a decimal integer representation of the AAL2
   packetization interval in microseconds.

   For instance, the 'profileDesc' media attribute line below defines
   the AAL2/custom 100 profile. This profile is reproduced in the Table 3
   below. For a description of the parameters in this profile such as
   M and the sequence number interval, see ITU I.366.2 [13].

     a=profileDesc:AAL2/custom 100 0-7 PCMG 40 5000 0-7 SIDG 1 5000 8-15
         G726-32 40 10000 8-15 SIDG 1 5000

   If the <packetTime> parameter is to be omitted or implied, then the
   same profile  can be represented as follows:

     a=profileDesc:AAL2/custom 100 0-7 PCMG 40 - 0-7 SIDG 1 - 8-15
          G726-32 40 - 8-15 SIDG 1 -

   If a gateway has a provisioned or hard coded definition of a
   profile, then any definition provided via the 'profileDesc' line
   overrides it. The exception to this rule is with regard to standard
   profiles such as ITU-defined profiles and ATMF-defined profiles. In



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   general, these should not be defined via a 'profileDesc' media
   attribute line. If they are, then the definition needs to be
   consistent with the standard definition else the SDP session
   descriptor should be rejected with an appropriate error code.


             Table 3: Example of a  custom AAL2 profile
   |---------------------------------------------------------------|
   | UUI  | Packet |Encoding |               |     |Packet|Seq.No. |
   | Code | Length |per ITU  |Description of |  M  |Time  |Interval|
   |point |(octets)|I.366.2  |  Algorithm    |     |(ms)  |(ms)    |
   |Range |        |  2/99   |               |     |      |        |
   |      |        | version |               |     |      |        |
   |---------------------------------------------------------------|
   | 0-7  |    40  |  Figure | PCM, G.711-64,|   1 |    5 |    5   |
   |      |        |  B-1    |  generic      |     |      |        |
   |------|--------|---------|---------------|-----|------|--------|
   | 0-7  |    1   |  Figure | Generic SID   |   1 |    5 |    5   |
   |      |        |  I-1    |               |     |      |        |
   |------|--------|---------|---------------|-----|------|--------|
   | 8-15 |    40  |  Figure | ADPCM,        |   2 |   10 |    5   |
   |      |        |  E-2    | G.726-32      |     |      |        |
   |------|--------|---------|---------------|-----|------|--------|
   | 8-15 |    1   |  Figure | Generic SID   |   1 |    5 |    5   |
   |      |        |  I-1    |               |     |      |        |
   |------|--------|---------|---------------|-----|------|--------|

5.6.3.6  The 'vsel' attribute

 The 'vsel' attribute indicates a prioritized list of one or more
 3-tuples for voice service. Each 3-tuple indicates a codec,  an optional
 packet length and an optional packetization period. This complements the 'm'
 line information and should be consistent with it.

 The 'vsel' line is structured as follows:

      a=vsel:<encodingName #1> <packetLength #1><packetTime #1>
                <encodingName #2> <packetLength #2><packetTime #2>
                ...
               <encodingName #N> <packetLength #N><packetTime #N>

   where the <encodingName> parameter can take one of the values in column 2 of
   Table 2. The <packetLength> is a decimal integer representation of the
   packet length in octets. The <packetTime> is a decimal integer
   representation of the packetization interval in microseconds. The parameters
   <packetLength>and <packetTime>  can be set to "-" when not needed. Also, the
   entire 'vsel' media attribute line can be omitted when not needed.

   For example,

        a=vsel:G729 10 10000 G726-32 40 10000




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   indicates first preference  of G.729 or G.729a (both are interoperable) as
   the voice encoding scheme. A packet length of 10 octets and a packetization
   interval of 10 ms are associated with this codec. G726-32 is  the second
   preference stated in this line, with an associated packet length of 40
   octets  and a packetization  interval of 10 ms. If the packet length and
   packetization interval are intended to be omitted, then this media attribute
   line becomes

        a=vsel:G729 - - G726-32 - -

   The media attribute line

         a=vsel:G726-32 40 10000

   indicates preference for or selection of 32 kbps ADPCM with a packet
   length of 40 octets and a packetization interval of 10 ms.

   This media attribute line can be used in ATM as well as non-ATM contexts.
   Within the ATM context, it can be applied to the AAL1, AAL2 and AAL5
   adaptations. The <packetLength> and <packetTime> are not meaningful
   in the AAL1 case and should be set to "-". In the AAL2 case,
   this line  determines the use of some or all of the rows in
   a given profile table. If multiple 3-tuples are present, they
   can indicate a hierarchical assignment of some rows in that
   profile to voice service e.g. row A preferred to row B etc.
   If multiple profiles are present on the 'm' line, the profile
   qualified by this attribute is the first
   profile. If a single profile that has been selected for a connection
   is indicated in the 'm' line, the 'vsel' attribute qualifies the
   use, for voice service,  of codecs within that profile.

   With most of the encoding names in Figure 2, the packet length
   and packetization period can be derived from each other. One of them
   can be set to "-" without a loss of information. There are some
   exceptions such as the IANA-registered encoding names G723, DVI4 and
   L16 for which this is not true. Therefore, there is a need to
   retain both the packet length and packetization period  in the
   definition of the 'vsel' line.

5.6.3.7  The 'dsel' attribute

 The 'dsel' attribute  indicates a prioritized list of
 one or more 3-tuples for voiceband data service. The <fxIncl>
 flag indicates whether this definition of voiceband data
 includes fax ("on" value) or not ("off" value). If <fxIncl> is
 "on", then the 'dsel' line  must be consistent with any 'fsel' line
 in the session description. In this case,  an error event is generated
 in the case of inconsistency. Each 3-tuple indicates a codec,
 an optional packet length and an optional packetization
 period. This complements the 'm' line information and should
 be consistent with it.




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   The 'dsel' line is structured as follows:

      a=dsel:<fxIncl> <encodingName #1> <packetLength #1><packetTime #1>
                <encodingName #2> <packetLength #2><packetTime #2>
                ...
               <encodingName #N> <packetLength #N><packetTime #N>

   where the <encodingName> parameter can take one of the values in
   column 2 of Table 2. The <packetLength> and <packetTime>
   parameters are per their definition, above, for the 'vsel'
   media attribute line. The parameters <packetLength>and <packetTime>)
   can be set to "-" when not needed. The <fxIncl> flag is presumed to be
   "off" if it is set to "-". Also, the entire 'dsel' media attribute line
   can be omitted when not needed.

   For example,

       a=dsel:-  G726-32 20 5000 PCMU 40 5000

   indicates that this line does not address facsimile, and that the
   first preference for the voiceband data codes is 32 kbps ADPCM,
   while the second preference is PCMU.  The packet length
   and the packetization interval associated with G726-32 are 20  octets and
   5 ms respectively. For PCMU, they are 40  octets and 5 ms respectively.

   This media attribute line can be used in ATM as well as non-ATM contexts.
   Within the ATM context, it can be applied to the AAL1, AAL2 and AAL5
   adaptations. The <packetLength> and <packetTime> are not meaningful
   in the AAL1 case and should be set to "-". In the AAL2 case,
   this line  determines the use of some or all of the rows in
   a given profile table. If multiple 3-tuples are present, they
   can indicate a hierarchical assignment of some rows in that
   profile to voiceband data service e.g. row A preferred to row B etc.
   If multiple profiles are present on the 'm' line, the profile
   qualified by this attribute is the first
   profile. If a single profile that has been selected for a connection
   is indicated in the 'm' line, the 'dsel' attribute qualifies the
   use, for voiceband data service,  of codecs within that profile.

   With most of the encoding names in Figure 2, the packet length
   and packetization period can be derived from each other. One of them
   can be set to "-" without a loss of information. There are some
   exceptions such as the IANA-registered encoding names G723, DVI4 and
   L16 for which this is not true. Therefore, there is a need to
   retain both the packet length and packetization period  in the
   definition of the 'dsel' line.

5.6.3.8  The 'fsel' attribute

   The 'fsel' attribute indicates a prioritized list of
   one or more 3-tuples for facsimile service. If an 'fsel' line
   is present, any 'dsel' line with <fxIncl> set to "on" in the session



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   description must be consistent with it. In this case,
   an  error event is generated in the case of inconsistency.
   Each 3-tuple indicates a codec, an optional packet length and an
   optional packetization period. This complements the 'm' line information
   and should be consistent with it.

   The 'fsel' line is structured as follows:

      a=fsel:<encodingName #1> <packetLength #1><packetTime #1>
                <encodingName #2> <packetLength #2><packetTime #2>
                ...
               <encodingName #N> <packetLength #N><packetTime #N>

   where the <encodingName> parameter can take one of the values in
   column 2 of Table 2. The <packetLength> and <packetTime>
   parameters are per their definition, above, for the 'vsel'
   media attribute line. The parameters <packetLength>and <packetTime> can
   be set to "-" when not needed. Also, the entire 'fsel' media attribute
   line can be omitted when not needed.

   For example,

        a=fsel:FXDMOD-3 - -

   indicates demodulation and remodulation of ITU-T group 3 fax at the
   gateway.


        a=fsel:PCMU 40 5000 G726-32 20 5000

   indicates  a first and second preference of Mu-law PCM and 32 kbps
   ADPCM as the facsimile encoding scheme.  The packet length
   and the packetization interval associated with G726-32 are 20  octets and
   5 ms respectively. For PCMU, they are 40  octets and 5 ms respectively.

   This media attribute line can be used in ATM as well as non-ATM contexts.
   Within the ATM context, it can be applied to the AAL1, AAL2 and AAL5
   adaptations.  The <packetLength> and <packetTime> are not meaningful
   in the AAL1 case and should be set to "-". In the AAL2 case,
   this line  determines the use of some or all of the rows in
   a given profile table. If multiple 3-tuples are present, they
   can indicate a hierarchical assignment of some rows in that
   profile to facsimile service e.g. row A preferred to row B etc.
   If multiple profiles are present on the 'm' line, the profile
   qualified by this attribute is the first
   profile. If a single profile that has been selected for a connection
   is indicated in the 'm' line, the 'fsel' attribute qualifies the
   use, for facsimile service,  of codecs within that profile.

   With most of the encoding names in Figure 2, the packet length
   and packetization period can be derived from each other. One of them
   can be set to "-" without a loss of information. There are some



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   exceptions such as the IANA-registered encoding names G723, DVI4 and
   L16 for which this is not true. Therefore, there is a need to
   retain both the packet length and packetization period  in the
   definition of the 'fsel' line.

5.6.3.9  The 'codecconfig' attribute

   When present, the 'codecconfig' attribute is used to represent the
   contents of the single codec information element (IE) defined in [57].
   The contents of this IE are: a single-octet Organizational Identifier
   (OID) field, followed by a single-octet Codec Type field, followed by
   zero or more octets of a codec configuration bit-map. The semantics of
   the codec configuration bit-map are specific to the organization
   [57, 58]. The 'codecconfig' attribute is represented as follows:

         a=codecconfig:<q7655scc>

   The <q7655scc> (Q.765.5 single codec IE contents) parameter is
   represented as a string of hex digits. The number of hex digits is
   even (range 4 -32). The "0x" prefix shall be omitted since this value
   is always hexadecimal. As with other hex values [Section 2.2],
   digits to the left are more significant than  digits to the right.
   Leading zeros shall not be omitted.

   An example of the use of this media attribute is:

         a=codecconfig:01080C

   The first octet indicates an Organizational Identifier of 0x01
   (the ITU-T). Using ITU Q.765.5 [57], the second octet (0x08) indicates
   a codec type of G.726 (ADPCM). The last octet, 0x0C indicates that
   16 kbps and 24 kbps rates are NOT supported, while the 32 kbps and
   40 kbps rates ARE supported.

5.6.3.10 The 'isup_usi' attribute

   When present, the 'isup_usi' attribute is used to represent the
   'User Information Layer 1 protocol' field within the bearer
   capability information element defined in Section 4.5.5 of [59], and
   reiterated as the user service information element (IE) in Section 3.57
   of [60]. The 'User Information Layer 1 protocol' field consists of
   the five least significant bits of Octet 5 of this information
   element. This field is represented by the USI property in Section C.9
   of the Megaco/H.248 protocol [26].

   Within SDP, the 'isup_usi' attribute is represented as follows:

         a=isup_usi:<isupUsi>

   The <isupUsi> parameter is represented as a string of two hex
   digits. The "0x" prefix shall be omitted since this value
   is always hexadecimal. As with other hex values [Section 2.2],



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   digits to the left are more significant than  digits to the right.
   These hex digits are constructed from an octet with three leading
   '0' bits and last five bits equal to the 'User Information Layer
   1 protocol' field described above.  As specified in [59] and [26],
   bit 5 of this field is the most significant bit. The resulting values
   of the <isupUsi> parameter are as follows:


    VALUE   MEANING
    0x01    CCITT standardized rate adaption V.110 and X.30
    0x02    Recommendation G.711 Mu-law
    0x03    Recommendation G.711 A-law
    0x04    Recommendation G.721 32 kbps ADPCM and Recommendation I.460
    0x05    Recommendations H.221 and H.242
    0x06    Recommendation  H.223 and H.245
    0x07    Non-ITU-T standardized rate adaption
    0x08    ITU-T standardized rate adaption V.120
    0x09    CCITT standardized rate adaption X.31 HDLC flag stuffing

5.6.4   Miscellaneous media attributes

   The 'chain' media attribute line, which is used to chain consecutive
   SDP descriptions,  cannot be classified as an ATM, AAL or service
   attribute. It is detailed in the following subsection.

5.6.4.1 The 'chain' attribute

   The start of an SDP descriptor is marked by a 'v' line. In some
   applications, consecutive SDP descriptions are alternative descriptions
   of the same session. In others, these describe different layers of the
   same connection (e.g. IP, ATM, frame relay). This is useful when these
   connectivity at these layers are established at the same time e.g. an
   IP-based session over an ATM SVC. To distinguish between the
   alternation and concatenation of SDP descriptions, a 'chain' attribute
   can be used in the case of concatenation.

   When present, the 'chain' attribute binds an SDP description to  the
   next or previous SDP description. The next or previous description is
   separated from the current one by a 'v' line. It is not necessary that
   this description also have a 'chain' media attribute line.

   Chaining averts the need to set up a single SDP description for a
   session that is simultaneously created at multiple layers. It allows
   the SDP descriptors for  different layers to remain simple and clean.
   Chaining is not needed in the Megaco context, where it is possible to
   create separate terminations for the different layers of a connection.

   The 'chain' media attribute line has the following format:

        a=chain:<chainPointer>





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   The <chainPointer> field can take on the following string values:
   "NEXT", "PREVIOUS" and "NULL". The value "NULL" is not equivalent to
   omitting the chain attribute from a description since it expressly
   precludes the possibility of chaining. If the 'chain' attribute is
   absent in an SDP description, chaining can still be realized by the
   presence of a chain media attribute line in the previous or next
   description.

5.6.5   Use of the second media-level part in H.323 Annex C applications

Section 4 mentions that H.323 annex C applications have a second media level
part for the ATM session description. This is used to convey information about
the RTCP stream. Although the RTP stream is encapsulated in AAL5 with no
intervening IP layer, the RTCP stream is sent to an IP address and RTCP port.
This media level part has the following format:

   m= control <rtcpPortNum> H323c -
   c= IN IP4 <rtcpIPaddr>

Consistency with rfc2327 is maintained in the location and format of these
lines. The <fmt list> in the 'm' line is set to "-". The 'c' line in the second
media-level part pertains to RTCP only.

The <rtcpPortNum> and <rtcpIPaddr> subparameters indicate the port number
and IP address on which the media gateway is prepared to receive RTCP packets.

Any of the subparameters on these lines can be set to "-" if they are known by
other means.

The range and format of the <rtcpPortNum> and <rtcpIPaddr> subparameters is per
[1]. The <rtcpPortNum> is a decimal number between 1024 and 65535. It is an odd
number. If an even number in this range is specified, the next odd number is
used. The <rtcpIPaddr> is expressed in the usual dotted decimal IP address
representation, from 0.0.0.0 to 255.255.255.255.

5.6.6   Use of the eecid media attribute in call establishment procedures

This informative section supplements the definition of the eecid
attribute (Section 5.6.1.1) by describing example procedures for its use.
These procedures assume a bearer-signaling mechanism for connection set-up
that is independent of service-level call control. These procedures are
independent of the media gateway control protocol (MGCP, Megaco, SIP etc.),
the protocol used between media gateway controllers (ITU Q.1901, SIP
etc.) and the protocol used for bearer connection set-up (Q.2931, UNI, PNNI,
AINI, IISP, Q.2630.1 etc.).










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                            Inter-MGC
               +---------+  Protocol        +---------+
               |   MGC   |------------------|   MGC   |
               +---------+                  +---------+
                    |                            |
                    |Media Gateway               |Media Gateway
                    |Control Protocol            |Control Protocol
                    |                            |
                +------------+  (ATM Network)   +------------+
                |Originating |------------------|Terminating |
                |Media       |  Bearer Setup    |Media       |
                |Gateway     |  Protocol        |Gateway     |
                +------------+                  +------------+

In the diagram above, the originating media gateway originates the service-
level call. The terminating media gateway terminates it. In the forward  bearer
connection  set-up  model,  the  originating  media  gateway  initiates  bearer
connection  set-up.  In  the  backward  bearer  connection  set-up  model,  the
terminating gateway initiates bearer connection set-up.

Example use of the Backward Bearer Connection Set-up Model:
(1) The originating media gateway controller (OMGC) initiates service-level
    call establishment by sending the appropriate control message to the
    originating media gateway (OMG).

(2) The originating media gateway (OMG) provides its NSAP address and an eecid
    value to the OMGC, using the following SDP description:


   v=0
   o=- 2873397496 0 ATM NSAP
      47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00
   s=-
   c=ATM NSAP
     47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00
   t=0 0
   m=audio $ AAL2/ITU 8
   a=eecid:B3D58E32

(3) The originating media gateway controller (OMGC) signals
    the terminating media gateway controller (TMGC) through
    the appropriate mechanism (ISUP with Q.1901 extensions, SIP etc.).
    It provides the TMGC with the NSAP address and the eecid provided
    by the OMG.

(4) The TMGC sends the appropriate control message to the TMG. This
    includes the session descriptor received from the OMG. This
    descriptor contains the NSAP address of the OMG and the EECID
    assigned by the OMG. Additionally, the TMGC instructs the TMG
    to set up an SVC to the OMG. It also requests the TMG to notify
    the TMGC when SVC set-up is complete. Depending on the control



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    protocol used, this can be done through a variety of means.
    In the Megaco context, the request to set-up an SVC (not the
    notification request for the SVC set-up event) can be made through
    the following local descriptor:

   v=0
   o=- 2873397497 0 ATM - -
   s=-
   c=ATM - -
   t=0 0
   m=audio $ - -
   a=bearerType:SVC on

   The 'bearerType' attribute indicates that an SVC is to be used and
   that the <localInitiation> flag is on i.e. the SVC is to be set up
   by the TMG.

(5) The TMG acknowledges the control message from the TMGC. It returns
    the following SDP descriptor with the acknowledge:

   v=0
   o=- 2873397498 0 ATM NSAP
      47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00
   s=-
   c=ATM NSAP
     47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00
   t=0 0
   m=audio $ AAL2/ITU 8

   The NSAP address information provided in this descriptor is not needed.
   It can be omitted (by setting it to "- -").

(6) The TMG sends an SVC set-up message to the OMG. Within the GIT
    information element, it includes eecid (B3D58E32) received from
    the OMG.

(7) The OMG uses the eecid to correlate the SVC set-up request with
    service-level control message received before from the OMGC.

(8) The OMG returns an SVC connect message to the TMG. On receiving
    this message, the TMG sends an event notification to the TMGC
    indicating successful SVC set-up.

    Note that, for this example,  the "v=", "o=", "s=" and "t=" lines can be
    omitted in the Megaco context.

 Example use of the Forward Bearer Connection Set-up Model:
(1) The originating media gateway controller (OMGC) initiates service-level
    call establishment by sending the appropriate control message to the
    originating media gateway (OMG).

(2) The originating media gateway (OMG) provides its NSAP address



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    to the OMGC, using the following SDP description:

   v=0
   o=- 2873397496 0 ATM NSAP
      47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00
   s=-
   c=ATM NSAP
     47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00
   t=0 0
   m=audio $ AAL2/ITU 8

   The NSAP address information provided in this descriptor is not needed.
   It can be omitted (by setting it to "- -").


(3) The originating media gateway controller (OMGC) signals
    the terminating media gateway controller (TMGC) through
    the appropriate mechanism (ISUP with Q.1901 extensions, SIP etc.).
    Although this is not necessary, it can provide the TMGC with the
    NSAP address provided by the OMG.

(4) The TMGC sends the appropriate control message to the TMG. This
    includes the session descriptor received from the OMG. This
    descriptor contains the NSAP address of the OMG.

(5) The TMG acknowledges the control message from the TMGC. Along with
    the acknowledgement, it provides an SDP descriptor with a locally
    assigned eecid.

   v=0
   o=- 2873397714 0 ATM NSAP
      47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00
   s=-
   c=ATM NSAP
     47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00
   t=0 0
   m=audio $ AAL2/ITU 8
   a=eecid:B3D58E32

(6) The terminating media gateway controller (TMGC) signals
    the originating media gateway controller (OMGC) through
    the appropriate mechanism (ISUP with Q.1901 extensions, SIP etc.).
    It provides the OMGC with the NSAP address and the eecid provided
    by the TMG.

 (7) The OMGC sends the appropriate control message to the OMG. This
    includes the session descriptor received from the TMG. This
    descriptor contains the NSAP address of the TMG and the EECID
    assigned by the TMG. Additionally, the OMGC instructs the OMG
    to set up an SVC to the TMG. It also requests the OMG to notify
    the OMGC when SVC set-up is complete. Depending on the control
    protocol used, this can be done through a variety of means.



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    In the Megaco context, the request to set-up an SVC (not the
    notification request for the SVC set-up event) can be made through
    the following local descriptor:

    v=0
    o=- 2873397874 0 ATM - -
    s=-
    c=ATM - -
    t=0 0
    m=audio $ - -
    a=bearerType:SVC on

   The 'bearerType' attribute indicates that an SVC is to be used and
   that the <localInitiation> flag is on i.e. the SVC is to be set up
   by the TMG.

(8) The OMG acknowledges the control message from the OMGC.

(9) The OMG sends an SVC set-up message to the TMG. Within the GIT
    information element, it includes eecid (B3D58E32) received from
    the TMG.

(10)The TMG uses the eecid to correlate the SVC set-up request with the
    service-level control message received before from the TMGC.

(11)The TMG returns an SVC connect message to the OMG. On receiving
    this message, the OMG sends an event notification to the OMGC
    indicating successful SVC set-up.

    Note that, for this example,  the "v=", "o=", "s=" and "t=" lines can be
    omitted in the Megaco context.
























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6.0   List of Parameters with  Representations

This section provides a list of the parameters used in this document,
and the formats used to represent them in SDP descriptions. In general, a
"-" value can be used for any field that is not specified, is inapplicable
or is implied.


PARAMETER           MEANING              REPRESENTATION

<username>          User name            Constant "-"

<sessionID>         Session ID           Up to 32 decimal or
                                         hex digits

<version>           Version of            "0" or 10 decimal digits
                    SDP descriptor

<networkType>       Network type         Constant "ATM" for ATM transport

<addressType>       Address type         String values:
                                         "NSAP", "E164", "GWID",
                                         "ALIAS"

<address>           Address              "NSAP":  40 hex digits, dotted
                                         "E164":  up to 15 decimal digits
                                         "GWID":  up to 32 characters
                                         "ALIAS": up to 32 characters

<sessionName>       Session name         Constant "-"

<startTime>         Session start        "0" or 10 decimal digits
                    time

<stopTime>          Session stop         Constant "0"
                    time

<vcci>              Virtual Circuit      Decimal or hex equivalent
                    Connection           of 16 bits
                    Identifier

<ex_vcci>           Explicit             "VCCI-" prefixed to <vcci>
                    representation
                    of <vcci>

<bcg>               Bearer Connection    Decimal or hex equivalent
                    Group                of 8 bits

<ex_bcg>            Explicit             "BCG-" prefixed to <bcg>
                    representation
                    of <bcg>




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<portId>            Port ID              Hex number of up to 32 digits


<ex_portId>         Explicit            "PORT-" prefixed to <portId>
                    representation
                    of <portId>

<vpi>               Virtual Path        Decimal or hex equivalent
                    Identifier          of 8 or 12 bits

<ex_vpi>            Explicit            "VPI-" prefixed to <vpi>
                    representation
                    of <vpi>


<vci>                Virtual Circuit     Decimal or hex equivalent
                     Identifier          of 16 bits

<ex_vci>             Explicit            "VCI-" prefixed to <vci>
                     representation
                     of <vci>

<vpci>               Virtual Path        Decimal or hex equivalent
                     Connection          of 16 bits
                     Identifier

<ex_vpci>            Explicit            "VPCI-" prefixed to <vpci>
                     representation
                     of <vpci>

<cid>                Channel              Decimal or hex equivalent
                     Identifier           of 8 bits

<ex_cid>             Explicit             "CID-" prefixed to <cid>
                     representation
                     of <cid>

<payloadType>        Payload               Decimal integer 0-127
                     Type

<transport>          Transport            Values listed in
                                          Table 1.

<profile>            Profile              Decimal integer 1-255

<eecid>              End-to-end            Up to 8 hex digits
                     Connection
                     Identifier







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<aalType>            AAL type              String values:
                                          "AAL1","AAL1_SDT","AAL1_UDT",
                                          "AAL2", "AAL3/4",
                                          "AAL5", "USER_DEFINED_AAL"

<asc>               ATM service           String values:
                    category defined      "CBR", "nrt-VBR", "rt-VBR",
                    by the ATMF           "UBR", "ABR", "GFR"

<atc>               ATM transfer          String values:
                    capability            "DBR","SBR","ABT/IT","ABT/DT",
                    defined by the        "ABR"
                    ITU

<subtype>            <asc>/<atc>          Decimal integer 1-10
                     subtype

<qosClass>           QoS Class            Decimal integer 0-5

<bcob>               Broadband Bearer     Decimal or hex representation
                     Class                of 5-bit field

<eetim>              End-to-end timing    String values: "on",
                     required             "off".

<stc>                Susceptibility      Decimal equivalent of
                     to clipping         a 2-bit field

<upcc>               User plane          Decimal equivalent of
                     connection          a 2-bit field
                     configuration

<cdvType>            CDV type            String values:
                                         "PP", "2P"

<acdv>               Acceptable CDV      Decimal equivalent
                                         of 24-bit field

<ccdv>               Cumulative CDV      Decimal equivalent
                                         of 24-bit field

<eetd>               End-to-end transit  Decimal equivalent
                     delay               of 16-bit field


<cmtd>               Cumulative transit  Decimal equivalent
                     delay               of 16-bit field


<aclr>               Acceptable           Decimal equivalent
                     Cell Loss Ratio      of 8-bit field




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<clpLvl>             CLP level            String values:
                                          "0", "0+1"

<pcr>                Peak                 Decimal
                     Cell Rate            equivalent of a 24-bit field.

<scr>                Sustained            Decimal
                     Cell Rate            equivalent of a 24-bit field

<mbs>                Maximum              Decimal
                     Burst Size           equivalent of 16-bit field

<cdvt>               CDVT                 Decimal equivalent of 24-bit
                                          field.

<mcr>                Minimum              Decimal
                     Cell Rate            equivalent of a 24-bit field

<mfs>                Maximum              Decimal
                     Frame Size           equivalent of a 16-bit field

<fd>                 Frame Discard        String Values:
                     Allowed              "on", "off"

<te>                 CLP tagging          String Values:
                                          "on", "off"

<nrm>                NRM                  Decimal/hex equivalent
                                          of 3 bit field

<trm>                TRM                  -ditto-

<cdf>                CDF                  -ditto-

<adtf>               ADTF                 Decimal/Hex  equivalent
                                          of 10 bit field

<ficr>               Forward Initial      Decimal equivalent of
                     Cell Rate            24-bit field

<bicr>               Backward Initial     Decimal equivalent of
                     Cell Rate            24-bit field

<ftbe>               Forward Transient    Decimal equivalent of
                     Buffer Exposure      24-bit field

<btbe>               Backward Transient   Decimal equivalent of
                     Buffer Exposure      24-bit field

<crmrtt>             Cumulative RM        Decimal equivalent of
                     round-trip time      24-bit field
                     (Microseconds)



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<frif>               Forward rate                Decimal integer
                     increase factor             0 -15

<brif>               Backward rate               Decimal integer
                     increase factor             0 -15

<frdf>               Forward rate                Decimal integer
                     decrease factor             0 -15

<brdf>               Backward rate               Decimal integer
                     decrease factor             0 -15

<bearerType>         Bearer Type                 String Values:
                                                 "PVC", "SVC", "CID"

<localInitiation>    Local Initiation             String values:
                                                  "on", "off"

<sci>                Screening Indication         Decimal or hex
                                                  equivalent of 4  bits.

<lsn>                Leaf Sequence Number         Decimal or hex
                                                  equivalent of 32 bits.

<cdStd>              Coding standard for          Decimal or hex
                     connection scope             equivalent of 2 bits.
                     selection IE
                     Definition: UNI 4.0 [5]

<conScpTyp>          Type of connection scope     Decimal or hex
                     Definition: UNI 4.0 [5]      equivalent of 4 bits

<conScpSel>          Connection scope selection   Decimal or hex equivalent
                     Definition: UNI 4.0 [5]      of 8 bits

<cacheEnable>        Enable SVC caching           String values: "on", "off"

<cacheTimer>        Timer for cached SVC          Decimal or hex equivalent
                    deletion                      of 32-bit field

<bearerSigIEType>   Bearer Signaling IE Type      2 hex digits

<bearerSigIELng>    Bearer Signaling IE Length    1-4 hex digits

<bearerSigIEVal>    Bearer Signaling IE Value     Even number of hex digits,
                                                  2-512








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<appClass>          Application                String values:
                    specification              "itu_h323c","af83",
                                               "AAL5_SSCOP",
                                               "itu_i3661_unassured",
                                               "itu_i3661_assured",
                                               "itu_i3662",
                                               "itu_i3651", "itu_i3652",
                                               "itu_i3653", "itu_i3654",
                                               "FRF5", "FRF8","FRF11",
                                               "itu_h2221"

<oui>               Organizationally          1 to  6 hex digits
                    Unique Identifier

<appId>             Application Identifier    1 to 8 digits

<cbrRate>           CBR Rate                 Two hex digits.

<sbc>               Subchannel Count         T1: Decimal integer 1-24
                                             or hex equivalent
                                             E1: Decimal integer 1-31
                                             or hex equivalent

<clkrec>             Clock Recovery         String values:
                     Method                 "NULL", "SRTS",
                                            "ADAPTIVE"

<fecEnable>          Forward Error          String values:
                     Correction Enable      "NULL", "LOSS_SENSITIVE"
                                            "DELAY_SENSITIVE"

<partialFill>        Partial Fill           Decimal integer 1-48
                                            or hex equivalent

<structureEnable>    Structure Present      String values:
                                            "on", "off"

<blksz>              Block Size              Decimal or hexadecimal
                                             equivalent of 16 bits

<cpcs>              Maximum                  AAL5: Decimal or hex
                    CPCS SDU size            equivalent of 16 bits
                                             AAL2: 45 or 64, decimal
                                             or hex representation

<cidLowerLimit>     CID lower limit          Decimal integer 8-255
                                             or hex equivalent

<cidUpperLimit>     CID upper limit          Decimal integer 8-255
                                             or hex equivalent





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<timerCU>           Timer, combined use      Integer decimal; range
                    (microseconds)           determined by application.
                                             Use decimal equivalent of
                                             32 bits.

<simplifiedCPS>     Simplified CPS [52]      String values:
                                             "on", "off"

<fSDUrate>          Forward SDU rate         Decimal equivalent of
                    (bits per second)        24-bit field

<bSDUrate>          Backward SDU rate        Decimal equivalent of
                    (bits per second)        24-bit field

<ted>               Transmission Error       String values:
                    Detection Enable         "on", "off"

<rastimer>          SSSAR reassembly        Integer decimal,
                    (microseconds)          Range determined by
                                            application. Use decimal
                                            equivalent of 32 bits.

<fsssar>            Maximum SSSAR-SDU        Decimal 1- 65568
                    size, forward            or hex equivalent
                    direction

<bsssar>            Maximum SSSAR-SDU        Decimal 1- 65568
                    size, backward           or hex equivalent
                    direction

<fsscopsdu>         Maximum SSCOP-SDU        Decimal 1- 65528
                    size, forward            or hex equivalent
                    direction

<bsscopsdu>         Maximum SSCOP-SDU        Decimal 1- 65528
                    size, backward           or hex equivalent
                    direction

<fsscopuu>          Maximum SSCOP-UU         Decimal 1- 65524
                    field size, forward      or hex equivalent
                    direction

<bsscopuu>          Maximum SSCOP-UU         Decimal 1- 65524
                    field size, backward     or hex equivalent
                    direction


<sap>               Service Access           String values:
                    Point                    "AUDIO", "MULTIRATE"

<circuitMode>       Circuit Mode             String values:
                    Enable                   "on", "off"



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<frameMode>         Frame Mode               String values:
                    Enable                   "on", "off"


<faxDemod>          Fax Demodulation        String values:
                    Enable                  "on", "off"

<cas>               Enable CAS transport     String values:
                    via Type 3 packets       "on", "off"

<dtmf>              Enable DTMF transport     String values:
                    via Type 3 packets        "on", "off"

<mfall>             Enable MF transport      String values:
                    via Type 3 packets       "on", "off"

<mfr1>              Enable MF (R1)           String values:
                    transport via             "on", "off"
                    Type 3 packets

<mfr2>              Enable MF (R2)           String values:
                    transport via             "on", "off"
                    Type 3 packets

<PCMencoding>       PCM encoding            String values:
                                            "PCMA", "PCMU"

<fmaxFrame>         Maximum length of a      Decimal or hex
                    frame mode data unit,    equivalent of
                    forward direction        16-bit field

<bmaxFrame>         Maximum length of a           -ditto-
                    frame mode data unit,
                    backward direction

<silenceSuppEnable>  Silence suppression  String values:
                     Enable               "on", "off"

<silenceTimer>       Kick-in timer        Decimal or hex representation
                     for silence          of 16-bit field
                     suppression


<suppPref>          Preferred Silence     String values:
                    Suppression Method    "standard", "custom"

<sidUse>            SID Use               String values:
                    Method                "No SID", "Fixed Noise",
                                          "Sampled Noise"





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<fxnslevel>         Fixed Noise           Decimal or hex representation
                    Level                 of a 7-bit field

<ecanEnable>        Enable Echo           String values:
                    Cancellation          "on", "off"

<ecanType>           Type of Echo         String values:
                     Cancellation         "G165", "G168"

<gcEnable>           Enable Gain          String values:
                     Control              "on", "off"

<gcLvl>              Level of inserted    Decimal or hex equivalent
                     Loss                 of 16-bit field

<aal2transport>      AAL2 transport       Values listed in Table 1
                                          that begin with the string
                                          "AAL2"

<uuiCodeRange>       UUI code range       Decimal integer 0-15

<encodingName>       Encoding name        String values:
                                          "PCMG", "SIDG", "SID729",
                                          any value from column 2
                                          of Table 2

<packetLength>      Packet length         Decimal integer 0-45

<packetTime>        Packetization         Decimal integer 1-65,536
                    Interval in microsec.

<fxIncl>            Facsimile included    String values: "on", "off"

<q7655scc>          Contents of the       Even number of hex
                    Q.765.5 Single        digits (4-32)
                    Codec IE

<isupUsi>           ISUP User Service     Two hex digits
                    Information

<chainPointer>     Chain pointer           String values: "NEXT",
                                           "PREVIOUS", "NULL"

<rtcpPortNum>      RTCP port number for     Odd decimal in range 1,024 to
                   H.323 Annex C            65,535.
                   applications             Preferred: Odd number in
                                            the range 49,152 to 65,535

<rtcpIPaddr>      IP address for  receipt   Dotted decimal, 7-15 chars
                  of RTCP packets





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7.0   Examples of ATM session descriptions using SDP

   An example of  a complete AAL1 session description in SDP is:

     v=0
     o=- A3C47F21456789F0 0 ATM NSAP
        47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
     s=-
     c=ATM NSAP
         47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
     t=0 0
     m=audio $ AAL1/AVP 18 0 96
     a=atmmap:96 X-G727-32
     a=eecid:B3D58E32

   An example of  a complete AAL2 session description in SDP is:

     v=0
     o=- A3C47F21456789F0 0 ATM NSAP
     47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
     s=-
     c=ATM NSAP
          47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
     t=0 0
     m=audio $ AAL2/ITU 8 AAL2/custom 100 AAL2/ITU 1
     a=eecid:B3E32

   The AAL2 session descriptor below is the same as the one above
   except that it states an explicit preference for a voice codec, a
   voiceband data codec and a voiceband fax codec. Further, it defines
   the profile AAL2/custom 100 rather than assume that the far-end is
   cognizant of the elements of this profile.

     v=0
     o=- A3C47F21456789F0 0 ATM NSAP
     47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
     s=-
     c=ATM NSAP
     47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
     t=0 0
     m=audio $ AAL2/ITU 8 AAL2/custom 100 AAL2/ITU 1
     a=eecid:B3E32
     a=profileDesc:AAL2/custom 100 0-7 PCMG 40 5000 0-7 SIDG 1
     5000 8-15 G726-32 40 10000 8-15 SIDG 1 5000
     a=vsel:G726-32 40 10000
     a=dsel:off PCMU - -
     a=fsel:G726-32 40 10000








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An example of an SDP session descriptor for an AAL5 switched virtual circuit
 for delivering MPEG-2 video:

    v=0
    o=- A3C47F21456789F0 0 ATM NSAP
    47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
    s=-
    c=ATM NSAP 47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
    t=0 0
    m=video $ AAL5/ITU 33
    a=eecid:B3E32
    a=aalType:AAL5
    a=bearerType:SVC on
    a=atmFtrfcDesc:0+1 7816 - - - - - off -
    a=atmBtrfcDesc:0+1 0 - - - - - on -
    a=fcpsSDUsize:20680
    a=aalApp:itu_h2221 - -

 An example of an SDP session descriptor for an AAL5 permanent virtual circuit
 for delivering MPEG-2 video:


    v=0
    o=- A3C47F21456789F0 0 ATM - -
    s=-
    c=ATM - -
    t=0 0
    m=video PORT-$/VPI-0/VCI-$ AAL5/ITU 33
    a=bearerType:PVC -
    a=atmFtrfcDesc:0+1 7816 - - - - - off -
    a=atmBtrfcDesc:0+1 0 - - - - - on -
    a=fcpsSDUsize:20680
    a=aalApp:itu_h2221 - -


8.0 Security Considerations

8.1  Bearer Security
   At present, standard means of encrypting ATM and AAL2 bearers
   are not conventionalized in the same manner as means of encrypting RTP
   payloads. Nor has the authentication of ATM or AAL2 bearer
   signaling.

   The SDP encryption key line (k=) defined in rfc2327 can be used
   to represent the encryption key and the method of obtaining the
   key. In the ATM and AAL2 contexts, the term 'bearer' can include
   'bearer signaling'  as well as 'bearer payloads'.

8.2  Security of the SDP description

   The SDP session descriptions might originate in untrusted areas
   such as equipment owned by end-subscribers or located at end-subscriber



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   premises. SDP relies on the security mechanisms of the encapsulating
   protocol or layers below the encapsulating protocol. Examples of
   encapsulating protocols are the Session Initiation Protocol (SIP),
   MGCP and Multimedia Gateway Control Protocol (MEGACO). No additional
   security mechanisms are needed. SIP, MGCP and MEGACO
   can use IPSec authentication as described in RFC1826 [Ref.
   27]. IPSec encryption can be optionally used with authentication to
   provide an additional, potentially more expensive level of security.
   IPSec security associations can be made between equipment located in
   untrusted areas and equipment located in trusted areas through
   configured shared secrets or the use of a certificate authority.

9.0  ATM SDP Grammar

   This appendix provides an Augmented BNF (ABNF) grammar for the ATM
   conventions for SDP. ABNF is defined in rfc2234. This is not a complete ABNF
   description of SDP. Readers are referred to [1] for an ABNF description
   of the SDP base line protocol, and to rfc2848, rfc2543, rfc2045 and rfc2326
   for application-specific conventions for SDP use.

; Constant definitions

safe = alpha-numeric / "'" / "-" / "." / "/" / ":" / "?" / DQUOTE / "#" /
   "$" / "&" / "*" / ";" / "=" / "@" / "[" / "]" / "^" / "_" / "`" / "{" /
   "|" / "}" / "+" / "~"
DQUOTE = %x22 ; double quote
alpha-numeric = ALPHA / DIGIT
ALPHA = "a" / "b" / "c" / "d" / "e" / "f" / "g" / "h" / "i" / "j" / "k" /
        "l" / "m" / "n" / "o" / "p" / "q" / "r" / "s" / "t" / "u" / "v" /
        "w" / "x" / "y" / "z" /
        "A" / "B" / "C" / "D" / "E" / "F" / "G" /  "H" / "I" / "J" / "K" /
        "L" / "M" / "N" / "O" / "P" / "Q" / "R" /  "S" / "T" / "U" / "V" /
        "W" / "X" / "Y" / "Z"
DIGIT = "0" / POS-DIGIT
POS-DIGIT = "1" / "2" / "3" / "4" / "5" / "6" / "7" / "8" / "9"
hex-prefix = "0" ("x"  /  "X")
HEXDIG = DIGIT  /  "a" / "b" / "c" / "d" / "e" / "f" /
                      "A" / "B" / "C" / "D" / "E" / "F"
space = %d32
EOL = (CR / LF / CRLF) ; as per Megaco RFC
CR = %d13
LF = %d10

decimal-uchar =       DIGIT
                         / POS-DIGIT DIGIT
                         / ("1" 2*(DIGIT))
                         / ("2" ("0"/"1"/"2"/"3"/"4") DIGIT)
                         / ("2" "5" ("0"/"1"/"2"/"3"/"4"/"5"))

generic-U8  = (hex-prefix hex-U8) / decimal-uchar
generic-U12 = (hex-prefix hex-U12) / 1*4 (DIGIT)
generic-U16 = (hex-prefix hex-U16) / 1*5(DIGIT)



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generic-U24 = (hex-prefix hex-U24) / 1*8(DIGIT)
generic-U32 = (hex-prefix hex-U32) / 1*10(DIGIT)
hex-U8  = 1*2(HEXDIG)
hex-U12 = 1*3(HEXDIG)
hex-U16 = 1*4(HEXDIG)
hex-U24 = 1*6(HEXDIG)
hex-U32 = 1*8(HEXDIG)
generic-U8-or-null  = generic-U8 / "-"
generic-U12-or-null = generic-U12 / "-"
generic-U16-or-null = generic-U16 / "-"
generic-U24-or-null = generic-U24 / "-"
generic-U32-or-null = generic-U32 / "-"
decimal-U8-or-null =  decimal-uchar / "-"
decimal-U12-or-null = 1*4(DIGIT) / "-"
decimal-U16-or-null = 1*5(DIGIT) / "-"
decimal-U24-or-null = 1*8 (DIGIT) / "-"
decimal-U32-or-null = 1*10(DIGIT) / "-"
on-off-or-null = "on" / "off" / "-"

; ABNF definition of SDP with ATM conventions

SDP-infoset    =  1*(announcement)announcement  =  proto-version  origin-field
session-name-field   information-field   uri-field   email-fields   phone-fields
connection-field bandwidth-fields time-fields key-field attribute-fields media-
descriptions

proto-version = ["v=" 1*4(DIGIT) EOL] ; use "v=0" for ATM SDP


origin-field = ["o=" username space sess-id space sess-version space
   net-type-addr EOL]


username = 1* safe ; for ATM use "-"

sess-id = (1*32 DIGIT) / (hex-prefix 1*32 HEXDIG)
sess-version = (1*10 DIGIT) / (hex-prefix 1*8 HEXDIG)

net-type-addr= nettype space addrtype-addr

netttype = "ATM" / "IN" / "TN" / "-" / "$"

 ; Other nettype values may be defined in the future in other documents
 ; Validity of  nettype and addrtype-addr combination to be checked at
 ;      application level, not protocol syntax level

addrtype-addr = atm-addrtype-addr / ip-addrtype-addr / tn-addrtype-addr
   ; ip-addrtype-addr per rfc2327
   ; tn-addrtype-addr per rfc2848






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; ATM address definition

atm-addrtype-addr =  atm-nsap-addr / atm-e164-addr / atm-alias-addr

atm-nsap-addr = ("NSAP" / "-" / "$")  space (nsap-addr / "-" / "$")
atm-e164-addr = ("E164" / "-" / "$") space (e164-addr / "-" / "$")
atm-alias-addr = ("GWID" / "ALIAS" / "-" / "$") space (alias-addr / "-" / "$")

nsap-addr = 2(HEXDIG) "." 9(4(HEXDIG) ".") 2(HEXDIG)

e164-addr = 1*15 (DIGIT)
alias-addr = 1*32(alpha-numeric / "-" / "." / "_")

session-name-field = ["s=" text EOL] ; for ATM use "s=-"
text = byte-string
byte-string = 1*(byte-string-char) ; definition per rfc2327
byte-string-char = %x01-09/ %x0B/ %x0C/ %x0E-FF ; all ASCII except NUL, CR & LF
; Definitions of information-field, uri-field, email-fields,
; phone-fields per rfc2327. These fields are omitted in
; ATM SDP descriptions. If received, they are ignored in the ATM context

connection-field = ["c=" c-net-type-addr]

         ; connection-field required, not optional, in ATM

c-net-type-addr = nettype space c-addrtype-addr
c-addrtype-addr = atm-addrtype-addr / c-ip-addrtype-addr / tn-addrtype-addr

   ; atm-addrtype-addr defined above

   ; c-ip-addrtype-addr per rfc2327
   ; difference in address usage between 'o' and 'c' lines per rfc2327

   ; tn-addrtype-addr per rfc2848


bandwidth-fields = *("b=" bwtype ":" bandwidth EOL)
bwtype = 1*(alpha-numeric)
bandwidth = 1*(DIGIT)

time-fields = *( "t=" start-time space stop-time *(EOL repeat-fields) EOL)
              [zone-adjustments EOL]
start-time = time / "0"
stop-time = time / "0" ; always "0" in ATM
time = POS-DIGIT 9*(DIGIT) ; same as rfc2327
 ; repeat-fields and zone-adjustments per rfc2327, not used in ATM

 ; Definition of optional key-field per rfc2327
 ;


attribute-fields = *("a=" attribute EOL)



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 ; SDP descriptors for ATM do not have session-level media attribute lines
 ; If these are provided, they should be ignored.

media-descriptions = *(media-description)
media-description  = media-field information-field *(connection-field)
                     bandwidth-fields key-field attribute-fields

; Definitions of information-field per rfc2327. This fields are omitted in
; ATM SDP descriptions. If received, they are ignored in the ATM context
;
; In ATM, the connection-field is used in media-description to indicate
; the IP address associated with the RTCP control protocol in H.323.C
; applications. In this case,  the connection field is per the rfc2327
; definition for IP v4-based connections. Otherwise, it is not used in
; media-description. If received as part of  media-description,
; it is ignored.
;
; Definition of optional bandwidth-fields as above.
: Definition of optional key-field as in rfc2327

media-field = rfc2327-media-field / rfc2848-media-field / atm-media-field
    ; rfc2327-media-field and rfc2848-media-field defined in those rfc's
atm-media-field = "m=" media space vcId space transport-fmts EOL
   ; superset of rfc2327 definition

media = "audio" / "video" / "data" / "application" / "control" /
        1*(alpha-numeric)

vcId = "$" / "-" / ex-vcci / (ex-vcci "/" ex-cid) /
     (atm-type-addr-m  "/" ex-vcci) /
     (atm-type-addr-m "/" ex-vcci "/" ex-cid) /
     (ex-bcg "/" ex-vcci) / (ex-bcg "/" ex-vcci "/" ex-cid)
     (ex-portid "/" ex-vpi "/" ex-vci) /
     (ex-portid "/" ex-vpi "/" ex-vci "/" ex-cid) /
     (ex-bcg "/" ex-vpi "/" ex-vci) /
     (ex-bcg "/" ex-vpi "/" ex-vci "/" ex-cid) /
     (ex-vpci "/" ex-vci) /
     (ex-vpci "/" ex-vci "/" ex-cid) /
     (atm-type-addr-m  "/" ex-vpci "/" ex-vci) /
     (atm-type-addr-m  "/" ex-vpci "/" ex-vci "/" ex-cid)

atm-type-addr-m = atm-nsap-addr-m / atm-e164-addr-m / atm-alias-addr-m
atm-nsap-addr-m =  ["NSAP-"] (nsap-addr / "$")
atm-e164-addr-m =  ["E164-"] (e164-addr / "$")
atm-alias-addr-m = ["GWID-" / "ALIAS-"] (alias-addr / "$")
 ; The -m at the end indicates use in the media field
 ; Wildcarding rules different from ATM address on 'o' and 'c' lines

ex-vcci    = "VCCI-"  vcci
ex-cid     = "CID-"   cid
ex-bcg     = "BCG-"   bcg



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ex-portid  = "PORT-"  portid
ex-vpi     = "VPI-"   vpi
ex-vci     = "VCI-"   vci
ex-vpci    = "VPCI-"  vpci

vcci   = generic-U16
cid    = generic-U8
bcg    = generic-U8
portid = 1*32 (HEXDIG)
vpi    = generic-U12
vci    = generic-U16
vpci   = generic-U16


transport-fmts = generic-transport-fmts / known-transport-fmts / "- -"
generic-transport-fmts = generic-transport 1*(space fmt)
generic-transport = 1*(alpha-numeric / "/")
fmt = 1*(alpha-numeric)

known-transport-fmts = aal1-transport space aal1-fmt-list /
                       aal2-transport space aal2-fmt-list
                       *(space aal2-transport space aal2-fmt-list) /
                       aal5-transport space aal5-fmt-list /
                       rtp-transport space rtp-fmt-list /
                       tn-proto space tn-fmt-list /
                       h323c-proto "-"
h323c-proto = "H323c"
    ; h323c-proto used for RTCP control ports in H.323 annex C applications
    ; tn-proto and tn-fmt-list per rfc2848

aal1-transport = "AAL1" "/" aal1-transport-list
aal1-transport-list = "ATMF" / "ITU" / "custom" / "IEEE:" oui /
                      corporate-name
corporate-name = 1*(safe)
aal2-transport = "AAL2" "/" aal2-transport-list
aal2-transport-list = aal1-transport-list
aal5-transport = "AAL5" "/" aal5-transport-list
aal5-transport-list = aal1-transport-list
rtp-transport = "RTP" "/" rtp-transport-list
rtp-transport-list = "AVP"


aal1-fmt-list = (payload-type *(space payload-type)) / "-"
payload-type = decimal-uchar
aal5-fmt-list = aal1-fmt-list
rtp-fmt-list = aal1-fmt-list
aal2-fmt-list = (profile *(space profile)) / "-"
profile = decimal-uchar

attribute-fields = *("a=" attribute EOL)
attribute = known-attribute / (generic-att-field ":" att-value) /
            generic-att-field



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generic-att-field = 1*(alpha-numeric)
att-value = byte-string
known-attribute = atm-attribute / PINT-attribute / rfc2327-attribute
         ; PINT-attribute as defined in rfc2848
         ; rfc2327 attribute as defined in that rfc

atm-attribute =
      "eecid" ":" eecid /
      "aalType" ":" aalType /
      "capability" ":" (asc / atc) space subtype /
      "qosclass" ":" qosclass /
      "bcob" ":" bcob space eetim /
      "stc" ":" stc /
      "upcc" ":" upcc /
      "atmQOSfparms" ":" cdvType space acdv space ccdv space eetd space cmtd
               space aclr /
      "atmQOSbparms" ":" cdvType space acdv space ccdv space eetd space cmtd
               space aclr /
      "atmFtrfcDesc" ":" clpLvl  space pcr space scr space mbs space cdvt space
               mcr space mfs space fd space te /
      "atmBtrfcDesc" ":" clpLvl  space pcr space scr space mbs space cdvt space
               mcr space mfs space fd space te /
      "abrFparms" ":" nrm space trm space cdf space adtf /
      "abrBparms" ":" nrm space trm space cdf space adtf /
      "abrSetup" ":" ficr space bicr space ftbe space btbe space
             crmrtt space frif space brif space frdf space brdf /
      "bearertype" ":" bearerType space localInitiation  /
      "lij" ":" sci space lsn /
      "anycast" ":" atmGroupAddress space cdStd space
                 conScpTyp space conScpSel /
      "cache" ":" cacheEnable space cacheTimer /
      "bearerSigIE" ":" bearerSigIEType space
               bearerSigIELng space bearerSigIEVal /
      "aalApp" ":" appClass space oui space appId /
      "cbrRate" ":" cbrRate /
      "sbc" ":" sbc /
      "clkrec" ":" clkrec /
      "fec" ":" fecEnable /
      "prtfl" ":" partialFill /
      "structure" ":" structureEnable space blksz /
      "fcpsSDUsize" ":" cpcs /
      "bcpsSDUsize" ":" cpcs /
      "aal2CPS" ":" cidLowerLimit space cidUpperLimit space
               timerCU space simplifiedCPS /
      "aal2CPSSDUrate" ":" fSDUrate space bSDUrate /
      "aal2sscs3661unassured" ":" ted space rastimer space fsssar
                space bsssar /
      "aal2sscs3661assured" ":" rastimer space fsssar space bsssar
           space fsscopsdu space bsscopsdu space fsscopuu space bsscopuu  /
      "aal2sscs3662" ":" sap space circuitMode space frameMode space faxDemod
           space cas space dtmf space mfall space mfr1
           space mfr2 space PCMencoding space fmaxFrame space bmaxFrame /



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      "aal5sscop" ":" fsscopsdu space bsscopsdu space fsscopuu
             space bsscopuu  /
      "atmmap" ":" payload-type space encoding-name /
      "silenceSupp" ":" silenceSuppEnable space silenceTimer space suppPref
               space sidUse space fxnslevel /
      "ecanf" ":" ecanEnable space ecanType /
      "ecanb" ":" ecanEnable space ecanType /
      "gcf" ":" gcEnable space gcLvl /
      "gcb" ":" gcEnable space gcLvl /

      "profileDesc" ":" aal2-transport space profile space
         1*(profile-row) /
      "vsel" ":" 1*(encoding-name space packet-length space
                                  packet-time space) /
      "dsel" ":" fxIncl space
                 1*(encoding-name space packet-length space
                                  packet-time space) /
      "fsel" ":" 1*(encoding-name space packet-length space
                                  packet-time space) /
      "codecconfig" ":" q7655scc /
      "isup_usi" ":" isupUsi /
      "chain" ":" chainPointer

eecid =  8 (HEXDIG)
aalType = "AAL1" / "AAL2" / "AAL3/4" / "AAL5" / "USER_DEFINED_AAL"
asc = "CBR" / "nrt-VBR" / "rt-VBR" / "UBR" / "ABR" / "GFR"
atc = "DBR" / "SBR" / "ABT/IT" / "ABT/DT" / "ABR"
subtype = decimal-U8-or-null
qosclass = decimal-U8-or-null
bcob = generic-U8
eetim = on-off-or-null
stc = decimal-uchar
upcc = decimal-uchar
cdvType = "PP" / "2P" / "-"
acdv = decimal-U32-or-null
ccdv = decimal-U32-or-null
eetd = decimal-U16-or-null
cmtd = decimal-U16-or-null
aclr = decimal-U8-or-null
clpLvl = "0" / "0+1" / "-"
pcr = decimal-U24-or-null
scr = decimal-U24-or-null
mbs = decimal-U16-or-null
cdvt = decimal-U24-or-null
mcr = decimal-U24-or-null
mfs = decimal-U16-or-null
fd = on-off-or-null
te = on-off-or-null
nrm = generic-U8-or-null
trm = generic-U8-or-null
cdf = generic-U8-or-null
adtf = generic-U16-or-null



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ficr = decimal-U24-or-null
bicr = decimal-U24-or-null
ftbe = decimal-U24-or-null
btbe = decimal-U24-or-null
crmrtt = decimal-U24-or-null
frif = 1*2 (DIGIT)
brif = 1*2 (DIGIT)
frdf = 1*2 (DIGIT)
brdf = 1*2 (DIGIT)
bearerType =  "PVC" / "SVC" / "CID"
localInitiation = on-off-or-null
sci = generic-U8-or-null
lsn = generic-U32-or-null
atmGroupAddress = atm-type-addr
cdStd = generic-U8-or-null
conScpTyp = generic-U8-or-null
conScpSel = generic-U8-or-null
cacheEnable = on-off-or-null
cacheTimer = generic-U32-or-null
bearerSigIEType = 2 * (HEXDIG)
bearerSigIELng = 1*4 (HEXDIG)
bearerSigIEVal = 2*512 (HEXDIG)
appClass =  "-" /
          "itu_h323c" / "af83" / "AAL5_SSCOP" / "itu_i3661_unassured" /
          "itu_ i3661_assured"/ "itu_i3662"/ "itu_i3651" /
          "itu_i3652" / "itu_i3653" / "itu_i3654" / "FRF11" / "FRF5" / "FRF8" /
          "itu_h2221"
oui = "-" / 1*6 (HEXDIG)
appId = "-" / 1*8 (HEXDIG)
cbrRate = 2 (HEXDIG)
sbc = generic-U8
clkrec = "NULL" / "SRTS" / "ADAPTIVE"
fecEnable = "NULL" / "LOSS_SENSITIVE"  / "DELAY_SENSITIVE"
partialFill = generic-U8
structureEnable = on-off-or-null
blksz = generic-U16-or-null
cpcs = generic-U16
cidLowerLimit = generic-U8-or-null
cidUpperLimit = generic-U8-or-null
timerCU = decimal-U32-or-null
simplifiedCPS = on-off-or-null
fSDUrate = decimal-U24-or-null
bSDUrate = decimal-U24-or-null
ted = on-off-or-null
rastimer = decimal-U32-or-null
fsssar = generic-U24-or-null
bsssar = generic-U24-or-null
fsscopsdu = generic-U16-or-null
bsscopsdu = generic-U16-or-null
fsscopuu = generic-U16-or-null
bsscopuu = generic-U16-or-null
sap = "AUDIO" / "MULTIRATE" / "-"



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circuitMode = on-off-or-null
frameMode = on-off-or-null
faxDemod = on-off-or-null
cas = on-off-or-null
dtmf = on-off-or-null
mfall = on-off-or-null
mfr1 = on-off-or-null
mfr2 = on-off-or-null
PCMencoding = "PCMA" / "PCMU" / "-"
fmaxframe = generic-U16-or-null
bmaxframe = generic-U16-or-null
silenceSuppEnable = on-off-or-null
silenceTimer = generic-U16-or-null
suppPref = "standard" / "custom" / "-"
sidUse = "No SID" / "Fixed Noise" / "Sampled Noise" / "-"
fxnslevel = generic-U8-or-null
ecanEnable = on-off-or-null
ecanType = "G165" / "G168" / "-"
gcEnable = on-off-or-null
gcLvl = generic-U16-or-null


profile-row  = uuiCodeRange space encoding-name space packet-length
                   space packet-time space
uuiCodeRange = decimal-uchar "-" decimal-uchar / "-"
encoding-name = "-" /
                "PCMG" / "SIDG" / "SID729" /
                "PCMU" / "G726-32" / "G723" / "PCMA" / "G722" / "G728" /
                "G729" / "X-G729a" / "X-G729b" / "X-G729ab" / "X-G726-16" /
                "X-G726-24" / "X-G726-40" / "X-G7231-H" / "X-G7231-L" /
                "X-G7231a-H" / "X-G7231a-L" /  "X-G727-16" / "X-G727-24" /
                "X-G727-32" /
                "X-CCD" / "X-CCD-CAS" / "GSM" / "GSM-HR" / "GSM-EFR" /
                "GSM-EHR" / "X-FXDMOD-3" / "1016" / "DVI4" / "L16" / "LPC" /
                "MPA" / "QCELP" / "H263" / "H263-1998" /
                "JPEG" / "H261" / "MPV" / "MP2T" / "nv" / "RED" /
                "CelB" / "L8" / "VDVI" / "MP1S" / "MP2P" / "BT656" /
                "FR-AMR" / "HR-AMR" / "HR-UMTS"
packet-length = decimal-U8-or-null
packet-time = decimal-U16-or-null
fxIncl = on-off-or-null
q7655scc = 4*32 (HEXDIG)
isupUsi = 2 (HEXDIG)

chainPointer = "NEXT" / "PREVIOUS" / "NULL"

References


[1]     IETF RFC 2327, 'SDP: Session Description Protocol', April '98,
        Mark Handley and Van Jacobson.




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[2]     IETF RFC 1889, 'RTP: A Transport Protocol for Real-Time
        Applications', Jan. 1996.

        RFC1889 will be obsoleted, in a substantially backwards compatible
        manner, by the RFC that evolves out of draft-ietf-avt-rtp-new-08.txt.

[3]     IETF RFC 1890, 'RTP Profile for Audio and Video Conferences
        with Minimal Control', Jan. 1996.

        RFC1890 will be obsoleted, in a fully backwards compatible manner,
        by the RFC that evolves out of draft-ietf-avt-profile-new-09.txt.

[4]     ATMF UNI 3.1 Specification,  af-uni-0010.002. Of special
        interest for this document is  Section 5.4.5.5,  ATM Adaptation
        Layer Parameters.

[5]     ATMF UNI 4.0 Signaling Specification, af-sig-0061.000.

[6]     ATMF Traffic Management Specification, Version 4.1, af-tm-
        0121.000.

[7]     ATMF Circuit Emulation Service (CES) Interoperability
        Specification, version 2.0, af-vtoa-0078.000, Jan. 97.

[8]     ATMF Voice and Telephony over ATM - ATM Trunking using AAL1 for
        Narrowband Services, version 1.0, af-vtoa-0089.000, July 1997.

[9]     ATMF Specifications of (DBCES) Dynamic Bandwidth Utilization -
        in 64kbps Timeslot Trunking over ATM  - using CES, af-vtoa-
        0085.000, July 1997.

[10]    ITU-T I.363.1, B-ISDN ATM Adaptation Layer Specification: Type
        1 AAL, August 1996.

[11]    ITU-T I.363.2, B-ISDN ATM Adaptation Layer Specification: Type
        2 AAL, Sept. 1997.

[12]    ITU-T I.366.1, Segmentation and Reassembly Service Specific
        Convergence Sublayer  for AAL Type 2, June 1998.

[13]    ITU-T I.366.2, AAL Type 2 Reassembly Service Specific
        Convergence Sublayer  for Trunking, Feb. 99.

[14]    Draft ietf-avt-telephone-tones-05.txt, RTP payloads for
        Telephone Signal Events, S.B.Petrack, Nov. 17, 1998.

[15]    ITU-T Q.2931, B-ISDN Application Protocol for Access Signaling.

[16]    Amendment 1, 2, 3 and 4 to ITU-T Q.2931, B-ISDN Application
        Protocol for Access Signaling.





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[17]    SAP: Session Announcement Protocol , draft-ietf-mmusic-sap-v2-
        04.txt, Mark Handley, Colin Perkins and Edmund Whelan .

[18]    rfc2543, Handley, M., H. Schulzrinne , Schooler, E. and
        Rosenberg, J., "Session Initiation Protocol (SIP)",   March
        1999.

[19]    rfc1349, Type of Service in the Internet Protocol Suite. P.
        Almquist. July 1992.

[20]    rfc2474, Definition of the Differentiated Services Field (DS
        Field) in the IPv4 and IPv6 Headers. K. Nichols, S. Blake, F.
        Baker, D. Black. December 1998.

[21]    ITU-T I.363.5, B-ISDN ATM Adaptation Layer Specification: Type
        5 AAL, Aug. 1996.

[22]    ATMF PNNI 1.0, af-pnni-0055.000, March 1996.

[23]    ietf-avt-rtp-new-05.txt, Oct. 21, 1999, RTP: A Transport
        Protocol for Real-Time Applications.

[24]    ietf-avt-profile-new-07.txt, Oct. 21, 1999, RTP Profile for
        Audio and Video Conferences with Minimal Control.

[25]    Media Gateway Control Protocol (MGCP), Mauricio Arango, Isaac
        Elliott, Christian Huitema, Scott Pickett, Version 1.0,
        RFC2705.

[26]    draft-ietf-Megaco-merged-00.txt, April, 2000, Media Gateway
        control (Megaco) protocol, Fernando Cuervo, Nancy Greene, Christian
        Huitema, Abdallah Rayhan, Brian Rosen, John Segers.

[27]    IP Authentication Header, R. Atkinson, August 1995, RFC1826.

[28]    ITU I.371, Traffic Control and Congestion Control in the BISDN.

[29]    ITU E.191, BISDN Numbering and Addressing.

[30]   ATM Forum Addressing: Reference Guide, af-ra-0106.000.

[31]    http://www.isi.edu/in-notes/iana/assignments/rtp-parameters
        for a list of codecs with static payload types.

[32]   ITU Q.2941-2, Digital Subscriber Signalling System No. 2
       (DSS 2): Generic identifier transport extensions.

[33]   ITU Q.2961, Digital subscriber signalling system no.2 (DSS 2)
       - additional traffic parameters. Also, Amendment 2 to Q.2961.

[34]   ITU Q. 2965.1, Digital subscriber signalling system no.2 (DSS 2)
       - Support of Quality of Service classes.



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[35]   ITU Q. 2965.2, Digital subscriber signalling system no.2 (DSS 2)
       - Signalling of individual Quality of Service parameters.

[36]   ITU Q.1901, Bearer Independent Call Control Protocol.

[37]   ITU Q.2630.1, AAL type 2 signaling protocol - capability set 1.

[38]   ITU I.363.5, B-ISDN ATM Adaptation Layer specification: Type 5
       AAL.

[39]   I.365.1,Frame relaying service specific convergence sublayer
       (FR-SSCS).

[40]   I.365.2, B-ISDN ATM adaptation layer sublayers: service
       specific coordination function to provide the connection
       oriented network service.

[41]  I.365.3, B-ISDN ATM adaptation layer sublayers: service
      specific coordination function to provide the
      connection-oriented transport service.

[42]  I.365.4, B-ISDN ATM adaptation layer sublayers: Service specific
      convergence sublayer for HDLC applications.

[43]  Q.2110, B-ISDN ATM adaptation layer - service specific connection
      oriented  protocol (SSCOP).

[44]  af-vtoa-0113.000, ATM trunking using AAL2 for narrowband services.

[45]  H.323-2, Packet-based multimedia communications systems.

[46]  af-vtoa-0083.000, Voice and Telephony Over ATM to the Desktop.

[47]  I.356, BISDN ATM layer cell transfer performance.

[48]  ITU Q.2957, Digital Subscriber Signaling System No. 2, User to user
      signaling.

[49]  rfc1305, Network Time Protocol, version 3.

[50]  TIA/EIA/IS-J-STD-025-A, Lawfully Authorized Electronic Surveillance,
      May 2000.

[51] ITU-T H.222.1, Multimedia multiplex and synchronization for audiovisual
     communication in ATM environments.

[52]  af-vmoa-0145.000, Voice and Multimedia over ATM, Loop Emulation Service
      using AAL2.

[53]  FRF.5, Frame Relay/ATM PVC Network Interworking Implementation Agreement.




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[54]  FRF.8.1, Frame Relay/ATM PVC Service Interworking
      Implementation Agreement.

[55]  FRF.11, Voice over Frame Relay Implementation Agreement.

[56]  rfc2234, Augmented BNF for Syntax Specifications: ABNF.

[57]  ITU Q.765.5, Application Transport Mechanism - Bearer Independent
      Call Control.

[58]  http://www.3gpp.org/ftp/Specs for specifications related to 3GPP,
      including AMR codecs.

[59]  ITU Q.931, Digital Subscriber Signaling System No. 1: Network Layer.

[60]  ITU Q.763, SS7 - ISUP formats and codes.

[61]  http://www.atmforum.com/atmforum/specs/specs.html, ATM Forum,
      Well-known addresses and assigned codes.


Acknowledgements
   The authors wish to thank several colleagues at Cisco and in the
   industry who have contributed towards the development of these SDP
   conventions, and who have reviewed, implemented and tested these
   constructs. Valuable technical ideas that have been incorporated
   into this internet draft have been provided by Hisham Abdelhamid,
   Flemming Andreasen, David Auerbach, Robert Biskner, Bruce Buffam,
   Steve Casner, Alex Clemm, Bill Foster, Snehal Karia, Raghu Thirumalai
   Rajan, Joe Stone, Bruce Thompson, Dan Wing and Ken Young of Cisco,
   Michael Brown, Rade Gvozdanovic, Graeme Gibbs, Tom-PT Taylor, Mark Watson
   and Sophia Scoggins of Nortel Networks, Brian Rosen, Tim Dwight and Michael
   Mackey of Marconi, Ed Guy and Petros Mouchtaris of Telcordia, Christian
   Groves of Ericsson, Charles Eckel of Vovida Networks, Tom Jepsen,
   Dal Chohan, Sagar Gordhan and Chris Gallon of Fujitsu, Mahamood
   Hussain of Hughes Software Systems and  Sean Sheedy of nCUBE
   Corporation, Narendra Tulpule of Intel, and Albrecht Schwarz of
   Alcatel. The authors also wish to thank the
   ISC device control group, and the MMUSIC and  MEGACO subgroups of the
   IETF, especially Bill Foster, Joerg Ott, Sean Sheedy and Brian Rosen
   for their help in the preparation of this document. Finally, thanks are
   due to Narendra Tulpule of Intel whose ABNF grammar was adapted for
   this document.

 Authors' Addresses

   Rajesh Kumar
   Cisco Systems, Inc.
   M/S SJC01/3
   170 West Tasman Drive
   San Jose, CA 95134-1706
   Phone: 1-800-250-4800



Rajesh Kumar, Mohamed Mostafa.                                   96
Internet Draft            ATM SDP                               January 2001


   Email: rkumar@cisco.com

   Mohamed Mostafa
   Cisco Systems, Inc.
   M/S SJC01/3
   170 West Tasman Drive
   San Jose, CA 95134-1706
   Phone: 1-800-250-4800
   Email: mmostafa@cisco.com














































Rajesh Kumar, Mohamed Mostafa.                                   97
Internet Draft            ATM SDP                               January 2001


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