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Versions: 00 01 draft-ietf-mmusic-sdp-misc-cap

MMUSIC WG                                               M. Garcia-Martin
Internet-Draft                                                  Ericsson
Intended status: Standards Track                         S. Veikkolainen
Expires: April 30, 2009                                            Nokia
                                                               R. Gilman
                                                                    NDCI
                                                        October 27, 2008


   Miscellaneous Capabilities Negotiation in the Session Description
                             Protocol (SDP)
                  draft-garcia-mmusic-sdp-misc-cap-00

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
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   This Internet-Draft will expire on April 30, 2009.

Abstract

   SDP has been extended with a capability negotiation mechanism
   framework that allows the endpoints to negotiate transport protocols
   and attributes.  This framework has been extended with a Media
   capabilities negotiation mechanism that allows endpoints to negotiate
   additional media-related capabilities.  This negotiation is embedded
   into the widely-used SDP offer/answer procedures.

   This memo extends the SDP capability negotiation framework to allow



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   endpoints to negotiate a number of miscellaneous SDP capabilities.
   In particular, this memo provides a mechanism to negotiate media
   titles ("i=" line for each media), connection data ("c=" line), and
   media bandwidth ("b=" line).


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions Used in This Document  . . . . . . . . . . . . . .  3
   3.  Protocol Description . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Extensions to SDP  . . . . . . . . . . . . . . . . . . . .  4
       3.1.1.  Bandwidth Capability . . . . . . . . . . . . . . . . .  5
       3.1.2.  Connection Data Capability . . . . . . . . . . . . . .  7
       3.1.3.  Information Capability . . . . . . . . . . . . . . . .  9
     3.2.  Session Level versus Media Level . . . . . . . . . . . . . 11
   4.  Field Replacement Rules  . . . . . . . . . . . . . . . . . . . 12
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
     5.1.  New SDP Attributes . . . . . . . . . . . . . . . . . . . . 12
     5.2.  New Option Tags  . . . . . . . . . . . . . . . . . . . . . 13
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   7.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 13
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 13
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
   Intellectual Property and Copyright Statements . . . . . . . . . . 16
























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1.  Introduction

   The Session Description Protocol (SDP) [RFC4566] is intended for
   describing multimedia sessions for the purposes of session
   announcement, session invitation, and other forms of multimedia
   session initiation.  SDP has been extended with a capability
   negotiation mechanism framework
   [I-D.ietf-mmusic-sdp-capability-negotiation] that allows the
   endpoints to negotiate capabilities, such as support for Realtime
   Transport Protocol (RTP) [RFC3550] and Secure Realtime Transport
   Protocol (SRTP) [RFC3711].  The SDP media capabilities
   [I-D.ietf-mmusic-sdp-media-capabilities] provides negotiation
   capabilities to media lines as well.

   This negotiation is embedded into the widely used SDP offer/answer
   procedures [RFC3264].  This memo provides the means to negotiate
   further capabilities than those specified in the SDP capability
   negotiation mechanism framework
   [I-D.ietf-mmusic-sdp-capability-negotiation] and the SDP media
   capabilities [I-D.ietf-mmusic-sdp-media-capabilities].  In
   particular, this memo provides a mechanism to negotiate media titles
   ("i="), connection data ("c="), and media bandwidth ("b=").  It would
   have been possible to define a mechanism to negotiate media
   encryption keys ("k=").  However, the usage of the media encryption
   keys ("k=") is highly discouraged in favour of other existing more
   sophisticated mechanisms.  Therefore, we are not providing a
   mechanism to provide capabilities for media encryption keys ("k=") at
   this stage.

   Since the three added capabilities are highly unconnected, it is not
   expected that implementations will support all three at the same
   time.  Instead, it is expected that applications will choose their
   needed capability for their specific purpose.  Due to this, we are
   writing the normative part pertaining to each capability in a self-
   contained section.  In particular, Section 3.1.1 describes the
   bandwidth capability extension, Section 3.1.2 describes the
   connection data capability extension, and Section 3.1.3 describes the
   information capability extension.  Separate option tags are defined
   for each capability.


2.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in BCP 14, RFC 2119
   [RFC2119] and indicate requirement levels for compliant
   implementations.



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3.  Protocol Description

3.1.  Extensions to SDP

   The SDP Capability Negotiation Framework
   [I-D.ietf-mmusic-sdp-capability-negotiation] and the SDP media
   capabilities [I-D.ietf-mmusic-sdp-media-capabilities] specify
   attributes for negotiating SDP capabilities.  These documents specify
   new attributes (e.g., 'acap', 'tcap', 'mcap') for achieving their
   purpose.  In this document we define a number of new additional
   capability attributes for SDP lines of the the general form:

      type=value

   for types "i", "c", and "b".  The corresponding capability attributes
   are defined as "icap", "ccap", and "bcap", respectively.

   From the sub-rules of "a=" line in SDP [RFC4566], SDP attributes are
   of the form:

   attribute          = (att-field ":" att-value) / att-field
   att-field          = token
   att-value          = byte-string

   Capability attributes use only the 'att-field:att-value' form.

   The new attributes may be referenced in potential configurations
   ("a=pcfg") or in latent configurations ("a=lcfg"), as productions
   conforming to the extension-config-list as defined in
   [I-D.ietf-mmusic-sdp-capability-negotiation].

   extension-config-list = ["+"] ext-cap-name "="
                                  ext-cap-list
   ext-cap-name          = 1*(ALPHA / DIGIT)
   ext-cap-list          = 1*VCHAR  ; defined in [RFC4234]

   The optional "+" is used to indicate that the entire configuration,
   not just the parameter, must be ignored if the parameter is not
   supported.  The attributes may be referenced in actual configurations
   as productions conforming to the sel-extension-config defined in
   [I-D.ietf-mmusic-sdp-capability-negotiation].

   sel-extension-config = ext-cap-name "=" 1*VCHAR

   The specific parameters are defined in the individual description of
   each capability, below.

   It is not the intention of this work to negotiate these new



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   capabilities at the session level, rather only at the media level.
   Therefore, capabilities referenced by any configuration attribute
   MUST appear at the media level when a configuration is "converted" to
   a corresponding media block.  For this reason, the "icap" attribute
   is called the "media information capability".  Specific values for
   each new attribute are described below.

3.1.1.  Bandwidth Capability

   According to RFC 4566 [RFC4566] the bandwidth field denotes the
   proposed bandwidth to be used by the session or media.  For what it
   concerns this memo, we focus on the bandwidth at the media level.
   This bandwidth field is specified in RFC 4566 [RFC4566] according to
   the following syntax:

      b=<bwtype>:<bandwidth>

   where <bwtype> is an alphanumeric modifier giving the meaning of the
   <bandwidth> figure.

   In this document, we define a new capability attribute: the bandwidth
   capability attribute "bcap".  This attribute lists bandwidth as
   capabilities according to the following definition:

      "a=bcap:" bw-cap-num 1*WSP bwtype ":" bandwidth CRLF

   where <bw-cap-num> is a unique ordinal identifier of the bandwidth
   capability, and the other elements are as defined for the "b=" field
   in [RFC4566].

   This format satisfies the general attribute production rules in
   [RFC4566] according to the following Augmented Backus-Naur Form
   (ABNF) [RFC5234] syntax:

   att-field       = "bcap"
   att-value       = bw-cap-num 1*WSP bwtype ":" bandwidth
   bw-cap-num      = 1*DIGIT   ; integer between 1 and 2^31-1, inclusive

   Negotiation of bandwidth per media stream can be useful when
   negotiating media encoding capabilities with different bandwidths.

3.1.1.1.  Configuration Parameters

   The SDP Capability Negotiation Framework
   [I-D.ietf-mmusic-sdp-capability-negotiation] provides for the
   existence of the "pcfg" and "acfg" attributes, which can carry one or
   more potential configurations to be negotiated.  The concept is
   extended by the the Media Capabilities Negotiation



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   [I-D.ietf-mmusic-sdp-media-capabilities] with an "lcfg" attribute
   that conveys latent configurations.  Extensions to the "pcfg" and
   "lcfg" attributes are defined through <extension-config-list>, and
   extensions to the "acfg" attribute are defined through the <sel-
   extension-config> as defined in
   [I-D.ietf-mmusic-sdp-capability-negotiation].

   In this document we extend the <extension-config-list> field to be
   able to convey lists of bandwidth capabilities in latent or potential
   configurations, according to the following Augmented Backus-Naur Form
   (ABNF) [RFC5234] syntax:

   extension-config-list  = bandwidth-config-list

   bandwidth-config-list  = ["+"] "b=" bw-cap-list *(BAR b-cap-list)
   bw-cap-list            = bw-cap-num *("," b-cap-num)
   bw-cap-num             = 1*DIGIT   ; 1 to 2^32-1 inclusive

       Figure 1: Syntax of the bandwidth parameter in lcfg and pcfg
                                attributes

   Each bandwidth capability configuration is a comma-separated list of
   bandwidth capability attribute numbers where 'b-cap-num' refers to
   the bw-cap-num bandwidth capability numbers defined explicitly
   earlier in this document, and hence must be between 1 and 2^31-1
   (both included).  Alternative bandwidth configurations are separated
   by a vertical bar ("|").

   The bandwidth parameter to the actual configuration attribute
   ("a=acfg") is formulated as a sel-extension-config with

      ext-cap-name = "b"

   hence

   sel-extension-config = sel-bandwidth-config
   sel-bandwidth-config = "b=" bw-cap-list  ; bw-cap-list as above.

      Figure 2: Syntax of the bandwidth parameter in acfg attributes

3.1.1.2.  Option tag

   The SDP Capability Negotiation Framework
   [I-D.ietf-mmusic-sdp-capability-negotiation] solution allows for
   capability negotiation extensions to be defined.  Associated with
   each such extension is an option tag that identifies the extension in
   question.  Hereby, we define a new option tag of "bcap-v0" that
   identifies support for the bandwidth capability.  This option tag



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   SHOULD be added to other existing option tags present in the "csup"
   and "creq" attributes in SDP, according to the procedures defined in
   the SDP Capability Negotiation Framework
   [I-D.ietf-mmusic-sdp-capability-negotiation].

3.1.2.  Connection Data Capability

   According to SDP [RFC4566], the connection data field in SDP contains
   the connection data, and it has the following syntax:

      c=<nettype> <addrtype> <connection-address>

   where <nettype> indicates the network type, <addrtype> indicates the
   address type, and the <connection-address> is the connection address,
   which is dependent on the address type.

   At the moment, the only network type defined is "IN", which indicates
   Internet network type.  The address types "IP4" and "IP6" indicate
   the type of IP addresses.

   SDP [RFC4566] permits specification of connection data at the session
   or at the media level.  In order to permit negotiation of connection
   data at the media level, we define the connection data capability
   attribute ("a=ccap") in the form:

      "a=ccap:" conn-cap-num 1*WSP nettype SP addrtype SP connection-
      address CRLF

   where <conn-cap-num> is a unique ordinal identifier of the connection
   data capability, and the other elements are as defined in [RFC4566].

   This format corresponds to the [RFC4566] attribute production rules
   according to the following Augmented Backus-Naur Form (ABNF)
   [RFC5234] syntax:

   att-field       = "ccap"
   att-value       = conn-cap-num 1*WSP nettype SP addrtype
                     SP connection-address
   conn-cap-num    = 1*DIGIT   ; integer between 1 and 2^31-1, inclusive

   The connection information capability can be used to negotiate the
   use of IPv4 or IPv6 addresses without resort to Interactive
   Connectivity Establishment(ICE) [I-D.ietf-mmusic-ice].  Note,
   however, that ICE provides for real-time reachability testing of
   multiple addresses, whereas use of the connection capability forces
   an early choice of connection address.





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3.1.2.1.  Configuration Parameters

   The SDP Capability Negotiation Framework
   [I-D.ietf-mmusic-sdp-capability-negotiation] provides for the
   existence of the "pcfg" and "acfg" attributes, which can carry one or
   more potential configurations to be negotiated.  The concept is
   extended by the the Media Capabilities Negotiation
   [I-D.ietf-mmusic-sdp-media-capabilities] with an "lcfg" attribute
   that conveys latent configurations.

   In this document we define a <connection-config> parameter to be used
   to specify a connection data capability in a potential or latent
   configuration attribute.  The parameter follows the form of an
   extension-config-list, with

      ext-cap-name = "c"

      ext-cap-list = conn-cap-list

   where, according to the following Augmented Backus-Naur Form (ABNF)
   [RFC5234] syntax:

   extension-config-list = conn-config-list
   conn-config-list      = "c=" conn-cap-list
   conn-cap-list         = conn-cap-num *(BAR conn-cap-num)
   conn-cap-num          = 1*DIGIT   ; 1 to 2^32-1 inclusive

    Figure 3: Syntax of the connection data parameter in lcfg and pcfg
                                attributes

   Each capability configuration alternative contains a single
   connection data capability attribute number and refers to the conn-
   cap-num capability number defined explicitly earlier in this
   document, and hence must be between 1 and 2^31-1 (both included).
   The connection data capability allows the expression of only a single
   capability in each alternative, rather than a list of capabilities,
   since no more than a single connection data field is permitted per
   media block.  Nevertheless, it is still allowed to express
   alternative potential connection configurations separated by a
   vertical bar ("|").

   The connection data parameter to the actual configuration attribute
   ("a=acfg") is formulated as a sel-extension-config with

      ext-cap-name = "c"

   hence




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   sel-extension-config = sel-connection-config
   sel-connection-config = "c=" conn-cap-num  ; as defined above.

   Figure 4: Syntax of the connection data parameter in acfg attributes

3.1.2.2.  Option tag

   The SDP Capability Negotiation Framework
   [I-D.ietf-mmusic-sdp-capability-negotiation] solution allows for
   capability negotiation extensions to be defined.  Associated with
   each such extension is an option tag that identifies the extension in
   question.  Hereby, we define a new option tag of "ccap-v0" that
   identifies support for the connection data capability.  This option
   tag SHOULD be added to other existing option tags present in the
   "csup" and "creq" attributes in SDP, according to the procedures
   defined in the SDP Capability Negotiation Framework
   [I-D.ietf-mmusic-sdp-capability-negotiation].

3.1.3.  Information Capability

   RFC 4566 [RFC4566] provides for the existence of an information field
   expressed in the format of the "i=" line, which can appear either at
   the session level or at the media level.  An "i=" line that is
   present at the session level is known as the "session name", and its
   purpose is to convey a human-readable textual information about the
   session.  We don't see much usage of capabilities related to the "i="
   line at the session level.

   The "i=" line in SDP can also appear at the media level, in which
   case it is used to label the media stream it is related to, so that
   it indicates the purpose of the media stream.  In this case, it is
   foreseen that applications declaring capabilities related to
   different media lines also need to provide different labels to media
   streams that are substantially different.  For example, if two media
   streams are offered one as alternative to the other, most likely
   their associated labels are different.  Hence, there is value in
   defining a mechanism to provide labels of media streams as
   capabilities.

   According to SDP [RFC4566], the media label has the following syntax:

      "i="text

   where "text" represents a human-readable text indicating the purpose
   of the media stream.

   In this document we define a new capability attribute: the
   information media capability, "icap".  This attribute lists



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   information media labels as capabilities, according to the following
   definition:

      "a=icap:" info-cap-num 1*WSP text

   where <info-cap-num> is the ordinal identifier of the particular
   media information capability and <text> is a human-readable text that
   indicates the purpose of the media stream it is supposed to
   characterize.

   As an example, one might use:

      a=icap:1 Document Camera

   to represent a purpose of a media stream identified with the
   capability number 1.

   The media information capability attribute satisfies the general
   attribute production rules in [RFC4566] according to the following
   Augmented Backus-Naur Form (ABNF) [RFC5234] syntax:

   att-field       = "icap"
   att-value       = info-cap-num 1*WSP text
                               ; text is defined in RFC 4566
   info-cap-num    = 1*DIGIT   ; integer between 1 and 2^31-1

3.1.3.1.  Configuration Parameters

   The SDP Capability Negotiation Framework
   [I-D.ietf-mmusic-sdp-capability-negotiation] provides for the
   existence of the "pcfg" and "acfg" attributes, which can carry one or
   more potential configurations to be negotiated.  The concept is
   extended by the the Media Capabilities Negotiation
   [I-D.ietf-mmusic-sdp-media-capabilities] with an "lcfg" attribute
   that conveys latent configurations.

   In this document, we define an <info-config-list> parameter to be
   used to convey information capabilities in a potential or latent
   configuration.  This parameter is defined as an <extension-config-
   list> with the following associations:

      ext-cap-name = "i"

      ext-cap-list = info-cap-list

   This leads to the following definition for the information capability
   parameter:




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   extension-config-list = info-config-list
   info-config-list      = "i=" info-cap-list
   info-cap-list         = info-cap-num *(BAR info-cap-num)
   info-cap-num          = 1*DIGIT   ; 1 to 2^32-1 inclusive
                            ; BAR defined in SDP capabilities
                            ; negotiation

   Figure 5: Syntax of the information capability parameter in lcfg and
                              pcfg attributes

   Each potential capability configuration contains a single information
   capability attribute number where 'info-cap-num' is the information
   capability number defined explicitly earlier in this document, and
   hence must be between 1 and 2^31-1 (both included).  The information
   capability allows the expression of only a single capability in each
   alternative, since no more than a single information field is
   permitted per media block.  Nevertheless, it is still allowed to
   express alternative potential information configurations separated by
   a vertical bar ("|").

3.1.3.2.  Option Tag

   The information field ("i=") in SDP, rather than providing
   information for a software application, provides information for a
   human user.  Therefore, it is questionable whether the text in the
   information field or the information capability is relevant for
   negotiating SDP capabilities.  In particular, unlike the bandwidth
   and the connection data capabilities, there are no compelling use
   cases that hint for the definition of an option tag for the
   information capability.  This is because it is not expected that an
   endpoint would declare that the negotiation should fail if the
   information field (which is for human consumption) is not understood.
   As a consequence, we do not define an option tag associated to the
   information capability.

3.2.  Session Level versus Media Level

   The icap, ccap, and bcap attributes can appear at the session level
   and/or at the media level, but MUST be interpreted as a media-level
   capability.  To avoid confusion, the <type-attr-num> for each line
   must be unique across all capability attributes of the same type
   within the entire session description.  As described below, these
   capability attributes may be referenced by acfg, pcfg and/or lcfg
   attributes.







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4.  Field Replacement Rules

   To simplify the construction of SDP records, given the need to
   include fields at the base level for endpoints that do not support
   capabilities negotiation, we define some simple field-replacement
   rules for those fields invoked by potential or latent configurations.
   In particular, any i-field or c-field invoked by a configuration MUST
   replace the corresponding field, if present at the base media level.
   Any b-field invoked by a configuration MUST replace any b-field of
   the same bandwidth type at the media level.


5.  IANA Considerations

5.1.  New SDP Attributes

   IANA is hereby requested to register the following new SDP
   attributes:

      Attribute name: icap

      Long form name: Information Capability

      Type of attribute: Media-level

      Subject to charset: No

      Purpose: Negotiate human-readable media information

      Appropriate values: See Section 3.1.3

      Attribute name: ccap

      Long form name: Connection Data Capability

      Type of attribute: Media-level

      Subject to charset: No

      Purpose: Negotiate media-level connection data

      Appropriate values: See Section 3.1.2

      Attribute name: bcap

      Long form name: Bandwidth Capability





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      Type of attribute: Media-level

      Subject to charset: No

      Purpose: Negotiate media-level bandwidths

      Appropriate values: See Section 3.1.1

5.2.  New Option Tags

   IANA is hereby requested to add the new option tags "ccap-v0" and
   "bcap-v0", defined herein, to the SDP Capability Negotiation Option
   Tag Registry.


6.  Security Considerations

   This document provides an extension on top of RFC 4566 [RFC4566], RFC
   3264 [RFC3264], SDP Capability Negotiation Framework
   [I-D.ietf-mmusic-sdp-capability-negotiation], and SDP Media
   Capabilities Negotiation [I-D.ietf-mmusic-sdp-media-capabilities].
   As such, the security considerations of those documents apply.


7.  Acknowledgments

   Thanks to Christer Holmberg, Alf Heidermark, and Ingemar Johansson
   for arguing for the existence of this document and early reviewing
   it.


8.  References

8.1.  Normative References

   [I-D.ietf-mmusic-sdp-capability-negotiation]
              Andreasen, F., "SDP Capability Negotiation",
              draft-ietf-mmusic-sdp-capability-negotiation-09 (work in
              progress), July 2008.

   [I-D.ietf-mmusic-sdp-media-capabilities]
              Gilman, R., Even, R., and F. Andreasen, "SDP media
              capabilities Negotiation",
              draft-ietf-mmusic-sdp-media-capabilities-05 (work in
              progress), July 2008.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.



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   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              June 2002.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

8.2.  Informative References

   [I-D.ietf-mmusic-ice]
              Rosenberg, J., "Interactive Connectivity Establishment
              (ICE): A Protocol for Network Address  Translator (NAT)
              Traversal for Offer/Answer Protocols",
              draft-ietf-mmusic-ice-19 (work in progress), October 2007.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.

   [RFC3711]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
              Norrman, "The Secure Real-time Transport Protocol (SRTP)",
              RFC 3711, March 2004.


Authors' Addresses

   Miguel A. Garcia-Martin
   Ericsson
   Calle Via de los Poblados 13
   Madrid,   28033
   Spain

   Phone: +34 91 339 1000
   Email: miguel.a.garcia@ericsson.com


   Simo Veikkolainen
   Nokia
   P.O. Box 407
   NOKIA GROUP, FI  00045
   Finland

   Phone: +358 50 486 4463
   Email: simo.veikkolainen@nokia.com




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   Robert R. Gilman
   NDCI
   3243 W. 11th Ave. Dr.
   Broomfield, Colorado  80020
   U.S.A.

   Phone: +1 303 898 9780
   Email: bob_gilman@comcast.net











































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Internet-Draft      Miscellaneous Capabilities in SDP       October 2008


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