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Versions: 00 01 02 03 RFC 3603

SIPPING Working Group                                W. Marshall, Editor
Internet Draft                                       AT&T
Document:<draft-dcsgroup-sipping-proxy-proxy-03.txt>
Category: Informational                              F. Andreasen, Editor
                                                     Cisco

                                                     March 2, 2003


    Private Session Initiation Protocol (SIP) Proxy-to-Proxy Extensions
         for Supporting the PacketCable Distributed Call Signaling
                               Architecture


Status of this Memo

   This document is an Internet-Draft and is in full compliance with
   all provisions of Section 10 of RFC 2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that
   other groups may also distribute working documents as Internet-
   Drafts. Internet-Drafts are draft documents valid for a maximum of
   six months and may be updated, replaced, or obsoleted by other
   documents 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

   In order to deploy a residential telephone service at very large
   scale across different domains, it is necessary for trusted elements
   owned by different service providers to exchange trusted information
   that conveys customer-specific information and expectations about
   the parties involved in the call. This document describes private
   extensions to the Session Initiation Protocol (RFC3261) for
   supporting the exchange of customer information and billing
   information between trusted entities in the PacketCable Distributed
   Call Signaling Architecture. These extensions provide mechanisms for
   access network coordination to prevent theft of service, customer
   originated trace of harassing calls, support for operator services
   and emergency services, and support for various other regulatory
   issues. The use of the extensions is only applicable within closed
   administrative domains, or among federations of administrative
   domains with previously agreed-upon policies where coordination of
   charging and other functions is required.



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Table of Contents

   Status of this Memo................................................1
   Abstract...........................................................1
   Table of Contents..................................................2
   1. Applicability Statement.........................................3
   2. Introduction....................................................3
   3. Trust Boundary..................................................5
   4. Conventions used in this document...............................5
   5. P-DCS-TRACE-PARTY-ID............................................6
   5.1 Syntax.........................................................6
   5.2 Procedures at an Untrusted User Agent Client (UAC).............7
   5.3 Procedures at a Trusted User Agent Client (UAC)................7
   5.4 Procedures at an Untrusted User Agent Server (UAS).............7
   5.5 Procedures at a Trusted User Agent Server (UAS)................7
   5.6 Procedures at Proxy............................................7
   5.6.1 Procedures at Originating Proxy..............................7
   5.6.2 Procedures at Terminating Proxy..............................8
   6. P-DCS-OSPS......................................................8
   6.1 Syntax.........................................................8
   6.2 Procedures at an Untrusted User Agent Client (UAC).............9
   6.3 Procedures at a Trusted User Agent Client (UAC)................9
   6.4 Procedures at an Untrusted User Agent Server (UAS).............9
   6.5 Procedures at a Trusted User Agent Server (UAS)...............10
   6.6 Procedures at Proxy...........................................10
   7. P-DCS-BILLING-INFO.............................................10
   7.1 Syntax........................................................11
   7.2 Procedures at an Untrusted User Agent Client (UAC)............13
   7.3 Procedures at a Trusted User Agent Client (UAC)...............13
   7.4 Procedures at an Untrusted User Agent Server (UAS)............14
   7.5 Procedures at a Trusted User Agent Server (UAS)...............14
   7.6 Procedures at Proxy...........................................14
   7.6.1 Procedures at Originating Proxy.............................15
   7.6.2 Procedures at Terminating Proxy.............................15
   7.6.3 Procedures at Tandem Proxy..................................16
   8. P-DCS-LAES and P-DCS-REDIRECT..................................16
   8.1 Syntax........................................................17
   8.2 Procedures at an Untrusted User Agent Client (UAC)............18
   8.3 Procedures at a Trusted User Agent Client (UAC)...............18
   8.4 Procedures at an Untrusted User Agent Server (UAS)............19
   8.5 Procedures at a Trusted User Agent Server (UAS)...............19
   8.6 Procedures at Proxy...........................................19
   8.6.1 Procedures at Originating Proxy.............................20
   8.6.2 Procedures at Terminating Proxy.............................21
   9. Security Considerations........................................22
   10. IANA Considerations...........................................22
   11. Notice Regarding Intellectual Property Rights.................23
   12. Normative References..........................................23
   13. Informative References........................................23
   14. Acknowledgements..............................................23
   15. Editor's Addresses............................................24
   Full Copyright Statement..........................................25
   Acknowledgement...................................................25

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1. Applicability Statement

   The SIP extensions described in this document make certain
   assumptions regarding network topology, linkage between SIP and
   lower layers, and the availability of transitive trust.  These
   assumptions are generally not applicable in the Internet as a whole.
   The use of these headers is only applicable within closed
   administrative domains, or among federations of administrative
   domains with previously agreed-upon policies where coordination of
   charging and other functions is required, as in for example the
   architecture presented in [6].  Use outside such a domain could
   result in the leakage of potentially sensitive or private
   information.  User consent to the privacy implications of the
   policies in [6] is strongly encouraged in those domains as well.

   Although RFC-2119 language is used in this document, the scope of
   the normative language is only for the area of applicability of the
   document and, like the technology, it does not apply to the general
   Internet.

2. Introduction

   In order to deploy a SIP[2]-based residential telephone service at
   very large scale across different domains, it is necessary for
   trusted elements owned by different service providers to exchange
   trusted information that conveys billing information and
   expectations about the parties involved in the call.

   There are many billing models used in deriving revenue from
   telephony services today. Charging for telephony services is tightly
   coupled to the use of network resources. It is outside the scope of
   this document to discuss the details of these numerous and varying
   methods.

   A key motivating principle of the DCS architecture described in [6]
   is the need for network service providers to be able to control and
   monitor network resources; revenue may be derived from the usage of
   these resources as well as from the delivery of enhanced services
   such as telephony. Furthermore, the DCS architecture recognizes the
   need for coordination between call signaling and resource
   management.  This coordination ensures that users are authenticated
   and authorized before receiving access to network resources and
   billable enhanced services.

   DCS Proxies, as defined in [6], have access to subscriber
   information and act as policy decision points and trusted
   intermediaries along the call signaling path.  Edge routers provide
   the network connectivity and resource policy enforcement mechanism
   and also capture and report network connectivity and resource usage
   information.  Edge routers need to be given billing information that
   can be logged with Record Keeping or Billing servers.  The DCS
   Proxy, as a central point of coordination between call signaling and

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   resource management, can provide this information based on the
   authenticated identity of the calling and called parties. Since
   there is a trust relationship among DCS Proxies, they can be relied
   upon to exchange trusted billing information pertaining to the
   parties involved in a call. See [6] for a description of the trust
   boundary and trusted versus untrusted entities.

   For these reasons, it is appropriate to consider defining SIP header
   extensions to allow DCS Proxies to exchange information during call
   setup. It is the intent that the extensions would only appear on
   trusted network segments, should be inserted upon entering a trusted
   network region, and removed before leaving trusted network segments.

   Significant amounts of information is retrieved by an originating
   DCS Proxy in its handling of a connection setup request from a user
   agent.  Such information includes location information about the
   subscriber (essential for emergency services calls), billing
   information, and station information (e.g. coin operated phone). In
   addition, while translating the destination number, information such
   as the local-number-portability office code is obtained and will be
   needed by all other proxies handling this call.

   For Usage Accounting records, it is necessary to have an identifier
   that can be associated with all the event records produced for the
   call.  The SIP Call-ID header field cannot be used as such an
   identifier since it is selected by the originating user agent, and
   may not be unique among all past calls as well as current calls.
   Further, since this identifier is to be used by the service
   provider, it should be chosen in a manner and in a format that meets
   the service provider's needs.

   Billing information may not necessarily be unique for each user
   (consider the case of calls from an office all billed to the same
   account).  Billing information may not necessarily be identical for
   all calls made by a single user (consider prepaid calls, credit card
   calls, collect calls, etc).  It is therefore necessary to carry
   billing information separate from the calling and called party
   identification.  Furthermore, some billing models call for split-
   charging where multiple entities are billed for portions of the
   call.

   The addition of a SIP General Header Field allows for the capture of
   billing information and billing identification for the duration of
   the call.

   It is the intent that the billing extensions would only appear on
   trusted network segments, and MAY be inserted by a DCS Proxy in
   INVITE and REFER requests and INVITE responses in a trusted network
   segment, and removed before leaving trusted network segments.

   In addition to support for billing, current residential telephone
   service includes the need for customer originated trace (of
   harassing or obscene calls), for operator services such as busy line

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   verification and emergency interrupt (initiated by an operator from
   an Operator Services Position System (OSPS)), for emergency services
   such as 9-1-1 calls to a Public Service Access Point (PSAP) and the
   subsequent call handling, and support for Electronic Surveillance
   and Law Enforcement access as required by applicable legislation and
   court orders.  In all of these cases, additional information about
   the call and about the subscribers involved in the call needs to be
   exchanged between the proxies.


3. Trust Boundary

   The DCS architecture [6] defines a trust boundary around the various
   systems and servers that are owned, operated by, and/or controlled
   by the service provider.  These trusted systems include the proxies
   and various servers such as bridge servers, voicemail servers,
   announcement servers, etc.  Outside of the trust boundary lie the
   customer premises equipment, and various application and media
   servers operated by third-party service providers.

   Certain subscriber-specific information, such as billing and
   accounting information, stays within the trust boundary.  Other
   subscriber-specific information, such as endpoint identity, may be
   presented to untrusted endpoints or may be withheld based on
   subscriber profiles.

   The User Agent (UA) may be either within the trust boundary or
   outside the trust boundary, depending on exactly what function is
   being performed and exactly how it is being performed.
   Accordingly, the procedures followed by a User Agent are different
   depending on whether the UA is within the trust boundary or outside
   the trust boundary.

   The following sections giving procedures for User Agents therefore
   are subdivided into trusted user agents and untrusted user agents.

4. 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 RFC-2119 [1].

   The term "private-URL" used in this document refers to a SIP URI
   that is generated by a proxy, contains a "hostport" that identifies
   the proxy, and contains a "userinfo" string that is generated by the
   proxy.  The "userinfo" typically contains (or points to) information
   that is not to be disclosed outside the trusted domain of the
   proxies, such as billing account numbers, electronic surveillance
   indication, electronic surveillance parameters, and call redirection
   information.  Consequently, the information is either stored locally
   by the proxy, or encrypted with a private key known only to the
   proxy and encoded in a character string in the "userinfo" portion of
   the URL.  A checksum is included in the "userinfo" data to detect

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   tampering.  The mechanism by which a proxy recognizes a "userinfo"
   as a private-URL and decodes and recovers the original information
   is local to the proxy and is not subject to standardization.  Some
   possible implementations include an initial magic cookie (e.g.
   z9hG4Bk followed by the pointer/information), or use of a reserved
   "user" name (e.g. "private") with the optional "password" containing
   the pointer/information.

5. P-DCS-TRACE-PARTY-ID

   In the telephone network, calling identity information is used to
   support regulatory requirements such as the Customer Originated
   Trace service, which provide the called party with the ability to
   report obscene or harassing phone calls to law enforcement.  This
   service is provided independently of caller-id, and works even if
   the caller requested anonymity.  The calling party is here
   identified as the station originating the call. In order for this
   service to be dependable, the called party must be able to trust
   that the calling identity information being presented is valid. One
   way to achieve this is described in [10].

   To initiate a customer-originated-trace from an untrusted UAC, an
   additional header is defined for the INVITE request.  This header is
   called P-DCS-Trace-Party-ID, and does not appear in any other
   request or response. The entity addressed by the Request-URI
   performs the service-provider-specific functions of recording and
   reporting the caller identity in the P-DCS-Trace-Party-ID for law
   enforcement action.  It then forwards the call to either an
   announcement server or to the service-provider's business office to
   collect further information about the complaint.  A trusted UAC does
   not use this header, as it initiates this action locally.

5.1 Syntax

   The ABNF description of this header is (some terms used in this ABNF
   are defined in [2]):

        P-DCS-Trace-Party-ID = "P-DCS-Trace-Party-ID" HCOLON
                                        name-addr

   This document adds the following entry to Table 2 of [2]:

         Header field         where proxy  ACK  BYE  CAN  INV  OPT  REG
         ------------         ----- -----  ---  ---  ---  ---  ---  ---
         P-DCS-Trace-Party-ID   R     dr    -    -    -    o    -    -


                                           SUB  NOT  REF  INF  UPD  PRA
                                           ---  ---  ---  ---  ---  ---
                                            -    -    -    -    -    -




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   The addr-spec contained in name-addr contains a URL that identifies
   the remote endpoint.  Addr-spec typically contains a tel: URL or SIP
   URI giving the identity of the remote endpoint, as provided in the
   signaling messages that established the session to be traced.

5.2 Procedures at an Untrusted User Agent Client (UAC)

   The UAC MUST insert a P-DCS-Trace-Party-ID header into the initial
   INVITE message for a customer-originated-trace request.  The UAC
   MUST use a SIP URI in the Request-URI with userinfo set to "call-
   trace" and hostport identifying the call tracing entity for the
   untrusted UA.

5.3 Procedures at a Trusted User Agent Client (UAC)

   A trusted UAC performs the customer-originated-trace in a manner
   similar to the trusted UAS, described below.  A trusted UAC MUST NOT
   include this header in any request.

5.4 Procedures at an Untrusted User Agent Server (UAS)

   This header MUST NOT appear in any response sent by a UAS.

5.5 Procedures at a Trusted User Agent Server (UAS)

   If the P-DCS-Trace-Party-ID header is present in the initial INVITE
   request from a UAC, and the Request-URI of the INVITE has userinfo
   set to "call-trace" and hostport set to the UAS, the UAS MUST
   perform the service-provider-specific functions of recording and
   reporting the caller identity for law enforcement action.  The UAS
   then MUST redirect the call, via a 3xx response, to either an
   announcement server or to the service-provider's business office to
   collect further information about the complaint.

   This header MUST NOT appear in any response sent by a UAS.

5.6 Procedures at Proxy

   Two sets of proxy procedures are defined: (1) the procedures at an
   originating proxy, and (2) the procedures at a terminating proxy.
   The originating proxy is a proxy that received the INVITE request
   from a non-trusted endpoint.

   The terminating proxy is a proxy that sends the INVITE request to a
   non-trusted endpoint.

   A proxy that both receives the INVITE request from an untrusted
   endpoint, and sends the INVITE request to an untrusted endpoint,
   performs both sets of procedures.

5.6.1 Procedures at Originating Proxy



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   If the P-DCS-Trace-Party-ID header is present in the initial INVITE
   request from the UAC, and the Request-URI of the INVITE has userinfo
   other than "call-trace" and hostport set to other than a potentially
   provisioned call tracing entity, then the Proxy MAY reject the
   request, or MAY remove the P-DCS-Trace-Party-ID header from the
   request.  If the header is present in a valid request, and contains
   a private-URL that identifies the Proxy in the hostport, then the
   Originating Proxy SHOULD replace the private-URL with its original
   contents (i.e. the verified identity of the caller of the session
   that is being traced).

5.6.2 Procedures at Terminating Proxy

   This header MUST NOT appear in any request or response sent by a
   terminating proxy to an untrusted endpoint.

6. P-DCS-OSPS

   Some calls have special call processing requirements that may not be
   satisfied by normal user agent call processing.  For example, when a
   user is engaged in a call and another call arrives, such a call
   might be rejected with a busy indication.  However, some PSTN
   operator services require special call processing.  In particular,
   the Busy Line Verification (BLV) and Emergency Interrupt (EI)
   services initiated by an operator from an Operator Services Position
   System (OSPS) on the PSTN network have such a need.  Similarly,
   emergency calls to a 9-1-1 Public Service Access Point (PSAP) may
   result in trunk signaling causing operator ringback using a howling
   tone or sustained ring on the originating line (country-specific
   variations may exist).

   In order to inform the SIP user agent that special treatment should
   be given to a call, we use a new P-DCS-OSPS header field, which may
   be set to a value indicating when a special type of call processing
   is requested.  We define three values in this header, namely "BLV"
   for busy line verification, "EI" for emergency interrupt, and "RING"
   for operator ringback (e.g., howling/sustained tone ring in the US).

   If the user agent decides to honor such a request, the response of
   the user agent to an INVITE with either "BLV" or "EI" will not be a
   busy indication. Since "EI" and "RING" only occur on established
   dialogs, they may also appear in UPDATE requests.

6.1 Syntax

   The ABNF description of the P-DCS-OSPS header is as follows (some
   terms used in this ABNF are defined in [2]):

        P-DCS-OSPS      = "P-DCS-OSPS" HCOLON OSPS-Tag
        OSPS-Tag        = "BLV" / "EI" / "RING" / token

   This document adds the following entry to Table 2 of [2]:


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         Header field         where proxy  ACK  BYE  CAN  INV  OPT  REG
         ------------         ----- -----  ---  ---  ---  ---  ---  ---
         P-DCS-OSPS             R     dr    -    -    -    o    -    -


                                           SUB  NOT  REF  INF  UPD  PRA
                                           ---  ---  ---  ---  ---  ---
                                            -    -    -    -    o    -

   The OSPS-Tag value of "token" is defined for extensibility, and is
   reserved for future use.

6.2 Procedures at an Untrusted User Agent Client (UAC)

   The P-DCS-OSPS header MUST NOT be sent in a request from an
   untrusted UAC.

6.3 Procedures at a Trusted User Agent Client (UAC)

   This header is typically only inserted by a Media Gateway Controller
   [6] that is controlling a Media Gateway with special trunks to a
   PSTN OSPS system or PSAP.  This trunk group is usually referred to
   as a BLV-trunk group and employs special signaling procedures that
   prevent inadvertent use.  Calls originating at the PSTN OSPS system
   are sent over this trunk group, and result in an INVITE request with
   the P-DCS-OSPS header.

   This header MAY be sent in an INVITE request, and MUST NOT appear in
   any message other than those listed below.

   OSPS-Tag value "BLV" MUST NOT appear in any request or response
   other than an initial INVITE request establishing a new dialog.

   OSPS-Tag value "EI" MUST NOT appear in any request or response other
   than (1) a subsequent INVITE within a pre-existing dialog
   established with the OSPS-Tag value of "BLV", or (2) an UPDATE
   request within a pre-existing dialog established with the OSPS-Tag
   value of "BLV".

   OSPS-Tag value "RING" MUST NOT appear in any request or response
   other than (1) a subsequent INVITE within a pre-existing dialog
   established by a UAC to an operator or PSAP, or (2) an UPDATE
   request within a pre-existing dialog established by a UAC to an
   operator or PSAP.

6.4 Procedures at an Untrusted User Agent Server (UAS)

   If the UAS receives an INVITE request with an OSPS-Tag of "BLV",
   dialog identification that matches an existing dialog, and the
   existing call was not established with the OSPS-Tag, it MUST reject
   the request with a 403-Forbidden error code.



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   If the UAS receives an INVITE/UPDATE request with an OSPS-Tag value
   of "EI" or "RING", with dialog identification that does not match an
   existing dialog, it MUST reject the request with a 403-Forbidden
   response code.

   If the UAS receives an INVITE that contains an OSPS-Tag value of
   "BLV" and is not willing to cooperate in offering this service, it
   MUST reject the request with a 403-Forbidden response code.

   The UAS SHOULD NOT reject an INVITE with a BLV OSPS-Tag due to a
   busy condition.  The UAS MUST NOT respond with a 3xx-Redirect
   response code to an INVITE with a BLV OSPS-Tag.  The UAS SHOULD NOT
   alert the user of the incoming call attempt if the BLV OSPS-Tag is
   present in the INVITE.

   If an INVITE with OSPS-Tag of "BLV" is accepted (e.g., meeting all
   QoS pre-conditions, etc.), the UAS MUST send an audio stream on this
   connection to the address and port given in the SDP of the INVITE.
   The UAS MAY perform a mixing operation between the two ends of an
   existing active call and send the resulting media stream to the
   address and port indicated.  Alternatively, the UAS MAY send a copy
   of the local voice stream, and (if no activity on the local voice
   stream) send a copy of the received voice stream of an existing
   call. If the state of the UAS is idle, the UAS SHOULD send a stream
   of silence packets to OSPS.  If the state of the UAS is ringing or
   ringback, the UAS SHOULD send a ringback stream to OSPS.

   If an INVITE/UPDATE with OSPS-Tag of "EI" is accepted, the UAS MUST
   enable communication between the UAC and the local user.  The UAS
   MAY put any existing call on hold, or initiate an ad-hoc conference.

   If an INVITE/UPDATE with OSPS-Tag of "RING" is accepted, the UAS
   MUST perform operator ringback in accordance with local procedures,
   e.g., generate a 3-second howling tone or a sustained ring,
   depending on the state of the user equipment.

6.5 Procedures at a Trusted User Agent Server (UAS)

   The procedures at a trusted UAS MUST be identical to those described
   in 6.4.

6.6 Procedures at Proxy

   In the DCS architecture, the OSPS is considered a trusted UAC.  If a
   proxy receives a P-DCS-OSPS header in a request from an untrusted
   source, it MUST either remove the header or reject the request with
   a 403-Forbidden response.

   A proxy that implements a call-forwarding service MUST NOT respond
   to an INVITE request with a 3xx response, if the request contained
   the P-DCS-OSPS header.

7. P-DCS-BILLING-INFO

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   There are many billing models used in deriving revenue from
   telephony services today. Charging for telephony services is tightly
   coupled to the use of network resources. It is outside the scope of
   this document to discuss the details of these numerous and varying
   methods.

   Proxies have access to subscriber information and act as policy
   decision points and trusted intermediaries along the call signaling
   path. Edge routers provide the network connection and resource
   policy enforcement mechanism and also capture and report network
   connection and resource usage information.  Edge routers need to be
   given billing information that can be logged with Record Keeping or
   Billing servers.  The proxy, as a central point of coordination
   between call signaling and resource management, can provide this
   information based on the authenticated identity of the calling and
   called parties. Since there is a trust relationship among proxies,
   they can be relied upon to exchange trusted billing information
   pertaining to the parties involved in a call.

   For Usage Accounting records, it is necessary to have an identifier
   that can be associated with all the event records produced for the
   call.  The SIP Call-ID header field cannot be used as such an
   identifier since it is selected by the originating user agent, and
   may not be unique among all past calls as well as current calls.
   Further, since this identifier is to be used by the service
   provider, it should be chosen in a manner and in a format that meets
   the service provider's needs.

   Billing information may not necessarily be unique for each user
   (consider the case of calls from an office all billed to the same
   account).  Billing information may not necessarily be identical for
   all calls made by a single user (consider prepaid calls, credit card
   calls, collect calls, etc).  It is therefore necessary to carry
   billing information separate from the calling and called party
   identification.  Furthermore, some billing models call for split-
   charging where multiple entities are billed for portions of the
   call.

   The addition of a SIP General Header Field allows for the capture of
   billing information and billing identification for the duration of
   the call.

   It is the intent that the billing extensions would only appear on
   trusted network segments, and MAY be inserted by a proxy or trusted
   UA in INVITE requests in a trusted network segment, and removed
   before leaving trusted network segments.  The P-DCS-Billing-Info
   header extension is used only on requests and responses between
   proxies and trusted User Agents.  It is never sent to, nor sent by,
   an untrusted UA.

7.1 Syntax


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   The DCS-Billing-Info header is defined by the following ABNF (some
   terms used in this ABNF are defined in [2]):

        P-DCS-Billing-Info      = "P-DCS-Billing-Info" HCOLON
                                   Billing-Correlation-ID "/" FEID
                                   *(SEMI Billing-Info-param)
        Billing-Correlation-ID  = 1*48(HEXDIG)
        FEID                    = 1*16(HEXDIG) "@" host
        Billing-Info-param      = RKS-Group-ID-param / Charge-param /
                                  Calling-param / Called-param /
                                  Routing-param / Loc-Routing-param /
                                  generic-param
        RKS-Group-ID-param      = "rksgroup" EQUAL RKS-Group-ID
        RKS-Group-ID            = token
        Charge-param            = "charge" EQUAL Acct-Charge-URI
        Acct-Charge-URI         = LDQUOT addr-spec RDQUOT
        Calling-param           = "calling" EQUAL Acct-Calling-URI
        Acct-Calling-URI        = LDQUOT addr-spec RDQUOT
        Called-param            = "called" EQUAL Acct-Called-URI
        Acct-Called-URI         = LDQUOT addr-spec RDQUOT
        Routing-param           = "routing" EQUAL Acct-Routing-URI
        Acct-Routing-URI        = LDQUOT addr-spec RDQUOT
        Loc-Routing-param       = "locroute" EQUAL Acct-Loc-Routing-URI
        Acct-Loc-Routing-URI    = LDQUOT addr-spec RDQUOT


   This document adds the following entry to Table 2 of [2]:

         Header field         where proxy  ACK  BYE  CAN  INV  OPT  REG
         ------------         ----- -----  ---  ---  ---  ---  ---  ---
         P-DCS-Billing-Info         admr    -    -    -    o    -    -


                                           SUB  NOT  REF  INF  UPD  PRA
                                           ---  ---  ---  ---  ---  ---
                                            -    -    -    -    -    -

   The P-DCS-Billing-Info extension contains an identifier that can be
   used by an event recorder to associate multiple usage records,
   possibly from different sources, with a billable account. It further
   contains the subscriber account information, and other information
   necessary for accurate billing of the service.  This header is only
   used between proxies and trusted User Agents.

   The Billing-Correlation-ID is specified in [9] as a 24-byte binary
   structure, containing 4 bytes of NTP timestamp, 8 bytes of the
   unique identifier of the network element that generated the ID, 8
   bytes giving the time zone, and 4 bytes of monotonically increasing
   sequence number at that network element. This identifier is chosen
   to be globally unique within the system for a window of several
   months.  This MUST be encoded in the P-DCS-Billing-Info header as a
   hexadecimal string of up to 48 characters.  Leading zeroes MAY be
   suppressed.

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   The Financial-Entity-ID (FEID) is specified in [9] as an 8-byte
   structure, containing the financial identifier for that domain,
   followed by a domain name.  FEID can be associated with a type of
   service and could be assigned to multiple domains by the same
   provider.  A domain could contain multiple assigned FEIDs.  This 8-
   byte structure MUST be encoded in the P-DCS-Billing-Info header as a
   hexadecimal string of up to 16 characters.  Trailing zeroes MAY be
   suppressed. "Host" contains the domain name.

   The RKS-Group-ID specifies a record keeping server (or group of
   cooperating servers) for event messages relating to this call.  It
   is used to control certain optimizations of procedures when multiple
   event message streams are being sent to the same Record Keeping
   Server.

   Additional parameters contain the information needed for generation
   of event message records.  Acct-Charge-URI, Acct-Calling-URI, Acct-
   Called-URI, Acct-Routing-URI, and Acct-Location-Routing-URI are each
   defined as URLs; they should all contain tel: URLs with E.164
   formatted addresses.  These fields are further defined in [9] under
   the element identifiers "Charge_Number" (element ID 16),
   "Calling_Party_Number" (element ID 4), "Called_Party_Number"
   (element ID 5), "Routing Number" (element ID 25), and
   "Location_Routing_Number" (element ID 22).

7.2 Procedures at an Untrusted User Agent Client (UAC)

   This header is never sent to an untrusted UAC, and is never sent by
   an untrusted UAC.

7.3 Procedures at a Trusted User Agent Client (UAC)

   The UAC MUST generate the Billing-Correlation-ID for the call, and
   insert it into the P-DCS-Billing-Info header in the initial INVITE
   message sent to the terminating proxy, along with the charging
   information for the call.  The UAC MUST include its FEID, and the
   RKS-Group-ID for the Record-Keeping-Server being used by the UAC.
   If the UAC performed a Local Number Portability (LNP) query, it MUST
   include the Routing Number and Location Routing Number returned by
   the query.

   If the response to the initial INVITE is a 3xx-Redirect, the UAC
   generates a new initial INVITE request to the destination specified
   in the Contact: header, as per standard SIP.  If a UAC receives a
   3xx-Redirect response to an initial INVITE, the new INVITE generated
   by the UAC MUST contain the P-DCS-Billing-Info header from the 3xx-
   Redirect response. If the UAC is acting as a B2BUA, instead of
   generating a new INVITE it MAY generate a private-URL and place it
   in the Contact header of a 3xx-Redirect response sent to the
   originating endpoint.  This private-URL MUST contain (or contain a
   pointer to) the P-DCS-Billing-Info value, which indicates the
   charging arrangement for the new call, and an expiration time very

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   shortly in the future, to limit the ability of the originator to re-
   use this private-URL for multiple calls.

   A UAC that includes a Refer-to header in a REFER request MUST
   include a P-DCS-Billing-Info header in the Refer-to's URL.  This P-
   DCS-Billing-Info header MUST include the accounting information of
   the initiator of the REFER.

7.4 Procedures at an Untrusted User Agent Server (UAS)

   This header is never sent to an untrusted UAS, and is never sent by
   an untrusted UAS.

7.5 Procedures at a Trusted User Agent Server (UAS)

   The UAS MUST include a P-DCS-Billing-Info header in the first
   reliable 1xx (except 100) or 2xx response to an initial INVITE
   message.  This P-DCS-Billing-Info header MUST include the Billing-
   Correlation-ID generated by the UAS, the FEID of the UAS, and the
   RKS-Group-ID of the Record-Keeping-Server being used by the UAS.
   The UAS MAY change the values of Acct-Charge-URI if it wishes to
   override the billing information that was present in the INVITE
   (e.g. for a toll-free call).  The decision to do this and the
   contents of the new Acct-Charge-URI MUST be determined by service
   provider policy provisioned in the UAS. If the UAS performed a LNP
   query, it MUST include the Routing Number and Location Routing
   Number returned by the query.

   The UAS MUST add a P-DCS-Billing-Info header to a 3xx-redirect
   response to an initial INVITE, giving the accounting information for
   the call forwarder, for the call segment from the destination to the
   forwarded-to destination.

7.6 Procedures at Proxy

   Three sets of proxy procedures are defined: (1) the procedures at an
   originating proxy, (2) the procedures at a terminating proxy, and
   (3) the procedures at a tandem proxy.

   The originating proxy is a proxy that received the INVITE request
   from a non-trusted endpoint.

   The terminating proxy is a proxy that sends the INVITE request to a
   non-trusted endpoint.

   A proxy that is neither an originating proxy, nor a terminating
   proxy, is a tandem proxy.

   For purposes of mid-call changes, such as call transfers, the proxy
   that receives the request from a non-trusted endpoint is considered
   the initiating proxy; the proxy that sends the request to a non-
   trusted endpoint is considered the recipient proxy.  Procedures for
   the initiating proxy are included below with those for originating

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   proxies, while procedures for the recipient proxy are included with
   those for terminating proxies.

   A proxy that both receives the INVITE request from an untrusted
   endpoint, and sends the INVITE request to a non-trusted endpoint,
   performs both sets of procedures.

7.6.1 Procedures at Originating Proxy

   The originating proxy MUST generate the Billing-Correlation-ID for
   the call, and insert it into the P-DCS-Billing-Info header in the
   initial INVITE message sent to the terminating proxy, along with the
   charging information for the call.  The originating proxy MUST
   include its FEID, and the RKS-Group-ID for the Record-Keeping-Server
   being used by the originating proxy.  If the originating proxy
   performed a LNP query, it MUST include the Routing Number and
   Location Routing Number returned by the query.  Any P-DCS-Billing-
   Info header present from an untrusted UA MUST be removed.

   If the Request-URI contains a private-URL, and the decoded username
   contains billing information, the originating proxy MUST generate a
   P-DCS-Billing-Info header with that decrypted information.
   Otherwise, the originating proxy MUST determine the accounting
   information for the call originator, and insert a P-DCS-Billing-Info
   header including that information.

   If the response to the initial INVITE is a 3xx-Redirect, received
   prior to a 18x, the originating proxy generates a new initial INVITE
   request to the destination specified in the Contact: header, as per
   standard SIP.  If an originating proxy receives a 3xx-Redirect
   response to an initial INVITE prior to a 18x response, the INVITE
   generated by the proxy MUST contain the P-DCS-Billing-Info header
   from the 3xx-Redirect response.

   If the response to the initial INVITE is a 3xx-Redirect, received
   after a 18x, the originating proxy generates a private-URL and
   places it in the Contact header of a 3xx-Redirect response sent to
   the originating endpoint.  This private-URL MUST contain (or contain
   a pointer to) the P-DCS-Billing-Info value, which indicate the
   charging arrangement for the new call, and an expiration time very
   shortly in the future, to limit the ability of the originator to re-
   use this private-URL for multiple calls.

   An originating proxy that processes a REFER request from an
   untrusted UA  MUST include a P-DCS-Billing-Info header in the Refer-
   to's URL.  This P-DCS-Billing-Info header MUST include the
   accounting information of the initiator.

7.6.2 Procedures at Terminating Proxy

   The terminating proxy MUST NOT send the P-DCS-Billing-Info header to
   an untrusted destination.


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   The terminating proxy MUST include a P-DCS-Billing-Info header in
   the first reliable 1xx (except 100) or 2xx response to an initial
   INVITE message.  This P-DCS-Billing-Info header MUST include the
   Billing-Correlation-ID generated by the terminating proxy, the FEID
   of the terminating proxy, and the RKS-Group-ID of the Record-
   Keeping-Server being used by the terminating proxy.  The terminating
   proxy MAY change the values of Acct-Charge-URI if it wishes to
   override the billing information that was present in the INVITE
   (e.g. for a toll-free call).  The decision to do this and the
   contents of the resulting P-DCS-Billing-Info header MUST be
   determined by service provider policy provisioned in the terminating
   proxy. If the terminating proxy performed a LNP query, it MUST
   include the Routing Number and Location Routing Number returned by
   the query.

   The terminating proxy MUST add P-DCS-Billing-Info headers to a 3xx-
   redirect response to an initial INVITE, giving the accounting
   information for the call forwarder, for the call segment from the
   destination to the forwarded-to destination.

   A proxy receiving a mid-call REFER request that includes a Refer-to
   header generates a private-URL and places it in the Refer-to header
   sent to the endpoint.  This private-URL MUST contain the P-DCS-
   Billing-Info value, which indicate the charging arrangement for the
   new call, and an expiration time very shortly in the future, to
   limit the ability of the endpoint to re-use this private-URL for
   multiple calls.

7.6.3 Procedures at Tandem Proxy

   If the tandem proxy performed a LNP query, it MUST insert the
   Routing Number and Location Routing Number returned by the query
   into the P-DCS-Billing-Info header in the first reliable 1xx/2xx/3xx
   (except 100) response.

8. P-DCS-LAES and P-DCS-REDIRECT

   NOTE:  According to RFC-2804[5], the IETF supports documentation of
   lawful intercept technology if it is necessary to develop it.  The
   following section provides such documentation.  The RFC-2119
   language, as stated above, describes the requirements of the
   specification only if implemented, and strictly within the
   applicability domain described above.  See RFC-2804 for description
   of issues regarding privacy, security, and complexity in relation to
   this technology.

   The P-DCS-LAES extension contains the information needed to support
   Lawfully Authorized Electronic Surveillance.  This header contains
   the address and port of an Electronic Surveillance Delivery Function
   for delivery of a duplicate stream of event messages related to this
   call.  The header may also contain an additional address and port
   for delivery of call content.  Security key information is included
   to enable pairs of Delivery Functions to securely exchange

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   surveillance information.  This header is only used between proxies
   and trusted User Agents.

   The P-DCS-Redirect extension contains call identifying information
   needed to support the requirements of Lawfully Authorized Electronic
   Surveillance of redirected calls.  This header is only used between
   proxies and trusted User Agents.

   Use of P-DCS-LAES and P-DCS-Redirect is controlled by a combination
   of legislation, regulation, and court orders, which MUST be
   followed.  In certain cases inclusion of these headers will be
   mandated, and therefore MUST be present in the requests and
   responses indicated.  In other cases inclusion of these headers will
   be forbidden, and therefore MUST NOT be present in the request and
   responses indicated.  In the sub-sections that follow, use of
   "SHOULD" is intended to capture these conflicting situations, e.g. a
   P-DCS-LAES header SHOULD be included in an initial INVITE means
   either that it MUST be included or that it MUST NOT be included,
   based on the applicable court orders.

8.1 Syntax

   The format of the P-DCS-LAES header is given by the following ABNF
   (some terms used in this ABNF are defined in [2] and [3]):

        P-DCS-LAES        = "P-DCS-LAES" HCOLON Laes-sig
                            *(SEMI Laes-param)
        Laes-sig          = hostport
        Laes-param        = Laes-content / Laes-key / generic-param
        Laes-content      = "content" EQUAL hostport
        Laes-key          = "key" EQUAL token

        P-DCS-Redirect    = "P-DCS-Redirect" HCOLON Called-ID
                            *(redir-params)
        Called-ID         = LDQUOT addr-spec RDQUOT
        redir-params      = redir-uri-param / redir-count-param /
                            generic-param
        redir-uri-param   = "redirector-uri" EQUAL Redirector
        Redirector        = LDQUOT addr-spec RDQUOT
        redir-count-param = "count" EQUAL Redir-count
        Redir-count       = 1*DIGIT

   This document adds the following entry to Table 2 of [2]:

         Header field         where proxy  ACK  BYE  CAN  INV  OPT  REG
         ------------         ----- -----  ---  ---  ---  ---  ---  ---
         P-DCS-LAES                  adr    -    -    -    o    -    -
         P-DCS-Redirect              adr    -    -    -    o    -    -


                                           SUB  NOT  REF  INF  UPD  PRA
                                           ---  ---  ---  ---  ---  ---
                                            -    -    -    -    -    -

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                                            -    -    -    -    -    -

   The values of Laes-sig and Laes-content are addresses of the
   Electronic Surveillance Delivery Function, and used as the
   destination address for call-identifying information and call-
   content, respectively.  Laes-key is a string generated by the proxy
   that is used by the Delivery Function to securely transfer
   information between them [8].

   The P-DCS-Redirect header contains redirection information. The
   redir-uri-param indicates the original destination requested by the
   user (e.g. dialed number), the Redirector indicates the new
   destination, and the Redir-count indicates the number of
   redirections that have occurred.

8.2 Procedures at an Untrusted User Agent Client (UAC)

   This header MUST NOT be sent to an untrusted UAC, and MUST NOT be
   sent by an untrusted UAC.

8.3 Procedures at a Trusted User Agent Client (UAC)

   The UAC checks for an outstanding lawfully authorized surveillance
   order for the originating subscriber, and, if present, includes this
   information in the Authorization for Quality of Service [7] or
   signals this information to the device performing the intercept
   (e.g. a Media Gateway).

   If the P-DCS-LAES header is present in the first reliable 1xx
   (except 100), 2xx or 3xx response (indicating surveillance is
   required on the terminating subscriber, but that the terminating
   equipment is unable to perform that function), the UAC MUST include
   this information in the Authorization for Quality of Service, or
   MUST signal this information to the device performing the intercept
   (e.g. a Media Gateway).

   If a 3xx-Redirect response is received to the initial INVITE
   request, and if a P-DCS-LAES header is present in the 3xx response,
   the UAC SHOULD include that header unchanged in the reissued INVITE.
   The UAC SHOULD also include a P-DCS-Redirect header containing the
   original dialed number, the new destination number, and the number
   of redirections that have occurred. Although it is technically
   possible for the originating equipment to perform this surveillance
   (or add to its existing surveillance of the call), the design of the
   surveillance system has the terminating equipment performing the
   surveillance for all the intermediate forwardings.

   A UAC that includes a Refer-to header in a REFER request, when the
   originating subscriber has an outstanding lawfully authorized
   surveillance order, SHOULD include a P-DCS-LAES header attached to
   the Refer-to. The P-DCS-LAES header SHOULD include the address and
   port of the local Electronic Surveillance Delivery Function for a
   copy of the call's event messages, SHOULD include the address and

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   port of the local Electronic Surveillance Delivery Function for the
   copy of call content if call content is to be intercepted, and
   SHOULD include a random string for use as a security key between the
   Delivery Functions.

   The trusted UAC MUST NOT send the P-DCS-LAES and P-DCS-Redirect
   headers to an untrusted entity.

8.4 Procedures at an Untrusted User Agent Server (UAS)

   This header MUST NOT be sent to an untrusted UAS, and MUST NOT be
   sent by an untrusted UAS.

8.5 Procedures at a Trusted User Agent Server (UAS)

   The UAS checks for an outstanding lawfully authorized surveillance
   order for the terminating subscriber, or presence of the P-DCS-LAES
   header in the INVITE request.  If either is present, the UAS
   includes this information in the authorization for Quality of
   Service[7].

   If the terminating equipment is unable to perform the required
   surveillance (e.g. if the destination is a voicemail server), the
   UAS SHOULD include a P-DCS-LAES header in the first reliable non-100
   response requesting the originating proxy to perform the
   surveillance.  The P-DCS-LAES header SHOULD include the address and
   port of the local Electronic Surveillance Delivery Function for a
   copy of the call's event messages, SHOULD include the address and
   port of the local Electronic Surveillance Delivery Function for the
   copy of call content if call content is to be intercepted, and
   SHOULD include a random string for use as a security key between the
   Delivery Functions.

   If the response to the initial INVITE request is a 3xx-Redirect
   response, and there is an outstanding lawfully authorized
   surveillance order for the terminating subscriber, the UAS SHOULD
   include a P-DCS-LAES header in the 3xx-Redirect response, with
   contents as described above.

   The trusted UAS MUST NOT send the P-DCS-LAES and P-DCS-Redirect
   headers to an untrusted entity.

8.6 Procedures at Proxy

   Two sets of proxy procedures are defined: (1) the procedures at an
   originating proxy, and (2) the procedures at a terminating proxy.
   The originating proxy is a proxy that received the INVITE request
   from a non-trusted endpoint.

   The terminating proxy is a proxy that sends the INVITE request to a
   non-trusted endpoint.



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   For purposes of mid-call changes, such as call transfers, the proxy
   that receives the request from a non-trusted endpoint is considered
   the initiating proxy; the proxy that sends the request to a non-
   trusted endpoint is considered the recipient proxy.  Procedures for
   the initiating proxy are included below with those for originating
   proxies, while procedures for the recipient proxy are included with
   those for terminating proxies.

   A proxy that both receives the INVITE request from an untrusted
   endpoint, and sends the INVITE request to a non-trusted endpoint,
   MUST NOT generate P-DCS-LAES nor P-DCS-Redirect headers.

   A proxy that is neither an originating proxy nor a terminating proxy
   SHOULD pass the P-DCS-Laes and P-DCS-Redirect headers in requests
   and responses.

8.6.1 Procedures at Originating Proxy

   The Originating Proxy MUST remove any P-DCS-LAES and P-DCS-Redirect
   headers in requests or responses to or from an untrusted proxy or
   untrusted UA.

   The originating proxy checks for an outstanding lawfully authorized
   surveillance order for the originating subscriber, and, if present,
   includes this information in the Authorization for Quality of
   Service[7] or signals this information to the device performing the
   intercept (e.g. a Media Gateway).

   If the P-DCS-LAES header is present in the first reliable 1xx
   (except 100), 2xx or 3xx response (indicating surveillance is
   required on the terminating subscriber, but that the terminating
   equipment is unable to perform that function), the originating proxy
   MUST include this information in the Authorization for Quality of
   Service, or MUST signal this information to the device performing
   the intercept (e.g. a Media Gateway).

   If the Request-URI in an initial INVITE request contains a private-
   URL, the originating proxy MUST decrypt the userinfo information to
   find the real destination for the call, and other special processing
   information. If electronic surveillance information is contained in
   the decrypted userinfo, the originating proxy SHOULD generate a P-
   DCS-LAES header with the surveillance information.

   If a 3xx-Redirect response is received to the initial INVITE request
   prior to a 18x, and if a P-DCS-LAES header is present in the 3xx
   response, the originating proxy SHOULD include that header unchanged
   in the reissued INVITE.  The originating proxy SHOULD also include a
   P-DCS-Redirect header containing the original dialed number, the new
   destination number, and the number of redirections that have
   occurred.

   If a 3xx-Redirect response is received to the initial INVITE request
   after a 18x, the originating proxy generates a private-URL and

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   places it in the Contact header of a 3xx-Redirect response sent to
   the originating endpoint.  If a P-DCS-LAES header is present in the
   3xx response, this private-URL MUST contain (1) the electronic
   surveillance information from the 3xx-Redirect response, (2) the
   original destination number, (3) the identity of the redirecting
   party, and (4) the number of redirections of this call.

   An originating proxy that processes a REFER request [4] from an
   untrusted UA, when the originating subscriber has an outstanding
   lawfully authorized surveillance order, becomes a B2BUA for that
   request.  It SHOULD reissue the request with a P-DCS-LAES header
   added to the Refer-to's URL. The P-DCS-LAES header SHOULD include
   (1) the address and port of the local Electronic Surveillance
   Delivery Function for a copy of the call's event messages, (2) the
   address and port of the local Electronic Surveillance Delivery
   Function for the copy of call content if call content is to be
   intercepted, and (3) a random string for use as a security key
   between the Delivery Functions.

   An initiating proxy that sends a mid-call REFER request including a
   Refer-to header, when the initiating subscriber has an outstanding
   lawfully authorized surveillance order, SHOULD include a P-DCS-LAES
   header in the Refer-to's URL.

   The originating proxy MUST NOT send the P-DCS-LAES and P-DCS-
   Redirect headers to an untrusted entity.

8.6.2 Procedures at Terminating Proxy

   The Terminating Proxy MUST remove any P-DCS-LAES and P-DCS-Redirect
   headers in requests or responses to or from an untrusted proxy or
   UA.

   The terminating proxy checks for an outstanding lawfully authorized
   surveillance order for the terminating subscriber.  If present, the
   terminating proxy includes this information in the authorization for
   Quality of Service[7].

   The terminating proxy MUST NOT send the P-DCS-LAES and P-DCS-
   Redirect headers to an untrusted entity, either as headers in the
   request or response, or as headers attached to URIs in the request
   or response.

   If the terminating equipment is unable to perform the required
   surveillance (e.g. if the destination is a voicemail server), the
   terminating proxy SHOULD include a P-DCS-LAES header in the first
   reliable 1xx/2xx/3xx (except 100) response requesting the
   originating proxy to perform the surveillance.  The P-DCS-LAES
   header SHOULD include the address and port of the local Electronic
   Surveillance Delivery Function for a copy of the call's event
   messages, SHOULD include the address and port of the local
   Electronic Surveillance Delivery Function for the copy of call
   content if call content is to be intercepted, and SHOULD include a

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   random string for use as a security key between the Delivery
   Functions.

   If the response to the initial INVITE request is a 3xx-Redirect
   response, and there is an outstanding lawfully authorized
   surveillance order for the terminating subscriber, the terminating
   proxy SHOULD include a P-DCS-LAES header in the 3xx-Redirect
   response, with contents as described above.

   A proxy receiving a mid-call REFER request [4] that includes a
   Refer-to header with a P-DCS-LAES header attached becomes a B2BUA
   for this request.  It MUST generate a private-URL and place it in
   the Refer-to header sent to the endpoint.  This private-URL MUST
   contain the P-DCS-LAES information from the attached header.

9. Security Considerations

   QoS gate coordination, billing information, and electronic
   surveillance information are all considered to be sensitive
   information that MUST be protected from eavesdropping and
   furthermore require integrity checking.  It is therefore necessary
   that the trusted UAs and proxies take precautions to protect this
   information from eavesdropping and tampering.  Use of IPSec or TLS
   between Proxies is REQUIRED.  Also REQUIRED is mutual authentication
   (1) between Proxies and (2) between trusted UAs and Proxies, both of
   which MAY be implemented with administratively pre-shared keys, or
   through consultation with another trusted third party.  If IPSec is
   to be used, the specification of the security policies and
   procedures of the administrative domain where these headers are
   applicable (and all connections between administrative domains in
   the federation) MUST define an interoperable set of options.

10. IANA Considerations

   This document defines a number of SIP extension headers, which
   should be included in the registry of SIP headers defined in [2].
   Registration information for new headers is as follows:

   Header Field Name:   P-DCS-Trace-Party-ID
        RFC Number:     XXXX [number of this document]
        Compact Form:   none

   Header Field Name:   P-DCS-OSPS
        RFC Number:     XXXX [number of this document]
        Compact Form:   none

   Header Field Name:   P-DCS-Billing-Info
        RFC Number:     XXXX [number of this document]
        Compact Form:   none

   Header Field Name:   P-DCS-LAES
        RFC Number:     XXXX [number of this document]
        Compact Form:   none

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   Header Field Name:   P-DCS-Redirect
        RFC Number:     XXXX [number of this document]
        Compact Form:   none


11. Notice Regarding Intellectual Property Rights

   The IETF has been notified of intellectual property rights claimed
   in regard to some or all of the specification contained in this
   document.  For more information consult the online list of claimed
   rights.

12. Normative References

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

   2. Rosenberg, J, et al, "The Session Initiation Protocol", RFC 3261,
      June 2002.

   3. Crocker, D., and Overell P., "Augmented BNF for Syntax
      Specifications: ABNF", RFC 2234, November 1997.

   4. Sparks, R., "The SIP REFER Method", RFC pending.

   5. IAB and IESG, "IETF Policy on Wiretapping", RFC 2804, May 2000.


13. Informative References

   6. DCS Group, "Architectural Considerations for Providing Carrier
      Class Telephony Services Utilizing SIP-based Distributed Call
      Control Mechanisms", draft-dcsgroup-sipping-arch-01.txt, January
      2003.

   7. PacketCable Dynamic Quality of Service Specification, pkt-sp-
      dqos-i05-021127.  November, 2002.

   8. PacketCable Security Specification, pkt-sp-sec-i07-021127.
      November, 2002.

   9. PacketCable Event Message Specification, pkt-sp-em-i05-021127.
      November, 2002.

   10. Jennings, C., Peterson, J., and Watson, M., Private Extensions
      to the Session Initiation Protocol (SIP) for Asserted Identity
      within Trusted Networks, RFC3325, November 2002.

14. Acknowledgements

   The Distributed Call Signaling work in the PacketCable project is
   the work of a large number of people, representing many different

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   companies.  The authors would like to recognize and thank the
   following for their assistance: John Wheeler, Motorola; David
   Boardman, Daniel Paul, Arris Interactive; Bill Blum, Jon Fellows,
   Jay Strater, Jeff Ollis, Clive Holborow, Motorola; Doug Newlin,
   Guido Schuster, Ikhlaq Sidhu, 3Com; Jiri Matousek, Bay Networks;
   Farzi Khazai, Nortel; John Chapman, Bill Guckel, Michael Ramalho,
   Cisco; Chuck Kalmanek, Doug Nortz, John Lawser, James Cheng, Tung-
   Hai Hsiao, Partho Mishra, AT&T; Telcordia Technologies; and Lucent
   Cable Communications.

   Previous versions further acknowledged, as co-authors, several
   people for providing the text of this document.  They are: Bill
   Marshall (wtm@research.att.com) and K. K. Ramakrishnan
   (kkrama@research.att.com), AT&T; Ed Miller
   (edward.miller@terayon.com), Terayon; Glenn Russell
   (G.Russell@Cablelabs.com), CableLabs; Burcak Beser
   (burcak@juniper.net) Juniper Networks, Mike Mannette
   (Michael_Mannette@3com.com) and Kurt Steinbrenner
   (Kurt_Steinbrenner@3com.com), 3Com; Dave Oran (oran@cisco.com) and
   Flemming Andreasen (fandreas@cisco.com), Cisco Systems; John Pickens
   (jpickens@com21.com), Com21; Poornima Lalwaney
   (poornima.lalwaney@nokia.com), Nokia; Jon Fellows
   (jfellows@coppermountain.com), Copper Mountain Networks; Doc Evans
   (n7dr@arrisi.com) Arris, and Keith Kelly (keith@netspeak.com),
   NetSpeak.


15. Editor's Addresses

   Bill Marshall
   AT&T
   Florham Park, NJ  07932
   Email: wtm@research.att.com

   Flemming Andreasen
   Cisco
   Edison, NJ
   Email: fandreas@cisco.com
















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Full Copyright Statement

   "Copyright (C) The Internet Society (2003). All Rights Reserved.
   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph
   are included on all such copies and derivative works. However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.  The limited permissions granted above are perpetual and
   will not be revoked by the Internet Society or its successors or
   assigns.  This document and the information contained herein is
   provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE
   INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR
   IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."

   This memo is filed as <draft-dcsgroup-sipping-proxy-proxy-03.txt>,
   and expires September 1, 2003.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.






















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