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Versions: 00 01 draft-ietf-cuss-sip-uui-isdn

Network Working Group                                      K. Drage, Ed.
Internet-Draft                                            Alcatel-Lucent
Intended status: Standards Track                             A. Johnston
Expires: March 23, 2012                                            Avaya
                                                      September 20, 2011


        Interworking ISDN Call Control User Information with SIP
                    draft-drage-cuss-sip-uui-isdn-01

Abstract

   The motivation and use cases for interworking and transporting ITU-T
   DSS1 User-user information element data in SIP are described in the
   "Problem Statement and Requirements for Transporting User to User
   Call Control Information in SIP" document.  As networks move to SIP
   it is important that applications requiring this data can continue to
   function in SIP networks as well as the ability to interwork with
   this ISDN service for end-to- end transparency.  This document
   defines a usage of the User-to-User header field to enable
   interworking with this ISDN service.

   This document is covers the interworking with both public ISDN and
   private ISDN capabilities, so the interworking with QSIG will also be
   addressed.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on March 23, 2012.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Summary of the ISDN User-to-User Service . . . . . . . . . . .  3
     3.1.  The service  . . . . . . . . . . . . . . . . . . . . . . .  3
     3.2.  Impacts of the ISDN service on SIP operation . . . . . . .  5
   4.  Relation to SIP-T  . . . . . . . . . . . . . . . . . . . . . .  6
   5.  Transition away from ISDN  . . . . . . . . . . . . . . . . . .  6
   6.  ISDN Usage of the User-to-User Header Field  . . . . . . . . .  7
   7.  UAC requirements . . . . . . . . . . . . . . . . . . . . . . .  7
   8.  UAS requirements . . . . . . . . . . . . . . . . . . . . . . .  9
   9.  UUI contents . . . . . . . . . . . . . . . . . . . . . . . . . 10
   10. Considerations for ISDN interworking gateways  . . . . . . . . 10
   11. Coding requirements  . . . . . . . . . . . . . . . . . . . . . 11
   12. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   13. Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   15. Changes since previous versions  . . . . . . . . . . . . . . . 12
   16. Normative References . . . . . . . . . . . . . . . . . . . . . 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14



















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1.  Terminology

   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].


2.  Overview

   This document describes a usage of the User-to-User header field
   defined in [johnston-cuss-sip-uui] to enable the transport of User to
   User Information (UUI) in ISDN interworking scenarios using SIP
   [RFC3261].  Specifically, this document discuss the interworking of
   call control related ITU-T DSS1 User-user information element [Q931],
   [Q957.1] and ITU-T Q.763 User-to-user information parameter [Q763]
   data in SIP.  UUI is widely used in the PSTN today in contact centers
   and call centers which are transitioning away from ISDN to SIP.

   This usage is not limited to scenarios where interworking will occur.
   Rather it describes a usage where interworking is possible if
   interworking is met.  That does not preclude its usage directly
   between two SIP terminals.


3.  Summary of the ISDN User-to-User Service

3.1.  The service

   ISDN defines a number of related services.  Firstly there is a user
   signalling bearer service, which uses the information elements /
   parameters in the signalling channel to carry the data, and does not
   establish a related circuit-switched connection.  For DSS1, this is
   specified in ITU-T Recommendation Q.931 section 3.3 and section 7
   [Q931].  It also defines a user-to-user signalling supplementary
   service, which uses the information elements / parameters in the
   signalling channel to carry additional data, but which is used in
   conjunction with the establishment of a related circuit-switched
   connection.  This reuses the same information elements / parameters
   as the user signalling bearer service, with the addition of other
   signalling information, and for DSS1 this is specified in ITU-T
   Recommendation Q.957.1 [Q957.1].

   ISDN defines three variants of the user-to-user signalling
   supplementary service as follows:






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   UUS1:  User-to-user information exchanged during the setup and
      clearing phases of a call, by transporting User-to-user
      information element within call control messages.  This in itself
      has two subvariants, UUS1 implicit and UUS1 explicit.  UUS1
      explicit uses additional supplementary service control information
      to control the request and granting of the service, as in USS2 and
      UUS3.  In UUS1 implicit, it is the presence of the user signalling
      data itself that constitutes the request for the service.  UUS1
      explicit as a result also allows the requester to additionally
      specify whether the parallel circuit-switched connection should
      proceed if the UUS1 service cannot be provided (preferred or
      required).

   UUS2:  User-to-user information exchanged from the sender's point of
      view during call establishment, between the DSS1 ALERTING and DSS1
      CONNECT messages, within DSS1 USER INFORMATION messages; and

   UUS3:  User-to-user information exchanged while a call is in the
      Active state, within DSS1 USER INFORMATION messages.

   The service is always requested by the calling user.

   This document defines only the application of the ISDN UUS1 implicit
   supplementary service to interworking scenarios, this being the most
   widely deployed and used of the various ISDN user-to-user services,
   and indeed the one that matches the requirements specified in
   draft-johnston-cuss-sip-uui-reqs.

   The ISDN UUS1 service has the following additional characteristics as
   to the data that can be transported:

      The maximum number of octets of user information that can be
      transported in 128 octets.  It is noted that some early ISDN
      implementations had a limitation of 32 octets, but it is
      understood that these are not currently deployed.  While this
      application does not prohibit longer data fields, the mechanism at
      any interworking point is to discard data elements that are too
      long to handle.  The handled length can normally be assumed to be
      128 octets.

      The content of the user information octets is described by a
      single octet protocol discriminator (see table 4-26 of ITU-T
      Recommendation Q.931) [Q931].  That protocol descriminator may
      describe the protocol used within the user data, the structure of
      the user data, or leave it entirely open.  Note that not all
      values within the protocol discriminator necessarily make sense
      for use in the user to user service, as the content is aligned
      with the protocol discriminator that appears at the start of all



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      DSS1 messages (see table 4-1 of ITU-T Recommendation Q.931)
      [Q931].  The protocol discriminator value has no impact on the
      interworking capability.

      Only a single user information package can be transported in each
      message.

      The ISDN service works without encryption or integrity protection.
      The user trusts the intermediate network elements, and therefore
      the operator of those elements, not to modify the data, and to
      deliver all the data to the remote user.  On a link by link basis,
      message contents are protected at layer 2 by standard CRC
      mechanisms - this allows loss on a link level basis to be
      detected, but does not guard against fraudulent attacks on the
      link itself.  This does not prevent the use of additional
      encryption or integrity protection within the payload itself,
      although the limit on the size of the payload (128 octets) will
      restrict this.

3.2.  Impacts of the ISDN service on SIP operation

   The ISDN service has the following impacts that need to be understood
   within the SIP environment.

   Call transfer  ISDN call transfer cancels all user-to-user
      supplementary services.  In the ISDN, if user-to-user data is
      required after call transfer, then UUS3 has to be renegotiated,
      which is not provided by this SIP extension.  The impact of this
      restriction on the SIP environment is that UUI header fields
      cannot be exchanged in transactions clearing down the SIP dialog
      after call transfer has occurred.

   Conference  ISDN conferencing allows the user to still exchange user-
      to-user data after the conference is created.  As far as UUS1 is
      concerned, this means that when an individual party clears, those
      clearing messages can still contain user-to-user data.  As a
      conferee this is sent to the conference controller.  As the
      conference controller, as this effectively clears the conference,
      it can be broadcast to all conferees, or sent to individual
      conferees [OPEN ISSUE - CHECK THIS IN THE PROTOCOL - DOES IT
      REQUIRE EXPLICIT].

      The ISDN three-party supplementary service is similar in many ways
      to conferencing, but is signalled using a different mechanism.
      This means that on clearing, the controller using UUS1 implicit
      does have the choice of sending data to either or both remote
      users.




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   Diversion  When ISDN diversion occurs, any UUS1 user-to-user data is
      sent to the forwarded-to-user (assuming that the call meets
      requirements for providing the service - this is impacted by the
      explicit service only).  If the type of diversion is such that the
      call is also delivered to the forwarding user, they will also
      receive any UUS1 user-to-user data.

   Contributors note: The above list needs to be studied further in
   regard to private ISDN service definitions, e.g. for the interworking
   of SIP and QSIG.


4.  Relation to SIP-T

   A method of transport of ISDN UUI is to use SIP-T [RFC3372] and
   transport the UUI information end-to-end, as part of an ISUP message
   or QSIG message) as a MIME body.  If the SIP-T method of
   encapsulation of ISDN instead of interworking is used, this is a
   reasonable mechanism and does not require any extensions to existing
   SIP-T.  However, if true ISDN interworking is being done, this
   approach is not reasonable.  Instead, the better approach is to
   interwork the ISDN UUI using the native SIP UUI transport mechanism,
   the User-to-User header field.  The rest of this document describes
   this approach.


5.  Transition away from ISDN

   This interworking usage of the SIP UUI mechanism will likely begin
   with one User Agent being an ISDN gateway while the other User Agent
   is a native SIP endpoint.  As networks transition away from ISDN, it
   is possible that both User Agents could become native SIP endpoints.
   In this case, there is an opportunity to transition away from this
   ISDN usage to a more general usage of [johnston-cuss-sip-uui].  This
   will be possible when both endpoints are aware of the actual
   application using the UUI.

   The SIP UUI mechanism provides a way to achieve this transition.  As
   an endpoint moves from being an ISDN gateway to a native SIP
   endpoint, and a usage application for the UUI has been standardized,
   the endpoint can carry the UUI both as ISDN and application encoding.
   This will permit the other endpoint to utlize the UUI if it is an
   ISDN gateway or a native SIP endpoint.  When all the endpoints have
   moved away from ISDN, the ISDN encoding usage can be discontinued.







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6.  ISDN Usage of the User-to-User Header Field

   This document defines the purpose usage of the ISDN interworking
   application of UUI which is to interoperate with ISDN User to User
   Signaling (UUS), a supplementary service in which the user is able to
   send/receive a limited amount of information to/from another ISDN
   user over the signalling channel in association with a call to the
   other ISDN user..

   Two examples of ISDN UUI with redirection (transfer and diversion)
   are defined in [ANSII] and [ETSI].

   The general principals of this application of the UUI mechanism are
   as follows:

      That the sending application is expected limit their sending
      requirements to the subset provided by the ISDN UUI service.

      That the SIP UA will not allow the reception of more that one
      User-to-User header field of the "isdn-uui" application in the
      same SIP request or response, and will only allow it in a request
      or response of the appropriate method (INVITE or BYE).  What
      happens to User-to-User header fields relating to different
      application is outside the scope of this document.

      That an interworking point trying to interwork application data
      that is too long will discard the application data, but proceed
      with the interworking.  There is no notification of such discard
      back to the sending user.  If the SIP user knows that it is
      interworking with the ISDN, then the UUI application at the SIP
      endpoint should limit its communication to 128 octet packets, in
      the knowledge that discard will occur if it does not.  The UUI
      application at the SIP endpoint has complete control over what
      occurs.  It should be noted that this was exactly the envisaged
      operation when early ISDN implementations that only supported 32
      octets interworked with those supporting 128 octets.  It also
      corresponds to the interworking with ISDNs that do not support the
      supplementary service at all, as discard will occur in these
      circumstances as well.  Note that failure to include the user-user
      data into the ISDN SETUP message (when discard occurs) will result
      in the service being unavailable for the remainder of the call
      when UUS1 implicit operation is used.


7.  UAC requirements

   The UAC MUST meet the requirements of [johnston-cuss-sip-uui] in
   addition to the requirements defined in this document.



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   The UAC MUST only use this application of the UUI mechanism extension
   in association with the initial INVITE method and BYE method relating
   to an INVITE dialog.  Usage on transactions associated with any other
   type of dialog, or on methods not associated with a dialog is
   precluded.

   If the UAC wishes to user or permit the sending of UUI data at any
   point in the dialog, the UAC MUST include in the INVITE request for
   that dialog a User-to-User header field with an "app" header field
   parameter set to "isdn-uui".  This initial header field constitutes
   the implicit request to use the UUI service, and is therefore
   included even when there is no data to send at that point in time.

   The UAC MUST NOT include the User-to-User header field with an "app"
   header field parameter set to "isdn-uui" in any message of an INVITE
   dialog if the original INVITE request did not include the User-to-
   User header field with an "app" header field parameter set to "isdn-
   uui"

   When sending UUI for the ISDN application, the UAC MUST set the User-
   to-User "app" header field parameter to "isdn-uui".  The UAC MUST NOT
   include more than one User-to-User header field for this application
   in any SIP request or response.

   When sending UUI, the sending application MUST include a protocol
   discriminator octet, conforming to table 4-26 of ITU-T Recommendation
   Q.931 [Q931] as the first octet of the payload information.

   When receiving UUI, when multiple User-to-User header fields are
   received in the same response with the "app" header field parameter
   to "isdn-uui", the UAS MUST discard all these header fields.  There
   are no mechanisms for determining which was the intended data packet
   so all are discarded.

   The application designer will need to take into account the ISDN
   service restrictions; failure to do so can result in information
   being discarded at any interworking point with the ISDN.  This
   document makes no further normative requirements based on those
   constraints, because those constraints may vary from one ISDN to
   another.  It is reasonable to expect that a limitation of 128 octets
   can be imposed by the ISDN, and therefore payloads longer than this
   will never reach the destination if such interworking occurs.

   [johnston-cuss-sip-uui] defines a "uui" option tag for use with the
   UUI mechanism extension.  Because for the ISDN UUI service, the
   service is service 1 implicit, the inclusion of the "uui" option tag
   in a Supported header field conveys no additional information over
   and above the presence of the User-to-User header field with the



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   "app" header field parameter to "isdn-uui" in the INVITE request.
   While there is no harm in including the "uui" option tag, and
   strictly it should be included if the extension is supported, it
   performs no function.  The presence of the "uui" option tag in the
   Require header field of an INVITE request will cause the request to
   fail if it reaches a UAS or ISDN interworking gateway that does not
   support this extension; such a usage is not precluded although it
   does not form part of the application.


8.  UAS requirements

   The UAS MUST meet the requirements of [johnston-cuss-sip-uui] in
   addition to the requirements defined in this document.

   The UAS MUST only use this application of the UUI mechanism extension
   in association with the initial INVITE method and BYE method relating
   to an INVITE dialog.  Usage on transactions associated with any other
   type of dialog, or on methods not associated with a dialog is
   precluded.

   The UAS MUST NOT include the User-to-User header field with an "app"
   header field parameter set to "isdn-uui" in any message of an INVITE
   dialog if the original INVITE request did not include the User-to-
   User header field with an "app" header field parameter set to "isdn-
   uui"

   The UAS MAY include the User-to-User header field in responses to the
   INVITE request, or subsequent BYE requests or responses within the
   dialog, only where the original INVITE request included a User-to-
   User header field with the "app" header field parameter to "isdn-
   uui".  When sending UUI for the ISDN application, the UAS MUST set
   the User-to-User "app" header field parameter to "isdn-uui".  The UAS
   MUST NOT include more than one User-to-User header field for this
   application in any SIP request or response.

   Where the UAS is acting as a redirect server, the UAS MUST NOT
   include the User-to-User header field in the header URI parameter in
   a 3xx response to an incoming request.

   When receiving UUI, when a User-to-User header field is received in a
   request that is not from the originating user with the "content"
   header field parameter to "isdn-uui", the UAC MUST discard this
   header fields.

   When receiving UUI, when multiple User-to-User header fields are
   received from the originating user in the same request with the
   "content" header field parameter to "isdn-uui", the UAC MUST discard



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   all these header fields.  There are no mechanisms for determining
   which was the intended data packet so all are discarded.


9.  UUI contents

   These requirements apply when the "app" header field parameter is set
   to "isdn-uui".  Processing for User-to-User header fields sent or
   received with values other than this value are outside the scope of
   this document, and the appropriate application document for that
   value applies.

   When sending UUI, the sending application MAY, but need not, include
   a "content" header field with a value set to "isdn-uui".  A receiving
   application MUST ignore a received User-to-User header field if the
   "content" header field parameter is present and the value is some
   other value that "isdn-uui".

   When sending UUI, the sending application MAY, but need not, include
   an "encoding" header field with a value set to "hex".  A receiving
   application MUST ignore a received User-to-User header field if the
   "encoding" header field parameter is present and the value is some
   other value that "hex".

   When sending UUI, the sending application MUST include a protocol
   discriminator octet, conforming to table 4-26 of ITU-T Recommendation
   Q.931 [Q931] as the first octet of the payload information.  It is up
   to the receiving application what it does with this value.


10.  Considerations for ISDN interworking gateways

   ISDN interworking gateways MUST support the requirements defined for
   UAS and UAC operation.

   ISDN interworking gateways MUST support only the "isdn-uui"
   application on dialogs that are interworked.

   When mapping data content from the ISDN to the SIP signalling, or
   from SIP signalling to the ISDN, the gateway needs to assume that all
   content is octet structured binary, irrespective of the value of the
   received protocol discriminator.  There are no requirements in the
   ISDN to ensure that the content matches the value of the protocol
   discriminator, and it is for the application usage to sort out any
   discrepancy.  The same applies to the ISDN protocol discrimination
   defined table 4-26 of ITU-T Recommendation Q.931 [Q931] as the first
   octet of the payload information; the interworking gateway will not
   perform any additional checking of this value.



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   [johnston-cuss-sip-uui] defines a "uui" option tag for use with the
   UUI mechanism extension.  The option tag is not interworked at an
   ISDN interworking gateway.  The ISDN interworking gateways MUST NOT
   take the omission of the "uui" option tag in a received INVITE
   request to indicate that interworking of a received header field is
   not to be performed.


11.  Coding requirements

   This document defines "isdn-uui" as a new value of the User-to-User
   "app" header field parameter.

   This document defines "isdn-uui" as a new value of the User-to-User
   "content" header field parameter.


12.  IANA Considerations

   This document adds the following row to the "UUI application values"
   section of the SIP parameter registry:

      Value: isdn-uui

      Meaning: The associated application is being used with constraints
      suitable for interworking with the ISDN user-to-user service, and
      therefore can be interworked at ISDN gateways.

      Reference: RFCXXXX

      Contact:

   This document adds the following row to the "UUI content values"
   section of the SIP parameter registry:

      Value: isdn-uui

      Meaning: The associated contents conforms to the content
      associated with the ISDN user-to-user service.  In the presence of
      the "app" header field parameter set to "isdn-uui" this is the
      default meaning and therefore need not be included in this case.

      Reference: RFCXXXX

      Contact:

   Editor's Note: [RFCXXXX] should be replaced with the designation of
   this document.



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13.  Security Considerations

   This document contains no specific requirements in regard to
   security.  The overlying use case will define the security measures
   required.  The underlying user-to-user extension provides a number of
   tools that can meet certain security requirements.  As a level of
   guidance, data that is used to assist in selecting which SIP UA
   should respond to the call would not be expected to carry any higher
   level of security than a media feature tag.  Information that might
   otherwise reveal private information about an individual, or where a
   level of authenticity needs to be guaranteed, may need a higher level
   of protection, and may indeed not be suitable for this application,
   particularly taking into account the statement in the following
   paragraph.

   As this capability to is defined to interwork with the ISDN, if the
   ISDN forms part of the route, any usage needs to assume that the
   security level of the ISDN is the highest level of security
   available.  As the ISDN security is itself not definable on an end-
   to-end basis, this can be an unknown quantity.  This is because ISDN
   security exists on a hop-by-hop basis, and is only as secure as the
   least secure component.  This can be high in some places (e.g. it can
   require physical access to a secure building) and in other places it
   can be low (e.g. the point where an ISDN access enters a building).
   If this level of security is not sufficient, then either a different
   user-to-user application, or indeed, a different method of data
   transfer, needs to be selected by the application user.


14.  Acknowledgements

   Joanne McMillen was a major contributor and co-author of earlier
   versions of this document.

   Thanks to Spencer Dawkins, Vijay Gurbani, and Laura Liess for their
   review of earlier versions of this document.  The authors wish to
   thank Francois Audet, Denis Alexeitsev, Paul Kyzivat, Cullen
   Jennings, and Mahalingam Mani for their comments.


15.  Changes since previous versions

   Note to RFC editor: This section is to be deleted before final
   publication.

   Changes since made in the creation of the -01 version from the -00
   version.




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      Closure of a number of open issues identified in the -00 version
      and the creation of appropriate procedures for the UAC, the UAS,
      and the ISDN interworking gateway.


16.  Normative References

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [Q931]     "ITU-T Recommendation Q.931: Digital subscriber Signalling
              System No. 1 - Network layer; ISDN user-network interface
              layer 3 specification for basic call control",
              http://www.itu.int/rec/T-REC-Q.931-199805-I/en .

   [Q957.1]   "ITU-T Recommendation Q.957.1: Digital subscriber
              Signalling System No. 1 - Stage 3 description for
              supplementary services using DSS 1; Stage 3 description
              for additional information transfer supplementary services
              using DSS 1: User-to-User Signalling (UUS)",
              http://www.itu.int/rec/T-REC-Q.957.1-199607-I .

   [Q763]     "ITU-T Q.763 Signaling System No. 7 - ISDN user part
              formats and  codes",
              http://www.itu.int/rec/T-REC-Q.931-199805-I/en .

   [ANSII]    "ANSI T1.643-1995, Telecommunications-Integrated Services
              Digital Network  (ISDN)-Explicit Call Transfer
              Supplementary Service".

   [ETSI]     "ETSI ETS 300 207-1 Ed.1 (1994), Integrated Services
              Digital Network  (ISDN); Diversion supplementary
              services".

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

   [RFC3372]  Vemuri, A. and J. Peterson, "Session Initiation Protocol
              for Telephones (SIP-T): Context and Architectures",
              BCP 63, RFC 3372, September 2002.

   [johnston-cuss-sip-uui-reqs]
              Johnston, A., McMillen, J., and L. Liess, "Problem
              Statement and Requirements for Transporting User to User
              Call Control Information in  SIP",
              draft-johnston-cuss-sip-uui-reqs-00 .



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Internet-Draft               SIP UUI for CC               September 2011


   [johnston-cuss-sip-uui]
              Johnston, A. and J. Rafferty, "A Mechanism for
              Transporting User to User Call Control Information in
              SIP", draft-johnston-cuss-sip-uui-00 .


Authors' Addresses

   Keith Drage (editor)
   Alcatel-Lucent
   Quadrant, Stonehill Green, Westlea
   Swindon
   UK

   Email: keith.drage@alcatel-lucent.com


   Alan Johnston
   Avaya
   St. Louis, MO  63124
   United States

   Email: alan.b.johnston@gmail.com




























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