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

Network Working Group                                        A. Johnston
Internet-Draft                                                     Avaya
Intended status: Standards Track                             J. McMillen
Expires: June 17, 2011                                      Unaffiliated
                                                             J. Rafferty
                                                                Dialogic
                                                       December 14, 2010


 A Mechanism for Transporting User to User Call Control  Information in
                                  SIP
                     draft-johnston-cuss-sip-uui-01

Abstract

   There is a need for applications using SIP to exchange User to User
   Information (UUI) data during session establishment.  This
   information, known as call control UUI, is a small piece of data
   inserted by an application initiating the session, and utilized by an
   application accepting the session.  This data is opaque to SIP and
   its function is unrelated to any basic SIP function.  Several
   approaches to transporting call control UUI in SIP have been
   proposed.  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 discusses three mechanisms to meet the
   requirements defined in the Requirements for SIP Call Control UUI
   document.  A new SIP header field which bests meets these
   requirements is proposed.

Status of this Memo

   This Internet-Draft is submitted to IETF 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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on June 17, 2011.

Copyright Notice



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   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   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.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Possible Mechanisms  . . . . . . . . . . . . . . . . . . . . .  3
     3.1.  Why INFO is Not Used . . . . . . . . . . . . . . . . . . .  3
     3.2.  Why Other Protocol Encapsulation UUI Mechanisms are
           Not Used . . . . . . . . . . . . . . . . . . . . . . . . .  3
     3.3.  Discovery Mechanism  . . . . . . . . . . . . . . . . . . .  4
     3.4.  MIME body Approach . . . . . . . . . . . . . . . . . . . .  4
     3.5.  URI Parameter  . . . . . . . . . . . . . . . . . . . . . .  5
     3.6.  Header Field Approach  . . . . . . . . . . . . . . . . . .  6
   4.  Recommendation . . . . . . . . . . . . . . . . . . . . . . . .  7
   5.  Syntax for UUI Header Field  . . . . . . . . . . . . . . . . .  8
     5.1.  Definition of New Parameter Values . . . . . . . . . . . .  8
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
     6.1.  Registration of Header Field . . . . . . . . . . . . . . .  9
     6.2.  Registration of Header Field Parameters  . . . . . . . . .  9
     6.3.  Registration of SIP Option Tag . . . . . . . . . . . . . .  9
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     9.1.  Informative References . . . . . . . . . . . . . . . . . . 10
     9.2.  Normative References . . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12












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1.  Overview

   This document describes the transport of User to User Information
   (UUI) using SIP [RFC3261].  Specifically, we discuss a mechanism for
   the transport of general application UUI and also for the transport
   of call control related ITU-T Q.931 User to User Information Element
   (UU IE) [Q931] 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 extension will also be used for native SIP endpoints
   implementing similar services and interworking with ISDN services.

   This mechanism was designed to meet the use cases, requirements, and
   call flows for SIP call control UUI detailed in
   [I-D.ietf-cuss-sip-uui-reqs].  All references to requirement numbers
   (REQ-N) and figure numbers refer to this document.


2.  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].


3.  Possible Mechanisms

   Three possible mechanisms for transporting UUI will be described:
   MIME body, URI parameter, and header field transport.

3.1.  Why INFO is Not Used

   Since the INFO method [RFC2976], was developed for ISUP interworking
   of user-to-user information, it might seem to be the logical choice
   here.  For non-call control user-to-user information, INFO can be
   utilized for end to end transport.  However, for transport of call
   control user-to-user information, INFO can not be used.  As the call
   flows in [I-D.ietf-cuss-sip-uui-reqs] show, the information is
   related to an attempt to establish a session and must be passed with
   the session setup request (INVITE), responses to that INVITE, or
   session termination requests.  As a result, it is not possible to use
   INFO in these cases.

3.2.  Why Other Protocol Encapsulation UUI Mechanisms are Not Used

   Other protocols have the ability to transport UUI information.  For
   example, consider the ITU-T Q.931 User to User Information Element



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   (UU IE) [Q931] and the ITU-T Q.763 User to User Information Parameter
   [Q763].  In addition, NSS (Narrowband Signaling System) [Q1980] is
   also able to transport UUI information.  Should one of these
   protocols be in use, and present in both User Agents, then utilizing
   these other protocols to transport UUI might be a logical solution.
   Essentially, this is just adding an additional layer in the protocol
   stack.  In these cases, SIP is not transporting the UUI; it is
   encapsulating another protocol, and that protocol is transporting the
   UUI.  Once a mechanism to transport that other protocol using SIP
   exists, the UUI transport function is essentially obtained without
   any additional effort or work.

   However, the authors believe that SIP needs to have its own native
   UUI transport mechanism.  It is not reasonable for a SIP UA to have
   to implement another entire protocol (either ISDN or NSS, for
   example) just to get the very simple UUI transport service.  Of
   course, this work does not preclude anyone from using other protocols
   with SIP to transport UUI information.

3.3.  Discovery Mechanism

   Two requirements, REQ-8 and REQ-10 relate to discovery of the
   mechanism and supported applications.  As such, these requirements
   are independent of the actual transport mechanism.  Mechanisms to
   support these requirements are now discussed.

   REQ-8 could be met by defining a new SIP option tag 'uui'.  The use
   of a 'Require: uui' in a request, or 'Supported: uui' in an OPTIONS
   response could be used to require or discover support of the
   mechanism.  REQ-10 could be met by creating a new class of SIP
   feature tags.  For example, the feature tag 'sip.uui.isdn' could be
   used to indicate support of the ISDN UUI service, or 'sip.uui.app1'
   could be used to indicate support for a particular application.

3.4.  MIME body Approach

   One method of transport is to use a MIME body.  This is in keeping
   with the SIP-T architecture [RFC3372] in which MIME bodies are used
   to transport ISUP information.  Since the INVITE will normally have
   an SDP message body, the resulting INVITE with SDP and UUI will be
   multipart MIME.  This is not ideal as many SIP UAs do not support
   multipart MIME INVITEs.

   A bigger problem is the insertion of a UUI message body by a redirect
   server or in a REFER.  The body would need to be encoded in the
   Contact URI of the 3xx response or the Refer-To URI of a REFER.
   Currently, the authors are not aware of any UAs that support this
   capability today for any body type.  As such, the complete set of



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   semantics for this operation would need to be determined and defined.
   Some issues will need to be resolved, such as, do all the Content-*
   header fields have to be escaped as well?  And, what if the escaped
   Content-Length does not agree with the escaped body?

   Since proxies cannot remove a body from a request or response, it is
   not at all clear how this mechanism could meet REQ-9.

   The requirement for integrity protection could be met by the use of
   an S/MIME signature over the body, as defined in Section 23.3 of RFC
   3261 "Securing MIME bodies".  Alternatively, this could be achieved
   using RFC 4474 [RFC4474].  The requirement for end-to-end privacy
   could be met using S/MIME encryption or using encryption at the
   application layer.  However, note that neither S/MIME or RFC 4474
   enjoys deployment in SIP today.

   An example:

   <allOneLine>
   Contact: <sip:+12125551212@gateway.example.com?Content-Type=
   application/uui&body=ZeGl9i2icVqaNVailT6F5iJ90m6mvuTS4OK05M0vDk0Q4Xs>
   </allOneLine>

   Note that the <allOneLine> tag convention from SIP  Torture Test
   Messages [RFC4475] is used to show that there are no line breaks in
   the actual message syntax.

   As such, the MIME body approach meets REQ-1, REQ-2, REQ-4, REQ-5,
   REQ-7, REQ-11, REQ-13, and REQ-14.  Meeting REQ-12 seems possible,
   although the authors do not have a specific mechanism to propose.
   Meeting REQ-3 is problematic, but not impossible for this mechanism.
   However, this mechanism does not seem to be able to meet REQ-9.

3.5.  URI Parameter

   Another proposed approach is to encode the UUI as a URI parameter.
   This UUI parameter could be included in a Request-URI or in the
   Contact URI or Refer-To URI.  It is not clear how it could be
   transported in a responses which does not have a Request-URI, or in
   BYE requests or responses.

  <allOneLine>
  Contact: <sip:+12125551212@gateway.example.com;uui=ZeGl9i2icVqaNVailT6
  F5iJ90m6mvuTS4OK05M0vDk0Q4Xs>
  </allOneLine>

   An INVITE sent to this Contact URI would contain UUI in the Request-
   URI of the INVITE.  The URI parameter has a drawback in that a URI



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   parameter carried in a Request-URI will not survive retargeting by a
   proxy as shown in Figure 2 of [I-D.ietf-cuss-sip-uui-reqs].  That is,
   if the URI is included with an Address of Record instead of a Contact
   URI, the URI parameter in the Reqeuest-URI will not be copied over to
   the Contact URI, resulting in the loss of the information.  Note that
   if this same URI was present in a Refer-To header field, the same
   loss of information would occur.

   The URI parameter approach would meet REQ-3, REQ-5, REQ-7, REQ-9, and
   REQ-11.  It is possible the approach could meet REQ-12 and REQ-13.
   The mechanism does not appear to meet REQ-1, REQ-2, REQ-4, and
   REQ-14.

3.6.  Header Field Approach

   Another approach that has been proposed is to use a header field to
   transport the UUI information.  The header field would be included in
   INVITE requests and responses and BYE requests and responses, and
   would pass transparently through proxies.

   For redirection and referral use cases and REQ-3, the header field
   would be escaped into the Contact or Refer-To URI.  Currently, UAs
   that support attended transfer support the ability to escape a
   Replaces header field into a Refer-To URI, and when acting upon this
   URI add the Replaces header field to the triggered INVITE.  This
   logic and behavior is identical for the proposed UUI header field.
   As such, the existing running code for this behavior could be easily
   extended to allow this to happen for the UUI header field.  Note that
   this does require code changes in UAs.

   To meet REQ-12 in redirection and referral use cases, a History-Info
   [I-D.ietf-sipcore-rfc4244bis] extension could be used.  During
   redirection or retargeting, History-Info captures the history and the
   identity of the entity performing the redirection or referral.  It
   seems likely that a new History-Info parameter could be defined to
   indicate that the UUI was inserted during this operation.  The source
   of UUI inserted during redirection or referral could then be
   determined by examination of the History-Info header field.

   The requirement for integrity protection in REQ-13 could be met by
   the use of an S/MIME signature over a subset of header fields, as
   defined in Section 23.4 of RFC 3261 "SIP Header Privacy and Integrity
   using S/MIME: Tunneling SIP".  It could not be achieved using RFC
   4474 without some sort of extension.  The requirement for end-to-end
   privacy could be met using S/MIME or using encryption at the
   application layer.  Note that the use of S/MIME to secure the UUI
   will result in an additional body being added to the request.
   However, note that neither S/MIME or RFC 4474 enjoys deployment in



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   SIP today.

   For example, here is an example User-to-User header field from
   message F1 in Figure 1 of [I-D.ietf-cuss-sip-uui-reqs]:

   User-to-User: 56a390f3d2b7310023a;encoding=hex;purpose=isdn-interwork
    ;content=isdn-uui

   As another example, here is an escaped User-to-User header field from
   the redirection response F2 of Figure 3:

   <allOneLine>
   Contact: <sip:+12125551212@gateway.example.com?User-to-User=
   56a390f3d2b7310023a%3Bencoding%3Dhex%3Bpurpose%3Disdn-interwork%3B
   content%3Disdn-uui>
   </allOneLine>

   The resulting INVITE F5 would contain:

   User-to-User: 56a390f3d2b7310023a;encoding=hex;purpose=isdn-interwork
    ;content=isdn-uui

   An escaped User-to-User header field from the REFER message response
   F1 of Figure 4:

   <allOneLine>
   Refer-To: <sip:+12125551212@gateway.example.com?User-to-User=
   56a390f3d2b7310023a%3Bencoding%3Dhex%3Bpurpose%3Disdn-interwork%3B
   content%3Disdn-uui>
   </allOneLine>

   This would result in the INVITE F4 containing:

   User-to-User: 56a390f3d2b7310023a;encoding=hex;purpose=isdn-interwork
    ;content=isdn-uui

   The header field approach meets REQ-1, REQ-2, REQ-3, REQ-4, REQ-5,
   REQ-7, REQ-9, REQ-11, REQ-13, and REQ-14.  The mechanism can likely
   meet REQ-12 with a History-Info extension.


4.  Recommendation

   The recommendation of this document is to define a new SIP header
   field "User-to-User" to transport call control UUI since this
   mechanism best supports the requirements in
   [I-D.ietf-cuss-sip-uui-reqs].  There are also existing
   implementations and running code for this header field approach.  The



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   remainder of this document is a start at defining the details of the
   mechanism.  Further work is needed.

   To help tag and identify the UUI used with this header field,
   "purpose", "content", and "encoding" parameters are defined.  This
   specification only defines "encoding=hex".  Other specifications can
   define other purposes and contents for this header field per the
   requirements of this document.


5.  Syntax for UUI Header Field

   The User-to-User header field can be present in INVITE requests and
   responses only and in BYE requests and responses.

   The following syntax specification uses the augmented Backus-Naur
   Form (BNF) as described in RFC 2234 and extends RFC 3261.

       UUI         = "User-to-User" HCOLON uui-data *(SEMI uui-param)
       uui-data    = token
       uui-param   = enc-param | cont-param | purp-param | generic-param
       enc-param   = "encoding="("hex" | token)
       cont-param  = "content=" token
       purp-param  = "purpose=" token

   If the encoding parameter is not present, the default value of "hex"
   MUST be assumed.  Other encoding methods of encoding MAY also be
   standardized.

   User-to-User header fields with different purpose parameters may be
   present in a request or response.  The number of User-to-User header
   fields which may be present in a request or response is defined for a
   particular purpose (application).  Any size limitations on the UUI
   for a particular purpose must be defined by that purpose.

5.1.  Definition of New Parameter Values

   This specification defines only the values of "hex" for the
   "encoding" parameter.  New values can be defined and added to the
   IANA registry with a standards track RFC, which needs to discuss the
   issues in this section.

   New "encoding" values must reference a common encoding scheme or
   define the exact new encoding scheme.

   New "content" values must describe the content of the UUI and give
   some example use cases.  The default "encoding" and other allowed
   encoding methods must be defined for this new content.



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   New "purpose" values must describe the new purpose and give some
   example use cases.  The default "content" value and other allowed
   contents must be defined for this new purpose.  Any restrictions on
   the size of the UUI data must be described for the new purpose.


6.  IANA Considerations

6.1.  Registration of Header Field

   This document defines a new SIP header field named "User-to-User".

   The following row shall be added to the "Header Fields" section of
   the SIP parameter registry:


                 +------------------+--------------+-----------+
                 | Header Name      | Compact Form | Reference |
                 +------------------+--------------+-----------+
                 | User-to-User     |              | [RFCXXXX] |
                 +------------------+--------------+-----------+

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

6.2.  Registration of Header Field Parameters

   This document defines the parameters for the header field defined in
   the preceding section.  The header field "User-to-User" can contain
   the parameters "encoding", "content", and "purpose".

   The following rows shall be added to the "Header Field Parameters and
   Parameter Values" section of the SIP parameter registry:


   +------------------+----------------+-------------------+-----------+
   | Header Field     | Parameter Name | Predefined Values | Reference |
   +------------------+----------------+-------------------+-----------+
   | User-to-User     | encoding       | hex               | [RFCXXXX] |
   +------------------+----------------+-------------------+-----------+

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

6.3.  Registration of SIP Option Tag

   This specification registers a new SIP option tag, as per the
   guidelines in Section 27.1 of [RFC3261].



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   This document defines the SIP option tag "uui".

   The following row has been added to the "Option Tags" section of the
   SIP Parameter Registry:

   +------------+------------------------------------------+-----------+
   | Name       | Description                              | Reference |
   +------------+------------------------------------------+-----------+
   | uui        | This option tag is used to indicate that | [RFCXXXX] |
   |            | a UA supports and understands the        |           |
   |            | User-to-User header field.               |           |
   +------------+------------------------------------------+-----------+

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


7.  Security Considerations

   User to user information can potentially carry sensitive information
   that might require privacy or integrity protection.  Standard
   deployed SIP security mechanisms such as TLS transport, offer these
   properties on a hop-by-hop basis.  To preserve multi-hop or end-to-
   end confidentiality and integrity of UUI, approaches using S/MIME or
   RFC 4474 can be used, as discussed in the draft.  However, the lack
   of deployment of these mechanisms means that applications can not in
   general rely on them.  As such, applications are encouraged to
   utilize their own security mechanisms.


8.  Acknowledgements

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


9.  References

9.1.  Informative References

   [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 .

   [Q931]     "ITU-T Q.931 User to User Information  Element (UU IE)",
              http://www.itu.int/rec/T-REC-Q.931-199805-I/en .



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

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

   [RFC2976]  Donovan, S., "The SIP INFO Method", RFC 2976,
              October 2000.

   [RFC4475]  Sparks, R., Hawrylyshen, A., Johnston, A., Rosenberg, J.,
              and H. Schulzrinne, "Session Initiation Protocol (SIP)
              Torture Test Messages", RFC 4475, May 2006.

   [Q1980]    "ITU-T Q.1980.1 The Narrowband Signalling Syntax (NSS) -
              Syntax Definition", http://www.itu.int/itudoc/itu-t/aap/
              sg11aap/history/q1980.1/q1980.1.html .

9.2.  Normative References

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

   [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.

   [RFC3324]  Watson, M., "Short Term Requirements for Network Asserted
              Identity", RFC 3324, November 2002.

   [I-D.ietf-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-ietf-cuss-sip-uui-reqs-00 (work in progress),
              November 2010.

   [RFC4474]  Peterson, J. and C. Jennings, "Enhancements for
              Authenticated Identity Management in the Session
              Initiation Protocol (SIP)", RFC 4474, August 2006.

   [I-D.ietf-sipcore-rfc4244bis]
              Barnes, M., Audet, F., Schubert, S., Netherlands, T., and
              C. Holmberg, "An Extension to the Session Initiation
              Protocol (SIP) for Request History Information",
              draft-ietf-sipcore-rfc4244bis-02 (work in progress),



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              October 2010.


Authors' Addresses

   Alan Johnston
   Avaya
   St. Louis, MO  63124

   Email: alan.b.johnston@gmail.com


   Joanne McMillen
   Unaffiliated

   Email: c.joanne.mcmillen@gmail.com


   James Rafferty
   Dialogic

   Email: james.rafferty@dialogic.com





























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