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Versions: 00 01 02                                                      
Internet Engineering Task Force                              J. Elwell
Internet Draft                                                 Siemens
                                                             R. Jesske
                                                      Deutsche Telekom
                                                           J. McMillen
                                                            Avaya Inc.
draft-elwell-sipping-redirection-reason-02.txt
Expires: December 2005                                       June 2005


      SIP Reason header extension for indicating redirection reasons

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress. "

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Copyright Notice

      Copyright (C) The Internet Society (2005). All Rights Reserved.

Abstract

   This proposes an extension to the SIP Reason header to provide
   additional information concerning retargeting in SIP, a particular
   motivation being improved interoperability with PSTN diversion.









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Table of Contents

   1 Introduction....................................................3
   2 Requirements....................................................3
   3 Overview of proposed solution...................................4
   4 Extension to the Reason header..................................4
   5 Inclusion of the Reason header in 3xx responses.................5
   6 Examples........................................................6
   6.1 Retargeting with reason "Forward Unconditional" to PSTN.......6
   6.2 Retargeting with reason "Forward Busy"........................7
   6.3 Recursion with reason "Forward Busy" to PSTN..................9
   6.4 Redirection request from PSTN................................10
   7 IANA considerations............................................12
   8 Security Considerations........................................13
   9 Author's Addresses.............................................13
   10 Normative References..........................................13


































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1 Introduction

   Central to SIP [2] is the concept of redirecting or retargeting a
   request by a proxy, whereby the Request-URI in the original request
   is replaced before forwarding the request on the next hop. Sometimes
   this is due to normal rerouting behaviour of the proxy (e.g.,
   resolving an address-of-record URI to a contact URI). At other times
   it is due to more application-related reasons, e.g., where a user has
   made arrangements for calls to that user under certain conditions to
   be forwarded to a different destination.

   The History-Info header [3] provides a means for conveying
   information about a retarget to the final destination UAS and also
   back to the UAC. In addition to providing the retargeted-from and
   retargeted-to URIs for each recorded retarget, this header also
   conveys a reason by means of the Reason header. The Reason header
   accompanies the retargeted-from URI and reflects the reason why
   attempts to reach that target failed, normally in the form of the SIP
   response code concerned.

   However, the repertoire of reasons available for use in the Reason
   header is sometimes insufficient to reflect application-related
   reasons for retargeting. In particular it cannot reflect accurately
   the range of reasons used in PSTN/ISDN for call "diversion". This
   makes it difficult to provide interworking with PSTN/IDSN for calls
   that undergo retargeting / diversion and also makes it difficult for
   SIP-based networks to offer a behaviour similar to that of diversion
   in PSTN/ISTN.

2 Requirements

   REQ-1. Provide a means for a gateway to provide information in a SIP
   INVITE request to reflect PSTN diversion reasons when mapping a
   diverted PSTN call request to a SIP INVITE request.

   REQ-2. Provide a means for a gateway to provide information in a
   response to a SIP INVITE request to reflect PSTN diversion reasons
   when mapping a response to a PSTN call establishment request to a
   response to a SIP INVITE request.

   REQ-3. Provide a means for a gateway to provide information in a 3xx
   response to a SIP INVITE request to reflect PSTN diversion reasons
   when mapping a PSTN call diversion request to a 3xx response to a SIP
   INVITE request.

   REQ-4. Provide a means for a gateway to obtain information from a SIP
   retargeted or recursed SIP INVITE request for deriving PSTN diversion



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   reasons when mapping the SIP INVITE request to a PSTN call
   establishment request.

   REQ-5. Provide a means for a gateway to obtain information from a
   response to a retargeted or recursed SIP INVITE request for deriving
   PSTN diversion reasons when mapping the SIP response to a response to
   a PSTN call establishment request.

   REQ-6. Provide a means for a gateway to obtain information from a 3xx
   response to a SIP INVITE request for deriving PSTN diversion reasons
   when mapping the SIP 3xx response to a PSTN call diversion request.

3 Overview of proposed solution

   The proposed solution is to enhance the Reason header with new values
   that reflect diversion reasons in PSTN/ISDN. This can be done by
   defining a new "protocol" value and then defining specific new reason
   values under the umbrella of the new "protocol" value. The enhanced
   Reason header can then be used as a parameter of a History-Info
   header field entry. This allows the forwarding of PSTN diversion
   reasons when mapping an INVITE request or response containing a
   History-Info header field to/from PSTN signalling.

   In addition the enhanced Reason header can be used in a 3xx response
   to an INVITE request. This fulfils two functions. First, it allows
   the forwarding of PSTN diversion reasons when mapping a 3xx response
   to an INVITE request to/from PSTN signalling. Secondly it provides
   information to a proxy or UAC for inclusion in the History-Info
   header field when the request undergoes recursion.

   Candidate reasons include forward unavailable, forward busy, forward
   no reply, forward unconditional, deflection immediate, deflection
   alerting, hunting, mobile not reachable.

   Note that selection of the new target may depend on several other
   conditions (e.g., relating to date, time, the source of the request
   or caller preferences), but the reasons suggested above should be
   sufficient to convey the main circumstance leading to the retarget.

4 Extension to the Reason header

   This document defines the following new protocol value for the
   protocol field of the Reason header field in [1]:

     Redirection: The cause parameter contains a reason for redirection
     of a request.

   This document defines the following redirection cause codes:



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     Value  Default Text           Description

     1      Normal redirection     The call has been retargeted for
                                   normal routing reasons

     2      Forward unavailable    The call has been retargeted
                                   because the called user is
                                   unavailable (no registered contact).

     3      Forward busy           The call has been retargeted
                                   because the called user is busy.

     4      Forward no reply       The call has been retargeted
                                   because the called user has been
                                   alerted but has failed to reply.

     5      Forward unconditional  The call has been retargeted
                                   immediately without determining
                                   whether the called user is
                                   unavailable or busy and without
                                   alerting the user.

     6      Deflection immediate   The call has been retargeted as a
                                   result of a request by the called
                                   user's device without alerting the
                                   called user.

     7      Deflection alerting    The call has been retargeted as a
                                   result of action by the called user
                                   in response to alerting.

     8      Hunting                The call has been retargeted to an
                                   individual member of the hunt group
                                   at which it was previously targeted.

     9      Mobile not reachable   The call has been retargeted
                                   because the called mobile user is
                                   not reachable

   Example syntax is as follows:

     Reason: redirection;cause=3 ;text="Forward busy"

5 Inclusion of the Reason header in 3xx responses

   [1] states that the Reason header field is not usually needed in
   responses because the status code and the reason phrase already
   provide sufficient information. However, this is not so in the case
   of a 3xx response, since there may be a need to provide a diversion


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   reason in the 3xx response for inclusion in the History-Info header
   field in the event of recursion or for mapping directly to/from PSTN.
   Therefore in order to satisfy this need, a 3xx response MAY contain a
   Reason header field.

     NOTE. [1] states that the Reason header can appear in any response
     whose status code explicitly allows the presence of this field. The
     statement above performs this function.

6 Examples

6.1 Retargeting with reason "Forward Unconditional" to PSTN

           Alice            Proxy           Bob              Gateway
             |                |              |                   |
             |    INVITE F1   |              |                   |
             |--------------->|              |                   |
             |                |              |                   |
             |(100 Trying) F2 |              |                   |
             |<---------------|              |                   |
             |                |              |    INVITE F3      |
             |                |--------------------------------->|
             |                |              | 180 Ringing F4    |
             |                |<---------------------------------|
             | 180 Ringing F5 |              |                   |
             |<---------------|              |      200 OK F6    |
             |                |              |                   |
             |                |<---------------------------------|
             |    200 OK F7   |              |                   |
             |<---------------|              |                   |
             |     ACK F8     |              |                   |
             |--------------->|              |     ACK F9        |
             |                |--------------------------------->|

   Assuming the entity sending the INVITE supports the History-Info
   header, the INVITE would look like this:

   F1 (INVITE) Alice -> Proxy

     INVITE  sip:Bob@example.com; SIP/2.0
     From: <sip:Alice@example.com>;tag=2
     To: <sip:Bob@example.com >
     Call-ID: 12345600@example.com
     CSeq: 1 INVITE
     History-Info: <sip:Bob@example.com>;index=1
     ...





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   The call is then retargeted to a contact URI
   <sip:12345@gateway.example.com>. The forwarded INVITE request would
   be as follows:

   F3 (INVITE) û Proxy -> Gateway

     INVITE  sip:12345@gateway.example.com SIP/2.0
     From: <sip:Alice@example.com>;tag=2
     To: <sip:Bob@example.com>
     Call-ID: 12345600@example.com
     CSeq: 1 INVITE
     History-Info: <sip:Bob@example.com? Reason=Redirection%3B
     cause%3D5%3Btext%3D%22Forward%20unconditional%22>;index=1,
     <sip:12345@gateway.example.com>;index=2

     Note that in accordance with [2] the following escape characters
     are used within parameters of URL headers: %3B for semicolon, %3D
     for equals, %22 for double quote and %20 for space.

   The "index 1" entry indicates that the call to Bob was retargeted
   because of redirection reason forward unconditional.

   The "index 2" entry indicates that the call to 12345 has not yet been
   further retargeted.

   The Reason header field provides a diversion reason that can be
   included in relevant PSTN messaging.

6.2 Retargeting with reason "Forward Busy"

           Alice            Proxy           Bob              Gateway
             |                |              |                   |
             |    INVITE F1   |              |                   |
             |--------------->|  INVITE F3   |                   |
             |                |------------->|                   |
             |(100 Trying) F2 |              |                   |
             |<---------------|              |                   |
             |                |  486 Busy    |                   |
             |                |   here F4    |                   |
             |                |<-------------|                   |
             |                |    ACK F5    |                   |
             |                |------------->|                   |
             |                |              |    INVITE F6      |
             |                |--------------------------------->|
             |                |              | 180 Ringing F7    |
             |                |<---------------------------------|
             | 180 Ringing F8 |              |                   |
             |<---------------|              |      200 OK F9    |
             |                |<---------------------------------|


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             |    200 OK F10  |              |                   |
             |<---------------|              |                   |
             |     ACK F11    |              |                   |
             |--------------->|              |     ACK F12       |
             |                |--------------------------------->|

   Assuming the entity sending the INVITE supports the History-Info
   header, the INVITE would look like this:

   F1 (INVITE) Alice -> Proxy

     INVITE  sip:Bob@example.com; SIP/2.0
     From: <sip:Alice@example.com>;tag=2
     To: <sip:Bob@example.com >
     Call-ID: 12345600@example.com
     CSeq: 1 INVITE
     History-Info: <sip:Bob@example.com>;index=1
     ...

   Bob indicates a Busy so that a 486 response is send back.

   F4 (486 Busy Here) Bob -> Proxy

     SIP/2.0 486 Busy Here
     From: <sip:Alice @example.com>;tag=2
     To: <sip:Bob@example.com>;tag=3
     Call-ID: 12345600@example.com
     CSeq: 1 INVITE


     à
   On receipt of F4 (486 Busy Here) and because of forwarding on busy
   provisioned at the proxy on behalf of Bob, the call is then
   retargeted to a URI <sip:12345@gateway.example.com>. This URI is pre-
   provisioned within the Proxy. The forwarded INVITE request would be
   as follows:

   F6 (INVITE) û Proxy -> Gateway

     INVITE  sip:12345@gateway.example.com SIP/2.0
     From: <sip:Alice@example.com>;tag=2
     To: <sip:Bob@example.com>
     Call-ID: 12345600@example.com
     CSeq: 1 INVITE
     History-Info: <sip:Bob@example.com? Reason=Redirection%3B
     cause%3D3%3Btext%3D%22Forward%20busy%22>;index=1,
     <sip:12345@gateway.example.com>;index=2

   The "index 1" entry indicates that the call to Bob was retargeted.


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   The "index 2" entry indicates that the call to 12345 has not yet been
   further retargeted.

   The Reason header field for index 1 provides a diversion reason that
   can be included in relevant PSTN messaging.

6.3 Recursion with reason "Forward Busy" to PSTN

           Alice            Proxy           Bob              Gateway
             |                |              |                   |
             |    INVITE F1   |              |                   |
             |--------------->|  INVITE F3   |                   |
             |                |------------->|                   |
             |(100 Trying) F2 |              |                   |
             |<---------------|              |                   |
             |                |  302 Moved   |                   |
             |                |Temporarily F4|                   |
             |                |<-------------|                   |
             |                |    ACK F5    |                   |
             |                |------------->|                   |
             |                |              |    INVITE F6      |
             |                |--------------------------------->|
             |                |              | 180 Ringing F7    |
             |                |<---------------------------------|
             | 180 Ringing F8 |              |                   |
             |<---------------|              |      200 OK F9    |
             |                |<---------------------------------|
             |    200 OK F10  |              |                   |
             |<---------------|              |                   |
             |     ACK F11    |              |                   |
             |--------------->|              |     ACK F12       |
             |                |--------------------------------->|

   Assuming the entity sending the INVITE supports the History-Info
   header, the INVITE would look like this:

   F1 (INVITE) Alice -> Proxy

     INVITE  sip:Bob@example.com; SIP/2.0
     From: <sip:Alice@example.com>;tag=2
     To: <sip:Bob@example.com >
     Call-ID: 12345600@example.com
     CSeq: 1 INVITE
     History-Info: <sip:Bob@example.com>;index=1
     ...





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   Because of forwarding on busy at Bob, the call is then redirected to
   a contact URI <sip:12345@gateway.example.com> in a 302 response. The
   response would be as follows:

   F4 (302 Moved Temporarily) Bob -> Proxy

     SIP/2.0 302 Moved temporarily
     From: <sip:Alice @example.com>;tag=2
     To: <sip:Bob@example.com>;tag=3
     Call-ID: 12345600@example.com
     CSeq: 1 INVITE
     Contact: <sip:12345@gateway.example.com>
     Reason=Redirection;cause=3;text="Forward busy"
     à

   The call then undergoes recursion to the contact URI
   <sip:12345@gateway.example.com>. The forwarded INVITE request would
   be as follows:

   F6 (INVITE) û Proxy -> Gateway

     INVITE  sip:12345@gateway.example.com SIP/2.0
     From: <sip:Alice@example.com>;tag=2
     To: <sip:Bob@example.com>
     Call-ID: 12345600@example.com
     CSeq: 1 INVITE
     History-Info: <sip:Bob@example.com? Reason=Redirection%3B
     cause%3D3%3Btext%3D%22Forward%20busy%22>;index=1,
     <sip:12345@gateway.example.com>;index=2

   The "index 1" entry indicates that the call to Bob was retargeted
   (recursed).

   The "index 2" entry indicates that the call to 12345 has not yet been
   further retargeted.

   The Reason header field for index 1 provides a diversion reason that
   can be included in relevant PSTN messaging.

6.4 Redirection request from PSTN

           Alice            Proxy         Gateway               Bob
             |                |              |                   |
             |    INVITE F1   |              |                   |
             |--------------->|  INVITE F3   |                   |
             |                |------------->|                   |
             |(100 Trying) F2 |              |                   |
             |<---------------|              |                   |
             |                |  302 Moved   |                   |


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             |                |Temporarily F4|                   |
             |                |<-------------|                   |
             |                |    ACK F5    |                   |
             |                |------------->|                   |
             |                |              |    INVITE F6      |
             |                |--------------------------------->|
             |                |              | 180 Ringing F7    |
             |                |<---------------------------------|
             | 180 Ringing F8 |              |                   |
             |<---------------|              |      200 OK F9    |
             |                |<---------------------------------|
             |    200 OK F10  |              |                   |
             |<---------------|              |                   |
             |     ACK F11    |              |                   |
             |--------------->|              |     ACK F12       |
             |                |--------------------------------->|

   Assuming the entity sending the INVITE supports the History-Info
   header, the INVITE would look like this:

   F1 (INVITE) Alice -> Proxy

     INVITE  sip:12345@gateway.example.com; SIP/2.0
     From: <sip:Alice@example.com>;tag=2
     To: <sip:12345@gateway.example.com >
     Call-ID: 12345600@example.com
     CSeq: 1 INVITE
     History-Info: <sip:12345@gateway.example.com>;index=1
     ...

   Because of forwarding on busy in the PSTN to a number that the
   gateway is able to resolve to Bob, the call is then redirected to a
   contact URI <sip:Bob@example.com> in a 302 response. The response
   would be as follows:

   F4 (302 Moved Temporarily) Gateway -> Proxy

     SIP/2.0 302 Moved temporarily
     From: <sip:Alice @example.com>;tag=2
     To: <sip:12345@gateway.example.com>;tag=3
     Call-ID: 12345600@example.com
     CSeq: 1 INVITE
     Contact: <sip:Bob@example.com>
     Reason=Redirection;cause=3;text="Forward busy"
     à

   The Reason header field is derived from PSTN messaging.




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   The call then undergoes recursion to the contact URI
   <sip:Bob@example.com>. The forwarded INVITE request would be as
   follows:

   F6 (INVITE) û Proxy -> Gateway

     INVITE  sip:Bob@example.com SIP/2.0
     From: <sip:Alice@example.com>;tag=2
     To: <sip:12345@gateway.example.com>
     Call-ID: 12345600@example.com
     CSeq: 1 INVITE
     History-Info: <sip:12345@gateway.example.com? Reason=Redirection%3B
     cause%3D3%3Btext%3D%22Forward%20busy%22>;index=1,
     <sip:Bob@example.com>;index=2

   The "index 1" entry indicates that the call to the PSTN was
   retargeted (recursed) with reason Forward busy, the Reason header
   field having been copied from the 302 response.

   The "index 2" entry indicates that the call to Bob has not yet been
   further retargeted.

7 IANA considerations

   This document defines one new value for the SIP Reason header [1]
   protocol namespace. The new value is "Redirection" and indicates the
   use of cause value defined in this document.

   This document also creates an IANA registry for cause values that
   populate the cause field of the Reason header when protocol value
   "Redirection" is used and corresponding default values that populate
   the text field. The current cause and text values in this new
   registry are as follows:

     Cause value  Default text value    Reference
     -----------  ------------------------------
     1            Normal redirection    This document
     2            Forward unavailable   This document
     3            Forward busy          This document
     4            Forward no reply      This document
     5            Forward unconditional This document
     6            Deflection immediate  This document
     7            Deflection alerting   This document
     8            Hunting               This document
     9            Mobile not reachable  This document

   New values for this registry can only be defined by means of a
   published standard.



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8 Security Considerations

   The security considerations of [1] apply. When the Reason header
   field is embedded within a History-Info header field, the security
   considerations of [3] apply.

   Unauthorised insertion, deletion of modification of the Reason header
   field can provide misleading information to users and applications.
   Eavesdropping on this header field can reveal information about a
   user. Securing of SIP connections by TLS can combat this problem.

   A SIP entity that can provide a redirection reason in a Reason header
   field SHOULD be able to suppress this in accordance with privacy
   requirements of the user concerned.

9 Author's Addresses

   John Elwell
   Siemens Communications
   Technology Drive
   Beeston
   Nottingham, UK, NG9 1LA
   email: john.elwell@siemens.com

   Roland Jesske
   Deutsch Telekom
   Am Kavalleriesand 3
   Germany-64295 Darmstadt
   email: r.jesske@t-com.net

   Joanne McMillen
   Avaya Inc.
   1300 W. 120th Ave.
   Westminster, CO 80234-2726
   email: joanne@avaya.com

10 Normative References

   [1] H. Schulzrinne, D. Oran, G. Camarillo, "The Reason Header for the
   Session Initiation Protocol (SIP)", RFC 3326.

   [2] J. Rosenberg, H. Schulzrinne, et al., "SIP: Session initiation
   protocol", RFC 3261.

   [3] M. Barnes, "An Extension to the Session Initiation Protocol for
   Request History Information", draft-ietf-sipping-history-info-03
   (work in progress).

Intellectual Property Statement


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   The IETF takes no position regarding the validity or scope of any
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Disclaimer of Validity

   This document and the information contained herein are provided on an
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   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
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Copyright Statement

   Copyright (C) The Internet Society (2005).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

Acknowledgement

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






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