Internet Draft M. Barnes
Document: draft-barnes-sipping-history-info-00.txt M. Watson
Category: Standards Track Nortel Networks
Cullen Jennings
Cisco
Expires: April, 2003 October 2002
An Extension to the Session Initiation Protocol for Request History
Information
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
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Abstract
This draft defines a standard mechanism for capturing the history
information associated with a SIP request. This capability enables
many enhanced services by providing the information as to how and
why a call arrives at a specific application or user. This draft
defines a new optional SIP header, History-Info, for capturing the
history information in requests. A new option tag, HistInfo, to be
included in the Supported header is defined to allow UAs to
indicate whether the HistInfo should be returned in responses to a
request which has captured the history information. The draft
suggests the use of a secure transport mechanism such as TLS and
the use of S/MIME for ensuring the security of the HistInfo.
Table of Contents
1 Request History Information Description........................3
2 Request History Information Protocol Details...................4
2.1 Protocol Structure of History-Info........................4
2.2 Protocol Examples.........................................5
2.3 Protocol usage............................................5
2.4 Security for History-Info.................................6
2.5 Example Applications using History-Info...................7
3 Security Considerations........................................8
References.......................................................9
Appendix A û Forking Scenarios..................................10
A.1 Sequentially forking (Hist-Info in Response).............10
A.2 Sequential Forking (with Success)........................11
Appendix B û Voicemail..........................................12
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Appendix C û Automatic Call Distribution Example................16
Appendix D û Solution options analysis..........................16
Full Copyright Statement........................................18
Overview
This document provides the solution for the Request History
requirements as defined in [1].
The fundamental functionality provided by the request history
information is the ability to inform proxies and UAs involved in
processing a request about the history or progress of that request.
This functionality provides a standard mechanism for capturing the
request history information to enable a wide variety of services
for networks and end users, without prescribing the operation of
those services.
Section 1 provides an overall description of the solution,
providing references to the appropriate requirements met by each
aspect of the solution. For background, further detail on some
aspects of the solution with regards to optionality and the
detailed protocol requirements is provided in Appendix D.
Section 2 provides the details of the additions to the SIP
protocol, which are required to capture the Request History
information. An example use of the request history information is
included in Section 2, with additional scenarios included in the
Appendix. It is anticipated that these would be moved and
progressed in the Service examples draft [2] or individual
informational drafts describing these specific services. Individual
drafts would be particularly useful for documenting services for
which there are multiple solutions (i.e. the use of the request
history information isnÆt prescriptive).
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 [7].
In order to provide a cross reference of the solution description
to the requirements defined in [1] without reiterating the entirety
of the requirements in this document, the requirements are
referenced as [REQNAME-req] following the text or paragraph which
explicitly satisfies the requirement.
Definitions
The following terminology is used in this document:
Retarget (as defined in [1]): The process of a Proxy Server/UAC
changing a URI in a request and thus changing the target of the
request.
Retargeted: past of Retarget.
Retargeted-from-URI: The URI or address from which the request was
retargeted.
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Retargeted-to-URI: The new URI or address to which the request is
in the process of being retargeted.
1 Request History Information Description
The fundamental functionality provided by the request history
information is the ability to inform proxies and UAs involved in
processing a request about the history or progress of that request
[CAPABILITY-req]. The solution for the capture of the Request
History Information defines a new header for SIP messages: History-
Info [CONTENT-req].
The Request History Information can appear in any request not
associated with an established dialog, which includes INVITE,
REGISTER, MESSAGE and OPTIONS [REQUEST-VALIDITY-req] and any valid
response to these requests.[ISSUER-req]
Request History Information is captured when a request is
retargeted. In some scenarios, it might be possible for more than
one instance of retargeting to occur within the same Proxy. A
proxy SHOULD also generate request history information for the
'internal retargeting'. An entity (UA or proxy) retargeting in
response to a redirect or REFER SHOULD include any Request History
information from the redirect/REFER in the new request [GENERATION-
req, FORWARDS-req].
The Request History Information is optional in that neither UAs nor
Proxies are required to support it. The requirement for Request
History information to be returned in Responses is indicated using
a new Supported header: HistInfo [BACKWARDS-req]. In addition,
local policy can define whether or not the information is captured
by the retargeting entity for any request, or a specific Request-
URI, being retargeted. In many instances, it is likely that this
could restrict the applicability of services which make us of the
Request History Information to be limited to retargeting within
domain(s) controlled by the same local policy, or between domain(s)
which negotiate policies with other domains to ensure support of
the given policy, or services for which "complete" History
Information isnÆt required to provide the service. [OPTIONALITY-
req] Thus, it is highly recommended that all applications making
use of the request history information clearly define the impact of
the information not being available and specify the processing of
such a request.
This draft defines a new header for SIP and builds on the security
model as defined in [4]. However, The Request History information
is being inserted by an entity retargeting a Request, resulting in
a slightly different problem than the basic SIP header or Identity
problem. It is primarily the Request-URIs that are the security
concern, since they can reflect some aspect of a userÆs identity
and service routing. Thus, the primary objective of the security
solution is to ensure that the information being captured is
protected from being accessed or manipulated by non-authorized
entities, with the fundamental assumption that retargeting entities
are implicitly authorized. The draft suggests the use of a secure
transport mechanism such as TLS [SEC-req-4]. The use of S/MIME in
a manner similar to that used for the Authenticated Identity Body
defined in [5] is recommended to protect the Request History
Information from being manipulated by a rogue application. Further
details of the use of this proposed mechanism to satisfy the
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security requirements are provided in section 2.4. The security
associated with the Request History Information is optional and
depends upon local policy and the impact on specific applications
of having the information compromised. Since, the Request History
Information itself is also optional and it has been recommended
that applications document the impact of the information not being
available, it is also suggested that the impact of not supporting
the security recommendations also be documented to ensure that it
is sufficiently addressed by the application.
In order to satisfy the requirements of ensuring that the privacy
associated with a retargeted request URI is maintained by the
retargeting entity [PRIV-req-1] and by the receiving entity [PRIV-
req-2], the retargeting entity must determine if there is any
privacy associated with a request URI being retargeted. In some
scenarios, the Privacy header would indicate whether a field in a
message should be privacy protected. However, the basic assumption
is that local policy would be used to determine whether a specific
request URI should have its privacy maintained and whether
maintaining that privacy means that the request URI would NOT be
captured or that it would be appropriately Privacy protected if it
were captured. The proposal for ensuring that the privacy is
protected is to assume the use of a Privacy Service as defined by
[6]. [EditorÆs note: Do we really want to solve the problem this
way OR assume that if there is any level of privacy for the request
URI, to just NOT capture it? Or, should this also be a local
policy thing? ] It is recognized that meeting the privacy
requirements can impact the functionality of this solution by
overriding the request to generate the information. As with the
optionality and security requirements, applications making use of
History-Info should address any impact this may have.
2 Request History Information Protocol Details
This section contains the details and usage of the proposed new SIP
protocol elements. It also discusses the security aspects of the
solution and provides some examples.
2.1 Protocol Structure of History-Info
History-Info is a header field as defined by [4]. It can appear in
any request not associated with an established dialog, which
includes INVITE, REGISTER, MESSAGE and OPTIONS and any valid
response to these requests.
It carries the following information:
History-Info = ("History-Info" / "h") HCOLON
HI-retargeted-from-uri
HI-retargeted-to-uri *( SEMI HI-param )
HI-retargeted-from-uri = name-addr
HI-retargeted-to-uri= name-addr
HI-param = HI-reason / HI-reason-cause
/ HI-reason-text / HI-extension
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HI-reason = "HI-reason" EQUAL HI-reason-protocol
HI-reason-protocol = "SIP" / "Q.850" / token
HI-reason-cause = "cause" EQUAL 1*DIGIT
HI-reason-text = "text" EQUAL quoted-string
HI-extension = generic-param
2.2 Protocol Examples
History-Info: <sip:UserA@ims.nortelnetworks.com>
<sip:UserB@ims.nortelnetworks.com> ;
HI-reason=SIP;cause=302;text="Moved Temporarily"; foo=bar
History-Info: <sip:UserB@ims.nortelnetworks.com>
<sip:45432@vm.nortelnetworks.com> ;
HI-reason=SIP;cause=486;text="Busy Here"
2.3 Protocol usage
This section describes the processing specific to UAs and Proxies
for the History-Info and the HistInfo option tag.
[EditorÆs note: Once the Security solution is fully fleshed out, it
may be reasonable to move this section 2.3 after section 2.4 and
provide the detailed security related processing prior to this
section, so that security aspects can be highlighted in this
section, as well.]
2.3.1 UAC Behavior
The UAC SHOULD include the HistInfo option tag in the Supported
header in any request not associated with an established dialog for
which the UAC would like the History-Info in the Response. The
processing of the History-Info received in the response is
application specific and outside the scope of this draft.
2.3.2 UAS Behavior
The processing of History-Info by a UAS in a Request depends upon
local policy and specific applications at the UAS which might make
use of the information. If the HistInfo option tag is received in
a request, the UAS should include any History-Info received in the
request in the subsequent response.
2.3.3 Proxy Behavior
The use of History-Info does not alter the fundamental processing
of proxies for determining request targets as defined in section
16.5 of [4]. Whether a proxy captures the History-Info depends
upon local policy and whether the Request contains the HistInfo
option tag in the Supported header. The following are further
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considerations for refinement of a local policy supporting History-
Info:
o Whether retargets within a Proxy are captured
o Whether the History-Info captured for a proxy/domain should go
outside that domain (e.g. a Proxy knows that the information
is potentially useful within that domain, however, policies
(for privacy, user and network security, etc.) prohibit the
exposure of that information outside that domain).
Each application making use of History-Info should address the
applicability and impacts of the local policies.
Consistent with basic SIP processing of optional headers, proxies
should maintain History-Info captured by other domains, received in
Requests which they forward, independent of whether local policy
supports History-Info.
If the proxy supports History-Info, the proxy SHOULD add any
History-Info collected as a result of a retarget to a Request as it
is forwarded. The History-Info SHOULD be added following any
History-Info received in the request being forwarded to preserve
the relative order of the information.
A proxy that receives a Request with the HistInfo option tag in the
Supported header and depending upon a local policy which supports
the capturing of History-Info SHOULD return captured History-Info
in subsequent responses to the Request.
Parallel forking, as with basic SIP processing, does introduce
somewhat of a special case. In the case of parallel forking, the
proxy SHOULD capture each of the Request-URIs to which the Request
is forked. Since, the forking is parallel, the order in which the
entries would be included in a response or subsequent non-forked
request would be up to local policy. Logically, with the
information in the History-Info, the end application would not
necessarily be able to determine that parallel forking occurred,
but rather would be able to reconstruct the tree of requests and
responses associated with the forking.
2.4 Security for History-Info
As discussed in Section 1, the security requirements are met
through the use of S/MIME to protect the Request History
Information from being manipulated by a rogue application. The
solution proposes the definition of an authenticated identity for
the retargeted-URI using S/MIME similar to the Authenticated
Identity Body defined in [5].
As defined in [1], there are 3 fundamental security requirements
associated with the History-Info:
1) Determination of whether any of the previously added History-
Info headers have been altered [SEC-req-1].
2) Preserving the chronological order of each History-Info header
content [SEC-req-2].
3) Ability to authenticate the identity represented by HI-
retargeted-from-URI and HI-retargeted-to-URI in the History-Info
[SEC-req-3]
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The third requirement can be satisfied by defining an authenticated
identity for the HI-retargeted-from-URI and HI-retargeted-to-URI
similar to the Authenticated Identity Body defined in [5]. In
addition to the mandatory fields specified in [5] for inclusion in
the Authenticated Identity body, HI-reason should also be included.
The second requirement can be met by signing the entirety of the
History-Info that is forwarded or returned in a response.
There are some slight differences between the Authentication
Service required for the History-Info and the Authentication
Service defined in [5]:
o The authenticated identity body relates to a History-Info
header field rather than the From field of the Request.
o The authenticated identity body is being requested to be
authenticated by the retargeting entity and NOT by the user
associated with the identity (i.e. the retargeted entity).
o There may be multiple History-Info headers in a message, thus
this may require multiple authenticated identity bodies.
2.4.1 Security examples
[EditorÆs Note: Need to add some protocol details based on the use
of S/MIME for protecting History-Info].
2.5 Example Applications using History-Info
This scenario highlights an example where the History-Info in the
response is primarily of use in not retrying routes that have
already been tried by another proxy. Note, that this is just an
example and that there may be valid reasons why a Proxy would want
to retry the routes and thus, this would like be a local proxy or
even user specific policy.
UA 1 sends a call to "Bob" to proxy 1. Proxy 1 forwards the request
to Proxy 2. Proxy 2 parallel forks and tries several places (UA2,
UA3 and UA4) before sending a response to Proxy 1 that all the
places are busy. Proxy 1, without the History-Info, would try
several of the same places (UA3 and UA4)based upon registered
contacts for "Bob", before completing at UA5. However, with the
History-Info, Proxy 1 determines that UA3 and UA4 have already
received the invite, thus the INVITE goes directly to UA5.
UA1 Proxy1 Proxy2 UA2 UA3 UA4 UA5
| | | | | | |
|--INVITE -->| | | | | |
| |-INVITE->| | | | |
Supported: HistInfo
History-Info: <sip:Bob@P1> <sip:Bob@P2>
| | | | | | |
| | |-INVITE>| | | |
History-Info: <sip:Bob@P1> <sip:Bob@P2>
History-Info: <sip:Bob@P2> <sip:User2@UA2>
| | | | | | |
| | |-----INVITE ---->| | |
History-Info: <sip:Bob@P1 > <sip:Bob@P2 >
History-Info: <sip:Bob@P2 > <sip:User3@UA3>
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| | | | | | |
| | |-------INVITE------------>| |
History-Info: <sip:Bob@P1 > <sip:Bob@P2 >
History-Info: <sip:Bob@P2 > <sip:User4@UA4 >
/* All Responses from the INVITEs indicate Busy. */
| | | | | | |
| |<-486 ---| | | | |
History-Info: <sip:Bob@P1 > <sip:Bob@P2 >
History-Info: <sip:Bob@P2 > <sip:User2@UA2>
History-Info: <sip:Bob@P2 > <sip:User3@UA3>
History-Info: <sip:Bob@P2 > <sip:User4@UA4>
| | | | | | |
/* Upon receipt of the response, P1 determines another route for the
INVITE, but finds that it matches some routes already attempted (e.g.
UA2 and UA3, thus the INVITE is only forwarded to UA5, where the
session is successfully established */
| | | | | | |
| |----------------INVITE --------------------->|
History-Info: <sip:Bob@P1 > <sip:Bob@P2 >
History-Info: <sip:Bob@P2 > <sip:User2@UA2>
History-Info: <sip:Bob@P2 > <sip:User3@UA3>
History-Info: <sip:Bob@P2 > <sip:User4@UA4>
History-Info: <sip:Bob@P1> <sip:User5@UA5>
| | | | | | |
| |<-----200 OK---------------------------------|
|<--200 OK---| | | | | |
| | | | | | |
|--ACK --------------------------------------------------->|
Additional detailed scenarios are available in the appendix.
3 Security Considerations
This draft provides a proposal for addressing the Security
requirements identified in [1] in sections 1 and 2.4 of this draft
by proposing the use of TLS between entities and the use of S/MIME
to protect the History-Info based upon the SIP Authenticated
Identity model defined in [5].
4 IANA Considerations
(Note to RFC Editor: Please fill in all occurrences of XXXX in this
section with the RFC number of this specification).
This document defines a new SIP header field name with a compact
form: History-Info and h respectively, and a new option tag:
HistInfo.
The following changes should be made to http:///www.iana.org/
assignments/sip-parameters
The following row should be added to the header field section:
Header Name Compact Form Reference
History-Info h [RFCXXXX]
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The following should be added to the Options Tags section:
Name Description Reference
HistInfo When used with the Supported header, [RFCXXXX]
this option tag indicates support
for the History Information to be
captured for requests and returned in
subsequent responses. This tag is not
used in a Proxy-Require or Requires
header field since support of
History-Info is optional.
References
[1] M. Barnes, M. Watson, C. Jennings, J. Peterson, "SIP Generic
Request History Capability û Requirements", draft-ietf-sipping-req-
history-00.txt, August, 2002.
[2] A. Johnson, "SIP Service Examples", draft-ietf-sipping-service-
examples-02.txt, June, 2002.
[3] H. Schulzrinne, D. Oran, G. Camarillo, "The Reason Header Field
for the Session Initiation Protocol", draft-ietf-sip-reason-01.txt, th May 14 , 2002.
[4] J. Rosenberg et al, "SIP: Session initiation protocol," RFC
3261, June, 2002.
[5] J. Peterson, "Enhancements for Authenticated Identity
Management in the Session Initiation Protocol (SIP)", draft-
peterson-sip-identity-01.txt, July 1, 2002.
[6] J. Peterson, "A Privacy Mechanism for the Session Initiation
Protocol (SIP)", draft-ietf-sip-privacy-general-01.txt, June, 2002.
[7] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997.
Acknowledgements
The authors would like to acknowledge the constructive feedback
provided by Robert Sparks, Scott Orton, Jayshree Bharatia, Anthony
Brown and Francois Audet.
AuthorsÆ Addresses
Mary Barnes
Nortel Networks
2380 Performance Drive Phone: 1-972-684-5432
Richardson, TX USA Email: mbarnes@nortelnetworks.com
Cullen Jennings
Cisco Systems
170 West Tasman Dr Tel: +1 408 527 9132
MS: SJC-21/3 Email: fluffy@cisco.com
Mark Watson
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Nortel Networks (UK)
Maidenhead Office Park (Bray House)
Westacott Way
Maidenhead,
Berkshire Tel: +44 (0)1628-434456
England Email: mwatson@nortelnetworks.com
Appendix A û Forking Scenarios
A.1 Sequentially forking (Hist-Info in Response)
This scenario highlights an example where the History-Info in the
response is useful to an application or user that originated the
request.
UA 1 sends a call to "Bob" via proxy 1. Proxy 1 sequentially tries
several places (UA2, UA3 and UA4) unsuccessfully before sending a
response to UA1.
This scenario is provided to show that by providing the History-
Info to UA1, the end user or an application at UA1 could make a
decision on how best to attempt finding "Bob". Without this
mechanism UA1 might well attempt UA3 (and thus UA4) and then re- rd attempt UA4 on a 3 manual attempting at reaching "Bob". With this
mechanism, either the end user or application could know that "Bob"
is busy on his home phone and is physically not in the office. If
there were an alternative address for "Bob" known to this end user
or application, that hasnÆt been attempted, then either the
application or the end user could attempt that. The intent here is
to highlight an example of the flexibility of this mechanism that
enables applications well beyond SIP as it is certainly well beyond
the scope of this draft to prescribe detailed applications.
UA1 Proxy1 UA2 UA3 UA4
| | | | |
|--INVITE -->| | | |
| | | | |
| |--INVITE -------->| | |
|<--100 -----| | | |
| |<-302 ------------| | |
| | | | |
| |-------INVITE ------------>| |
| | | | |
| |<-------180 ---------------| |
|<---180 ----| | | |
| . . |-------INVITE------------->| |
| | timeout | | |
| | | | |
| |------INVITE ---------------------->|
|<--100 -----| | | |
| | | | |
| |<-486 ------------------------------|
| | | | |
| |-- ACK ---------------------------->|
|<--486------| | | |
| | | | |
|--ACK ----->| | | |
| | | | |
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[EditorÆs Note: Need to detail the message flow.]
A.2 Sequential Forking (with Success)
This scenario highlights an example where the History-Info in the
request is primarily of use in not retrying routes that have
already been tried by another proxy. Note, that this is just an
example and that there may be valid reasons why a Proxy would want
to retry the routes and thus, this would like be a local proxy or
even user specific policy.
UA 1 sends a call to "Bob" to proxy 1. Proxy 1 sequentially tries
several places (UA2, UA3 and UA4) before retargeting the call to
Proxy 2. Proxy 2, without the History-Info, would try several of
the same places (UA3 and UA4)based upon registered contacts for
"Bob", before completing at UA5. However, with the History-Info,
Proxy 2 determines that UA3 and UA4 have already received the
invite, thus the INVITE goes directly to UA5.
UA1 Proxy1 Proxy2 UA2 UA3 UA4 UA5
| | | | | | |
|--INVITE -->| | | | | |
| | | | | | |
| |--INVITE -------->| | | |
|<--100 -----| | | | | |
| |<-302 ------------| | | |
| | | | | | |
| |-------INVITE ------------>| | |
| | | | | | |
| |<-------180 ---------------| | |
|<---180 ----| | | | | |
| . . |-------INVITE------------->| | |
| | timeout | | | |
| | | | | | |
| |------INVITE ---------------------->| |
|<--100 -----| | | | | |
| |<-302 ------------------------------| |
| | | | | | |
| |-INVITE->| | | | |
| | | | | | |
| | | | | | |
| | |------INVITE --------------------->|
| | | | | | |
| | |<-----200 OK---------------------->|
|<--200 OK-------------| | | | |
| | | | | | |
|--ACK --------------------------------------------------->|
[EditorÆs Note: Need to add the details of the messages here.]
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Appendix B û Voicemail
This scenario highlights an example where the History-Info in the
request is primarily of use by an edge service (e.g. Voicemail
Server).
UA 1 called UA A which had been forwarded to UA B which forwarded
to a UA VM (voicemail server). Based upon the retargeted URIs and
Reasons in the INVITE, the VM server makes a policy decision about
what mailbox to use, which greeting to play etc.
UA1 Proxy UA-A UA-B UA-VM
| | | | |
|--INVITE F1-->| | | |
| | | | |
| |--INVITE F2-->| | |
|<--100 F3-----| | | |
| |<-302 F4------| | |
| | | | |
| |--------INVITE F5---------->| |
| | | | |
| |<--------180 F6-------------| |
|<---180 F7----| | | |
| . . . | | | |
| |------retransmit INVITE-----|--------->|
| . . . | | | |
| | (timeout) | |
| | | | |
| |-------INVITE F8---------------------->|
| | | | |
| |<-200 F9-------------------------------|
| | | | |
|<-200 F10-----| | | |
| | | | |
|--ACK F11-------------------------------------------->|
Message Details
INVITE F1 UA1->Proxy
INVITE sip:UserA@nortelnetworks.com SIP/2.0
Via: SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@nortelnetworks.com>
Call-Id: 12345600@here.com
CSeq: 1 INVITE
Contact: BigGuy <sip:User1@here.com>
Content-Type: application/sdp
Content-Length: <appropriate value>
v=0
o=UserA 2890844526 2890844526 IN IP4 client.here.com
s=Session SDP
c=IN IP4 100.101.102.103
t=0 0
m=audio 49170 RTP/AVP 0
a=rtpmap:0 PCMU/8000
/*Client for UA1 prepares to receive data on port 49170
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from the network. */
INVITE F2 Proxy->UA-A
INVITE sip:UserA@ims.nortelnetworks.com SIP/2.0
Via: SIP/2.0/UDPims.nortelnetworks.com:5060;branch=1
Via: SIP/2.0/UDP here.com:5060
Record-Route: <sip:UserA@nortelnetworks.com>
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@nortelnetworks.com>
Call-Id: 12345600@here.com
CSeq: 1 INVITE
Contact: BigGuy <sip:User1@here.com>
Content-Type: application/sdp
Content-Length: <appropriate value>
v=0
o=UserA 2890844526 2890844526 IN IP4 client.here.com
s=Session SDP
c=IN IP4 100.101.102.103
t=0 0
m=audio 49170 RTP/AVP 0
a=rtpmap:0 PCMU/8000
100 Trying F3 Proxy->UA1
SIP/2.0 100 Trying
Via: SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@nortelnetworks.com>
Call-Id: 12345600@here.com
CSeq: 1 INVITE
Content-Length: 0
302 Moved Temporarily F4 UserA->Proxy
SIP/2.0 302 Moved Temporarily
Via: SIP/2.0/UDP ims.nortelnetworks.com:5060;branch=1
Via: SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@nortelnetworks.com>;tag=3
Call-Id: 12345600@here.com
CSeq: 1 INVITE
Contact: <sip:UserB@nortelnetworks.com>
Content-Length: 0
INVITE F5 Proxy-> UA-B
INVITE sip:UserB@nortelnetworks.com SIP/2.0
Via: SIP/2.0/UDP ims.nortelnetworks.com:5060;branch=2
Via: SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@nortelnetworks.com>
Call-Id: 12345600@here.com
History-Info: <sip:UserA@ims.nortelnetworks.com>
<sip:UserB@nortelnetworks.com>;
HI-reason=SIP; cause=302; text="Moved Temporarily"
CSeq: 1 INVITE
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SIP Request History Information October 2002
Contact: BigGuy <sip:User1@here.com>
Content-Type: application/sdp
Content-Length: <appropriate value>
v=0
o=User1 2890844526 2890844526 IN IP4 client.here.com
s=Session SDP
c=IN IP4 100.101.102.103
t=0 0
m=audio 49170 RTP/AVP 0
a=rtpmap:0 PCMU/8000
180 Ringing F6 UA-B ->Proxy
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP there.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@nortelnetworks.com>;tag=5
Call-ID: 12345600@here.com
CSeq: 1 INVITE
Content-Length: 0
180 Ringing F7 Proxy-> UA1
SIP/2.0 180 Ringing
SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@nortelnetworks.com>
Call-Id: 12345600@here.com
CSeq: 1 INVITE
Content-Length: 0
/* User B is not available. INVITE is sent multiple
times until it times out. */
/* The proxy forwards the INVITE to UA-VM after adding the
additional History Information entry. */
INVITE F8 Proxy-> UA-VM
INVITE sip:VM@nortelnetworks.com SIP/2.0
Via: SIP/2.0/UDP ims.nortelnetworks.com:5060;branch=3
Via: SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@nortelnetworks.com>
Call-Id: 12345600@here.com
History-Info: <sip:UserA@ims.nortelnetworks.com>
<sip:UserB@nortelnetworks.com>;
HI-reason=SIP;cause=302;text="Moved Temporarily"
History-Info: <sip:UserB@ims.nortelnetworks.com>
<sip:VM@nortelnetworks.com>;
HI-reason=SIP;cause=480;text="Temporarily Unavailable"
CSeq: 1 INVITE
Contact: BigGuy <sip:User1@here.com>
Content-Type: application/sdp
Content-Length: <appropriate value>
v=0
o=User1 2890844526 2890844526 IN IP4 client.here.com
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SIP Request History Information October 2002
s=Session SDP
c=IN IP4 100.101.102.103
t=0 0
m=audio 49170 RTP/AVP 0
a=rtpmap:0 PCMU/8000
200 OK F9
SIP/2.0 200 OK UA-VM->Proxy
Via: SIP/2.0/UDP ims.nortelnetworks.com:5060;branch=3
Via: SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@nortelnetworks.com>;tag=3
Call-Id: 12345600@here.com
CSeq: 1 INVITE
Contact: TheVoiceMail <sip:VM@nortelnetworks.com>
Content-Type: application/sdp
Content-Length: <appropriate value>
v=0
o=UserA 2890844527 2890844527 IN IP4 vm.nortelnetworks.com
s=Session SDP
c=IN IP4 110.111.112.114
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000
200 OK F10 Proxy->UA1
SIP/2.0 200 OK
Via: SIP/2.0/UDP ims.nortelnetworks.com:5060;branch=3
Via: SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@nortelnetworks.com>;tag=3
Call-Id: 12345600@here.com
CSeq: 1 INVITE
Contact: TheVoiceMail <sip:VM@nortelnetworks.com>
Content-Type: application/sdp
Content-Length: <appropriate value>
v=0
o=UserA 2890844527 2890844527 IN IP4 vm.nortelnetworks.com
s=Session SDP
c=IN IP4 110.111.112.114
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000
ACK F11 UA1-> UA-VM
ACK sip:VM@nortelnetworks.com SIP/2.0
Via: SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy<sip:UserA@nortelnetworks.com>;tag=3
Call-Id: 12345600@here.com
CSeq: 1 ACK
Content-Length: 0
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SIP Request History Information October 2002
/* RTP streams are established between UA1 and
UA-VM. UA-VM starts announcement for UA1 */
Appendix C û Automatic Call Distribution Example
Appendix D û Solution options analysis
This section is included to capture some background analysis which
formed the basis for the solution proposed in this document. This
section can be deleted from a subsequent version once the content
of this document is sufficiently developed and well understood.
D.1 Optionality Requirements.
In many cases, it is anticipated that whether the history is added
to the Request would be a local policy decision enforced by the
specific application, thus no specific protocol element is needed.
However, due to the capability being "optional" from the SIP
protocol perspective, the impact to an application of not having
the "Request History" must be described. For example, in a scenario
where there is sequential forking and retargeting, some of the
destinations previously tried could be retried. The impact of not
having the "Request History" information for this sample
application is that routing is inefficient. However, another
scenario involving a voicemail application, the impact of not
having the "Request History" information would be the service could
not operate without having the information as to why the call was
retargeted and the initial target for the call. Thus, the
expectation would be that the policy in a system that intended to
support this voicemail application would have to require the
entities within its domain which are capable of retargeting to
capture "Request History" information.
Thus, there are several aspects to the optionality requirement:
o Optionality with regards to whether the History Information is
to be included in responses to the original Request.
o Optionality with regards to whether a particular retargeting
entity records the History Information.
o Due to the Privacy requirement, the information MUST not be
captured for Request URIs that have indicated a requirement
for privacy.
The optionality mechanisms also depends upon whether the need for
the "Request History" is based upon an end user based service (e.g.
a GUI that provides the list of tried entities for an unsuccessful
call setup, thus ensuring that the caller doesnÆt re-attempt an
entity in that list or attendant services) or a network based
service whose use of the "Request History" would likely be
transparent to the UA (e.g. the Voicemail example).
The Supported header is the chosen mechanism for a UAC to indicate
that the information should be included in subsequent responses.
Whether a server processing the request supports the mechanism
would be based upon local policy for that domain.
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SIP Request History Information October 2002
D.2 Content-req
The Content-req specifies the following:
Retargeted-to-URI
Retargeted-from-URI
Reason
Chronological ordering
The following summarizes the solution considerations for each of
these content requirements:
D.2.1 Is the Retargeted-to-URI required when it can be derived at
the next hop, which would capture this as the Retargeted-from-URI
for subsequent retargeting?
In a series of Request History Information, the Retargeted-to-URI
becomes the Retargeted-from-URI for the next occurrence of
retargeting, thus it would be possible in a scenario where the
Request History functionality is supported by each of the
retargeting entities to derive a complete set of Retargeted-to and
Retargeted-from URIs from the sequence of History Information
rather than including both Retargeted-to and Retargeting-from URI
in each occurrence of History Information.
However, for the scenario where a particular proxy retargets, but
local policy does not support the Request History Information, this
approach could result in a potential loss of information. In
addition, the support of the BACKWARDS-Req does require that the
retargeted-to URI also be captured to ensure completeness of
information (to the extent possible based on policies, privacy,
etc.) in Responses.
D.2.2 Reason
The Reason header field [3] seems like a possible solution for
carrying the Reason associated with the Retargeting, however, this
header field is limited to a single instance for a particular
protocol in a given request within a dialog. In addition, most
instances of the retargeting are anticipated to be based upon the
Status-Code in SIP Responses. Thus, Request History Information
defines its own reason field based on the reason-value format
defined in [3].
D.2.3 Chronological ordering
The Chronological ordering requirement should not require a
specific protocol element if the History-Info entries are
recommended to be added in the order they are generated and
collected. Certainly, an explicit counter or index would seem to
facilitate and maintain the order, however, a simple counter would
have problems with parallel forking. The following were considered
as alternatives for maintaining the logical order of the parallel
forking:
o Indexing using a dot delimiter to indicate hops and forking
(e.g. 1.1.1, 1.1.2 would indicate 2 hops with 2 retargeted nd URIs at the 2 hop.)
o ABNF reflecting the nesting/hops (whether this is even
feasible was not determined).
Barnes Expires - April 2003 [Page 17]
SIP Request History Information October 2002
o Allowing the same value for the count/index (i.e. not worrying
about duplicates as the value indicates only relative order).
However it was decided to remove the count/index altogether, as
logically the application that is concerned about knowing something
about forking can generate the tree by using the Retargeted-to and
Retargeted-from URIs in the History-Info. ItÆs not possible to
determine the exact time order in which the requests were forked,
but this requirement would be well beyond the scope of the intent
of the History-Info (i.e. History-Info is not intended to be a
realtime trace, but rather to provide some logical information as
to the entities which received a particular request and reasons as
to why a request would have been retargeted).
Full Copyright Statement
Copyright (C) The Internet Society (2002). 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."
Barnes Expires - April 2003 [Page 18]