Internet Draft M. Barnes
Document: draft-ietf-sip-history-info-01.txt Editor
Category: Standards Track Nortel Networks
Expires: April, 2004 October, 2003
An Extension to the Session Initiation Protocol for Request History
Information
Status of this Memo
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all provisions of Section 10 of RFC2026.
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
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 History-Info should be returned in responses to a request which
has captured the history information.
Table of Contents
1 Request History Information Description.........................3
1.1 Optionality of History-Info................................4
1.2 Securing History-Info......................................4
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1.3 Ensuring the Privacy of History-Info.......................5
2 Request History Information Protocol Details....................5
2.1 Protocol Structure of History-Info.........................5
2.2 Protocol Examples..........................................6
2.3 Protocol usage.............................................7
2.4 Security for History-Info.................................10
2.5 Example Applications using History-Info...................11
3. Security Considerations.......................................13
References.......................................................14
Appendix A Forking Scenarios....................................16
A.1 Sequentially forking (Hist-Info in Response)..............16
A.2 Sequential Forking (with Success).........................17
Appendix B Voicemail............................................18
Appendix C Automatic Call Distribution Example..................23
Full Copyright Statement.........................................25
Overview
This document defines a solution for the Request History requirements
as defined in [1], providing the capability to inform proxies and UAs
involved in processing a request about the history or progress of
that request. This draft defines a new SIP header, History-Info, to
provide a standard mechanism for capturing the request history
information to enable a wide variety of services for networks and end
users. The History-Info header provides a building block for
development of new services.
Section 1 provides an overall description of the solution, providing
references to the appropriate requirements.
Section 2 provides the details of the additions to the SIP protocol.
An example use of the new header is included in Section 2, with
additional scenarios included in the Appendix. It is anticipated that
these would be moved and progressed in a general Service examples
draft such as [2] or individual informational drafts describing these
specific services, since the History-Info header is just one of the
building blocks for implementing these services. Individual drafts
would be particularly useful for documenting services for which there
are multiple solutions, since the use of the request history
information isn't prescriptive. As well, as these example
applications, the History-Info header can be used to enhance basic
SIP functionality by providing additional diagnostic information. In
addition, the inclusion of the History-Info header in messages
strengthens the overall SIP security solution. When the History-Info
header is secured as described in section 2.4, it provides an
additional means by which the initiator of a request can be assured
that the forwarding and any retargeting of that request was valid.
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Section 3 summarizes the security solution as described in section
2.4.
Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [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.
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 is to capture the Request-URIs as a
request is forwarded in a new header for SIP messages: History-Info
[CONTENT-req]. This allows for the capturing of the history of a
request that would be lost with the normal SIP processing involved in
the subsequent forwarding of the request. This solution proposes no
changes in the fundamental determination of request targets or in the
request forwarding as defined in sections 16.5 and 16.6 of the SIP
protocol specification [4].
The History-Info header can appear in any request not associated with
an established dialog, which includes INVITE, REGISTER, MESSAGE,
REFER and OPTIONS [REQUEST-VALIDITY-req] and any valid response to
these requests.[ISSUER-req]
The History-Info header is added to a Request when a new request is
created by a UAC or Proxy, or when the target of a request is
changed. The term 'retarget' was introduced in [1] to refer to this
changing of the target of a request and the subsequent forwarding of
that request. It should be noted that retargeting only occurs when
the Request-URI indicates a domain for which the processing entity is
responsible. In terms of the SIP protocol, the processing associated
with retargeting is described in sections 16.5, and 16.6 of [4]. As
described in section 16.5 of [4], it is possible for the target of a
request to be changed by the same proxy multiple times (referred to
as 'internal retargeting' in [1]), as the proxy MAY add targets to
the target set after beginning Request Forwarding. Section 16.6 of
[1] describes Request Forwarding. It is during this process of
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Request Forwarding, that the History Information is captured as an
optional, additional header field. Thus, the addition of the History-
Info header does not impact fundamental SIP Request Forwarding. An
entity (UA or proxy) changing the target of a request in response to
a redirect or REFER SHOULD also propagate any History-Info header
from the initial Request in the new request [GENERATION-req,
FORWARDS-req].
1.1 Optionality of History-Info
The History-Info header is optional in that neither UAs nor Proxies
are required to support it. A new Supported header, Histinfo, is
included in the Request to indicate whether the History-Info header
is returned in Responses [BACKWARDS-req]. In addition to the Histinfo
Supported header, local policy determines whether or not the header
is added to any request, or for a specific Request-URI, being
retargeted. It is possible that this could restrict the applicability
of services which make use 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 isn't required to provide the service.
[OPTIONALITY-req] All applications making use of the History-info
header MUST clearly define the impact of the information not being
available and specify the processing of such a request.
1.2 Securing History-Info
This draft defines a new header for SIP. The draft does RECOMMEND the
use of a secure transport mechanism such as TLS to ensure the overall
confidentiality of the History-Info headers[SEC-req-4]. However, the
problem is slightly different than the hop by hop security problem
solved by TLS, as each hop is not required to add the History-Info
header. Since the History-Info header is being inserted by an entity
as it targets and forwards a Request, the resulting security
requirements also introduce a slightly different problem than the
basic SIP header or Identity [8] problem, which are focused on
securing the information in the initial request end to end. For the
History-Info header, the general requirement is to secure a header
that is inserted by an intermediary and then subsequently referenced,
by other intermediaries to build the next header entry, or by an end
application using the information to provide a service. Thus, the
general requirement takes the form of a middle to middle and middle
to end security solution, which is addressed in a separate draft [5].
The use of the middle-to-end security solution discussed in [5]
allows the integrity of the History-Info to be ascertained as it
traverses the intermediaries. Thus, including the History-Info
header in SIP Requests and securing in this manner adds an additional
level of security end to end, assuring the initiator of a Request
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that it has indeed reached the intended recipient. Further
discussion of the security mechanism for History-Info is provided in
section 2.4.
1.3 Ensuring the Privacy of History-Info
Since the History-Info header can inadvertently reveal information
about the requestor as described in [6], the Privacy header SHOULD be
used to determine whether an intermediary can include the History-
Info header in a Request that it receives and forwards [PRIV-req-2]
or that it retargets [PRIV-req-1]. Thus, the History-Info header
SHOULD not be included in Requests where the requestor has indicated
a priv-value of Session or Header level privacy.
In addition, the History-Info header can reveal general routing
information, which may be viewed by a specific intermediary or
network, to be subject to privacy restrictions. Thus, local policy
MAY also be used to determine whether to include the History-Info
header, or if it would only be included in the Request as it is
retargeted within a specific domain.
It is recognized that satisfying 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, REFER and OPTIONS and any valid response
to these requests.
It carries the following information:
o Targeted-to-URI: the Request URI captured as the Request is
forwarded.
o Index: A mandatory parameter for History-Info reflecting the
chronological order of the information, indexed to also reflect
the forking and nesting of requests. The format for this
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parameter is a string of digits, separated by dots to indicate
the number of forward hops and retargets. This results in a tree
representation of the history of the request, with the lowest
level index reflecting a branch of the tree. By including the
index and securing the header, the ordering of the History-info
headers in the request is assured.[SEC-req-2]
o Reason: An optional parameter for History-info. The reason for
the retargeting is captured by including the Reason Header [3]
associated with the Request URI being retargeted. Thus, a
reason is not included for a Request URI when it is first added
in a History-info header, but rather is added when that
particular Request-URI is retargeted. Note, that this does
appear to complicate the security problem, however, retargeting
only occurs when the Request-URI indicates a domain for which
the processing entity is responsible, thus it would be the same
processing entity that initially added the Request-URI to the
header that would be updating it with the Reason.
The following summarizes the syntax of the History-Info header, based
upon the standard SIP syntax [4]:
History-Info = ("History-Info" / "h") HCOLON
hist-info *(COMMA hist-info)
hist-info = hi-targeted-to-uri *( SEMI hi-param )
hi-targeted-to-uri= name-addr
hi-param = hi-index / hi-extension
hi-index = "index" EQUAL 1*DIGIT *(DOT 1*DIGIT)
hi-extension = generic-param
2.2 Protocol Examples
History-Info:<sip:UserA@ims.nortelnetworks.com?Reason=SIP;
cause=302;text="Moved Temporarily">; index=1; foo=bar
History-Info: <sip:UserA@ims.nortelnetworks.com?Reason=SIP;
cause=302; text="Moved Temporarily">; index=1.1,
<sip:UserB@nortelnetworks.com? Reason=SIP;cause=486;
text="Busy Here">;index=1.2,
<sip:45432@vm.nortelnetworks.com> ; index=1.3
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[Editor's note: need to insert row for Table 2].
2.3 Protocol usage
This section describes the processing specific to UAs and Proxies for
the History-Info header and the Histinfo option tag. As discussed in
section 1, the fundamental objective is to capture the target
Request-URIs as a request is forwarded. This allows for the
capturing of the history of a request that would be lost due to
subsequent (re)targeting and forwarding. To accomplish this for the
entire history of a request, either the UAC must capture the Request-
URI in the initial request or a proxy must add History-Info headers
for both the Request-URI in the initial request and the target
Request-URI as the request is forwarded. The basic processing is for
each entity forwarding a request to add a History-Info header for the
target Request-URI, updating the index and adding the Reason as
appropriate for any retargeted Request-URI.
[Editor's 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 detailed 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. In
addition, the UAC SHOULD initiate the capturing of the History
Information by adding a History-Info header using the Request-URI of
the request as the hi-targeted-to-uri and initializing the index to 1
in the History-Info header
The processing of the History-Info header received in the Response is
application specific and outside the scope of this draft. However,
the validity of the information SHOULD be ensured prior to any
application usage. [Editor's note: Further detail to be provided once
the security solution is available.]
2.3.2 UAS Behavior
The processing of the History-Info header by a UAS in a Request
depends upon local policy and specific applications at the UAS which
might make use of the information. Prior to any application usage of
the information, the validity SHOULD be ascertained. [Editor's note:
Further detail to be provided once the security solution is
available.]
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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 inclusion of the History-Info header in a Request does not alter
the fundamental processing of proxies for determining request targets
as defined in section 16.5 of [4]. Whether a proxy adds the the
History-Info header as it forwards a Request depends upon local
policy, with the following being considerations in the definition of
that policy:
o Whether the Request contains the Histinfo option tag in the
Supported header.
o Whether the proxy supports the History-Info header.
o Whether any History-Info header added for a proxy/domain
should go outside that domain. An example being the use of
the History-Info header within the specific domain in which
it is retargeted, however, policies (for privacy, user and
network security, etc.) prohibit the exposure of that
information outside that domain. An example of such an
application is provided in Appendix C.
o Whether the History-Info header is added for a specific
Request URI due to local privacy policy considerations.
An example policy would be a proxy that only adds the History-Info
header if the Histinfo option tag is in the Supported header. Other
proxies may have a policy that they always add the header, but never
forward it outside a particular domain.
Each application making use of the History-Info header SHOULD address
the impacts of the local policies on the specific application (e.g.
what specification of local policy is optimally required for a
specific application and any potential limitations imposed by local
policy decisions).
Consistent with basic SIP processing of optional headers, proxies
SHOULD maintain History-Info headers, received in messages being
forwarded, independent of whether local policy supports History-Info.
The specific processing by proxies for adding the History-Info
headers in Requests and Responses is described in detail in the
following sections.
2.3.3.1 Adding the History-Info header to Requests
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If the proxy supports the History-Info header, the proxy SHOULD add a
History-Info header as it forwards a Request. Section 16.6 of [4]
defines the steps to be followed as the proxy forwards a Request.
Step 5 prescribes the addition of optional headers. Although, this
would seem the appropriate step for adding the History-info header,
the interaction with Step 6 "Postprocess routing information" and the
impact of a strict route in the Route header could result in the
Request-URI being changed, thus adding the History-info header
between steps 8 and 9 is RECOMMENDED. Note, that in the case of loose
routing, the Request-URI does not change during the forwarding of a
Request, thus the capturing of History-Info for such a request would
result in duplicate Request-URIs with different indices. The History-
Info header SHOULD be added following any History-Info header
received in the request being forwarded. Additionally, if a request
is received that doesn't include a History-Info header, the proxy MAY
add an additional History-Info header preceding the one being added
for the current request being forwarded. The index for this entry is
RECOMMENDED to start at 1.
For retargets that are the result of an explicit SIP response, the
SIP Response Code that triggered the retargeting MUST be included in
the Reason header field of the Request URI that has been retargeted.
For retargets as a result of timeouts or internal events, a Reason
MAY be included in the Reason header field of the Request URI that
has been retargeted.
In order to maintain ordering and accurately reflect the nesting and
retargeting of the request, an index MUST be included along with the
Targeted-to-URI being captured. Per the ABNF in section 2.1, the
index consists of a dot delimited series of digits (e.g. 1.1.2), with
each dot reflecting the number of hops or level of nesting of the
request. Thus, the indexing results in a logical tree representation
for the history of the Request. It is recommended that for each level
of indexing, the index start at 1. For retargets within a proxy, the
proxy MUST maintain the current level of nesting by incrementing the
lowest/last digit of the index for each instance of retargeting, thus
reflecting the number of retargets within the proxy.
The basic rules for adding the index are summarized as follows:
1. If the Request-URI in the original request indicates a resource
for which this proxy is responsible, then the proxy reads the value
from the History-Info header in the received request, if available,
and adds another level of indexing. For example, if the index in
the last History-Info header field in the received request is 1.1,
this proxy would initialize its index to 1.1.1. For each
subsequent target that is forwarded by the same proxy, a new index
is used by incrementing the last/lowest digit.
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2. If the Request-URI indicates a resource that this proxy is not
responsible for, then the lowest/last digit of the index is
incremented (i.e. a new level is not created). For example, if the
index in the History-Info header of the received request was 1,
then the index in the History-Info header field added by this proxy
would be 2.
If the request forwarding is done in parallel, the proxy MUST capture
each of the Request-URIs to which the Request is forwarded in the
manner previously described per rule 1 above. The index MUST be
captured for each forked request per the rules above, with each new
Request having a unique index. The proxy builds the subsequent
requests and responses using the amalgamated information associated
with each of those requests and including the header entries in the
order indicated by the indexing. Section 2.5 provides an example of
a parallel request scenario, highlighting this indexing mechanism.
2.3.3.2 Processing History-Info in Responses
A proxy that receives a Request with the Histinfo option tag in the
Supported header, and depending upon a local policy supporting the
capture of History-Info, SHOULD return captured History-Info in
subsequent, provisional and final responses to the Request.
It should be noted that local policy considerations, for network and
intermediary privacy, MAY restrict the sending of the History-Info
headers added by the intermediary in subsequent responses. Thus, in
such cases, the proxy MAY remove from these responses the History-
Info headers which it inserted in the original forwarded request.
2.3.4 Redirect Server Behavior
A redirect server SHOULD NOT add any new History-Info, as that would
be done by the entity receiving the 3xx response. However, a redirect
server MAY include History-Info in responses by adding any History-
Info headers received in a request to a subsequent response.
2.4 Security for History-Info
As discussed in Section 1, the security requirements are partially
met by recommending the use of TLS (a basic SIP requirement per [4])
for hop by hop security. In addition, the use of the middle-to-end
security solution discussed in [5] allows the integrity of the
History-Info to be ascertained as it traverses the intermediaries.
For the History-Info header, the general requirement is to secure a
header that is inserted by an intermediary and then subsequently
referenced, by other intermediaries to build the next header entry or
by an end application using the information to provide a service. In
terms of exactly what is being secured, it is primarily the captured
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Request-URIs that are the security concern, since they can reflect
some aspect of a user's identity and service routing. However, the
indices are also important in that they can be used to determine if
specific Request-URIs have been removed from the header. Thus, the
primary objective of the security solution is to ensure that the
entire History-Info header is protected from being accessed or
manipulated by non-authorized entities, with the fundamental
assumption that retargeting entities are implicitly authorized.
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 by the
application to ensure that the impacts have been sufficiently
addressed by the application.
2.4.1 Security examples
[Editor's Note: Need to add some protocol details for protecting
History-Info once [5] is further along].
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 sends the requests in parallel 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 -->| | | | | |
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| |-INVITE->| | | | |
Supported: Histinfo
History-Info: <sip:Bob@P1>;index=1,
<sip:Bob@P2>; index=2
| | | | | | |
| | |-INVITE>| | | |
History-Info: <sip:Bob@P1>;index=1,
<sip:Bob@P2>; index=2,
<sip:User2@UA2>; index=2.1
| | | | | | |
| | |-----INVITE ---->| | |
History-Info: <sip:Bob@P1>;index=1,
<sip:Bob@P2 >; index=2,
<sip:User3@UA3>; index=2.2
| | | | | | |
| | |-------INVITE------------>| |
History-Info: <sip:Bob@P1>;index=1,
<sip:Bob@P2 >; index=2,
<sip:User4@UA4 >; index=2.3
/* All Responses from the INVITEs indicate non-success/non-
availability*/
| | | | | | |
| |<-480 ---| | | | |
History-Info: <sip:Bob@P1>;index=1,
<sip:Bob@P2>; index=2,
<sip:User2@UA2?Reason:SIP;
cause=408;text="RequestTimeout">;index=2.1,
<sip:User3@UA3?Reason:SIP;
cause=487;text="Request Terminated">; index=2.2,
<sip:User4@UA4?Reason:SIP;
cause=603;text="Decline">; index=2.3
| | | | | | |
/* 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>;index=1,
<sip:Bob@P2>; index=2,
<sip:User2@UA2?Reason:SIP;cause=408;
text="RequestTimeout">;index=2.1,
<sip:User3@UA3?Reason:SIP;cause=487;
text="Request Terminated">; index=2.2,
<sip:User4@UA4?Reason:SIP;cause=603;
text="Decline">; index=2.3
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<sip:User5@UA5>;index=1.1
| | | | | | |
| |<-----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 1.2 and 2.4 of this draft
by proposing the use of TLS between entities, and by securing the
History-Info headers added by proxies as described 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]
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 Require
header field since support of
History-Info is optional.
5. Changes since last version
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Changes from the û00 to the û01 version:
o Attempted to be more explicit about the fundamental processing
associated with the header. Removed definitions of new terms,
only referencing the terms from the requirements in the context
of the fundamental SIP processing implied by the terms.
o Attempted to clarify the Index and the related processing.
o Added more detail addressing the privacy requirements.
o Added a bit more detail on security. The security solution
remains in a separate document and this document will need
updating once that is completed.
o Updated the examples (in section 2.5 and appendix) and clarified
the definition and the maintenance of the Index in sections 2.1
and 2.3.3.1.
o Clarified the Reason description in section 2.1. There had been
an error in the description of the processing that was a remnant
of the change to include only a single URI for each History-Info
header.
o Miscellaneous editorial changes (i.e. HistInfo -> Histinfo,
etc.)
Changes from individual draft-barnes-sipping-history-info-02 to the û
00 WG version:
o Updated references and added reference to Security solution
draft.
o Removed appendix D which included background on analysis of
solution options.
o Cleaned up the document format per rfc2223bis.
o Strengthened the inclusion of the INDEX as a MUST (per
discussion at IETF-56).
o Added text around the capturing of the Reason (SHOULD be
captured for SIP responses and MAY be captured for other
things such as timeouts).
o Clarified the response processing 2.3.3.2 to include
provisional responses and the sending of a 183 to convey
History-Info.
o Added section 2.3.4 to address Redirect Server behavior.
References
[1] M. Barnes, M. Watson, C. Jennings, J. Peterson, "SIP Generic
Request History Capability Requirements", draft-ietf-sipping-req-
history-04.txt, June, 2003.
[2] A. Johnson, "SIP Service Examples", draft-ietf-sipping-service-
examples-05.txt, November, 2002.
[3] H. Schulzrinne, D. Oran, G. Camarillo, "The Reason Header Field
for the Session Initiation Protocol", RFC 3326, December, 2002.
Barnes Expires April 2004 [Page 14]
SIP Request History Information October 2003
[4] J. Rosenberg et al, "SIP: Session initiation protocol," RFC 3261,
June, 2002.
[5] M. Barnes, "A Mechanism to Secure SIP Headers Inserted by
Intermediaries", draft-barnes-sipping-inserted-info-01.txt, October,
2003.
[6] J. Peterson, "A Privacy Mechanism for the Session Initiation
Protocol (SIP)", RFC 3323, November, 2002.
[7] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997.
[8] J. Peterson, "Enhancements for Authenticated Identity Management
in the Session Initiation Protocol (SIP)", draft-ietf-sip-identity-
01.txt, February, 2003.
[9] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
Acknowledgements
The editor would like to acknowledge the constructive feedback
provided by Robert Sparks, Paul Kyzivat, Scott Orton, John Elwell,
Nir Chen, Francois Audet, Palash Jain, Brian Stucker, Norma Ng,
Anthony Brown, and Jayshree Bharatia.
The editor would like to acknowledge the significant input from
Rohan Mahy on some of the normative aspects of the ABNF, particularly
around the need for and format of the index and around the enhanced
SIP security aspects enabled by this draft
Contributors' Addresses
Cullen and Mark provided substantial input in the form of email
discussion in the development of the initial version of this
individual solution document.
Cullen Jennings
Cisco Systems
170 West Tasman Dr
MS: SJC-21/3
Tel: +1 408 527 9132
Email: fluffy@cisco.com
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Mark Watson
Nortel Networks (UK)
Maidenhead Office Park (Bray House)
Westacott Way
Maidenhead,
Berkshire
England
Tel: +44 (0)1628-434456
Email: mwatson@nortelnetworks.com
Author's Address
Mary Barnes
Nortel Networks
2380 Performance Drive
Richardson, TX USA
Phone: 1-972-684-5432
Email: mary.barnes@nortelnetworks.com
Appendix A Forking Scenarios
A.1 Sequentially forking (History-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-attempt UA4 on a rd 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 hasn't 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.
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UA1 Proxy1 UA2 UA3 UA4
| | | | |
|--INVITE -->| | | |
| | | | |
| |--INVITE -------->| | |
|<--100 -----| | | |
| |<-302 ------------| | |
| | | | |
| |-------INVITE ------------>| |
| | | | |
| |<-------180 ---------------| |
|<---180 ----| | | |
| . . |-------INVITE------------->| |
| | timeout | | |
| | | | |
| |------INVITE ---------------------->|
|<--100 -----| | | |
| | | | |
| |<-486 ------------------------------|
| | | | |
| |-- ACK ---------------------------->|
|<--486------| | | |
| | | | |
|--ACK ----->| | | |
| | | | |
[Editor's 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.
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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 --------------------------------------------------->|
[Editor's Note: Need to add the details of the messages here.]
Appendix B 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). It should be noted that this isn't intended to be a complete
specification for this specific edge service as it is quite likely
that additional information is need by the edge service. History-Info
is just one building block that this service makes use of.
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 (and other information) in the INVITE, the VM server makes a
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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
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a=rtpmap:0 PCMU/8000
/*Client for UA1 prepares to receive data on port 49170
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
History-Info: <sip:UserA@ims.nortelnetworks.com>; index=1
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
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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?Reason=SIP;
cause=302; text="Moved Temporarily">; index=1,
<sip:UserB@nortelnetworks.com>;index=2
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
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. */
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/* 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?Reason=SIP;
cause=302; text="Moved Temporarily">;index=1,
<sip:UserB@nortelnetworks.com?Reason=SIP;cause=480;text="Temporarily
Unavailable" >;index=2,
<sip:VM@nortelnetworks.com>;index=3
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
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
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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
/* RTP streams are established between UA1 and
UA-VM. UA-VM starts announcement for UA1 */
Appendix C Automatic Call Distribution Example
This scenario highlights an example of an Automatic Call Distribution
service, where the agents are divided into groups based upon the type
of customers they handle. In this example, the Gold customers are
given higher priority than Silver customers, so a Gold call would get
serviced even if all the agents servicing the Gold group (ACDGRP1)
were busy, by retargeting the request to the Silver Group. Upon
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receipt of the call at the agent assigned to handle the incoming
call, based upon the History-Info header in the message, the
application at the agent can provide an indication that this is a
Gold call, from how many groups it might have overflowed before
reaching the agent, etc. and thus can be handled appropriately by the
agent.
For scenarios whereby calls might overflow from the Silver to the
Gold, clearly the alternate group identification, internal routing or
actual agent that handles the call SHOULD not be sent to UA1, thus
for this scenario, one would expect that the Proxy would not support
the sending of the History-Info in the response, even if requested by
the calling UA.
As with the other examples, this is not prescriptive of how one would
do this type of service but an example of a subset of processing that
might be associated with such a service. In addition, this example
is not addressing any aspects of Agent availability, which might also
be done via a SIP interface.
UA1 Proxy ACDGRP1 Svr ACDGRP2 Svr UA2-ACDGRP2
| | | | |
|--INVITE F1-->| | | |
Supported:Histinfo
| | | | |
| |--INVITE F2-->| | |
Supported:Histinfo
History-Info: <sip:Gold@ACD.com>; index=1
History-Info: <sip:ACDGRP1@ACD.com>; index=1.1
| | | | |
| |<-302 F3------| | |
Contact: <sip:ACDGRP2@ACD.com>
| | | | |
| |--------INVITE F4---------->| |
History-Info: <sip:Gold@ACD.com>; index=1
History-Info: <sip:ACDGRP1@ACD.com>; index=1.1
History-Info: <sip:ACDGRP2@ACD.com>; index=1.2
| | | | |
| | | | |
| | | |INVITE F5>|
History-Info: <sip:Gold@ACD.com>; index=1
History-Info: <sip:ACDGRP1@ACD.com>; index=1.1
History-Info: <sip:ACDGRP2@ACD.com>; index=1.2
| | | | |
| | | |<-200 F6--|
| | | | |
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| |<-200 F7--------------------| |
History-Info: <sip:Gold@ACD.com>; index=1
History-Info: <sip:ACDGRP1@ACD.com>; index=1.1
History-Info: <sip:ACDGRP2@ACD.com>; index=1.2
|<-200 F8------| | | |
No History-Info included in the response due to Local Policy>
| | | | |
|--ACK F9--------------------------------------------->|
Message Details
[To be completed]
Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved.
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Barnes Expires April 2004 [Page 25]