Internet Draft Mark Watson
Document: draft-watson-sipping-req-history-02.txt Mary Barnes
Nortel Networks
Cullen Jennings
Cisco
Jon Peterson
Category: Informational NeuStar
Expires December 2002 June 2002
Generic Request History Capability û Requirements
Status of this Memo
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Abstract
Many services that SIP is anticipated to support require the ability
to determine why and how the call arrived at a specific application.
Examples of such services include (but are not limited to) sessions
initiated to call centers via "click to talk" SIP URLs on a web page,
"call history/logging" style services within intelligent "call
management" software for SIP UAs and calls to voicemail servers and
call centers. While SIP implicitly provides the redirect/retarget
capabilities that enable calls to be routed to chosen applications,
there is currently no standard mechanism within SIP for communicating
the history of such a request. This "request history" information
allows the receiving application to determine hints about how and why
the call arrived at the application/user.
This draft discusses the motivations in support of a mechanism which
records the "request history" and proposes detailed requirements for
such a generic "request history" capability.
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Table of Contents
1. Introduction: Why define a Generic "Request History" capability?.
2
2. Conventions used in this document................................3
3. "Request History" Requirements...................................3
4. Further Requirements Related Considerations......................4
5. Security Considerations..........................................5
6. Going forward....................................................7
7. IANA Considerations..............................................7
8. Appendix A - Scenarios...........................................9
1. Introduction: Why define a Generic "Request History" capability?
SIP implicitly provides redirect/retarget capabilities that enable
calls to be routed to specific applications as defined in [1]. The
term retarget will be used henceforth in this draft to refer to the
process of a Proxy Server/UAC changing a URI in a request and thus
changing the target of the request. This term is chosen to avoid
associating this request history only with the specific SIP
Redirect Server capability that provides for a response to be sent
back to a UAC requesting that the UAC should retarget the original
request to an alternate URI. The rules for determining request
targets as described in section 16.5 of [1] are believed to be
consistent with the use of the retarget term in this draft.
The motivation for the request history is that in the process of
retargeting old routing information can be forever lost. This lost
information may be important history that allows elements to which
the call is retargeted to process the call in a locally defined,
application specific manner. The proposal in this draft is to
provide a mechanism for transporting the request history. It is
not proposing any behavior for a Proxy or UA upon receipt of the
information. Indeed, such behavior should be a local decision for
the recipient application.
Current network applications provide the ability for elements
involved with the call to exchange additional information relating
to how and why the call was routed to a particular destination.
The following are examples of such applications:
1) Web "referral" applications, whereby an application residing
within a web server determines that a visitor to a website has
arrived at the site via an "associate" site which will receive
some "referral" commission for generating this traffic,
2) Email forwarding whereby the forwarded-to user obtains a
"history" of who sent the email to whom and at what time
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3) Traditional telephony based call redirection services such as
Voicemail, call-center "automatic call distribution", and
"follow-me" style services.
Several of the aforementioned applications, and specifically those
applications based on email or WWW, define application specific
mechanisms through which it is possible to obtain the necessary
history information.
In order to prevent differing proprietary mechanisms emerging to
obtain the required "request history" information, it is proposed
that the SIPPING WG evaluate the requirements and determine a
generic mechanism for the transport of such "request history"
information.
2. 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.
3. "Request History" Requirements
The following list constitutes a set of requirements for a "Request
History" capability. Note that some of these requirements may be
met using existing elements within SIP û whether and what SIP
extensions would be needed to meet these requirements is out of
scope of this draft.
The requirements have been enumerated and tagged to facilitate
reference to each requirement:
1) CAPABILITY-req: The "Request History" capability will provide a
capability to inform proxies and UAs involved in processing a
request about the history/progress of that request. While this is
inherently provided when the retarget is in response to a SIP
redirect, it is deemed useful for non-redirect retargeting
scenarios, as well.
2) GENERATION-req: "Request History" information is generated when
the request is retargetted [see section 4.1 for further discussion
of this requirement].
3) ISSUER-req: "Request History" information can be generated by a
UA, proxy or redirect server. It can be passed in both requests and
responses.
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4) CONTENT-req: The "Request History" information for each
occurrence of retargeting, shall include the following:
4.1) The new URI or address to which the request is in the
process of being retargeted
4.2) The URI or address from which the request was retargeted.
4.3) The reason for the Request-URI modification [See section 4.2
for further description of this requirement].
4.4) Chronological ordering of the Request History information.
5) REQUEST-VALIDITY-req: Request-History is applicable to requests
not sent within an established dialog. (i.e. INVITE, REGISTER,
MESSAGE, and OPTIONS).
6) BACKWARDS-req: Request-History information may be passed from
the generating entity backwards towards the UAC. This is needed to
enable services which inform the calling party about the dialog
establishment attempts.
7) FORWARDS-req: Request-History information may also be included
by the generating entity in the request, if it is forwarded
onwards.
8) REDIRECT-RESP-req: An entity (UA or proxy) retargeting in
response to a redirect or REFER shall include any Request History
information from the redirect/REFER in the new request.
4. Further Requirements Related Considerations
This section of the document further addresses some concerns that
arise out of the Requirements specification in section 3.
4.1 Further considerations for capturing retargeting
The original request URI of a retargeted request SHOULD identify
the user, service or resource, which performed the retargeting, as
captured in requirement 4.2 in section 3. In some scenarios, it
might be possible for more than one instance of retargeting to
occur within the same Proxy. It is recommended that a proxy SHOULD
NOT 'internally retarget' a request to a different user, service or
resource on the same proxy, without generating Request History
information for the 'internal retargeting' as well. It should be
highlighted that an underlying requirement is to ensure that any
retargeting maintains the privacy associated with the original
Request URI. This requirement is addressed, along with additional
security specific requirements in Section 5.
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4.2 Reason for retargeting
The reason for the retargeting is only known to the application
performing the retargeting. However, it does make sense to define
a set of reasons, which will be commonly required. It is proposed
that [6] provides a reasonable starting point for the definition
for the set of reasons.
4.3 Optionality of the "Request History" capability
Requirement 2 in section 3 specifies that "Request History"
information is generated when the request is retargeted. 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. Appendix A of this document
in section 8 provides further details of these examples.
5. Security Considerations
The Request History information is being inserted by a network
element retargeting a Request, resulting in a slightly different
problem than the basic SIP header problem, thus requiring specific
consideration. In addition, there may be privacy implications
associated with some of the Request History information.
The potential security problems introduced include the following:
1) A rogue application could insert a bogus Request History entry
either by adding an additional entry as a result of retargeting or
entering invalid information.
2) A rogue application could delete an entry added by a previous
retargeting. While this may be a valid scenario for some
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applications, this may indicate a loss of integrity of the Request
History content, which could significantly impact other
applications.
3) Loss of privacy associated with forwarding a specific Request
URI in the Request History.
4) A rogue application could re-arrange the Request History
information to change the nature of the end application or to
mislead the receiver of the information.
Thus, any solution to "Request History" capability must meet the
following requirements:
1) SEC-req-1: The entity receiving the Request History must be able
to determine whether any of the previously added Request History
content has been altered.
2) SEC-req-2: The ordering of the Request History information must
be preserved at each instance of retargeting.
3) SEC-req-3: The entity receiving the Request History must be able
to determine whether a previously added Request History content has
been removed.
4) SEC-req-4: The entity receiving the information conveyed by the
Request History must be able to authenticate the source of the
information.
It is likely that the solutions to several of the requirements are
inter-related. For example, with the requirement for Chronological
ordering [Requirement 4.4 in section 3], it is likely that the
solution to SEC-req-1 would also meet SEC-req-2. Following on this,
if SEC-req-2 is met, then SEC-req-3 could make use of the
Chronological ordering to detect if information had been removed.
It should also be noted that these requirements apply to any entity
making use of the Request History information, either by
retargeting and capturing the information, or as an application
making use of the information in a Request or Response. However,
to ensure the overall integrity of this information as it traverses
the network, an additional requirement with regards to the security
of the transport is introduced:
5) SEC-req-5: To ensure the overall integrity of the chain of
Request History information, the transport must be secure.
In addition, there are general privacy requirements that MUST be
met:
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6) PRIV-req-1: The entity retargeting the Request must ensure that
it maintains the privacy (as described in [7]) associated with the
original Request URI which is retargeted.
7) PRIV-req-2: The entity receiving the Request History must
maintain the privacy associated with the information.
It is recognized that meeting the privacy requirements may impact
the functionality of this solution. The applicability guidelines
for a solution must clearly address this impact.
6. Going forward
The authors request that the SIPPING WG study this contribution and
come to consensus regarding the set of requirements necessary for a
Generic Request History mechanism. A next step is proposed to
document the analysis of the various mechanisms proposed for this
problem domain [2][3][4] and [5] and determine the extent to which
these meet the agreed requirements. Such an analysis would thus
provide suitable grounds for determining what extensions are
necessary to SIP in order to support the agreed requirements.
In addition, it is proposed that further analysis of the
requirements resulting in a solution would include the following:
1) Further analysis of the security requirements and potential
solutions. The solution to some of the security requirements
appears to be in the same problem domain as the security
requirements for the Referredby header [10] and further analysis
is required to determine if this is case and whether there is
potential for synergy in the security solutions.
2) Further scenarios, highlighting in more detail some of the
issues that will be encountered due to the optionality of the
"Request History" capability. This will enable the solution
documentation to provide more explicit guidelines on the
applicability of the solution.
7. IANA Considerations
This document does not have any implications for IANA.
References
[1] J. Rosenberg et al, "SIP: Session initiation protocol," draft-
ietf-sip-rfc2543bis-09.txt, February 27th, 2002.
[2] B. Campbell, R. Sparks, "Control of Service Context using SIP
Request-URI", RFC 3087, April 2001.
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[3] S. Levy, B. Byerly, J. Yang, "Diversion Indication in SIP",
draft-levy-sip-diversion-03.txt, November, 2001.
[4] W. Marshall et al, "SIP Extensions for Caller Identity and th Privacy", draft-ietf-sip-privacy-04.txt, February 27 , 2002.
[5] D. Oran, H. Schulzrinne, "SIP extension for tracking locations
attempted", oran-sip-visited-00.txt, August 6, 2000.
[6] H. Schulzrinne, D. Oran, G. Camarillo, "The Reason Header Field
for the Session Initiation Protocol", draft-schulzrinne-sip-reason- th 01.txt, February, 28 , 2002.
[7] J. Peterson, "SIP Privacy", draft-ietf-sip-privacy-general-
01.txt, June, 2002.
[8] R. Sparks, "The SIP Referredby Header Field", draft-ietf-sip-
referredby-00.txt, May, 2002.
Contributors
Robert Sparks contributed excellent feedback and direction for
the Security considerations section of this document. In
addition, he highlighted the importance of addressing the
optionality aspects of the "Request History" capability.
Acknowledgments
The authors would like to thank Chris Hogg for serving as the
editor for the initial (-00) version of this draft. In addition,
Sanjoy Sen provided useful comments and suggestions related to
this draft.
AuthorsÆ Addresses
Mark Watson
Nortel Networks (UK)
Maidenhead Office Park (Bray House)
Westacott Way
Maidenhead,
Berkshire Tel: +44 (0)1628-434456
England Email: mwatson@nortelnetworks.com
Mary Barnes
Nortel Networks Tel: +1 972-684-5432
Richardson, Texas Email: mbarnes@nortelnetworks.com
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Jon Peterson
NeuStar, Inc.
1800 Sutter Street, Suite 570
Concord, CA 94520 Email: Jon.Peterson@NeuStar.com
Cullen Jennings
Cisco Systems
170 West Tasman Dr Tel: +1 408 527 9132
MS: SJC-21/3 Email: fluffy@cisco.com
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8.Appendix A - Scenarios
This section highlights some scenarios under which the Request
History Capability could be applicable.
Certainly, various other solutions can be applied in some fashion
to each of these scenarios, however, the objective of this draft
has been to abstract the requirements from these scenarios towards
providing a more robust solution for each and at the same time
providing fundamental building block(s) applicable to future
applications.
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8.1 Sequentially forking with Retargetting
This scenario is as follows:
o UA 1 sends a call to proxy 1. Proxy 1 sequentially tries
several places (UA2, UA3 and UA4) before retargetting the call
to Proxy 2. Proxy 2 unfortunately tries several of the same
places (UA3 and UA4), before completing at UA5.
UA1 Proxy1 Proxy2 UA2 UA3 UA4 UA5
| | | | | | |
|--INVITE -->| | | | | |
| | | | | | |
| |--INVITE -------->| | | |
|<--100 -----| | | | | |
| |<-302 ------------| | | |
| | | | | | |
| |-------INVITE ------------>| | |
| | | | | | |
| |<-------180 ---------------| | |
|<---180 ----| | | | | |
| . . |-------INVITE------------->| | |
| | timeout | | | |
| | | | | | |
| |------INVITE ---------------------->| |
|<--100 -----| | | | | |
| |<-302 ------------------------------| |
| | | | | | |
| |-INVITE->| | | | |
| | | | | | |
| | |---INVITE ------>| | |
| | | | | | |
| | |<---180----------| | |
|<---180 --------------| | | | |
| | | | | | |
| . . | |----INVITE------>| | |
| | | timeout | | |
| | | | | | |
| | |------INVITE ------------>| |
|<--100 ---------------| | | | |
| | |<-302 --------------------| |
| | | | | | |
| | |------INVITE --------------------->|
| | | | | | |
| | |<-----200 OK---------------------->|
|<--200 OK-------------| | | | |
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| | | | | | |
|--ACK --------------------------------------------------->|
| | | | | | |
This scenario is provided to show the duplication of messaging when
there isnÆt sufficient knowledge to optimize a sequential attempt
at reaching an end user. With the "Request History" capability,
this flow could be optimized as follows:
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 --------------------------------------------------->|
| | | | | | |
8.2 Voicemail
This scenario is as follows:
o UA 1 called UA A which had been forwarded to UA B which
forwarded to a UA VM (voicemail server) which needs
information (e.g. reason the call was retargeted, original
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Request URI) to make a policy decision about what mailbox to
use, which greeting to play etc. This scenario shows that
something like the "Request History" capability must be used
for this service to function.
UA1 Proxy UA-A UA-B UA-VM
| | | | |
|--INVITE ---->| | | |
| | | | |
| |--INVITE ---->| | |
|<--100 -------| | | |
| |<-302 --------| | |
| | | | |
| |--------INVITE ------------>| |
| | | | |
| |<--------180 ---------------| |
|<---180 ------| | | |
| . . . |--------INVITE------------->| |
| | timeout | |
| | | | |
| |-------INVITE ------------------------>|
| | | | |
| |<-200 ---------------------------------|
| | | | |
|<-200---------| | | |
| | | | |
|--ACK ----------------------------------------------->|
| | | | |
| | | | |
Certainly, another valid scenario for the support of voicemail would
be that this 'policy decision' on which mailbox to use (etc.) is made
by the UA which forwarded to voicemail (UA B), or by the Proxy which
performed the forwarding on behalf of B. In this case, the UA or Proxy
can put all the information that the Voicemail server needs to
identity the correct mailbox, etc., into the Request-URI. This fits
with the SIP service paradigm where the Request-URI identifies the
resource (namely, the particular mailbox/greeting etc.) that is
required.
However, whilst this model is certainly applicable and required in
SIP, it places service intelligence away from the system providing the
key aspect of the service (the VM server).
The proposal in this draft is to rely on generic information-
providing capabilities in the UA/Proxy, allowing the Voicemail system
to provide more and better voicemail-related services without relying
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on specific capabilities in the UA/Proxy. This would allow voicemail
service providers to innovate independently of the particular UA/Proxy
that their customers are using, and its capabilities. Presently, with
the information loss problem, VM service providers, and any other
similar service providers, are limited in the services they can
provide because they do not have complete information about how the
call reached them. They rely on the UA/proxy of their customers having
the necessary capabilities to formulate a Request-URI identifying
exactly what should happen next. Finally, there is obviously a desire
to use existing voicemail platforms based on PSTN/ISDN technology
which operate according to the paradigm in this example.
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