Internet Draft Mary Barnes,Editor
Document: draft-ietf-sipping-req-history-01.txt Mark Watson
Nortel Networks
Cullen Jennings
Cisco
Jon Peterson
Category: Informational NeuStar
Expires June 2003 December 2002
SIP Generic Request History Capability û Requirements
Status of this Memo
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.
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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 for
recording 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. Security Considerations........................................5
5. Privacy Considerations.........................................6
6. IANA Considerations............................................6
7. References.....................................................6
8. Contributors...................................................6
9. Acknowledgments................................................7
10. Appendix A - Scenarios.........................................8
10.1 Sequentially forking with Retargeting.................8
10.2 Voicemail............................................10
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 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
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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
3. Traditional telephony services such as Voicemail, call-center
"automatic call distribution", and "follow-me" style services.
Several of the aforementioned applications define application
specific mechanisms through which it is possible to obtain the
necessary history information.
In addition, request history information could be used to enhance
basic SIP functionality by providing:
4. Some diagnostic information for debugging SIP requests.
5. A stronger security solution for SIP. A side effect is that each
proxy which captures the "request history" information in a
secure manner provides an additional means (without requiring
signed keys) for the original requestor to be assured that the
request was properly retargeted.
This draft summarizes the requirements for defining a generic
mechanism for the transport of request history information.
Example scenarios are provided in the appendix illustrating how a
SIP building block that provides request history information could
be used by some applications. It is not the intent, nor is it
within the scope, of this requirementÆs draft to prescribe a
complete solution for any of these applications.
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. It is anticipated that some of these
requirements can be met using existing elements within SIP; whether
and what SIP extensions would be needed to meet these requirements
is out of scope of this draft.
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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) OPTIONALITY-req: The "Request History" information is optional.
2.1) 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.
2.2) 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. Applicability guidelines to be
addressed by applications using this capability must be provided as
part of the solution to these requirements.
3) GENERATION-req: "Request History" information is generated when
the request is retargeted.
3.1) 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'.
3.2) 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.
4) ISSUER-req: "Request History" information can be generated by a
UA, proxy or redirect server. It can be passed in both requests and
responses.
5) CONTENT-req: The "Request History" information for each
occurrence of retargeting, shall include the following:
5.1) The new URI or address to which the request is in the
process of being retargeted,
5.2) The URI or address from which the request was retargeted,
5.3) The reason for the Request-URI modification,
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5.4) Chronological ordering of the Request History information.
6) REQUEST-VALIDITY-req: Request-History is applicable to requests
not sent within an established dialog. (i.e. INVITE, REGISTER,
MESSAGE, and OPTIONS).
7) BACKWARDS-req: Request-History information may be passed from
the generating entity backwards towards the UAC. This is needed to
enable services that inform the calling party about the dialog
establishment attempts.
8) FORWARDS-req: Request-History information may also be included
by the generating entity in the request, if it is forwarded
onwards.
4. 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. It is recognized that these security requirements
can be generalized to a basic requirement of being able to secure
information that is inserted by proxies.
The potential security problems 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) Loss of privacy associated with forwarding a specific Request
URI in the Request History.
3) 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, a security solution for "Request History" 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.
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3) SEC-req-3: The entity receiving the information conveyed by the
Request History must be able to authenticate the source of the
information.
4) SEC-req-4: To ensure the confidentiality of the Request History
information, only entities which process the request should have
visibility to the information.
It should be noted that these security 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.
5.Privacy Considerations
Since the Request URI that is captured could inadvertently reveal
information about the originator, there are general privacy
requirements that MUST be met:
1) PRIV-req-1: The entity retargeting the Request must ensure that
it maintains the network-provided privacy (as described in [2])
associated with the Request as it is retargeted.
2) 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 can impact
the functionality of this solution by overriding the request to
generate the information. The applicability guidelines for a
solution must clearly address this impact.
6.IANA Considerations
This document does not have any implications for IANA.
7.References
[1] J. Rosenberg et al, "SIP: Session initiation protocol," RFC
3261, June, 2002.
[2] J. Peterson, "A Privacy Mechanism for the Session Initiation
Protocol (SIP)", RFC 3323, November, 2002.
8. Contributors
Robert Sparks contributed excellent feedback and direction for
the Security considerations section of this document. In
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addition, he highlighted the importance of addressing the
optionality aspects of the "Request History" capability.
9. Acknowledgments
The editor would like to thank Sanjoy Sen, Ben Campbell, Rohan
Mahy and Jonathan Rosenberg for providing 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
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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must be followed, or as required to translate it into languages
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10. 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.
10.1 Sequentially forking with Retargeting
This scenario is as follows:
UA 1 sends a call to proxy 1. Proxy 1 sequentially tries several
places (UA2, UA3 and UA4) before retargeting 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 ----| | | | | |
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| . . |-------INVITE------------->| | |
| | timeout | | | |
| | | | | | |
| |------INVITE ---------------------->| |
|<--100 -----| | | | | |
| |<-302 ------------------------------| |
| | | | | | |
| |-INVITE->| | | | |
| | | | | | |
| | |---INVITE ------>| | |
| | | | | | |
| | |<---180----------| | |
|<---180 --------------| | | | |
| | | | | | |
| . . | |----INVITE------>| | |
| | | timeout | | |
| | | | | | |
| | |------INVITE ------------>| |
|<--100 ---------------| | | | |
| | |<-302 --------------------| |
| | | | | | |
| | |------INVITE --------------------->|
| | | | | | |
| | |<-----200 OK---------------------->|
|<--200 OK-------------| | | | |
| | | | | | |
|--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------------->| | |
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| | timeout | | | |
| | | | | | |
| |------INVITE ---------------------->| |
|<--100 -----| | | | | |
| |<-302 ------------------------------| |
| | | | | | |
| |-INVITE->| | | | |
| | | | | | |
| | | | | | |
| | |------INVITE --------------------->|
| | | | | | |
| | |<-----200 OK---------------------->|
|<--200 OK-------------| | | | |
| | | | | | |
|--ACK --------------------------------------------------->|
| | | | | | |
10.2 Voicemail
This scenario is as follows:
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 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 ------------------------>|
| | | | |
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| |<-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 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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