INTERNET-DRAFT M. Barnes
Document: draft-ietf-sip-history-info-03.txt Editor
Category: Standards Track Nortel Networks
Expires: January 8, 2005 July 8, 2004
An Extension to the Session Initiation Protocol for Request History
Information
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Copyright (C) The Internet Society (2004). 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. A new priv-value, history, is
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added to the Privacy header to allow for privacy handling of the
History-Info header.
Table of Contents
1.Background: Why define a Generic "Request History" capability?.3
2. "Request History" Requirements.................................4
2.1 Security Requirements......................................6
2.2 Privacy Requirements.......................................7
3. Request History Information Description........................7
3.1 Optionality of History-Info................................8
3.2 Securing History-Info......................................8
3.3 Ensuring the Privacy of History-Info.......................9
4 Request History Information Protocol Details...................10
4.1 Protocol Structure of History-Info........................10
4.2 Protocol Examples.........................................12
4.3 Protocol usage............................................12
4.4 Security for History-Info.................................17
4.5 Example Applications using History-Info...................18
5. Application Considerations....................................22
6. Security Considerations.......................................23
7. IANA Considerations...........................................23
Normative References.............................................26
Informational References.........................................27
Appendix A Forking Scenarios....................................28
A.1 Sequentially forking (History-Info in Response)...........28
A.2 Sequential Forking (with Success).........................30
Appendix B Voicemail............................................31
Appendix C Automatic Call Distribution Example..................36
Appendix D Session via Redirect and Proxy Servers................37
Full Copyright Statement.........................................40
Overview
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 defines a new
SIP header, History-Info, to provide a standard mechanism for
capturing the request history information to enable a wide variety of
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services for networks and end users. The History-Info header
provides a building block for development of new services.
Section 1 provides additional background motivation for the Request
History capability. Section 2 identifies the requirements for a
solution, with Section 3 providing an overall description of the
solution.
Section 4 provides the details of the additions to the SIP protocol.
Example uses of the new header are included in Section 4.5, 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 [SIPSVCEX] 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, as it is not the
intent, nor is it within the scope, of this draft to prescribe a
complete solution for any of these applications.
Section 5 summarizes the application considerations identified in the
previous sections. Section 6 summarizes the security solution.
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 [RFC2119].
In order to provide a cross reference of the solution description to
the requirements without reiterating the entirety of the requirements
inline, the requirements are referenced as [REQNAME-req] following
the text or paragraph which explicitly satisfies the requirement.
1.Background: 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 [RFC3261].
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 [RFC3261] are consistent with
the use of the retarget term in this draft.
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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 application specific 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
3. Traditional telephony services such as Voicemail, call-center
"automatic call distribution", and "follow-me" style services.
Several of the aforementioned applications currently 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 the following:
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.
2. "Request History" Requirements
The following list constitutes a set of requirements for a "Request
History" capability.
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1) CAPABILITY-req: The "Request History" capability provides 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
or proxy. 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 or address modification,
5.4) Chronological ordering of the Request History information.
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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.
2.1 Security Requirements
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) 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.
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.
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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 received in either a Request or
Response.
2.2 Privacy Requirements
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 [RFC3323])
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.
In addition, local policy at a proxy may identify privacy
requirements associated with the Request URI being captured in the
Request History information.
3) PRIV-req-3: Request History information subject to privacy
requirements shall not be included in outgoing messages unless it is
protected as described in [RFC3323].
3. 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 [RFC3261].
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]
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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' is introduced 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
[RFC3261]. As described in section 16.5 of [RFC3261], it is possible
for the target of a request to be changed by the same proxy multiple
times (referred to as 'internal retargeting' in section 2), as the
proxy MAY add targets to the target set after beginning Request
Forwarding. Section 16.6 of [RFC3261] describes Request Forwarding.
It is during this process of 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].
3.1 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.
3.2 Securing History-Info
This draft defines a new header for SIP. The draft RECOMMENDs the use
of TLS as a mandatory mechanism to ensure the overall confidentiality
of the History-Info headers [SEC-req-4]. This results in History-Info
having at least the same level of security as other headers in SIP
which are inserted by intermediaries. With the level of security
provided by TLS [SEC-req-3], the information in the History-Info
header can thus be evaluated to determine if information has been
removed by evaluating the indices for gaps [SEC-req-1, SEC-req-2].
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It would be up to the application to define whether it can make use
of the information in the case of missing entries.
A more robust security solution would need to consider the aspects of
the problem that are different than the hop by hop security problem
solved by TLS, as each hop is not required to add the History-Info
header. History-Info also introduces a slightly different problem
than the basic SIP header or Identity [SIPATHID] problems, which is
focused on securing the information in the initial request end to
end. The History-Info header is being inserted by an entity as it
targets and forwards a Request, thus the requirements for the
security solution are similar to the Via and Record-Route headers.
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 for a more robust security solution for
SIP takes the form of a middle to middle and middle to end security
solution, which is addressed in a separate document [SIPIISEC]. The
use of the middle-to-end security solution discussed in [SIPIISEC]
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 would add an
additional level of security end to end, assuring the initiator of a
Request that it has indeed reached the intended recipient.
3.3 Ensuring the Privacy of History-Info
Since the History-Info header can inadvertently reveal information
about the requestor as described in [RFC3323], 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 at all, whether to capture a specific Request-URI in the
header, or whether it be included only in the Request as it is
retargeted within a specific domain. [PRIV-req-3] This is
accomplished by adding a new priv-value to the Privacy header [RFC
3323] indicating whether any or a specific History-Info header(s)
SHOULD be forwarded.
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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.
4 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.
4.1 Protocol Structure of History-Info
History-Info is a header field as defined by [RFC3261]. It is an
optional header field and MAY appear in any request or response not
associated with a dialog or which starts a dialog. For example,
History-Info MAY appear in INVITE, REGISTER, MESSAGE, REFER and
OPTIONS and any valid responses, plus NOTIFY requests which initiate
a dialog.
The History-Info header carries the following information, with the
mandatory parameters REQUIRED when the header is included a request
or response:
o Targeted-to-URI (hi-targeted-to-uri): A mandatory parameter for
capturing the Request URI for the specific Request as it is
forwarded.
o Index (hi-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 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] In addition,
applications MAY extract a variety of metrics (total number of
retargets, total number of retargets from a specific branch,
etc.) based upon the index values.
o Reason: An optional parameter for History-info, reflected in the
History-Info header by including the Reason Header [RFC3326]
escaped in the Request URI being retargeted. 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
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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.
o Privacy: An optional parameter for History-info, reflected in
the History-Info header by including the Privacy Header
[RFC3323] with a priv-value of "history" escaped in the Request
URI or by adding the Privacy header with a priv-value of
"history" to the Request. The use of the Privacy Header with a
priv-value of "history" indicates whether a specific or all
History-Info headers SHOULD NOT be forwarded.
o Extension (hi-extension): An optional parameter to allow for
future optional extensions. As per the [RFC3261], any
implementation not understanding an extension SHOULD ignore it.
The following summarizes the syntax of the History-Info header, based
upon the standard SIP syntax [RFC3261]:
History-Info = "History-Info" 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
This document adds the following entry to Table 2 of [RFC3261].
Additions to this table are also provided for extension methods
at the time of publication of this document. This is provided as a
courtesy to the reader and is not normative in any way.
Header field where proxy ACK BYE CAN INV OPT REG MSG
------------ ----- ----- --- --- --- --- --- --- ---
History-Info amdr - - - o o o o
SUB NOT REF INF UPD PRA PUB
--- --- --- --- --- --- ---
History-Info amdr - o o - - - -
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4.2 Protocol Examples
The following provides some examples of the History-Info header. Note
that the backslash, CRLF, and spacing between the fields in the
examples below are for readability purposes only.
History-Info:<sip:UserA@ims.example.com?Reason=SIP;\
cause=302;text="Moved Temporarily">; index=1; foo=bar
History-Info: <sip:UserA@ims.example.com?Reason=SIP;\
cause=302; text="Moved Temporarily">; index=1.1,
<sip:UserB@example.com?Privacy=history&Reason=SIP;cause=486;\
text="Busy Here">;index=1.2,
<sip:45432@vm.example.com>;index=1.3
4.3 Protocol usage
This section describes the processing specific to UAs and Proxies for
the History-Info header, the Histinfo option tag and the priv-value
of "history". 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.
4.3.1 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
the RECOMMENDED value of 1 in the History-Info header.
In the case where the request is routed to a redirect server and the
UAC receives a 3xx response with a Contact header, the UAC MAY
maintain the previous History-Info entry(-ies) in the request. A new
History-Info entry MAY then be added for the URI from the Contact
header (which will become the new Request-URI). In this case, the
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index is created by reading and incrementing the value of the index
from the previous history entry, thus following the same rules as
those prescribed for a proxy in retargeting, described in section
4.3.3.1.3. An example of this scenario can be found in Appendix D.
A UAC that does not want History-Info headers added due to privacy
considerations SHOULD include a Privacy header with a priv-value(s)
of "session", "header" or "history" in the request.
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. For example, the entries MAY be evaluated to
determine gaps in indices, which could indicate that an entry has
been maliciously removed or removed for privacy reasons. Either way,
an application MAY want to be notified of potentially missing
information.
4.3.2 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. For example,
the entries MAY be evaluated to determine gaps in indices, which
could indicate that an entry has been maliciously removed or removed
for privacy reasons. Either way, an application MAY want to be
notified of potentially missing 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.
4.3.3 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 [RFC3261]. Whether a proxy adds the
the History-Info header as it forwards a Request depends upon the
following considerations:
1. Whether the Request contains the Histinfo option tag in the
Supported header.
2. Whether the proxy supports the History-Info header.
3. Whether the Request contains a Privacy header with a priv-
value of "session", "header" or "history".
4. Whether any History-Info header added for a proxy/domain
should go outside that domain. An example being the use of
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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. A proxy MAY insert the
Privacy header with a priv-value of "history" to indicate
this. An example of such an application is provided in
Appendix C.
5. Whether the History-Info header is added for a specific
Request URI due to local privacy policy considerations. A
proxy MAY add the Privacy header with a priv-value of
"history" associated with the specific hi-targeted-to-uri.
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, accomplishing this by adding
a Privacy header with a priv-value of "history" to allow the
information to be collected for internal retargeting only.
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.
4.3.3.1 Adding the History-Info header to Requests
Upon evaluation of the considerations under which the History-Info
header is to be included in requests (e.g. no Privacy header
overriding inclusion, local policy supports, etc.), detailed in
section 4.3.3, a 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
(adding Via header) and 9 (adding Content-Length) 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
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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. The following subsections define the details of creating
the information associated with and in the History-Info header.
4.3.3.1.1 Privacy in the History-Info header
If the proxy's local policies, per consideration 4 in section 4.3.3,
indicate that this History-Info entry and any entries added due to
subsequent retargeting should not be forwarded beyond the domain for
which this intermediary is responsible, then a Privacy header with a
priv-value of "history" SHOULD be added to the request, if there is
not already one, provided the request is being forwarded to a
specific URI associated with the domain(s) for which this entity is
responsible.
If a request is being forwarded to a Request URI associated with a
domain for which the proxy is not responsible, the proxy needs to
determine if there are any entries to be removed prior to forwarding.
Any headers associated with the domain(s) for which this proxy is
responsible SHOULD be removed prior to forwarding.
If through local policy, there is knowledge of privacy associated
with a specific URI being captured as the hi-targeted-to-uri, a
Privacy header with a priv-value of "history" SHOULD be associated
with this specific URI as the request is forwarded, if it is being
forwarded to a Request URI associated with a domain for which the
processing entity is responsible.
If a request is being forwarded to a Request URI, for which the
processing entity is not responsible, the proxy needs to determine if
there are any entries, that need to be removed prior to forwarding.
The proxy needs to determine if any of the specific URIs that have
been captured in the History-Info entries, associated with the
domain(s) for which it is responsible, have a priv-value of
"history". Each of these header entries SHOULD be removed from the
Request prior to forwarding.
4.3.3.1.2 Reason in the History-Info header
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.
This should occur prior to the forwarding of the request, as it
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associated with the previous hi-targeted-to-uri, since it reflects
the reason why the Request to that specific URI was not successful.
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.
4.3.3.1.3 Indexing in the History-Info header
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 4.1, 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. Within each level, the number reflects the number of peer
entities to which the request has been routed. 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. It is recommended that an increment of 1 is used for
advancing to a new branch. For retargets within a proxy, the proxy
MUST maintain the current level of nesting by incrementing by 1 the
lowest/last digit of the index for each instance of retargeting, thus
reflecting the number of retargets (branches) within the proxy.
The basic rules for adding the index are summarized as follows:
1. Basic Forwarding: In the case of a Request that is being
forwarded, the index is determined by adding another level of
indexing since the depth/length of the branch is increasing. To
accomplish this, the proxy reads the value from the History-Info
header in the received request, if available, and adds another
level of indexing by appending the DOT delimiter followed by an
initial index for the new level RECOMMENDED to be 1. 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 and
forward the request.
2. Retargeting within a Proxy - 1st instance: For the first
instance of retargeting within a Proxy, the calculation of the
index follows that prescribed for basic forwarding.
3. Retargeting within a Proxy - subsequent instance: For each
subsequent retargeting of a request by the same proxy, another
branch is added. With the index for each new branch calculated by
incrementing the last/lowest digit at the current level, thus the
index in the next request forwarded by this same proxy, following
the example above, would be 1.1.2.
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4. Retargeting based upon a Response: In the case of retargeting
due to a specific response (e.g. 302), the index would be
calculated per rule 3. That is, the lowest/last digit of the index
is incremented (i.e. a new branch is created), with the increment
RECOMMENDED to be 1. For example, if the index in the History-Info
header of the received request was 1.2, then the index in the
History-Info header field for the new hi-targeted-to-URI would be
1.3.
5. Retargeting the request in parallel: If the request forwarding
is done in parallel, the index MUST be captured for each forked
request per the rules above, with each new Request having a unique
index. The only difference in the messaging for this scenario and
the messaging produced per basic proxy retargeting in rules 2 and 3
is these forwarded requests do not have History-Info entries
associated with their peers. The proxy builds the subsequent
response (or request) using the amalgamated information associated
with each of those requests and including the header entries in the
order indicated by the indexing. Section 4.5 provides an example
of a parallel request scenario, highlighting this indexing
mechanism.
4.3.3.2 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.
4.3.4 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.
4.4 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
[RFC3261]) for hop by hop security. In addition, the use of the
middle-to-end security solution discussed in [SIPIISEC] allows the
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integrity of the History-Info to be ascertained as it traverses the
intermediaries.
4.5 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 likely 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 some of the same places (e.g. UA3) based upon registered
contacts for "Bob", before completing at UA5. However, with the
History-Info, Proxy 1 determines that UA3 has already received the
invite, thus the INVITE goes directly to UA5.
Section 4.5.1 provides this same scenario using one of the privacy
mechanism, with Proxy2 adding the Privacy header indicating that the
History-Info header is not to be propagated outside P2's domain. This
scenario highlights the potential functionality lost with the use of
"history" privacy in the Privacy header for the entire request and
the need for careful consideration on the use of privacy for History-
Info.
Section 4.5.2 also provides the same scenario using one of the
privacy mechanisms, however, due to local policy at Proxy2, only one
of the Request-URIs (UA4) in the History-Info contains a priv-value
of "history", thus allowing some optimized functionality in the
routing of the request, but still maintaining privacy for specific
URIs.
Additional detailed scenarios are available in the appendix.
UA1 Proxy1 Proxy2 UA2 UA3 UA4 UA5
| | | | | | |
|--INVITE -->| | | | | |
| |-INVITE->| | | | |
Supported: Histinfo
History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>; index=2
| | | | | | |
| | |-INVITE>| | | |
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History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>;index=2,
<sip:User2@UA2.example.com>;index=2.1
| | | | | | |
| | |-----INVITE ---->| | |
History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>; index=2,
<sip:User3@UA3.example.com>; index=2.2
| | | | | | |
| | |-------INVITE------------>| |
History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>; index=2,
<sip:User4@UA4.example.com>; index=2.3
/* All Responses from the INVITEs indicate non-success/non-
availability*/
| | | | | | |
| |<-480 ---| | | | |
History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>; index=2,
<sip:User2@UA2.example.com?Reason=SIP;\
cause=480;text="RequestTimeout">;index=2.1,
<sip:User3@UA3.example.com?Reason=SIP; \
cause=487;text="Request Terminated">; index=2.2,
<sip:User4@UA4.example.com?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 a route already attempted
(e.g. UA3, thus the INVITE is only forwarded to UA5, where
the session is successfully established */
| | | | | | |
| |----------------INVITE --------------------->|
History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>; index=2,
<sip:User2@UA2.example.com?Reason=SIP;cause=480;\
text="RequestTimeout">;index=2.1,
<sip:User3@UA3.example.com?Reason=SIP;cause=487;\
text="Request Terminated">; index=2.2,
<sip:User4@UA4.example.com?Reason=SIP;cause=603;\
text="Decline">; index=2.3
<sip:User5@UA5.example.com>;index=1.1
| | | | | | |
| |<-----200 OK---------------------------------|
|<--200 OK---| | | | | |
| | | | | | |
|--ACK --------------------------------------------------->|
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4.5.1 Example with Privacy header for entire request at Proxy2
UA1 Proxy1 Proxy2 UA2 UA3 UA4 UA5
| | | | | | |
|--INVITE -->| | | | | |
| |-INVITE->| | | | |
Supported: Histinfo
History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>; index=2
| | | | | | |
| | |-INVITE>| | | |
Privacy: history
History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>;index=2,
<sip:User2@UA2.example.com>;index=2.1
| | | | | | |
| | |-----INVITE ---->| | |
Privacy: history
History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>; index=2,
<sip:User3@UA3.example.com>; index=2.2
| | | | | | |
| | |-------INVITE------------>| |
Privacy: history
History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>; index=2,
<sip:User4@UA4.example.com>; index=2.3
/* All Responses from the INVITEs indicate non-success/non-
availability and only the initial, received History-Info entries
are NOT returned to P1 due to the Privacy header value.*/
| | | | | | |
| |<-480 ---| | | | |
History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>; index=2
| | | | | | |
/* Upon receipt of the response, P1 determines another route for the
INVITE, including UA3 which was attempted by P2, but due to
Privacy P1 is not aware of this, so UA3 is re-attempted prior to
forwarding the INVITE to UA5, where the session is successfully
established */
| | | | | | |
| |--------------INVITE ----->| | |
History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>; index=2,
<sip:User3@UA3.example.com>; index=1.1
| | | | | | |
| |<-- 486 -------------------| | |
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History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>; index=2,
<sip:User3@UA3.example.com>; index=1.1
| | | | | | |
| |----------------INVITE --------------------->|
History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>; index=2,
<sip:User3@UA3.example.com?Reason=SIP;cause=486;\
text=Busy Here">;index=1.1,
<sip:User5@UA5.example.com>;index=1.2
| | | | | | |
| |<-----200 OK---------------------------------|
|<--200 OK---| | | | | |
| | | | | | |
|--ACK --------------------------------------------------->|
4.5.2 Example with Privacy header for specific URI (UA4) at Proxy2
UA1 Proxy1 Proxy2 UA2 UA3 UA4 UA5
| | | | | | |
|--INVITE -->| | | | | |
| |-INVITE->| | | | |
Supported: Histinfo
History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>; index=2
| | | | | | |
| | |-INVITE>| | | |
History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>;index=2,
<sip:User2@UA2.example.com>;index=2.1
| | | | | | |
| | |-----INVITE ---->| | |
History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>; index=2,
<sip:User3@UA3.example.com>; index=2.2
| | | | | | |
| | |-------INVITE------------>| |
History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>; index=2,
<sip:User4@UA4.example.com?\
Privacy=history>; index=2.3
/* All Responses from the INVITEs indicate non-success/non-
availability. The History-Info associated with UA4 is not returned
in the response due to the privacy header associated with that URI */
| | | | | | |
| |<-480 ---| | | | |
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History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>; index=2,
<sip:User2@UA2.example.com?Reason=SIP;\
cause=480;text="RequestTimeout">;index=2.1,
<sip:User3@UA3.example.com?Reason=SIP; \
cause=487;text="Request Terminated">; index=2.2,
| | | | | | |
/* Upon receipt of the response, P1 determines another route for the
INVITE, but finds that it matches a route already attempted
(e.g. UA3), thus the INVITE is only forwarded to UA5, where
the session is successfully established */
| | | | | | |
| |----------------INVITE --------------------->|
History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>; index=2,
<sip:User2@UA2.example.com?Reason=SIP;cause=480;\
text="RequestTimeout">;index=2.1,
<sip:User3@UA3.example.com?Reason=SIP;cause=487;\
text="Request Terminated">; index=2.2,
<sip:User5@UA5.example.com>;index=1.1
| | | | | | |
| |<-----200 OK---------------------------------|
|<--200 OK---| | | | | |
| | | | | | |
|--ACK --------------------------------------------------->|
5. Application Considerations
As seen by the example scenarios in the appendix, History-Info
provides a very flexible building block that can be used by
intermediaries and UAs for a variety of services. As such, any
services making use of History-Info must be designed with the
following considerations:
1) History-Info is optional, thus a service should define default
behavior for requests and responses not containing History-Info
headers.
2) History-Info may be impacted by privacy considerations.
Applications requiring History-Info need to be aware that if
Header, Session or History level privacy is requested by a UA (or
imposed by an intermediary) that History-Info may not be
available in a request or response. This would be addressed by
an application in the same manner as the previous consideration
by ensuring there is reasonable default behavior should the
information not be available.
3) History-Info may be impacted by local policy. 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
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specific application and any potential limitations imposed by
local policy decisions). Note, that this is related to the
optionality and privacy considerations identified in 1 and 2
above, but goes beyond that. For example, due to the optionality
and privacy considerations, an entity may receive only partial
History-Info entries; will this suffice? Note, that this would be
a limitation for debugging purposes, but might be perfectly
satisfactory for some models whereby only the information from a
specific intermediary is required.
4) The security associated with the Request History Information is
optional. Whether there is security applied to the entries
depends upon local policy. The impact of lack of having the
information compromised depends upon the nature of the specific
application (e.g. is the information something that appears on a
display or is it processed by automata which could have negative
impacts on the subsequent processing of a request?). It is
suggested that the impact of an intermediary not supporting the
security recommendations should be evaluated by the application
to ensure that the impacts have been sufficiently addressed by
the application.
6. Security Considerations
This draft provides a proposal in sections 3.2 and 4.4 for addressing
the Security requirements identified in section 2.1 by mandating the
use of TLS between entities. With TLS, History-Info headers are no
less, nor no more, secure than other SIP headers, which generally
have even more impact on the subsequent processing of SIP sessions
than the History-Info header. A more robust security solution, which
would secure headers added by proxies, SHOULD be used for History-
Info implementations once there is a solution to the requirements
identified in [SIPIISEC].
7. IANA Considerations
(Note to RFC Editor: Please fill in all occurrences of XXXX in this
section with the RFC number of this specification).
7.1 Registration of new SIP History-Info header
This document defines a new SIP header field name: History-Info 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
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----------- ------------ ---------
History-Info none [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.
7.2 Registration of "history" for SIP Privacy header
This document defines a new priv-value for the SIP Privacy header:
history
The following changes should be made to
http://www.iana.org/assignments/sip-priv-values
The following should be added to the registration for the SIP
Privacy header:
Name Description Registrant Reference
---- ----------- ---------- ---------
history Privacy requested for Mary Barnes [RFCXXXX]
History-Info header(s) mary.barnes@nortelnetworks.com
Changes since last version
Changes from the û02 to the û03 version:
o Editorial changes: Updating to the new template to reflect new
IPR guidelines, ensuring that the normative text is complete
and accurate in section 4.1, removing "Editor's Notes", etc.
o Section 4.5: Fixed error in cause (408 -> 480).
o Examples: changed the domain to "example.com", IP addresses to
the 192.0.2.0/24 range, changed occurrences of "Reason:" to
"Reason=", added use of Privacy header to examples.
o Added text to reflect WG consensus on Issue-1: Privacy
indication for History-Info entries. Proposed an extension to
the priv-values defined in RFC 3323 in abstract and section
3.3, impacting the protocol structure in section 4.1 and
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processing in 4.3.3 (and 4.3.3.1 and 4.3.3.2). In addition,
the new priv-value needs to be registered with IANA, per
section 7.
o Removed Open Issues section. For Issue-2, there was not WG
consensus to define an algorithm for bounding the number of
History-Info entries, but rather that is left as an
implementation decision.
o Updated Security discussions to reflect WG consensus that TLS
is mandatory and sufficient for general History-Info
implementation. The e2m and m2m security solutions can be
applied to History-Info when they become available to provide a
more robust SIP solution.
o Section 4.1: Added additional text to ensure that all the
information in the History-Info header is appropriately and
normatively described (in text).
o Added text in section 4.3.1 and an example to the appendices to
address the UAC having added multiple History-Info headers for
the case where the 3xx response goes back to the UAC and it's
the UAC that retargets the INVITE request.
o Clarified the addition of the Reason header in section
4.3.3.1.2.
o Further delineated the basic rules in section 4.3.3.1.3 for
calculating the index for various scenarios, as this was still
causing some confusion.
Changes from the û01 to the û02 version:
o Merged the SIPPING WG requirements draft into this document.
Note that this increments the section references in the
remainder of the document by 2 (and by 3 for Security and IANA
considerations due to new section added). Also, removed
redirect server from ISSUER-req since the solution identified
this as not being required (or desirable).
o Added an explicit privacy requirement (PRIV-req-3) for the
proxy's role in recognizing and maintaining privacy associated
with a Request-URI being captured in History-Info due to local
policy. (Note, that the text was already there, it just wasn't
highlighted as an explicit requirement).
o Clarified the use of CRLF and spacing in the example headers in
section 4.2.
o Removed the compact form for the header since unknown headers
with multiple entries would not be recognized (i.e. this may
cause parsing problems).
o Added a summary of Application Considerations to address
concerns about the optional usage of History-Info.
o Converted the references from numbers to labels to avoid the
continual problem of renumbering.
o Minor editorial changes (per NITS highlighted by Rohan and Eric
and some minor rewording for clarity).
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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.
Normative References
[RFC3261] J. Rosenberg et al, "SIP: Session initiation protocol," RFC
3261, June, 2002.
[RFC3326] H. Schulzrinne, D. Oran, G. Camarillo, "The Reason Header
Field for the Session Initiation Protocol", RFC 3326, December, 2002.
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[RFC3323] J. Peterson, "A Privacy Mechanism for the Session
Initiation Protocol (SIP)", RFC 3323, November, 2002.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[SIPIISEC] M. Barnes, "A Mechanism to Secure SIP Headers Inserted by
Intermediaries", draft-barnes-sipping-inserted-info-01.txt, October,
2003.
Informational References
[SIPSVCEX] A. Johnson, "SIP Service Examples", draft-ietf-sipping-
service-examples-05.txt, November, 2002.
[SIPATHID] J. Peterson, "Enhancements for Authenticated Identity
Management in the Session Initiation Protocol (SIP)", draft-ietf-sip-
identity-01.txt, February, 2003.
[RFC3665] A. Johnson et al, "SIP Basic Call Flow Examples", RFC 3665,
BCP 75, December, 2003.
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, Jayshree Bharatia, Jonathan Rosenberg, Eric Burger and
Martin Dolly.
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, Mark and Jon contributed to the development of the initial
requirements.
Cullen and Mark provided substantial input in the form of email
discussion in the development of the initial version of the
individual solution document.
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Cullen Jennings
Cisco Systems
170 West Tasman Dr
MS: SJC-21/3
Tel: +1 408 527 9132
Email: fluffy@cisco.com
Jon Peterson
NeuStar, Inc.
1800 Sutter Street, Suite 570
Concord, CA 94520
USA
Phone: +1 925-363-8720
EMail: Jon.Peterson@NeuStar.biz
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.
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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
third manual attempt 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.
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.]
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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-------------| | | | |
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| | | | | | |
|--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
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
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INVITE F1 UA1->Proxy
INVITE sip:UserA@example.com SIP/2.0
Via: SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@example.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 192.0.2.3
t=0 0
m=audio 49170 RTP/AVP 0
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.example.com SIP/2.0
Via: SIP/2.0/UDPims.example.com:5060;branch=1
Via: SIP/2.0/UDP here.com:5060
Record-Route: <sip:UserA@example.com>
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@example.com>
Call-Id: 12345600@here.com
CSeq: 1 INVITE
History-Info: <sip:UserA@ims.example.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 192.0.2.3
t=0 0
m=audio 49170 RTP/AVP 0
a=rtpmap:0 PCMU/8000
100 Trying F3 Proxy->UA1
SIP/2.0 100 Trying
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Via: SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@example.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.example.com:5060;branch=1
Via: SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@example.com>;tag=3
Call-Id: 12345600@here.com
CSeq: 1 INVITE
Contact: <sip:UserB@example.com>
Content-Length: 0
INVITE F5 Proxy-> UA-B
INVITE sip:UserB@example.com SIP/2.0
Via: SIP/2.0/UDP ims.example.com:5060;branch=2
Via: SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@example.com>
Call-Id: 12345600@here.com
History-Info: <sip:UserA@ims.example.com?Reason=SIP;\ cause=302;
text="Moved Temporarily">; index=1,
<sip:UserB@example.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 192.0.2.3
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
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From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@example.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@example.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@example.com SIP/2.0
Via: SIP/2.0/UDP ims.example.com:5060;branch=3
Via: SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@example.com>
Call-Id: 12345600@here.com
History-Info:<sip:UserA@ims.example.com?Reason=SIP;\ cause=302;
text="Moved Temporarily">;index=1,
<sip:UserB@example.com?Reason=SIP;cause=480;\
text="Temporarily Unavailable" >;index=2,
<sip:VM@example.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 192.0.2.3
t=0 0
m=audio 49170 RTP/AVP 0
a=rtpmap:0 PCMU/8000
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200 OK F9
SIP/2.0 200 OK UA-VM->Proxy
Via: SIP/2.0/UDP ims.example.com:5060;branch=3
Via: SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@example.com>;tag=3
Call-Id: 12345600@here.com
CSeq: 1 INVITE
Contact: TheVoiceMail <sip:VM@example.com>
Content-Type: application/sdp
Content-Length: <appropriate value>
v=0
o=UserA 2890844527 2890844527 IN IP4 vm.example.com
s=Session SDP
c=IN IP4 192.0.2.4
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.example.com:5060;branch=3
Via: SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@example.com>;tag=3
Call-Id: 12345600@here.com
CSeq: 1 INVITE
Contact: TheVoiceMail <sip:VM@example.com>
Content-Type: application/sdp
Content-Length: <appropriate value>
v=0
o=UserA 2890844527 2890844527 IN IP4 vm.example.com
s=Session SDP
c=IN IP4 192.0.2.4
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000
ACK F11 UA1-> UA-VM
ACK sip:VM@example.com SIP/2.0
Via: SIP/2.0/UDP here.com:5060
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From: BigGuy <sip:User1@here.com>
To: LittleGuy<sip:UserA@example.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
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
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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--|
| | | | |
| |<-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]
Appendix D Session via Redirect and Proxy Servers
In this scenario, Alice places a call to Bob using first a Redirect
server then a Proxy Server. The INVITE message is first sent to the
Redirect Server. The Server returns a 302 Moved Temporarily response
(F2) containing a Contact header with Bob's current SIP address.
Alice then generates a new INVITE with Bob's current SIP address
included in another History-Info entry. The INVITE is then sent to
Bob via the Proxy Server, with Bob receiving the complete History
information; the call then proceeds normally. The complete call flow
for this scenario, without the use of History-Info is described in
the SIP Basic Call Flow Examples [RFC3665].
Alice Redirect Server Proxy 3 Bob
| | | |
| INVITE F1 | | |
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|--------------->| | |
| 302 F2 | | |
|<---------------| | |
| ACK F3 | | |
|--------------->| | |
| INVITE F4 | |
|-------------------------------->| INVITE F5 |
| 100 F6 |--------------->|
Message Details
F1 INVITE Alice -> Redirect Server
INVITE sip:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bKbf9f44
Max-Forwards: 70
From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
To: Bob <sip:bob@biloxi.example.com>
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 1 INVITE
History-Info: <sip:bob@biloxi.example.com>; index=1
Contact: <sip:alice@client.atlanta.example.com>
Content-Length: 0
F2 302 Moved Temporarily Redirect Proxy -> Alice
SIP/2.0 302 Moved Temporarily
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bKbf9f44
;received=192.0.2.1
From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
To: Bob <sip:bob@biloxi.example.com>;tag=53fHlqlQ2
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 1 INVITE
History-Info: <sip:bob@biloxi.example.com>; index=1
Contact: <sip:bob@chicago.example.com;transport=tcp>
Content-Length: 0
F3 ACK Alice -> Redirect Server
ACK sip:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bKbf9f44
Max-Forwards: 70
From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
To: Bob <sip:bob@biloxi.example.com>;tag=53fHlqlQ2
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
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CSeq: 1 ACK
Content-Length: 0
F4 INVITE Alice -> Proxy 3
INVITE sip:bob@chicago.example.com SIP/2.0
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
Max-Forwards: 70
From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
To: Bob <sip:bob@biloxi.example.com>
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 2 INVITE
History-Info: <sip:bob@biloxi.example.com?Reason=SIP;cause=302>\
text="Moved Temporarily">; index=1,
<sip:bob@chicago.example.com>; index=2
Contact: <sip:alice@client.atlanta.example.com;transport=tcp>
Content-Length: 0
F5 INVITE Proxy 3 -> Bob
INVITE sip:bob@client.chicago.example.com SIP/2.0
Via: SIP/2.0/TCP ss3.chicago.example.com:5060;branch=z9hG4bK721e.1
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.1
Max-Forwards: 69
Record-Route: <sip:ss3.chicago.example.com;lr>
From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
To: Bob <sip:bob@biloxi.example.com>
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 2 INVITE
History-Info: <sip:bob@biloxi.example.com?Reason=SIP;cause=302>\
text="Moved Temporarily">; index=1,
<sip:bob@chicago.example.com>; index=2,
<sip:bob@client.chicago.example.com>; index=2.1
Contact: <sip:alice@client.atlanta.example.com;transport=tcp>
Content-Length: 0
Detailed Call Flow continues per section 6.3 in [RFC 3665].
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