An Extension to the Session Initiation Protocol (SIP) for Request History Information
draft-ietf-sip-history-info-06
The information below is for an old version of the document that is already published as an RFC.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 4244.
|
|
|---|---|---|---|
| Author | Mary Barnes | ||
| Last updated | 2015-10-14 (Latest revision 2005-01-18) | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | (None) | |
| Document shepherd | (None) | ||
| IESG | IESG state | Became RFC 4244 (Proposed Standard) | |
| Action Holders |
(None)
|
||
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | Allison J. Mankin | ||
| Send notices to | rohan@ekabal.com |
draft-ietf-sip-history-info-06
INTERNET-DRAFT M. Barnes
Document: draft-ietf-sip-history-info-06.txt Editor
Category: Standards Track Nortel Networks
Expires: July 17th, 2005 Jan 17th, 2005
An Extension to the Session Initiation Protocol for Request History
Information
Status of this Memo
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patent or other IPR claims of which I am aware have been disclosed,
and any of which I become aware will be disclosed, in accordance with
RFC 3668.
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This Internet-Draft will expire on July 17th, 2005.
Copyright Notice
Copyright (C) The Internet Society (2005). All Rights Reserved.
Abstract
This document 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 document
defines a new optional SIP header, History-Info, for capturing the
history information in requests.
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Table of Contents
1.Background: Why define a Generic "Request History" capability?.3
2. "Request History" Requirements.................................4
2.1 Security Requirements......................................5
2.2 Privacy Requirements.......................................6
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.......................8
4 Request History Information Protocol Details....................9
4.1 Protocol Structure of History-Info.........................9
4.2 Protocol Examples.........................................11
4.3 Protocol usage............................................11
4.4 Security for History-Info.................................18
4.5 Example Applications using History-Info...................18
5. Application Considerations....................................23
6. Security Considerations.......................................24
7. IANA Considerations...........................................24
Normative References.............................................25
Informational References.........................................25
Appendix. Example Scenarios......................................27
Appendix A. Sequentially forking (History-Info in Response)......27
Appendix B. Voicemail...........................................32
Appendix C. Automatic Call Distribution Example.................38
Appendix D. Session via Redirect and Proxy Servers...............39
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 Uniform Resource
Locators (URLs) on a web page, "call history/logging" style services
within intelligent "call management" software for SIP User Agents
(UAs) and calls to voicemail servers. 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 document defines a new SIP header, History-Info, to provide a
standard mechanism for capturing the request history information to
enable a wide variety of services for networks and end users. The
History-Info header provides a building block for development of new
services.
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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.
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].
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 document to refer
to the process of a Proxy Server/User Agent Client (UAC) changing a
Uniform Resource Identifier(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 document.
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 document 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:
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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:
o Some diagnostic information for debugging SIP requests.
o 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.
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
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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.
6) REQUEST-VALIDITY-req: Request-History is applicable to requests
not sent within an established dialog. (e.g. 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
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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.
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.
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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 (e.g. INVITE, REGISTER, MESSAGE, REFER and
OPTIONS, PUBLISH and SUBSCRIBE, etc.) (REQUEST-VALIDITY-req) and any
valid response to these requests. (ISSUER-req)
The History-Info header is added to a Request when a new request is
created by a UAC or forwarded by a 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)
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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 document defines a new header for SIP. The document strongly
RECOMMENDs the use of the Transport Layer Security (TLS) protocol
[RFC2246] 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. If TLS is not
available for the connection over which the request is being
forwarded, then the request MUST not include the History-Info header
or the request MUST be redirected to the client, including the
History-Info header, so that the request can be retargeted by the
client.
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). It would be up to the application
to define whether it can make use of the information in the case of
missing entries.
3.3 Ensuring the Privacy of History-Info
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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). In the latter
case, this is accomplished by adding a new priv-value, history, to
the Privacy header [RFC 3323] indicating whether any or a specific
History-Info header(s) SHOULD be forwarded.
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 or MUST explain why it does not impact the
application.
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, OPTIONS,
SUBSCRIBE and PUBLISH and any valid responses, plus NOTIFY requests
which initiate a dialog.
This document adds the following entry to Table 2 of [RFC3261]. The
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
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SUB NOT REF INF UPD PRA PUB
--- --- --- --- --- --- ---
History-Info amdr o o o - - - o
The History-Info header carries the following information, with the
mandatory parameters required when the header is included in 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 adding
the new entries in order (i.e. following existing entries per
the details in section 4.3.3.1), 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 hi-targeted-to-uri. A reason is not included for
a hi-targeted-to-uri when it is first added in a History-info
header, but rather is added when the retargeting actually
occurs. Note, that this does appear to complicate the security
problem, however, retargeting only occurs when the hi-targeted-
to-uri indicates a domain for which the processing entity is
responsible, thus it would be the same processing entity that
initially added the hi-targeted-to-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 field values by including the Privacy
Header [RFC3323] with a priv-value of "history" escaped in the
hi-targeted-to-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.
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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
hi-entry *(COMMA hi-entry)
hi-entry = 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
4.2 Protocol Examples
The following provides some examples of the History-Info header. Note
that the backslash and CRLF between the fields in the examples below
are for readability purposes only.
History-Info:<sip:UserA@ims.example.com?Reason=SIP%3B\
cause%3D302>;index=1;foo=bar
History-Info: <sip:UserA@ims.example.com?Reason=SIP%3B \
cause%3D302>; index=1.1,
<sip:UserB@example.com?Privacy=history&Reason=SIP%3B\
cause%3D486>;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
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the Request-URI in a History-Info header in the initial request or a
proxy must add a History-Info header with both an hi-entry for the
Request-URI in the initial request and an hi-entry for the target
Request-URI as the request is forwarded. The basic processing is for
each entity forwarding a request to add an hi-entry for the target
Request-URI, updating the index and adding the Reason as appropriate
for any retargeted Request-URI.
4.3.1 User Agent Client (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 header 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 hi-entry.
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 hi-entry(s) in the request. In this case, the
reason header SHOULD be associated with the hi-targeted-to-uri in the
previous (last) hi-entry, as described in section 4.3.3.1.2. A new
hi-entry MAY then be added for the URI from the Contact header (which
becomes the new Request-URI). In this case, the index is created by
reading and incrementing the value of the index from the previous hi-
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 the History-Info header added due to privacy
considerations SHOULD include a Privacy header with a priv-value(s)
of "session", "header" or "history" in the request.
With the exception of the processing of a 3xx response described
above, the processing of the History-Info header received in the
Response is application specific and outside the scope of this
document. 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 aware of potentially
missing information.
4.3.2 User Agent Server (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
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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 aware
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
History-Info header or a new hi-entry 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
the History-Info header within the specific domain in which
it is retargeted, however, policies (for privacy, user and
network security, etc.) would prohibit the exposure of that
information outside that domain. To accommodate such a
scenario, a proxy MAY insert the Privacy header with a priv-
value of "history" when the request is being forwarded within
the same domain. An example of such an application is
provided in Appendix C.
5. Whether an hi-entry 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 each hi-
entry 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.
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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 the History-Info header(s), 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, to accommodate the considerations
outlined above, 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 an hi-entry as it forwards a
Request. Section 16.6 of [RFC3261] 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 History-Info for such
a request would result in duplicate Request-URIs with different
indices. The hi-entry MUST be added following any hi-entry received
in the request being forwarded. Additionally, if a request is
received that doesn't include a History-Info header, the proxy MAY
add a History-Info header with an hi-entry preceding the one being
added for the current request being forwarded. The index for this
hi-entry is RECOMMENDED to start at 1. The following subsections
define the details of creating the information associated with each
hi-entry.
4.3.3.1.1 Privacy in the History-Info header
If there is a Privacy header in the request with a priv-value of
"session", "header" or "history", an hi-entry MAY be added, if the
request is being forwarded to a Request URI associated with a domain
for which the processing entity is responsible (and provided local
policy supports the History-Info header, etc.). If a request is
being forwarded to a Request URI associated with a domain for which
the proxy is not responsible and there is a Privacy header in the
request with a priv-value of "session", "header" or "history", the
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proxy SHOULD remove any hi-entry(s) prior to forwarding, depending
upon local policy and whether the proxy might know a priori that it
can rely on a downstream privacy service to apply the requested
privacy.
For the scenario where there is no Privacy header in the request and
the request is being forwarded to a Request URI associated with the
domain(s) for which this entity is responsible, there are several
additional considerations:
o If there is no local policy associated with privacy, then an hi-
entry MAY be added to the Request.
o If the proxy's local policies, per consideration 4 in section
4.3.3, indicate that the History-Info header 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 associated with each hi-entry added by that
proxy in this scenario.
o If the proxy's policy per consideration 5 in section 4.3.3,
indicates that History-Info for a specific Request URI 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 associated with the specific hi-entry, for
that specific hi-targeted-to-uri, added by that proxy in this
scenario.
If a request is being forwarded to a Request URI associated with a
domain for which the proxy is not responsible and local policy
requires privacy associated with any, or with specific hi-entries it
has added, any hi-entry with a priv-value of "history" SHOULD be
removed 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, a
Reason MUST be associated with the hi-targeted-to-uri. If the SIP
response does not include a Reason header, the SIP Response Code that
triggered the retargeting MUST be included as the Reason associated
with the hi-targeted-to-uri that has been retargeted. If the
response contains a non-SIP Reason header (e.g. Q.850), it MUST be
captured as an additional Reason associated with the hi-targeted-to-
uri that has been retargeted, along with the SIP Response Code. If
the Reason header is a SIP reason, then it MUST be used as the Reason
associated with the hi-targeted-to-uri rather than the SIP response
code.
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For retargets as a result of timeouts or internal events, a Reason
MAY be associated with the hi-targeted-to-uri that has been
retargeted.
The addition of the Reason should occur prior to the forwarding of
the request (which may add a new hi-entry with a new hi-targeted-to-
uri) as it is associated with the hi-targeted-to-uri that has been
retargeted, since it reflects the reason why the Request to that
specific URI was not successful.
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). Each
dot reflects a hop or level of nesting, thus the number of hops is
determined by the total number of dots. Within each level, the
integer 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.
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 (forking): 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 aggregated information
associated with each of those requests and including the header
entries in the order indicated by the indexing. Responses are
processed as described in section 16.7 of [RFC3261] with the
aggregated History-Info entries processed similar to step 7
"Aggregate Authentication Header Field Values". 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, subject
to the following considerations for privacy:
o If the response is being forwarded to a Request URI associated
with a domain for which the proxy is not responsible and there
was a Privacy header, in the request received by the proxy, with
a priv-value of "session", "header" or "history", the proxy MUST
remove the History-Info header (i.e. all hi-entries) prior to
forwarding.
o If a request is being forwarded to a Request URI associated with
a domain for which the proxy is not responsible and local policy
requires privacy associated with any or all hi-entry(s) it has
added, any hi-entry with a priv-value of "history" MUST be
removed prior to forwarding.
o If a proxy receives a response, from another intermediary
associated with a domain for which it is responsible, including
hi-entry(s) with privacy headers and that response is to be
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forwarded to a domain for which it is not responsible, then
those hi-entry(s) MUST be removed.
The processing of History-Info in responses follows the methodology
described in section 16.7 of [RFC3261], with the processing of
History-Info headers adding an additional step, just before step 9
"Forwarding the Response".
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 3, the security requirements are met by
recommending the use of TLS (a basic SIP requirement per [RFC3261])
for hop by hop security. If TLS is not available on the connection
over which a request, containing a History-Info header, is being
forwarded, then either of the following two options MUST be
implemented:
o The History-Info header MUST be removed prior to forwarding the
request, or
o The request MUST be redirected, including the History-Info header
in the response, to allow the UAC to securely issue the request,
including the History-Info header.
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.
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Section 4.5.1 provides this same scenario using one of the privacy
mechanisms, 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=1.1
| | | | | | |
| | |-INVITE>| | | |
History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>;index=1.1,
<sip:User2@UA2.example.com>;index=1.1.1
| | | | | | |
| | |-----INVITE ---->| | |
History-Info:<sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>; index=1.1,
<sip:User3@UA3.example.com>;index=1.1.2
| | | | | | |
| | |-------INVITE------------>| |
History-Info:<sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>;index=1.1,
<sip:User4@UA4.example.com>;index=1.1.3
/* 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=1.1,
<sip:User2@UA2.example.com?Reason=SIP;\
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cause=408;text="RequestTimeout">;index=1.1.1,
<sip:User3@UA3.example.com?Reason=SIP; \
cause=487;text="Request Terminated">; index=1.1.2,
<sip:User4@UA4.example.com?Reason=SIP;\
cause=603;text="Decline">; index=1.1.3
| | | | | | |
/* 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=1.1,
<sip:User2@UA2.example.com?Reason=SIP;cause=408;\
text="RequestTimeout">;index=1.1.1,
<sip:User3@UA3.example.com?Reason=SIP;cause=487;\
text="Request Terminated">; index=1.1.2,
<sip:User4@UA4.example.com?Reason=SIP;cause=603;\
text="Decline">; index=1.1.3
<sip:User5@UA5.example.com>;index=1.2
| | | | | | |
| |<-----200 OK---------------------------------|
|<--200 OK---| | | | | |
| | | | | | |
|--ACK --------------------------------------------------->|
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=1.1
| | | | | | |
| | |-INVITE>| | | |
Privacy: history
History-Info:<sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>;index=1.1,
<sip:User2@UA2.example.com>;index=1.1.1
| | | | | | |
| | |-----INVITE ---->| | |
Privacy: history
History-Info:<sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>; index=1.1,
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<sip:User3@UA3.example.com>;index=1.1.2
| | | | | | |
| | |-------INVITE------------>| |
Privacy: history
History-Info:<sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>;index=1.1,
<sip:User4@UA4.example.com>;index=1.1.3
/* 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=1.1
| | | | | | |
/* 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=1.1,
<sip:User3@UA3.example.com>; index=1.2
| | | | | | |
| |<-- 486 -------------------| | |
History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>; index=1.1,
<sip:User3@UA3.example.com>; index=1.2
| | | | | | |
| |----------------INVITE --------------------->|
History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>; index=1.1,
<sip:User3@UA3.example.com?Reason=SIP;cause=486;\
text="Busy Here">;index=1.2,
<sip:User5@UA5.example.com>;index=1.3
| | | | | | |
| |<-----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
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| | | | | | |
|--INVITE -->| | | | | |
| |-INVITE->| | | | |
Supported: histinfo
History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>; index=1.1
| | | | | | |
| | |-INVITE>| | | |
History-Info:<sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>;index=1.1,
<sip:User2@UA2.example.com>;index=1.1.1
| | | | | | |
| | |-----INVITE ---->| | |
History-Info:<sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>;index=1.1,
<sip:User3@UA3.example.com>;index=1.1.2
| | | | | | |
| | |-------INVITE------------>| |
History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>;index=1.1,
<sip:User4@UA4.example.com?\
Privacy=history>; index=1.1.3
/* 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 ---| | | | |
History-Info: <sip:Bob@P1.example.com>;index=1,
<sip:Bob@P2.example.com>; index=1.1,
<sip:User2@UA2.example.com?Reason=SIP;\
cause=408;text="RequestTimeout">;index=1.1.1,
<sip:User3@UA3.example.com?Reason=SIP; \
cause=487;text="Request Terminated">; index=1.1.2,
| | | | | | |
/* 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=1.1,
<sip:User2@UA2.example.com?Reason=SIP;cause=408;\
text="RequestTimeout">;index=1.1.1,
<sip:User3@UA3.example.com?Reason=SIP;cause=487;\
text="Request Terminated">; index=1.1.2,
<sip:User5@UA5.example.com>;index=1.2
| | | | | | |
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| |<-----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 MUST 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
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 History-Info header requires the
use of TLS. In the case of TLS not being available for a
connection over which a request is being forwarded, the History-
Info header may be removed from a request. The impact of lack of
having the information 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.
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6. Security Considerations
The threat model and related security and privacy requirements for
the History-Info header are described in section 2.1 and 2.2 of this
document. Sections 3.2, 3.3 and 4.4 provide normative
recommendations related to security and privacy fulfilling these
requirements. The use of TLS is mandated between the entities (i.e.
UAC to Proxy, Proxy to Proxy, and Proxy to UAS) which use the
History-Info header. The appropriate handling of a request in the
case that TLS is not available for a specific connection is described
in section 5.
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.
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
----------- ------------ ---------
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.
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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
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.
[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.
[RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
Informational References
[SIPSVCEX] A. Johnson, "SIP Service Examples", draft-ietf-sipping-
service-examples-07.txt, July, 2004.
[RFC3665] A. Johnson et al, "SIP Basic Call Flow Examples", RFC 3665,
BCP 75, December, 2003.
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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,
Martin Dolly, Roland Jesske, Takuya Sawada, Sebastien Prouvost and
Sebastien Garcin.
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 security
aspects.
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.
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
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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. Example Scenarios
The scenarios in Appendix A-D provide sample use cases for the
History-Info header for informational purposes only. They are not
intended to be normative and the formatting is for visual purposes,
thus the headers in the URI are not shown properly formatted for
escaping. Refer to section 4.2 examples with the proper formatting.
Appendix A. 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.
"Alice" at UA 1sends a call to "Bob" via proxy 1. Proxy 1
sequentially tries several places (UA2, UA3 and UA4) unsuccessfully
before sending a response to "Alice".
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 document
to prescribe detailed applications.
UA1 Proxy1 UA2 UA3 UA4
| | | | |
|-INVITE F1->| | | |
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| | | | |
| |--INVITE F2------>| | |
|<--100 F3---| | | |
| |<-302 F4----------| | |
| | | | |
| |-------INVITE F5 --------->| |
| | | | |
| |<-------180 F6 ------------| |
|<---180 F7--| | | |
| . . |---retransmit INVITE ----->| |
| | | | |
| | ( timeout ) | | |
| | | | |
| |------INVITE F8 ------------------->|
|<--100 F9 --| | | |
| | | | |
| |<-486 F10 --------------------------|
| | | | |
| |-- ACK F11------------------------->|
|<--486 F12--| | | |
| | | | |
|--ACK F13-->| | | |
| | | | |
Message Details
F1 INVITE UA1 ->Proxy1
INVITE sip:UserA@example.com SIP/2.0
Via: SIP/2.0/UDP example.net:5060
From: Alice <sip:User1@example.net>
To: Bob <sip:UserA@example.com>
Call-Id: 12345600@example.net
CSeq: 1 INVITE
Contact: Alice <sip:User1@example.net>
Content-Type: application/sdp
Content-Length: <appropriate value>
v=0
o=UserA 2890844526 2890844526 IN IP4 client.example.net
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. */
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F2 INVITE Proxy1 ->UA2
INVITE sip:UserA@ims.example.com SIP/2.0
Via: SIP/2.0/UDP ims.example.com:5060;branch=1
Via: SIP/2.0/UDP example.net:5060
Record-Route: <sip:UserA@example.com>
From: Alice <sip:User1@example.net>
To: Bob <sip:UserA@example.com>
Call-Id: 12345600@example.net
CSeq: 1 INVITE
History-Info: <sip:UserA@ims.example.com>; index=1
Contact: Alice <sip:User1@example.net>
Content-Type: application/sdp
Content-Length: <appropriate value>
v=0
o=UserA 2890844526 2890844526 IN IP4 client.example.net
s=Session SDP
c=IN IP4 192.0.2.3
t=0 0
m=audio 49170 RTP/AVP 0
a=rtpmap:0 PCMU/8000
F3 100 Trying Proxy1 ->UA1
SIP/2.0 100 Trying
Via: SIP/2.0/UDP example.net:5060
From: Alice <sip:User1@example.net>
To: Bob <sip:UserA@example.com>
Call-Id: 12345600@example.net
CSeq: 1 INVITE
Content-Length: 0
F4 302 Moved Temporarily UA2 ->Proxy1
SIP/2.0 302 Moved Temporarily
Via: SIP/2.0/UDP ims.example.com:5060;branch=1
Via: SIP/2.0/UDP example.net:5060
From: Alice <sip:User1@example.net>
To: Bob <sip:UserA@example.com>;tag=3
Call-Id: 12345600@example.net
CSeq: 1 INVITE
Contact: <sip:UserB@example.com>
Content-Length: 0
F5 INVITE Proxy1 -> UA3
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INVITE sip:UserB@example.com SIP/2.0
Via: SIP/2.0/UDP ims.example.com:5060;branch=2
Via: SIP/2.0/UDP example.net:5060
From: Alice <sip:User1@example.net>
To: Bob <sip:UserA@example.com>
Call-Id: 12345600@example.net
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: Alice <sip:User1@example.net>
Content-Type: application/sdp
Content-Length: <appropriate value>
v=0
o=User1 2890844526 2890844526 IN IP4 client.example.net
s=Session SDP
c=IN IP4 192.0.2.3
t=0 0
m=audio 49170 RTP/AVP 0
a=rtpmap:0 PCMU/8000
F6 180 Ringing UA3 ->Proxy1
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP example.net:5060
From: Alice <sip:User1@example.net>
To: Bob <sip:UserA@example.com>;tag=5
Call-ID: 12345600@example.net
CSeq: 1 INVITE
Content-Length: 0
F7 180 Ringing Proxy1 -> UA1
SIP/2.0 180 Ringing
SIP/2.0/UDP example.net:5060
From: Alice <sip:User1@example.net>
To: Bob <sip:UserA@example.com>
Call-Id: 12345600@example.net
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 UA4 after adding the
additional History Information entry. */
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F8 INVITE Proxy1 -> UA4
INVITE sip:UserC@example.com SIP/2.0
Via: SIP/2.0/UDP ims.example.com:5060;branch=3
Via: SIP/2.0/UDP example.net:5060
From: Alice <sip:User1@example.net>
To: Bob <sip:UserA@example.com>
Call-Id: 12345600@example.net
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:UserC@example.com>;index=3
CSeq: 1 INVITE
Contact: Alice <sip:User1@example.net>
Content-Type: application/sdp
Content-Length: <appropriate value>
v=0
o=User1 2890844526 2890844526 IN IP4 client.example.net
s=Session SDP
c=IN IP4 192.0.2.3
t=0 0
m=audio 49170 RTP/AVP 0
a=rtpmap:0 PCMU/8000
F9 100 Trying Proxy1 ->UA1
SIP/2.0 100 Trying
Via: SIP/2.0/UDP example.net:5060
From: Alice <sip:User1@example.net>
To: Bob <sip:UserA@example.com>
Call-Id: 12345600@example.net
CSeq: 1 INVITE
Content-Length: 0
F10 486 Busy Here UA4 -> Proxy1
SIP/2.0 486 Busy Here
Via: SIP/2.0/UDP ims.example.com:5060;branch=3
Via: SIP/2.0/UDP example.net:5060
From: Alice <sip:User1@example.net>
To: Bob <sip:UserA@example.com>
Call-Id: 12345600@example.net
CSeq: 1 INVITE
Content-Length: 0
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F11 ACK Proxy1 -> UA4
ACK sip:UserC@example.com SIP/2.0
Via: SIP/2.0/UDP example.net:5060
From: Alice <sip:User1@example.net>
To: Bob <sip:UserA@example.com>
Call-Id: 12345600@example.net
CSeq: 1 ACK
Content-Length: 0
/* The proxy forwards the 486 to Alice after adding the
associated History Information entries from the series of
INVITES */
F12 486 Busy Here Proxy1 -> UA1
SIP/2.0 486 Busy Here
Via: SIP/2.0/UDP example.net:5060
From: Alice <sip:User1@example.net>
To: Bob <sip:UserA@example.com>
Call-Id: 12345600@example.net
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:UserC@example.com>;index=3
CSeq: 1 INVITE
Content-Length: 0
F13 ACK Alice -> Proxy 1
ACK sip:UserA@example.com SIP/2.0
Via: SIP/2.0/UDP example.net:5060
From: Alice <sip:User1@example.net>
To: Bob <sip:UserA@example.com>
Call-Id: 12345600@example.net
CSeq: 1 ACK
Content-Length: 0
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
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that additional information is needed 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
INVITE F1 UA1->Proxy
INVITE sip:UserA@example.com SIP/2.0
Via: SIP/2.0/UDP example.net:5060
From: BigGuy <sip:User1@example.net>
To: LittleGuy <sip:UserA@example.com>
Call-Id: 12345600@example.net
CSeq: 1 INVITE
Contact: BigGuy <sip:User1@example.net>
Content-Type: application/sdp
Content-Length: <appropriate value>
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v=0
o=UserA 2890844526 2890844526 IN IP4 client.example.net
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 example.net:5060
Record-Route: <sip:UserA@example.com>
From: BigGuy <sip:User1@example.net>
To: LittleGuy <sip:UserA@example.com>
Call-Id: 12345600@example.net
CSeq: 1 INVITE
History-Info: <sip:UserA@ims.example.com>; index=1
Contact: BigGuy <sip:User1@example.net>
Content-Type: application/sdp
Content-Length: <appropriate value>
v=0
o=UserA 2890844526 2890844526 IN IP4 client.example.net
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
Via: SIP/2.0/UDP example.net:5060
From: BigGuy <sip:User1@example.net>
To: LittleGuy <sip:UserA@example.com>
Call-Id: 12345600@example.net
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 example.net:5060
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From: BigGuy <sip:User1@example.net>
To: LittleGuy<sip:UserA@example.com>;tag=3
Call-Id: 12345600@example.net
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 example.net:5060
From: BigGuy <sip:User1@example.net>
To: LittleGuy <sip:UserA@example.com>
Call-Id: 12345600@example.net
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@example.net>
Content-Type: application/sdp
Content-Length: <appropriate value>
v=0
o=User1 2890844526 2890844526 IN IP4 client.example.net
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 example.net:5060
From: BigGuy <sip:User1@example.net>
To: LittleGuy <sip:UserA@example.com>;tag=5
Call-ID: 12345600@example.net
CSeq: 1 INVITE
Content-Length: 0
180 Ringing F7 Proxy-> UA1
SIP/2.0 180 Ringing
SIP/2.0/UDP example.net:5060
From: BigGuy <sip:User1@example.net>
To: LittleGuy <sip:UserA@example.com>
Call-Id: 12345600@example.net
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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 example.net:5060
From: BigGuy <sip:User1@example.net>
To: LittleGuy <sip:UserA@example.com>
Call-Id: 12345600@example.net
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@example.net>
Content-Type: application/sdp
Content-Length: <appropriate value>
v=0
o=User1 2890844526 2890844526 IN IP4 client.example.net
s=Session SDP
c=IN IP4 192.0.2.3
t=0 0
m=audio 49170 RTP/AVP 0
a=rtpmap:0 PCMU/8000
200 OK F9
SIP/2.0 200 OK UA-VM->Proxy
Via: SIP/2.0/UDP ims.example.com:5060;branch=3
Via: SIP/2.0/UDP example.net:5060
From: BigGuy <sip:User1@example.net>
To: LittleGuy <sip:UserA@example.com>;tag=3
Call-Id: 12345600@example.net
CSeq: 1 INVITE
Contact: TheVoiceMail <sip:VM@example.com>
Content-Type: application/sdp
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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 example.net:5060
From: BigGuy <sip:User1@example.net>
To: LittleGuy <sip:UserA@example.com>;tag=3
Call-Id: 12345600@example.net
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 example.net:5060
From: BigGuy <sip:User1@example.net>
To: LittleGuy<sip:UserA@example.com>;tag=3
Call-Id: 12345600@example.net
CSeq: 1 ACK
Content-Length: 0
/* RTP streams are established between UA1 and
UA-VM. UA-VM starts announcement for UA1 */
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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@example.com>; index=1
History-Info: <sip:ACDGRP1@example.com>; index=1.1
| | | | |
| |<-302 F3------| | |
Contact: <sip:ACDGRP2@ACD.com>
| | | | |
| |--------INVITE F4---------->| |
History-Info: <sip:Gold@example.com>; index=1
History-Info: <sip:ACDGRP1@example.com>; index=1.1
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History-Info: <sip:ACDGRP2@example.com>; index=1.2
| | | | |
| | | | |
| | | |INVITE F5>|
History-Info: <sip:Gold@example.com>; index=1
History-Info: <sip:ACDGRP1@example.com>; index=1.1
History-Info: <sip:ACDGRP2@example.com>; index=1.2
| | | | |
| | | |<-200 F6--|
| | | | |
| |<-200 F7--------------------| |
History-Info: <sip:Gold@example.com>; index=1
History-Info: <sip:ACDGRP1@example.com>; index=1.1
History-Info: <sip:ACDGRP2@example.com>; index=1.2
|<-200 F8------| | | |
< No History-Info included in the response due to Local Policy>
| | | | |
|--ACK F9--------------------------------------------->|
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
section 3.6 of the SIP Basic Call Flow Examples [RFC3665].
Alice Redirect Server Proxy 3 Bob
| | | |
| INVITE F1 | | |
|--------------->| | |
| 302 F2 | | |
|<---------------| | |
| ACK F3 | | |
|--------------->| | |
| INVITE F4 | |
|-------------------------------->| INVITE F5 |
| 100 F6 |--------------->|
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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
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>
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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].
Appendix E. Changelog
NOTE TO THE RFC-Editor: Please remove this section prior to
publication as an RFC.
Changes from the 05 to 06 version:
o General changes to tidy document:
o Change the term "this draft" to "this document".
o Spell out first use of acronyms (ex: UA, UAC, UAS, URI,
URL, TLS)
o Change Histinfo to "histinfo"
o Abstract: delete last 2 sentences in Abstract
o Overview:
o Insert paragraph break just before "This draft defined a new
SIP header..."
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o 2nd to last paragraph of Overview, delete all but first
sentence." (the other stuff on where examples would be
further documented isn't really relevant to what this draft
does and had been there for purposes of WG discussion
during development of document).
o Background: Put "retarget" in single quotes when the term is
introduced in the second sentence (consistent with reference in
section 3.
o Section 3, 2nd para, add SUBSCRIBE and PUBLISH as appropriate
methods (consistent with section 4.1)
o Section 3.2: Changed "RECOMMENDs the use of TLS" to "strongly
RECOMMENDS the use of TLS".
o Section 4.1, Privacy bullet item, clarified the first reference
of "History-Info header" as "History-Info header field values".
o Section 4.2:
oFor clarity in the examples, removed the text phrases escaped
into the URI.
oChange capitalized "Cause" to LC "cause".
o Section 6 (Security): deleted the last two paragraphs (on AIB,
Body additions, Security of Inserted Info since those are not
relevant to the security solution required for History-Info),
and restated what security mechanisms are mandatory to
implement, including references to the sections of the document
dealing with those mechanisms.
o References: Updated references: Added TLS and removed body-add,
AIB, and sec-inserted.
Changes from the 04 to 05 version:
o Section 3, 3rd paragraph: Clarified that the Proxy does not
create the requests, but rather forwards. (SP - individual email
Nov. 18)
o Section 4.3.1:
- 2nd paragraph: Added text for handling the reason, referring
to section 4.3.3.1.2 for details(JRE-individual email Nov.
15)
- last paragraph: Clarified that with the exception of 3xx
responses, handling of responses is application specific.
o Section 4.3.3.1.1, lst paragraph, last statment: changed "...the
proxy MUST remove any hi-entry(s) prior to forwarding."
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to:
"...the proxy SHOULD remove any hi-entry(s) prior to forwarding,
depending upon local policy and whether the proxy might know
apriori that it can rely on a downstream privacy service to
apply the requested privacy." (WG mailing list - conclusion
posted on Nov. 17)
o Section 4.3.3.1.2, last paragraph : a "is" has been added
between "it" and "associated" in the phrase "as it associated
with the hi-targeted-to-uri ..." (SP - individual email Nov.
18)
o Section 4.5 examples:
o Fixed indexing (2 should have been 1.1, which affects the
whole series). (WG mailing list response to TS posted on
Nov. 3rd)
o Fixed the 480 "timeouts" which should be 408s (note this
error was introduced with changes made in this section in
the 03 version. (NC-individual email Oct 31)
o Fixed missing " on the "Busy Here" on the INVITE to UA5 in
4.5.1. (NC-individual email Oct 31)
Changes from the 03 to the 04 version:
o Editorial nits:
o Removed second reference to "call center" in Overview
section. (EB)
o Changed square brackets on references to requirements to
parenthesis so they wouldn't appear to be external
references. (EB)
o Moved the updates to table 2 in section 4.1, so that it
appears right after the paragraph discussing in which
messages the header can appear. (RM)
o Section 3.2:
o Moved discussion of new security solution proposals per
updated identity draft and rohan's body addition to section
6 as they're not relevant to the solution in this document
(per (JRE-1)).
o Per IETF-60 discussion and Rohan's input, added a statement
that if TLS isn't available on the connection over which
the History-info is being forwarded, either a redirection
(per identity document) is required or the History-info is
not forwarded.
o Section 3.3:
o 2nd paragraph: adding clarification text "In the latter
case,.." to the last sentence. (JRE-2)
o Last paragraph: Clarified in the last sentence that if there
is no impact on the application due to privacy
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considerations, why that is so MUST also be explained by
that application. (EB)
o Section 4.1:
o Added SUBSCRIBE and PUBLISH to the list of messages in which
History-Info header may appear. (JRE-3/10)
o Changed the wording in the text descriptions of the fields
to be non-normative (i.e. not caps for the reserved words
in RFC 2119). (KD)
o In the text description for the Index, clarified that the
entries are added in a specific order, with the indexing to
ensure the proper ordering. (JRE-4)
o In the text descriptions for the Reason and Privacy
parameters, changed the references of "Request URI" to "hi-
targeted-to-uri" to explicitly refer to the field in the
header entry. (JRE-5)
o In the ABNF syntax, changed the "hist-info" field name to
"hi-entry". This is then used throughout the remainder of
the document to refer to a "History-Info header entry".
(Note, this impacted the text primarily in section 4.3 -
specifically )(JRE-8/9)
o Section 4.2: Added appropriate hex characters for the escaped
headers in the example (e.g. for ", = and ;). (LIST 10/15)
o Section 4.3.1: changed "notified" to "aware" in terms of
application interface to be less specific about interface to
application (consistent with 4.3.2)
o Section 4.3.2: same change as in 4.3.1. Capitalized "should" in
last sentence. (EB)
o Section 4.3.3: Clarified item 4 to be specific that the privacy
header may be used when the request is being forwarded within
the same domain (accomodating the scenario which allows
information to only be forwarded within the domain in which it
was retargeted). (JRE-11)
o Section 4.3.3.1: rewording to include explicit references to hi-
entry [JRE-8/9] and changed the "header should be added
following..." to "the hi-entry MUST be added following..." (JRE-
4)
o Section 4.3.3.1.1: Reworded privacy section for clarity.
Basically, need to tag each of the entires with
"privacy=history" for retargeting within the domain and strip
out the entries when leaving the domain IF the request has a
privacy header of Session, Header or History or local policy
requires. (JRE-13)
o Section 4.3.3.1.2: Added the use of a Reason header in a
response, as the Reason field associated with a retargeted URI.
(LIST-10/5)
o Section 4.3.3.1.3:
o Clarified that the number of hops is reflected by the total
number of dots (and not the value of the digits) (JRE-14.1)
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o Deleted last sentence of 1st paragraph as that was a
holdover from a previous version. (JRE-14.2)
o Item 5: clarified that the referenced scenario is forking
and that the response consists of the aggregated (rather
than the word "amalgamated") information. (JRE-15)
o Section 4.3.3.2:
o Clarified that response processing for History-Info follows
the general processing described in section 16.7 of
RFC3261. (related to JRE-15)
o More detail added on the processing of responses with
Privacy header. (LIST-8/18)
o Section 4.4: Added text addressing the security when TLS is not
available, per Rohan's comment above.
o Section 5:
o Changed the "should" to a "MUST" in the 1st application
consideration in terms of the requirement to define default
behavior should the information not be available, due to
History-Info being an optional header. (EB)
o Updated the 5th consideration for security to reflect the
lack of information due to potential TLS inavailability for
a connection, thus the potential for no History-Info header
(per Rohan's comment).
oSection 6:
o Updated security considerations per TLS issue (Rohan) and to
reference the new security solution proposals.
o Added discussion of new security solution proposals per
updated identity document and rohan's body addition.
oAppendix:
o Added overview clarifying that flows are informational and
not normative.
o Changed domains to appropriate example.com and example.net
ones.
o A.1 Added message details
o A.2 Removed as this is redundant since this example is what
is now in section 4.2.
Changes from the 02 to the 03 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
processing in 4.3.3 (and 4.3.3.1 and 4.3.3.2). In addition,
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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 01 to the 02 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 00 to the 01 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
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.
Added section 2.3.4 to address Redirect Server behavior.
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