Network Working Group M. Barnes
Internet-Draft F. Audet
Obsoletes: RFC4244 Nortel
(if approved) June 4, 2009
Intended status: Standards Track
Expires: December 6, 2009
An Extension to the Session Initiation Protocol (SIP) for Request
History Information
draft-barnes-sipcore-rfc4244bis-00.txt
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Abstract
This document defines a standard mechanism for capturing the history
information associated with a Session Initiation Protocol (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. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Conventions and Terminology . . . . . . . . . . . . . . . 4
1.3. Background: Why define a Generic Request History
Header? . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Request History Requirements . . . . . . . . . . . . . . . . . 6
2.1. Security Requirements . . . . . . . . . . . . . . . . . . 7
2.2. Privacy Requirements . . . . . . . . . . . . . . . . . . . 8
3. Request History Information Description . . . . . . . . . . . 9
3.1. Optionality of History-Info . . . . . . . . . . . . . . . 10
3.2. Ensuring the Privacy of History-Info . . . . . . . . . . . 10
4. Request History Information Protocol Details . . . . . . . . . 10
4.1. Protocol Structure of History-Info . . . . . . . . . . . . 11
4.2. Protocol examples . . . . . . . . . . . . . . . . . . . . 13
4.3. Protocol Usage . . . . . . . . . . . . . . . . . . . . . . 14
4.3.1. User Agent Client (UAC) Behavior . . . . . . . . . . . 14
4.3.2. User Agent Server (UAS) Behavior . . . . . . . . . . . 15
4.3.3. Proxy Behavior . . . . . . . . . . . . . . . . . . . . 15
4.3.4. Redirect Server Behavior . . . . . . . . . . . . . . . 20
4.4. Example Call Flows with History-Info Header . . . . . . . 20
4.4.1. Basic Call with History-Info . . . . . . . . . . . . . 20
4.4.2. History-Info with Privacy Header . . . . . . . . . . . 21
4.4.3. Privacy Header for a Specific History-Info Entry . . . 23
5. Application Considerations . . . . . . . . . . . . . . . . . . 24
6. Security Considerations . . . . . . . . . . . . . . . . . . . 25
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
7.1. Registration of New SIP History-Info Header . . . . . . . 26
7.2. Registration of "history" for SIP Privacy Header . . . . . 27
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 27
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 27
10. Changes since last Version . . . . . . . . . . . . . . . . . . 27
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
11.1. Normative References . . . . . . . . . . . . . . . . . . . 29
11.2. Informative References . . . . . . . . . . . . . . . . . . 29
Appendix A. Detailed call flows . . . . . . . . . . . . . . . . . 30
A.1. Sequentially Forking (History-Info in Response) . . . . . 30
A.2. Voicemail . . . . . . . . . . . . . . . . . . . . . . . . 37
A.3. Automatic Call Distribution . . . . . . . . . . . . . . . 39
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 41
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1. Introduction
1.1. 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. Although 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 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.
1.2. Conventions and Terminology
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 [RFC2119].
The term "retarget" is used 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 based on a lookup in a location service
and thus changing the target of the request.
The term "forward" is used consistent with the terminology in
[RFC3261]. However, it should be noted that uses the term
"forwarding" to describe a proxy's handling of requests for domains
for which is not responsible, as well as to describe the basic
"forwarding" of a request (in section 16.6) once a target has been
determined, whether it's a "retargeted", "redirected" or "forwarded"
request. Thus, the usage of "forward" in this document, other than
in reference to the usage in section 16.6 of [RFC3261], refers to the
request being forwarded to a next hop proxy.
The terms "location service" and "redirect" are used consistent with
the terminology in [RFC3261].
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1.3. Background: Why define a Generic Request History Header?
SIP implicitly provides retargeting, redirection and forwarding
capabilities that enable calls to be routed to specific applications
as defined in [RFC3261]. The term 'retarget' is used 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 based
on a lookup in a location service and thus changing the target of the
request. The target(s) for a user can be created through
registration or other means, which are outside the scope of this
document and [RFC3261]. The rules for determining request targets as
described in Section 16.5 of [RFC3261].
The motivation for capturing the request history is that in the
process of retargeting and forwarding a request, 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. This document defines a mechanism for transporting
the request history. It does not define 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 that 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,:
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o Some diagnostic information for debugging SIP requests. (Note
that the diagnostic utility of this mechanism is limited by the
fact that its use by entities that retarget is optional.)
o Capturing aliases and Globally Routable User Agent URIs (GRUUs)
[I-D.ietf-sip-gruu], which can be overwritten by a home proxy upon
receipt of the initial request.
o Facilitating the use of limited use addresses (minted on demand)
and sub-addressing.
o Preserving service specific URIs that can be overwritten by a
downstream proxy, such as those defined in [RFC3087], and control
of network announcements and IVR with SIP URI [RFC4240].
o A stronger security solution for SIP. A side effect is that each
proxy that 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. Although
this is inherently provided when the retarget is in response to a
SIP redirect, it is deemed useful for non-redirect retargeting
scenarios, as well.
2. GENERATION-req: "Request History" information is generated when
the request is retargeted or forwarded (to a next hop proxy).
A. 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'.
B. 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.
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3. ISSUER-req: "Request History" information can be generated by a
UA or proxy. It can be passed in both requests and responses.
4. CONTENT-req: The "Request History" information for each
occurrence of retargeting or forwarding shall include the
following:
A. The new URI or address to which the request is in the process
of being retargeted or forwarded,
B. The URI or address from which the request was retargeted or
forwarded,
C. An indication as to whether the request was retargeted versus
forwarded,
D. The reason for the Request-URI or address modification,
E. Chronological ordering of the Request History information.
5. REQUEST-VALIDITY-req: Request History is applicable to requests
not sent within an established dialog (e.g., INVITE, REGISTER,
MESSAGE, and OPTIONS).
6. BACKWARDS-req: Request History information may be passed from the
generating entity backwards towards the UAC. This is needed to
enable services that inform the calling party about the dialog
establishment attempts.
7. FORWARDS-req: Request History information may also be included by
the generating entity in the request, if it is forwarded onwards.
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.
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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.
3. A rogue application could delete some or all of the Request
History 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 entity providing
the request.
4. SEC-req-4: To ensure the confidentiality of the Request History
information, only entities that 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 or
forwarded.
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.
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3. PRIV-req-3: Request History information subject to privacy shall
not be included in ougoing messages unless it is protected as
described in [RFC3323] (i.e., anonymized).
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" refers 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).
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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 send by a UAC to indicate whether the
History-Info header should be returned in Responses (BACKWARDS-req).
In addition to the "histinfo" Supported header, local policy
determines whether or not the header added to any request is
anonymized (as per [RFC3323]).
3.2. 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 as is, whether it be included only in the Request as it is
retargeted within a specific domain, or whether it is anonymized when
being retargeted outside a specific domain (PRIV-req-3). The latter
two cases can be accomplished with a new priv-value, history, added
to the Privacy header [RFC3323]. The details as to the use of the
new priv-value with the Privacy header are provided in section
Section 4.
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.
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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
that initiate a dialog.
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
in the same situations in which the retarget parameter is added.
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 latter case indicates that the
History-Info headers SHOULD be anonymized prior to forwarding or
they SHOULD NOT be forwarded, whereas the use of the Privacy
header escaped in the hi-targeted-to-uri means that a specific hi-
entry SHOULD be anonymized or it SHOULD NOT be forwarded. It is
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RECOMMENDED that the entries be anonymized, rather than not
forwarded, to minimize the impact on applications making use of
the History-Info header.
o Target (hi-target): A mandatory parameter for the History-Info
indicating the reason for the new target, based on the procedures
of 16.5/[RFC3261]. Note that hi-target is not added for a hi-
entry when it is first added in a History-Info header field, but
rather is added when the retargeting actually occurs - i.e., the
parameter indicates that the specific hi-targeted-to-uri was
retargeted and thus the previous information in the request-URI is
"lost". Note that 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
adding the retarget parameter. Upon receipt of a request or
response containing the History-Info header, a UA can determine
the "lost" target for a specific request by traversing the HI
entries in reverse order to find the first one tagged with the
retarget parameter. The following values are defined:
* "noop": There is no change whatsoever in the target. The
Request-URI is unchanged. This would apply for example when a
proxy merely forwards a request to a next hop proxy and loose
routing is used.
* "predetermined": This is the case where retargeting is
predetermined by the content of the request itself, i.e., the
Request-URI contained a maddr, the domain of the Request-URI
indicates a domain the proxy is not responsible for, or strict
routing is used and the request is forwarded to another proxy.
* "reg-uri": The Request-URI is replaced with a registered
Contact bound to the AOR indicated by the Request-URI. For
example, if the REGISTER message had a To header field with the
AOR <sip:bob@example.com>, and a Contact header field of
<sip:bob@192.168.0.3> , the Request-URI <sip:bob@example.com>
would be changed to <sip:bob@192.168.0.3>.
* "reg-uri-alias": The Request-URI is replaced with a registered
Contact bound to an AOR that is an alias of the Request-URI.
An AOR is an Alias of another AOR if both entities belong to
the same implicit registration set, are linked to the same
profile and have the same data configured. For example, if
<sip:+14085551212@example.com;user=phone> and
<sip:bob.smith@example.com> are configured as aliases for the
AOR sip:bob@example.com> (where the registered Contact of
<sip:bob@192.168.0.3> is bound to <sip:bob@example.com>, a
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Request-URI of <sip:bob.smith@example.com> or
<sip:+14085551212@example.com;user=phone> would be changed to
<sip:bob@192.168.0.3>.
* "mapped": The Request-URI is replaced with another URI that is
not a Contact associated with the AOR in the Request-URI or one
of its aliases. For example, this would apply when the request
is retargeted to a different user.
*
OPEN ISSUE: The values for hi-target are tentative and are
still behing debated. They will be changed to reflect the
consensus so that it is meaningful to the applications such
as those described in
[I-D.rosenberg-sip-target-uri-delivery] and is unambigous
with regards to SIP terminology in [RFC3261]. For example,
it has been suggested that "noop" and "predetermined" be
combined into a single value.
o Extension (hi-extension): An optional parameter to allow for
future optional extensions. As per [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-index *(SEMI hi-target)
*( SEMI hi-extension )
hi-targeted-to-uri = name-addr
hi-index = "index" EQUAL 1*DIGIT *("." 1*DIGIT)
hi-target = "noop" / "predetermined" / "reg-uri"
/ "reg-uri-alias" / "mapped"
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.
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History-Info: <sip:UserA@ims.example.com>;index=1;foo=bar
History-Info: <sip:UserA@ims.example.com?Reason=SIP%3B\
cause%3D302>;index=1.1;mapped,\
<sip:UserB@example.com?Privacy=history&Reason=SIP%3B\
cause%3D486>;index=1.2;mapped,\
<sip:45432@192.168.0.3>;index=1.3;reg-uri
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 1.3, 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 a History-Info header in the
initial request or a proxy must add a History-Info header with both a
hi-entry for the Request-URI in the initial request and a hi-entry
for the target Request-URI as the request is forwarded. The basic
processing is for each entity forwarding a request to add a hi-entry
for the target Request-URI, updating the index and adding the Reason
and Retarget parameters as appropriate for any retargeted Request-
URIs.
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 MAY add a History-Info header, using the Request-
URI of the request as the hi-target-to-uri, in which case the index
MUST be set to a value of 1 in the hi-entry. As a result,
intermediaries and the UAS will know at least the original Request-
URI, and if the Request-URI was modified by a previous hop.
Normally, UACs are not expected to include a History-Info header in
an initial request as it is more of a Proxy function; the reason it
is allowed is for B2BUAs who are performing proxy-like functions like
routing.
In the case where a UAC receives a 3xx response with a Contact
header, the UAC SHOULD maintain the previous hi-entry(s) in the
request. The previous (last) hi-entry in the response SHOULD have a
an hi-target parameter which had been added by the entity that
returned the 3xx response, if the entity has implemented this
specification. If there is no hi-target parameter in the previous
hi-entry, the UAC MUST NOT add an hi-target parameter to the hi-
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entry.
In either case, a new hi-entry MUST 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.
A UAC that does not want the History-Info header added due to privacy
considerations MUST 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 can 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 information in the History-Info header by a UAS
in a Request depends upon local policy and specific applications at
the UAS that 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 MUST
include any History-Info received in the request in the subsequent
response.
4.3.3. Proxy Behavior
4.3.3.1. Adding the History-Info Header to Requests
A proxy conforming to this specification MUST add a 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
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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 results in duplicate Request-URIs
with different indices, and with hi-target set to "noop." 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 a hi-entry preceding the one being added for the current
request being forwarded. The index for this hi-entry is MUST 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", a hi-entry SHOULD 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
proxy MAY anonymize hi-entry(s) as per [RFC3323] 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.
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
anonymized 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
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code.
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 syntax 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. For each level of
indexing, the index MUST start at 1. An increment of 1 MUST be 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 of 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, the
index in the next request forwarded by this same proxy, following
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the example above, would be 1.1.2.
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
of 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".
4.3.3.1.4. Request Target in the History-Info Header
An hi-target attribute MUST be included in a request forwarded by a
proxy. The addition of the hi-target parameter MUST 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.
If the incoming request already contains a History-Info header field,
and the hi-targeted-to-uri in the last hi-entry is identical to the
Request-URI of the received request, the proxy MUST add a hi-target
attribute with value "noop" to that hi-entry. In the case that the
request did not contain a History-Info header, or if the last hi-
entry is not identical to the Request-URI of the received request,
the proxy MUST add another History-Info header field value as
described in Section 4.3.3.1 and MUST add a hi-target attribute to
this hi-entry.
If the Request-URI itself predetermined the routing as per the
procedures of 16.5/[RFC3261], i.e., if there was a maddr parameter,
or if the domain indicates a domain that the proxy is not responsible
for, or strict routing is used and the request is forwarded to
another proxy, the hi-target attribute MUST be set to
"predetermined."
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If the Request-URI is being replaced with a registered Contact
header, bound to the AOR indicated by the Request-URI, the hi-target
attribute MUST be set to "reg-uri."
If the Request-URI is replaced with a registered Contact bound to an
AOR that is an alias of the Request-URI, the hi-target attribute MUST
be set to "reg-uri-alias."
If the request is being forwarded based on the receipt of a 3xx
response with a Contact header and the previous (last) hi-entry
already has an hi-target parameter, then another hi-target attribute
MUST not be added to the hi-entry. This would occur in the case of a
redirect server that has implemented this specification.
In all other cases, the Request-URI is replaced with another URI that
is not a Contact associated with the AOR in the Request-URI or one of
its aliases. In this case, the hi-target attribute MUST be set to
"mapped."
The index is set as defined in Section 4.3.3.1.3.
Once the proxy has translated the Request-URI into a contact URI
based on a location service lookup, it MUST add an additional hi-
entry containing the Contact URI for each request to be forwarded as
described in Section 4.3.3.1. The hi-target attribute MUST NOT be
added to this hi-entry.
4.3.3.2. Sending History-Info in Responses
A proxy that receives a Request with the "histinfo" option tag SHOULD
return captured History-Info in subsequent, non-100 provisional, and
final responses to the Request. The proxy MUST add the reason to the
last hi-entry received in the request to the last hi-entry in the
response. For non-3XXresponses, the proxy MUST NOT add a hi-target
attribute to the last hi-entry received in the request to the last
hi-entry in the response. For 3XX response, the proxy MUST add the
hi-target attribute to the last hi-entry received in the request to
the last hi-entry in the response per the rules defined in
Section 4.3.3.1.4.
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".
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4.3.4. Redirect Server Behavior
A redirect server SHOULD include the History-Info headers received in
the request in the 3XX response. The redirect server MUST also add
the appropriate hi-target attribute to the last hi-entry received in
the request to the last hi-entry in the response per the rules
defined in Section 4.3.3.1.4.
4.4. Example Call Flows with History-Info Header
This section contains some basic call examples using the History-Info
header, including the use of privacy and the hi-target attribute.
All the examples in this section are using loose routing procedures.
If strict routing procedures were used, instead of entries with hi-
target set to "noop", there would be entries with hi-target set to
"predetermined" instead.
The formatting in these scenarios is for visual purposes; thus,
backslash and CRLF are used between the fields for readability and
the headers in the URI are not shown properly formatted for escaping.
Refer to Section 4.2 for the proper formatting. Additional detailed
scenarios are available in the Appendix A.
4.4.1. Basic Call with History-Info
In this example, Alice (sip:alice@atlanta.example.com) calls Bob
(sip:bob@biloxi.example.com). Alice's home proxy (sip:
atlanta.example.com) forwards the request to Bob's proxy (sip:
biloxi.example.com). When the request arrives at sip:
biloxi.example.com, it does a location service lookup for
bob@biloxi.example.com and changes the target of the request to Bob's
Contact URI provided as part of normal SIP registration.
One important thing illustrated by this call flow is that without
History-Info, Bob would "lose" the target information, including any
parameters in the request URI. Bob can now recover that information
by looking for the last hi-entry marked as "reg-uri" or "reg-uri-
alias" hi-target.
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Alice atlanta.example.com biloxi.example.com Bob
| | | |
| INVITE sip:bob@biloxi.example.com;p=x |
|--------------->| | |
| Supported: histinfo | |
| | | |
| | INVITE sip:bob@biloxi.example.com;p=x
| |--------------->| |
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1;noop
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1.1
| | | |
| | | INVITE sip:bob@192.0.2.3
| | |--------------->|
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1;noop
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1.1;reg-uri
| History-Info: <sip:bob@192.0.2.3>;index=1.1.1
| | | |
| | | 200 |
| | |<---------------|
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1;noop
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1.1;reg-uri
| History-Info: <sip:bob@192.0.2.3>;index=1.1.1
| | | |
| | 200 | |
| |<---------------| |
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1;noop
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1.1;reg-uri
| History-Info: <sip:bob@192.0.2.3>;index=1.1.1
| | | |
| 200 | | |
|<---------------| | |
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1;noop
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1.1;reg-uri
| History-Info: <sip:bob@192.0.2.3;index=1.1.1
| | | |
| ACK | | |
|--------------->| ACK | |
| |--------------->| ACK |
| | |--------------->|
Figure 1: Basic Call
4.4.2. History-Info with Privacy Header
The next example provides the basic call scenario Section 4.4.1 using
one of the privacy mechanisms, with sip:biloxi.example.com adding the
Privacy header indicating that the History-Info header information is
anonymized outside the biloxi.example.com domain. This scenario
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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.
Alice atlanta.example.com biloxi.example.com Bob
| | | |
| INVITE sip:bob@biloxi.example.com;p=x |
|--------------->| | |
| Supported: histinfo | |
| | | |
| | INVITE sip:bob@biloxi.example.com;p=x
| |--------------->| |
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1;noop
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1.1
| | | |
| | | INVITE sip:bob@192.0.2.3
| | |--------------->|
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1;noop
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1.1;reg-uri
| History-Info: <sip:bob@192.0.2.3>;index=1.1.1
| | | |
| | | 200 |
| | |<---------------|
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1;noop
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1.1;reg-uri
| History-Info: <sip:bob@192.0.2.3>;index=1.1.1
| | | |
| | 200 | |
| |<---------------| |
| History-Info: <sip:anonymous@anonymous.invalid>;index=1;noop
| History-Info: <sip:anonymous@anonymous.invalid>;index=1.1;reg-uri
| History-Info: <sip:anonymous@anonymous.invalid>;index=1.1.1
| | | |
| 200 | | |
|<---------------| | |
| History-Info: <sip:anonymous@anonymous.invalid>;index=1;noop
| History-Info: <sip:anonymous@anonymous.invalid>;index=1.1;reg-uri
| History-Info: <sip:anonymous@anonymous.invalid>;index=1.1.1
| | | |
| ACK | | |
|--------------->| ACK | |
| |--------------->| ACK |
| | |--------------->|
Figure 2: Example with Privacy Header
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4.4.3. Privacy Header for a Specific History-Info Entry
This example also provides the basic call scenario Section 4.4.1
using one of the privacy mechanisms, however, due to local policy at
sip:biloxi.example.com, only the final hi-entry in the History-Info,
which is Bob's local URI, contains a priv-value of "history", thus
providing Alice with some information about the history of the
request, but anonymizing Bob's local URI.
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Alice atlanta.example.com biloxi.example.com Bob
| | | |
| INVITE sip:bob@biloxi.example.com;p=x |
|--------------->| | |
| Supported: histinfo | |
| | | |
| | INVITE sip:bob@biloxi.example.com;p=x
| |--------------->| |
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1;noop
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1.1
| | | |
| | | INVITE sip:bob@192.0.2.3
| | |--------------->|
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1;noop
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1.1;reg-uri
| History-Info: <sip:bob@192.0.2.3?Privacy=history>;index=1.1.1
| | | |
| | | 200 |
| | |<---------------|
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1;noop
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1.1;reg-uri
| History-Info: <sip:bob@192.0.2.3?Privacy=history>;index=1.1.1
| | | |
| | 200 | |
| |<---------------| |
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1;noop
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1.1;reg-uri
| History-Info: <sip:anonymous@anynymous.invalid>;index=1.1.1
| | | |
| 200 | | |
|<---------------| | |
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1;noop
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1.1;reg-uri
| History-Info: <sip:anonymous@anynymous.invalid>;index=1.1.1
| | | |
| ACK | | |
|--------------->| ACK | |
| |--------------->| ACK |
| | |--------------->|
Figure 3: Example with Privacy Header for Specific URI
5. Application Considerations
As seen by the example scenarios in the Appendix A, History-Info
provides a very flexible building block that can be used by
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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.
6. Security Considerations
This document defines a new header for SIP. The use of the Transport
Layer Security (TLS) protocol [RFC5246] as a mechanism to ensure the
overall confidentiality of the History-Info headers (SEC- req-4) is
strongly RECOMMENDED. This results in History-Info having at least
the same level of security as other headers in SIP that are inserted
by intermediaries. 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.
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
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to define whether it can make use of the information in the case of
missing entries.
Note that while using the SIPS scheme (as per [I-D.ietf-sip-sips])
protects History-Info from tampering by arbitrary parties outside the
SIP message path, all the intermediaries on the path are trusted
implicitly. A malicious intermediary could arbitrarily delete,
rewrite, or modify History- Info. This specification does not
attempt to prevent or detect attacks by malicious intermediaries.
7. IANA Considerations
This document requires several IANA registrations detailed in the
following sections.
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 have been made to
http:///www.iana.org/assignments/sip-parameters The following row has
been added to the header field section:
Header Name Compact Form Reference
----------- ------------ ---------
History-Info none [RFCXXXX]
The following has been added to the Options Tags section:
Name Description Reference
---- ----------- ---------
histinfo When used with the Supported header, [RFCXXXX]
this option tag indicates the UAC
supports 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.
Note to RFC Editor: Please replace RFC XXXX with the RFC number of
this specification.
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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 have been made to
http://www.iana.org/assignments/sip-priv-values The following has
been 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@nortel.com
Note to RFC Editor: Please replace RFC XXXX with the RFC number of
this specification.
8. Contributors
Cullen Jennings, Mark Watson, and Jon Peterson contributed to the
development of the initial requirements for [RFC4244].
Jonathan Rosenberg produced the initial document that provided the
basis for the addition of the "target" parameter to the History-Info
header, as well as some content for this document.
9. Acknowledgements
The editor would like to acknowledge the constructive feedback
provided by Robert Sparks, Paul Kyzivat, Scott Orton, John Elwell,
Nir Chen, 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 in the development of [RFC4244]. The editor would like to
acknowledge the significant input from Rohan Mahy on some of the
normative aspects of the ABNF for [RFC4244], particularly around the
need for and format of the index and around the security aspects.
Many thanks to Hans Eric Van Elburg, Christer Holmberg and Shida
Shubert for the help on this update to [RFC4244], especially
regarding the requirements for preserving target-URI information all
the way to the UAS. Thanks to Ian Elz for his feedback on privacy.
10. Changes since last Version
NOTE TO THE RFC-Editor: Please remove this section prior to
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publication as an RFC.
Changes from RFC4244 to individual -00:
1. Clarified that HI captures both retargeting as well as cases of
just forwarding a request.
2. Added descriptions of the usage of the terms "retarget",
"forward" and "redirect" to the terminology section.
3. Added additional examples for the functionality provided by HI
for core SIP.
4. Added hi-target parameter values to HI header to ABNF and
protocol description, as well as defining proxy, UAC and UAS
behavior for the parameter.
5. Simplified example call flow in section 4.5. Moved previous
call flow to appendix.
6. Fixed ABNF per RFC4244 errata "dot" -> "." and added new
parameter.
7. Fixed all the examples. Made sure loose routing was used in all
of them.
8. Removed example where a proxy using strict routing is using
History-Info for avoiding trying same route twice.
9. Remove redundant Redirect Server example.
10. Index are now mandated to start at "1" instead of recommended.
11. Clarified 3xx behavior as the entity sending the 3XX response
MUST add the hi-target attribute to the previous hi-entry to
ensure that it is appropriately tagged (i.e., it's the only one
that knows how the contact in the 3xx was determined.)
12. Removed lots of ambiguity by making many "MAYs" into "SHOULDs"
and "some "SHOULDs" into "MUSTs".
13. Privacy is now recommended to be done by anonymizing entries as
per RFC 3323 instead of by removing or omitting hi-entry(s).
14. Requirement for TLS is now same level as per RFC 3261.
11. References
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11.1. Normative References
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC3326] Schulzrinne, H., Oran, D., and G. Camarillo, "The Reason
Header Field for the Session Initiation Protocol (SIP)",
RFC 3326, December 2002.
[RFC3323] Peterson, J., "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", BCP 14, RFC 2119, March 1997.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC4244] Barnes, M., "An Extension to the Session Initiation
Protocol (SIP) for Request History Information", RFC 4244,
November 2005.
11.2. Informative References
[I-D.ietf-sip-gruu]
Rosenberg, J., "Obtaining and Using Globally Routable User
Agent (UA) URIs (GRUU) in the Session Initiation Protocol
(SIP)", draft-ietf-sip-gruu-15 (work in progress),
October 2007.
[I-D.ietf-sip-sips]
Audet, F., "The use of the SIPS URI Scheme in the Session
Initiation Protocol (SIP)", draft-ietf-sip-sips-09 (work
in progress), November 2008.
[I-D.rosenberg-sip-target-uri-delivery]
Rosenberg, J., Elburg, H., Holmberg, C., Audet, F., and S.
Schubert, "Delivery of Request-URI Targets to User
Agents", draft-rosenberg-sip-target-uri-delivery-01 (work
in progress), March 2009.
[RFC3087] Campbell, B. and R. Sparks, "Control of Service Context
using SIP Request-URI", RFC 3087, April 2001.
[RFC4240] Burger, E., Van Dyke, J., and A. Spitzer, "Basic Network
Media Services with SIP", RFC 4240, December 2005.
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Appendix A. Detailed call flows
The scenarios in this section provide sample use cases for the
History-Info header for informational purposes only. They are not
intended to be normative.
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.
Alice sends a call to Bob via sip:example.com. The proxy sip:
example.com sequentially tries Bob on a SIP UA that has bound a
contact with the sip:bob@example.com AOR, and then several alternate
addresses (Office and Home) unsuccessfully before sending a response
to Alice. In this example, note that Office and Home are not the
same AOR as sip:bob@example.com, but rather different AORs that have
been configured as alternate contacts for Bob in the proxy. In other
words, Office and Bob are not bound through SIP Registration with
Bob's AOR. This type of arrangement is common for example when a
"routing" rule to a PSTN number is manually configured in a Proxy.
This scenario is provided to show that by providing the History-Info
to Alice, the end-user or an application at Alice could make a
decision on how best to attempt finding Bob. Without this mechanism,
Alice might well attempt Office (and thus Home) and then re-attempt
Home on a third manual attempt at reaching Bob. With this mechanism,
either the end-user or application could know that Bob is not
answering in the Office, and his busy on his home phone. 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.
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Alice example.com Bob Office Home
| | | | |
| INVITE F1 | | | |
|----------->| INVITE F2 | | |
| |----------------->| | |
| 100 Trying F3 | | |
|<-----------| 302 Move Temporarily F4 | |
| |<-----------------| | |
| | ACK F5 | | |
| |----------------->| | |
| | INVITE F6 | |
| |-------------------------->| |
| | 180 Ringing F7 | |
| |<--------------------------| |
| 180 Ringing F8 | |
|<-----------| retransmit INVITE | |
| |-------------------------->| |
| | ( timeout ) | |
| | INVITE F9 |
| |----------------------------------->|
| | 100 Trying F10 |
| |<-----------------------------------|
| | 486 Busy Here F11 |
| |<-----------------------------------|
| 486 Busy Here F12 |
|<-----------| ACK F13 |
| |----------------------------------->|
| ACK F14 | |
|----------->| |
Message Details
F1 INVITE alice -> example.com
INVITE sip:alice@example.com SIP/2.0
Via: SIP/2.0/TCP 192.0.2.3:5060
From: Alice <sip:alice@example.com>
To: Bob <sip:bob@example.com>
Supported: histinfo
Call-Id: 12345600@example.com
CSeq: 1 INVITE
Contact: Alice <sip:alice@192.0.2.3>
Content-Type: application/sdp
Content-Length: <appropriate value>
<!-- SDP Not Shown -->
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F2 INVITE example.com -> Bob
INVITE sip:bob@192.0.2.4 SIP/2.0
Via: SIP/2.0/TCP proxy.example.com:5060
Via: SIP/2.0/TCP 192.0.2.3:5060
From: Alice <sip:alice@example.com>
To: Bob <sip:bob@example.com>
Supported: histinfo
Call-Id: 12345600@example.com
CSeq: 1 INVITE
Record-Route: <sip:proxy.example.com;lr>
History-Info: <sip:bob@example.com>;index=1;reg-uri
History-Info: <sip:bob@192.0.2.4>;index=1.1
Contact: Alice <sip:alice@192.0.2.3>
Content-Type: application/sdp
Content-Length: <appropriate value>
<!-- SDP Not Shown -->
F3 100 Trying example.com -> alice
SIP/2.0 100 Trying
Via: SIP/2.0/TCP 192.0.2.3:5060
From: Alice <sip:alice@example.com>
To: Bob <sip:bob@example.com>
Call-Id: 12345600@example.com
CSeq: 1 INVITE
Content-Length: 0
F4 302 Moved Temporarily Bob -> example.com
SIP/2.0 302 Moved Temporarily
Via: SIP/2.0/TCP proxy.example.com:5060
Via: SIP/2.0/TCP 192.0.2.3:5060
From: Alice <sip:alice@example.com>
To: Bob <sip:bob@example.com>;tag=3
Call-Id: 12345600@example.com
CSeq: 1 INVITE
Record-Route: <sip:proxy.example.com;lr>
History-Info: <sip:bob@example.com>;index=1;reg-uri
History-Info: <sip:bob@192.0.2.4>;index=1.1
Contact: <sip:office@example.com>
Content-Length: 0
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F5 ACK 192.0.2.4 -> Bob
ACK sip:home@example.com SIP/2.0
Via: SIP/2.0/TCP proxy.example.com:5060
From: Alice <sip:alice@example.com>
To: Bob <sip:bob@example.com>
Call-Id: 12345600@example.com
CSeq: 1 ACK
Content-Length: 0
F6 INVITE example.com -> office
INVITE sip:office@192.0.2.3.com SIP/2.0
Via: SIP/2.0/TCP proxy.example.com:5060;branch=2
Via: SIP/2.0/TCP 192.0.2.3:5060
From: Alice <sip:alice@example.com>
To: Bob <sip:bob@example.com>
Supported: histinfo
Call-Id: 12345600@example.com
Record-Route: <sip:proxy.example.com;lr>
History-Info: <sip:bob@example.com>;index=1;reg-uri
History-Info: <sip:bob@192.0.2.4?Reason=SIP;cause=302>;\
index=1.1;mapped
History-Info: <sip:office@example.com>;index=1.2;reg-uri
History-Info: <sip:office@192.0.2.5>;index=1.2.1
CSeq: 1 INVITE
Contact: Alice <sip:alice@192.0.2.3>
Content-Type: application/sdp
Content-Length: <appropriate value>
<!-- SDP Not Shown -->
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F7 180 Ringing office -> example.com
SIP/2.0 180 Ringing
Via: SIP/2.0/TCP proxy.example.com:5060;branch=2
Via: SIP/2.0/TCP 192.0.2.3:5060
From: Alice <sip:alice@example.com>
To: Bob <sip:bob@example.com>;tag=5
Supported: histinfo
Call-ID: 12345600@example.com
Record-Route: <sip:proxy.example.com;lr>
History-Info: <sip:bob@example.com>;index=1;reg-uri
History-Info: <sip:bob@192.0.2.4?Reason=SIP;cause=302>;\
index=1.1;mapped
History-Info: <sip:office@example.com>;index=1.2;reg-uri
History-Info: <sip:office@192.0.2.5>;index=1.2.1
CSeq: 1 INVITE
Content-Length: 0
F8 180 Ringing example.com -> alice
SIP/2.0 180 Ringing
Via: SIP/2.0/TCP example.com:5060
From: Alice <sip:alice@example.com>
To: Bob <sip:bob@example.com>
Supported: histinfo
Call-Id: 12345600@example.com
History-Info: <sip:bob@example.com>;index=1;reg-uri
History-Info: <sip:bob@192.0.2.4?Reason=SIP;cause=302>;\
index=1.1;mapped
History-Info: <sip:office@example.com>;index=1.2;reg-uri
History-Info: <sip:office@192.0.2.5>;index=1.2.1
CSeq: 1 INVITE
Content-Length: 0
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F9 INVITE example.com -> home
INVITE sip:home@192.0.2.6 SIP/2.0
Via: SIP/2.0/TCP proxy.example.com:5060;branch=3
Via: SIP/2.0/TCP 192.0.2.3:5060
From: Alice <sip:alice@example.com>
To: Bob <sip:bob@example.com>
Supported: histinfo
Call-Id: 12345600@example.com
Record-Route: <sip:proxy.example.com;lr>
History-Info: <sip:bob@example.com>;index=1;reg-uri
History-Info: <sip:bob@192.0.2.4?Reason=SIP;cause=302>;\
index=1.1;mapped
History-Info: <sip:office@example.com>;index=1.2;reg-uri
History-Info: <sip:office@192.0.2.5?Reason=SIP;cause=480>;\
index=1.2.1;mapped
History-Info: <sip:home@example.com>;index=1.3;reg-uri
History-Info: <sip:home@192.0.2.6>;index=1.3.1
CSeq: 1 INVITE
Contact: Alice <sip:alice@192.0.2.3>
Content-Type: application/sdp
Content-Length: <appropriate value>
<!-- SDP Not Shown -->
F10 100 Trying home -> example.com
SIP/2.0 100 Trying
Via: SIP/2.0/TCP proxy.example.com:5060;branch=3
Via: SIP/2.0/TCP 192.0.2.3:5060
From: Alice <sip:alice@example.com>
To: Bob <sip:bob@example.com>
Call-Id: 12345600@example.com
CSeq: 1 INVITE
Content-Length: 0
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F11 486 Busy Here home -> example.com
SIP/2.0 486 Busy Here
Via: SIP/2.0/TCP proxy.example.com:5060;branch=3
Via: SIP/2.0/TCP 192.0.2.3:5060
From: Alice <sip:alice@example.com>
To: Bob <sip:bob@example.com>
Call-Id: 12345600@example.com
Record-Route: <sip:proxy.example.com;lr>
History-Info: <sip:bob@example.com>;index=1;reg-uri
History-Info: <sip:bob@192.0.2.4?Reason=SIP;cause=302>;\
index=1.1;mapped
History-Info: <sip:office@example.com>;index=1.2;reg-uri
History-Info: <sip:office@192.0.2.5?Reason=SIP;cause=480>;\
index=1.2.1;mapped
History-Info: <sip:home@example.com>;index=1.3;reg-uri
History-Info: <sip:home@192.0.2.6>;index=1.3.1
CSeq: 1 INVITE
Content-Length: 0
F12 486 Busy Here example.com -> alice
SIP/2.0 486 Busy Here
Via: SIP/2.0/TCP 192.0.2.3:5060
From: Alice <sip:alice@example.com>
To: Bob <sip:bob@example.com>
Call-Id: 12345600@example.com
History-Info: <sip:bob@example.com>;index=1;reg-uri
History-Info: <sip:bob@192.0.2.4?Reason=SIP;cause=302>;\
index=1.1;mapped
History-Info: <sip:office@example.com>;index=1.2;reg-uri
History-Info: <sip:office@192.0.2.5?Reason=SIP;cause=480>;\
index=1.2.1;mapped
History-Info: <sip:home@example.com>;index=1.3;reg-uri
History-Info: <sip:home@192.0.2.6>;index=1.3.1
CSeq: 1 INVITE
Content-Length: 0
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F13 ACK example.com -> home
ACK sip:home@example.com SIP/2.0
Via: SIP/2.0/TCP proxy.example.com:5060
From: Alice <sip:alice@example.com>
To: Bob <sip:bob@example.com>
Call-Id: 12345600@example.com
CSeq: 1 ACK
Content-Length: 0
F14 ACK alice -> example.com
ACK sip:bob@example.com SIP/2.0
Via: SIP/2.0/TCP 192.0.2.3:5060
From: Alice <sip:alice@example.com>
To: Bob <sip:bob@example.com>
Call-Id: 12345600@example.com
Route: <sip:proxy.example.com;lr>
CSeq: 1 ACK
Content-Length: 0
A.2. 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 is not intended to be a
complete specification for this specific edge service as it is quite
likely that additional information is needed by the edge service.
History-Info is just one building block that this service makes use
of.
Alice called Bob, which had been forwarded to Carol, which forwarded
to 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.
Alice example.com Bob Carol VM
| INVITE sip:bob@example.com | | |
|------------->| | | |
| | INVITE sip:bob@192.0.2.3 | |
| |------------->| | |
History-Info: <sip:bob@example.com>;index=1;reg-uri
History-Info: <sip:bob@192.0.2.3>;index=1.1
| | | | |
| 100 Trying | | | |
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|<-------------| 302 Moved Temporarily | |
| |<-------------| | |
History-Info: <sip:bob@example.com>;index=1;reg-uri
History-Info: <sip:bob@192.0.2.3>;index=1.1
| | | | |
| | INVITE sip:Carol@192.0.2.4 | |
| |--------------------------->| |
History-Info: <sip:bob@example.com>;index=1;reg-uri
History-Info: <sip:bob@192.0.2.3>;index=1.1;mapped
History-Info: <sip:carol@example.com>;index=2;reg-uri
History-Info: <sip:carol@192.0.2.4>;index=2.1
| | | | |
| | 180 Ringing | |
| |<---------------------------| |
History-Info: <sip:bob@example.com>;index=1;reg-uri
History-Info: <sip:bob@192.0.2.3>;index=1.1;mapped
History-Info: <sip:carol@example.com>;index=2;reg-uri
History-Info: <sip:carol@192.0.2.4>;index=2.1
| | | | |
| 180 Ringing | | | |
|<-------------| | | |
| | | | |
| . . . | retransmit INVITE | |
| |--------------------------->| |
History-Info: <sip:bob@example.com>;index=1;reg-uri
History-Info: <sip:bob@192.0.2.3>;index=1.1;mapped
History-Info: <sip:carol@example.com>;index=2;reg-uri
History-Info: <sip:carol@192.0.2.4>;index=2.1
| . . . | | | |
| | (timeout) | |
| | | | |
| | INVITE sip:vm@192.0.2.5 |
| |-------------------------------------->|
History-Info: <sip:bob@example.com>;index=1;reg-uri
History-Info: <sip:bob@192.0.2.3>;index=1.1;mapped
History-Info: <sip:carol@example.com>;index=2;reg-uri
History-Info: <sip:carol@192.0.2.4>;index=2.1;mapped
History-Info: <sip:vm@example.com>;index=3;reg-uri
History-Info: <sip:vm@192.0.2.5>;index=3.1
| | | | |
| | 200 OK |
| |<--------------------------------------|
History-Info: <sip:bob@example.com>;index=1;reg-uri
History-Info: <sip:bob@192.0.2.3>;index=1.1;mapped
History-Info: <sip:carol@example.com>;index=2;reg-uri
History-Info: <sip:carol@192.0.2.4>;index=2.1;mapped
History-Info: <sip:vm@example.com>;index=3;reg-uri
History-Info: <sip:vm@192.0.2.5>;index=3.1
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| 200 OK | | | |
|<-------------| | | |
| | | | |
| ACK | | | |
|------------->| ACK |
| |-------------------------------------->|
A.3. Automatic Call Distribution
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 were busy,
by retargeting the request to the Silver Group for delivery to an
agent. 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 Alice.
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.
Alice example.com Gold Silver Agent
| | | | |
| INVITE sip:Gold@example.com | | |
|------------->| | | |
| Supported: histinfo
| | | | |
| | INVITE sip:Gold@example.com |
| |------------->| | |
History-Info: <sip:Gold@example.com>;index=1;noop
History-Info: <sip:Gold@gold.example.com>;index=1.1
| | | | |
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| | 302 Moved Temporarily | |
| |<-------------| | |
History-Info: <sip:Gold@example.com>;index=1;noop
History-Info: <sip:Gold@gold.example.com>;index=1.1
Contact: <sip:Silver@example.com>
| | | |
| | INVITE sip:Silver@example.com |
| |--------------------------->| |
History-Info: <sip:Gold@example.com>;index=1;noop
History-Info: <sip:Gold@gold.example.com?Reason=SIP;cause=302>;\
index=1.1;mapped
History-Info: <sip:Silver@example.com>;index=2;noop
History-Info: <sip:Silver@silver.example.com>;index=2.1
| | | | |
| | | INVITE sip:Silver@192.0.2.7
| | | |----------->|
History-Info: <sip:Gold@example.com>;index=1;noop
History-Info: <sip:Gold@gold.example.com?Reason=SIP;cause=302>;\
index=1.1;mapped
History-Info: <sip:Silver@example.com>;index=2;noop
History-Info: <sip:Silver@silver.example.com>;index=2.1;reg-id
History-Info: <sip:Silver@192.0.2.7>;index=2.1.1>
| | | | |
| | | | 200 OK |
| | | |<-----------|
History-Info: <sip:Gold@example.com>;index=1;noop
History-Info: <sip:Gold@gold.example.com?Reason=SIP;cause=302>;\
index=1.1;mapped
History-Info: <sip:Silver@example.com>;index=2;noop
History-Info: <sip:Silver@silver.example.com>;index=2.1;reg-id
History-Info: <sip:Silver@192.0.2.7>;index=2.1.1>
| | | | |
| | 200 OK | |
| |<---------------------------| |
History-Info: <sip:Gold@example.com>;index=1;noop
History-Info: <sip:Gold@gold.example.com?Reason=SIP;cause=302>;\
index=1.1;mapped
History-Info: <sip:Silver@example.com>;index=2;noop
History-Info: <sip:Silver@silver.example.com>;index=2.1;reg-id
History-Info: <sip:Silver@192.0.2.7>;index=2.1.1>
| | | | |
200 OK | | | |
|<-------------| | | |
| | | | |
| ACK | | | |
|------------->| ACK |
| |---------------------------------------->|
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Authors' Addresses
Mary Barnes
Nortel
Richardson, TX
Email: mary.barnes@nortel.com
Francois Audet
Nortel
4655 Great America Parkway
Santa Clara, CA 95054
US
Email: audet@nortel.com
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