Internet DRAFT - draft-ietf-sipcore-rfc4244bis
draft-ietf-sipcore-rfc4244bis
Network Working Group M. Barnes
Internet-Draft Polycom
Obsoletes: 4244 (if approved) F. Audet
Intended status: Standards Track Skype
Expires: April 4, 2014 S. Schubert
NTT
J. van Elburg
Detecon International Gmbh
C. Holmberg
Ericsson
Oct 2013
An Extension to the Session Initiation Protocol (SIP) for Request
History Information
draft-ietf-sipcore-rfc4244bis-12.txt
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 SIP request arrives at a specific
application or user. This document defines an optional SIP header
field, History-Info, for capturing the history information in
requests. The document also defines SIP header field parameters for
the History-Info and Contact header fields to tag the method by which
the target of a request is determined. In addition, this
specification defines a value for the Privacy header field that
directs the anonymization of values in the History-Info header field.
This document obsoletes RFC 4244.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on April 4, 2014.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 4
3. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. History-Info Header Field Protocol Structure . . . . . . . . . 7
5.1. History-Info Header Field Example Scenario . . . . . . . . 10
6. User Agent Handling of the History-Info Header Field . . . . . 13
6.1. User Agent Client (UAC) Behavior . . . . . . . . . . . . . 13
6.2. User Agent Server (UAS) Behavior . . . . . . . . . . . . . 13
6.3. Back-2-Back User Agent (B2BUA) Behavior . . . . . . . . . 13
7. Proxy/Intermediary Handling of History-Info Header Fields . . 14
8. Redirect Server Handling of History-Info Header Fields . . . . 14
9. Handling of History-Info Header Fields in Requests and
Responses . . . . . . . . . . . . . . . . . . . . . . . . . . 15
9.1. Receiving a Request . . . . . . . . . . . . . . . . . . . 15
9.2. Sending a Request with History-Info . . . . . . . . . . . 15
9.3. Receiving a Response with History-Info or Request
Timeouts . . . . . . . . . . . . . . . . . . . . . . . . . 16
9.4. Sending History-Info in Responses . . . . . . . . . . . . 17
10. Processing the History-Info Header Field . . . . . . . . . . . 17
10.1. Privacy in the History-Info Header Field . . . . . . . . . 17
10.1.1. Indicating Privacy . . . . . . . . . . . . . . . . . 17
10.1.2. Applying Privacy . . . . . . . . . . . . . . . . . . 18
10.2. Reason in the History-Info Header Field . . . . . . . . . 19
10.3. Indexing in the History-Info Header Field . . . . . . . . 20
10.4. Mechanism for Target Determination in the History-Info
Header Field . . . . . . . . . . . . . . . . . . . . . . . 21
11. Application Considerations . . . . . . . . . . . . . . . . . . 23
12. Application Specific Usage . . . . . . . . . . . . . . . . . . 25
12.1. PBX Voicemail . . . . . . . . . . . . . . . . . . . . . . 25
12.2. Consumer Voicemail . . . . . . . . . . . . . . . . . . . . 25
13. Security Considerations . . . . . . . . . . . . . . . . . . . 26
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
14.1. Registration of New SIP History-Info Header Field . . . . 27
14.2. Registration of "history" for SIP Privacy Header Field . . 27
14.3. Registration of Header Field Parameters . . . . . . . . . 28
15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28
16. Changes from RFC 4244 . . . . . . . . . . . . . . . . . . . . 29
16.1. Backwards compatibility . . . . . . . . . . . . . . . . . 30
17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 32
17.1. Normative References . . . . . . . . . . . . . . . . . . . 32
17.2. Informative References . . . . . . . . . . . . . . . . . . 32
Appendix A. Request History Requirements . . . . . . . . . . . . 33
A.1. Security Requirements . . . . . . . . . . . . . . . . . . 34
A.2. Privacy Requirements . . . . . . . . . . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35
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1. Introduction
Many services that SIP is anticipated to support require the ability
to determine why and how a SIP request 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 retarget capabilities that enable SIP
requests to be routed to chosen applications, there is a need for a
standard mechanism within SIP for communicating the retargeting
history of the requests. This "request history" information allows
the receiving application to obtain information about how and why the
SIP request arrived at the application/user.
This document defines a SIP header field, 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. SIP
header field parameters are defined for the History-Info and Contact
header fields to tag the method by which the target of a request is
determined. This specification also defines a value, "history", for
the Privacy header field. In addition a SIP option tag, "histinfo",
is defined.
The History-Info header field provides a building block for
development of SIP based applications and services. The requirements
for the solution described in this specification are included in
Appendix A. Example scenarios using the History-Info header field
are available in [I-D.ietf-sipcore-rfc4244bis-callflows].
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 specification to refer to the
process of a SIP entity changing the request-URI [RFC3261, section
7.1] in a request based on the rules for determining request targets
as described in Section 16.5 of [RFC3261] and of the subsequent
forwarding of that request as described in step 2 in section 16.6 of
[RFC3261]. This includes changing the Request-URI due to a location
service lookup and redirect processing. This also includes internal
(to a Proxy/SIP intermediary) changes of the URI prior to forwarding
of the request.
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The terms "location service", "forward", "redirect" and "AOR" are
used consistently with the terminology in [RFC3261].
The terms "target user" is used in this specification as the human
user associated with particular AoR or AoRs (in case the human user
has multiple alias).
The references to "domain for which the SIP entity/Proxy/Intermediary
is responsible" are consistent with and intended to convey the same
context as the usage of that terminology in [RFC3261]. The
applicability of History-Info to architectures or models outside the
context of [RFC3261] is outside the scope of this specification.
3. Background
SIP implicitly provides retargeting capabilities that enable SIP
requests to be routed to specific applications as defined in
[RFC3261]. The motivation for capturing the request history is that
in the process of retargeting a request, old routing information can
be forever lost. This lost information may be important history that
allows elements to which the request is retargeted to process the
request in a locally defined, application-specific manner. This
document defines a mechanism for transporting the request history.
Application-specific behavior is outside the scope of this
specification.
Current network applications for other protocols provide the ability
for elements involved with the request to obtain additional
information relating to how and why the request 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 relaying whereby the recipient obtains a detailed "trace of
the path" of the message from originator to receiver, including
the time of each relay.
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.
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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 Capturing aliases and Globally Routable User Agent URIs (GRUUs)
[RFC5627], which can be overwritten by a registrar or a "home
proxy" (a proxy serving as the terminal point for routing an
address-of-record) 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].
4. Overview
The fundamental functionality provided by the request history
information is the ability to inform proxies and user agents (UAs)
involved in processing a request about the history or progress of
that request. The solution is to capture the Request-URIs as a
request is retargeted, in a SIP header field: History-Info. This
allows for the capturing of the history of a request that would be
lost with the normal SIP processing involved in the subsequent
retargeting of the request.
The History-Info header field is added to a Request when a new
request is created by a user agent client (UAC) or forwarded by a
Proxy, or when the target of a request is changed. It is possible
for the target of a request to be changed by the same proxy/SIP
intermediary multiple times (referred to as 'internal retargeting').
A SIP entity changing the target of a request in response to a
redirect also propagates any History-Info header field from the
initial request in the new request. The ABNF and detailed
description of the History-Info header field parameters along with
examples, is provided in Section 5. Section 6, Section 7 and
Section 8 provide the detailed handling of the History-Info header
field by SIP User Agents, Proxies and Redirect Servers respectively.
This specification also defines three new SIP header field
parameters, "rc", "mp" and "np", for the History-Info and Contact
header fields, to tag the method by which the target of a request is
determined. Further detail on the use of these header field
parameters is provided in Section 5.
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This specification also defines a priv-value for the Privacy header,
"history", that requires anonymization of all the History-Info header
field entries in a Request or to a specific History-Info header field
hi-entry as described above. Further detail is provided in
Section 10.1.
In addition a SIP option tag, "histinfo", is defined. The use of
this option tag is described in Section 6.1.
5. History-Info Header Field Protocol Structure
The History-Info header field defined in this specification defines
the usage in out-of-dialog requests or initial requests for a dialog
(e.g., INVITE, REGISTER, MESSAGE, REFER and OPTIONS, PUBLISH and
SUBSCRIBE, etc.) and any non-100 provisional or final responses to
these requests.
The following provides details for the information that is captured
in the History-Info header field entries for each target used for
forwarding a request:
o hi-targeted-to-uri: A mandatory parameter for capturing the
Request-URI for the specific request as it is forwarded.
o hi-index: A mandatory parameter for History-Info reflecting the
chronological order of the information, indexed to reflect the
forking and retargeting of requests. The format for this
parameter is a sequence of non-negative integers, 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 leaf. By adding the new
entries in chronological order (i.e., following existing entries
per the details in Section 10.3), including the index and sending
the messages using a secure transport, the ordering of the
History-Info header fields in the request is assured. 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 hi-target-param: An optional parameter reflecting the mechanism by
which the Request URI captured in the hi-targeted-to-uri in the
History-Info header field value (hi-entry) was determined. This
parameter is either an "rc", "mp" or "np" header field parameter,
which is interpreted as follows:
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"rc": The hi-targeted-to-URI represents a change in Request-URI
while the target user remains the same. This occurs for
example when user has multiple AoRs as an alias. The "rc"
header field parameter contains the value of the hi-index in
the hi-entry with an hi-targeted-to-uri that reflects the
Request-URI that was retargeted
"mp": The hi-targeted-to-URI represents a user other than the
target user associated with the Request-URI in the incoming
request that was retargeted. This occurs when a request is
statically or dynamically retargeted to another user
represented by an AoR unassociated with the AoR of the original
target user. The "mp" header field parameter contains the
value of the hi-index in the hi-entry with an hi-targeted-to-
uri that reflects the Request-URI that was retargeted, thus
identifying the "mapped from" target.
"np": The hi-targeted-to-URI represents that there was no
change in Request-URI. This would apply for example when a
proxy merely forwards a request to a next hop proxy and loose
routing is used. The "np" header field parameter contains the
value of the hi-index in the hi-entry with an hi-targeted-to-
uri that reflects the Request-URI that was copied unchanged
into the request represented by this hi-entry. That value will
usually be the hi-index of the parent hi-entry of this hi-
entry.
o Extension (hi-extension): A parameter to allow for future optional
extensions. As per [RFC3261], any implementation not
understanding an extension MUST ignore it.
The ABNF syntax [RFC5234] for the History-Info header field and
header field parameters is as follows:
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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-target-param / hi-extension
hi-index = "index" EQUAL index-val
index-val = number *("." number)
number = [ %31-39 *DIGIT ] DIGIT
hi-target-param = rc-param / mp-param / np-param
rc-param = "rc" EQUAL index-val
mp-param = "mp" EQUAL index-val
np-param = "np" EQUAL index-val
hi-extension = generic-param
The ABNF definitions for "generic-param", "name-addr", "HCOLON",
"COMMA", "SEMI" and "EQUAL" are from [RFC3261].
This document also extends the "contact-params" for the Contact
header field as defined in [RFC3261] with the "rc", "mp" and "np"
header field parameters defined above.
In addition to the parameters defined by the ABNF, an hi-entry may
also include a Reason header field and/or a Privacy header field,
which are both included in the "headers" component of the hi-
targeted-to-uri as described below:
o Reason: An optional parameter for History-Info, reflected in the
History-Info header field by including the Reason header field
[RFC3326] included in the hi-targeted-to-uri. A reason is
included in the hi-targeted-to-uri of an hi-entry to reflect
information received in a response to the request sent to that
URI.
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", as defined in this
document, included in the hi- targeted-to-uri or by adding the
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Privacy header field with a priv-value of "history" to the
request. The latter case indicates that the History-Info entries
for all History-Info entries whose hi-targeted-to-uri has the same
domain as the domain for which the SIP entity processing the
message is responsible MUST be anonymized prior to forwarding,
whereas the use of the Privacy header field included in the hi-
targeted-to-uri means that a specific hi-entry MUST be anonymized.
Note that since both the Reason and Privacy parameters are included
in the hi-targeted-to-uri, these fields will not be available in the
case that the hi-targeted-to-uri is a Tel-URI [RFC3966].
The following provides examples of the format for the History-Info
header field. Note that the backslash, CRLF and whitespace between
the lines in the examples below are inserted for readability purposes
only. Note, however, that History-Info can be broken into multiple
lines due to the SWS (sep whitespace) that is part of HCOLON, COMMA
and SEMI, and there can be multiple History-Info header fields due to
the rule of section 7.3 [RFC3261]. Additional detailed examples are
available in [I-D.ietf-sipcore-rfc4244bis-callflows].
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,\
<sip:UserB@example.com?Privacy=history&Reason=SIP%3B\
cause%3D486>;index=1.2;mp=1.1,\
<sip:45432@192.168.0.3>;index=1.3;rc=1.2
5.1. History-Info Header Field Example Scenario
The following is an illustrative example of usage of History-Info.
In this example, Alice (sip:alice@atlanta.example.com) calls Bob
(sip:bob@biloxi.example.com). Alice's proxy in her home domain (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 URIs provided as part of normal SIP registration. In this
example, Bob is simultaneously contacted on a PC client and on a
phone, and Bob answers on the PC client.
One important thing illustrated by this call flow is that without
History-Info, Bob would "lose" the original target information or the
initial request-URI, including any parameters in the request URI.
Bob can recover that information by locating the last hi-entry with
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an "rc" header field parameter. This "rc" header field parameter
contains the index of the hi-entry containing the lost target
information - i.e., the sip:bob@biloxi.example.com hi-entry with
index=1.1. Note that in the 200 response to Alice, an hi-entry is
not included for the fork to sip:bob@192.0.2.7 (index 1.1.1) since
biloxi.example.com had not received a response from that fork at the
time it sent the 200 OK that ultimately reached Alice.
Additional detailed examples are available in
[I-D.ietf-sipcore-rfc4244bis-callflows].
Note: This example uses loose routing procedures.
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Alice atlanta.example.com biloxi.example.com Bob@pc Bob@phone
| | | | |
| INVITE sip:bob@biloxi.example.com;p=x | |
|--------------->| | | |
| Supported: histinfo | | |
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1 |
| | | | |
| | INVITE sip:bob@biloxi.example.com;p=x |
| |--------------->| | |
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1 |
| History-Info: <sip:bob@biloxi.example.com;p=x>;np=1;index=1.1
| | | | |
| | | INVITE sip:bob@192.0.2.3|
| | |--------------->| |
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1
| History-Info: <sip:bob@biloxi.example.com;p=x>;np=1;index=1.1
| History-Info: <sip:bob@192.0.2.3>;index=1.1.1;rc=1.1
| | | | |
| | | INVITE sip:bob@192.0.2.7|
| | |-------------------------->|
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1
| History-Info: <sip:bob@biloxi.example.com;p=x>;np=1;index=1.1
| History-Info: <sip:bob@192.0.2.7>;index=1.1.2;rc=1.1
| | | 200 | |
| | |<---------------| |
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1
| History-Info: <sip:bob@biloxi.example.com;p=x>;np=1;index=1.1
| History-Info: <sip:bob@192.0.2.3>;index=1.1.1;rc=1.1
| | | | |
| | 200 | | |
| |<---------------| | |
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1
| History-Info: <sip:bob@biloxi.example.com;p=x>;np=1;index=1.1
| History-Info: <sip:bob@192.0.2.3>;index=1.1.1;rc=1.1
| | | | |
| | | Proxy Cancels INVITE |
| | |<=========================>|
| | | | |
| 200 | | | |
|<---------------| | | |
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1
| History-Info: <sip:bob@biloxi.example.com;p=x>;np=1;index=1.1
| History-Info: <sip:bob@192.0.2.3>;index=1.1.1;rc=1.1
| | | | |
| ACK | | | |
|--------------->| ACK | | |
| |--------------->| ACK | |
| | |--------------->| |
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Figure 1: Basic Call
6. User Agent Handling of the History-Info Header Field
This section describes the processing specific to UAs(UACs, UASs and
B2BUAs) for the History-Info header."
6.1. User Agent Client (UAC) Behavior
The UAC MUST include the "histinfo" option tag in the Supported
header field in any out-of-dialog requests or initial requests for a
dialog for which the UAC would like the History-Info header field in
the response. When issuing a request, the UAC MUST follow the
procedures in Section 9.2. In the case of an initial request, except
where the UAC is part of a B2BUA, there is no cache of hi- entries
with which to populate the History-Info header field and the hi-index
is set to 1 per Section 10.3. When receiving a response the UAC MUST
follow the procedures in Section 9.3.
If the UAC generates further forks of the initial request (either due
to acting on a 3xx response or internally-directed forking to
multiple destinations), the successive requests will add hi-entries
with hi-indexes of 2, 3, etc.
6.2. User Agent Server (UAS) Behavior
When receiving a request, a UAS MUST follow the procedures defined in
Section 9.2. When sending a response other than a 3xx response, a
UAS MUST follows the procedures as defined in Section 9.4. When
sending a 3xx response, the UAS MUST follow the procedures defined
for a redirect server per Section 8. An application at the UAS can
make use of the cached hi-entries as described in Section 11.
6.3. Back-2-Back User Agent (B2BUA) Behavior
A back-to-back user agent (B2BUA) MAY follow the behavior of a SIP
intermediary, per Section 7, as an alternative to following the
behavior of a user agent server (UAS) per Section 6.2 and a UAC per
Section 6.1. In behaving as an intermediary, a B2BUA carries forward
hi-entries received in requests at the UAS to requests being
forwarded by the UAC, as well as carrying forward hi-entries in
responses received at the UAC to the responses forwarded by the UAS,
subject to privacy considerations per Section 10.1.
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7. Proxy/Intermediary Handling of History-Info Header Fields
This section describes the procedures for proxies and other SIP
intermediaries for the handling of the History-Info header fields for
each of the following scenarios:
Receiving a Request: An intermediary MUST follow the procedures in
Section 9.1 for the handling of hi-entries in incoming SIP
requests.
Sending a Request: For each outgoing request relating to a target in
the target set, the intermediary MUST follow the procedures of
Section 9.2.
Receiving a Response or Timeout: An intermediary MUST follow the
procedures of Section 9.3 when a SIP response is received or a
request times out.
Sending a Response: An intermediary MUST follow the procedures of
Section 9.4 for the handling of the hi-entries when sending a SIP
response.
In some cases, an intermediary may retarget a request more than once
before forwarding - i.e., a request is retargeted to a SIP entity
that is "internal" to the intermediary before the same intermediary
retargets the request to an external target . A typical example
would be a proxy that retargets a request first to a different user
(i.e., it maps to a different AOR) and then forwards to a registered
contact bound to the same AOR. In this case, the intermediary MUST
add a hi-entry for (each of) the internal target(s) per the
procedures in Section 9.2. The intermediary MAY include a Reason
header field in the hi-entry with the hi-targeted-to-uri that has
been retargeted. Note, that this is shown in the INVITE (F6) in the
example entitled "Sequentially Forking (History-Info in Response)" in
[I-D.ietf-sipcore-rfc4244bis-callflows].
8. Redirect Server Handling of History-Info Header Fields
A redirect server MUST follow the procedures in Section 9.1 when it
receives a SIP Request. A redirect server MUST follow the procedures
in Section 9.4 when it sends a SIP Response. When generating the
Contact header field in a 3xx response, the redirect server MUST add
the appropriate "mp", "np" or "rc" header field parameter to each
Contact header field as described in Section 10.4, if applicable.
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9. Handling of History-Info Header Fields in Requests and Responses
This section describes the procedures for SIP entities for the
handling of the History-Info header field in SIP requests and
responses.
9.1. Receiving a Request
When receiving a request, a SIP entity MUST keep a copy of the hi-
entries from the incoming request. This document describes this copy
in terms of a cache containing the hi-entries associated with the
request. The hi-entries MUST be added to the cache in the order in
which they were received in the request.
If the Request-URI of the incoming request does not match the hi-
targeted-to-uri in the last hi-entry (i.e., the previous SIP entity
that sent the request did not include a History-Info header field),
the SIP entity MUST add a hi-entry to end of the cache, on behalf of
the previous SIP entity before proceeding to Section 9.2, as follows:
The SIP entity MUST set the hi-targeted-to-uri to the value of the
Request-URI in the incoming request. If the Request-URI is a Tel-
URI, it SHOULD be transformed into a SIP URI per section 19.1.6 of
[RFC3261] before being added as a hi-targted-to-uri.
If privacy is required, the SIP entity MUST follow the procedures
of Section 10.1.
The SIP entity MUST set the hi-index parameter as described in
Section 10.3.
The SIP entity MUST NOT include an "rc", "mp" or "np" header field
parameter.
9.2. Sending a Request with History-Info
When sending a request, a SIP entity MUST include all the hi-entries
from the cache that was created per Section 9.1. In addition, the
SIP entity MUST add a new hi-entry to the outgoing request, but the
SIP entity MUST NOT add the hi-entry to the cache at this time. The
hi-entries in the outgoing request's History-Info header field is the
preorder of the tree of hi-entries, that is, by the lexicographic
ordering of the hi-indexes. The new hi-entry is populated as
follows:
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hi-targeted-to-uri: The hi-targeted-to-uri MUST be set to the value
of the Request-URI of the current (outgoing) request.
privacy: If privacy is required, the procedures of Section 10.1 MUST
be followed.
hi-index: The SIP entity MUST include an hi-index for the hi-entry
as described in Section 10.3.
rc/mp/np: The SIP entity MUST include an "rc", "mp" or "np" header
field parameter in the hi-entry, if applicable, per the procedures
in Section 10.4.
9.3. Receiving a Response with History-Info or Request Timeouts
When a SIP entity receives a non-100 response or a request times out,
the SIP entity performs the following steps:
Step 1: Add hi-entry to cache
The SIP entity MUST add the hi-entry that was added to the request
that received the non-100 response or timed out to the cache, if
it was not already cached. The hi-entry MUST be added to the
cache in ascending order as indicated by the values in the hi-
index parameters of the hi-entries (e.g., 1.2.1 comes after 1.2
but before 1.2.2 or 1.3).
Step 2: Add Reason header field
If the response is not a 100 or 2xx response, the SIP entity adds
one or more Reason header fields to the hi-targeted-to-uri in the
(newly) cached hi-entry reflecting the SIP response code in the
non-100 or non-2xx response, per the procedures of Section 10.2.
Step 3: Add additional hi-entries
The SIP entity MUST also add to the cache any hi-entries received
in the response that are not already in the cache. This situation
can occur when the entity that generated the non-100 response
retargeted the request before generating the response. As per
Step 1, the hi-entries MUST be added to the cache in ascending
order as indicated by the values in the hi-index parameters of the
hi-entries
It is important to note that the cache (and the request or response)
does not contain hi-entries for requests that have not yet received a
non-100 response, so there can be gaps in indices (e.g., 1.2 and 1.4
could be present but not 1.3).
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9.4. Sending History-Info in Responses
When sending a response other than a 100, a SIP entity MUST include
all the cached hi-entries in the response, subject to the privacy
consideration in Section 10.1.2, and with the following exception: If
the received request contained no hi-entries and there is no
"histinfo" option tag in the Supported header field, the SIP entity
MUST NOT include History-Info in the response.
10. Processing the History-Info Header Field
The following sections describe the procedures for processing the
History-Info header field. These procedures are applicable to SIP
entities such as Proxies/Intermediaries, Redirect Servers or User
Agents.
10.1. Privacy in the History-Info Header Field
The privacy requirements for this document are described in
Appendix A.2. Section 10.1.1 describes the insertion of the Privacy
header field defined in [RFC3323] to indicate the privacy to be
applied to the History-Info header field entries. Section 10.1.2
describes how to apply privacy to a request or response that is being
forwarded, based on the presence of the Privacy header field.
10.1.1. Indicating Privacy
As with other SIP headers described in [RFC3323], the hi-targeted-to-
uris in the History-Info header field can inadvertently reveal
information about the initiator of the request. Thus, the UAC needs
a mechanism to indicate that the hi-targeted-to-uris in the hi-
entries need to be privacy protected. The Privacy header field is
used by the UAC to indicate that privacy is to be applied to all the
hi-entries in the request as follows:
o If the UAC is including a Privacy header field with a priv-value
of "header" in the request, then the UAC SHOULD NOT include a
priv-value of "history" in the Privacy header field in the
Request.
o If the UAC is including any priv-values other than "header" in the
Privacy header field, then the UAC MUST also include a priv-value
of "history" in the Privacy header field in the Request.
o If the UAC is not including any priv-values in the Privacy header
field in the request, then the UAC MUST add a Privacy header
field, with a priv-value of "history", to the request. The UAC
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MUST NOT include a priv-value of "critical" in the Privacy header
field in the Request in this case.
In addition, the History-Info header field can reveal general routing
and diverting information within an intermediary, which the
intermediary wants to privacy protect. In this case, the
intermediary MUST construct a Privacy header field with the single
priv-value of "history" and include the Privacy header field in the
hi-targeted-to-uri, for each new hi-entry created by the intermediary
whose hi-targeted-to-uri it wishes to privacy protect. Note that the
priv-value in the Privacy header for the incoming request does not
necessarily influence whether the intermediary includes a Privacy
header field in the hi-entries. For example, even if the Privacy
header for the incoming request contained a priv-value of "none", the
Proxy can still set a priv-value of "history" in the Privacy header
field included in the hi-targeted-to-uri.
Finally, the UAS may not want to reveal the final reached target to
the originator. In this case, the UAS MUST include a Privacy header
field with a priv-value of "history" in the hi-targeted-to-uri in the
last hi-entry, in the response. As noted above, the UAS of the
request MUST NOT use any other priv-values in the Privacy header
field included in the hi-entry.
10.1.2. Applying Privacy
When a SIP message is forwarded to a domain for which the SIP
intermediary is not responsible, a Privacy Service at the boundary of
the domain applies the appropriate privacy based on the value of the
Privacy header field in the message header or in the "headers"
component of the hi-targeted-to-uri in the individual hi-entries.
If there is a Privacy header field in the message header of a request
or response, with a priv-value of "header" or "history", then all the
hi-targeted-to-uris in the hi-entries, associated with the domain for
which the SIP intermediary is responsible, are anonymized by the
Privacy Service. The Privacy Service MUST change any hi-targeted-to-
uris in these hi-entries that have not been anonymized (evidenced by
their domain not being "anonymous.invalid") to anonymous URIs
containing a domain of anonymous.invalid as recommended in section
4.1.1.3 of [RFC3323]. As defined in section 4.1.1.2 of [RFC3323] the
recommendations of [RFC3261] for anonymyzing the URI Username SHOULD
be followed (i.e., "anonymous" in the user portion of the URI). If
there is a Privacy header field in the "headers" component of the hi-
targeted-to-uri in the hi-entries, then the Privacy header field
value MUST be removed from the hi- entry. Once all the appropriate
hi-entries have been anonymized, the Privacy Service MUST remove the
priv-value of "history" from the Privacy header field in the message
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header of the request or response. If there are no remaining priv-
values in the Privacy header field, the Privacy Service MUST remove
the Privacy header field from the request or response per [RFC3323].
If there is not a Privacy header field in the message header of the
request or response that is being forwarded, but there is a Privacy
header field with a priv-value of "history" in the "headers"
component in any of the hi-targeted-uris in the hi-entries associated
with the domain for which a SIP intermediary is responsible, then the
Privacy Service MUST update those hi-targeted-to-uris as described
above. Any other priv-values in the Privacy header field in the
"headers" component of the hi-targeted-to-uris in the hi-entries MUST
be ignored. In any case, the Privacy Service MUST remove the Privacy
header field from the "headers" compenent of the hi-targeted-to-uris
in the hi-entries prior to forwarding.
10.2. Reason in the History-Info Header Field
A Reason header field is added to the "headers" component in an hi-
targeted-to-uri when the hi-entry is added to the cache based upon
the receipt of a SIP response that is neither a 100 nor a 2xx
response, as described in Section 9.3. If the Reason header field is
being added due to receipt of an explicit SIP response and the
response contains any Reason header fields (see [RFC3326]), then the
SIP entity MUST include the Reason header fields in the "headers"
component of the hi-targeted-to-uri in the last hi-entry added to the
cache, unless the hi-targeted-to-uri is a Tel-URI. If the SIP
response does not contain a Reason header field, the SIP entity MUST
include a Reason header field, containing the SIP Response Code, in
the "headers" component of the hi-targeted-to-uri in the last hi-
entry added to the cache, unless the hi-targeted-to-uri is a Tel-URI.
If a request has timed out (instead of being explicitly rejected),
the SIP entity MUST update the cache as if the request received a SIP
error response code of 408 "Request Timeout".
A request can receive multiple responses, that are neither 100 nor
2xx responses, which carry or imply (for responses without Reason
headers, and for timeouts) multiple, possibly duplicated, reason-
values to be applied to an hi- targeted-to-uri. In these situations,
the SIP entity creating History-Info header value would choose the
appropriate Reason header field value.
A SIP entity MAY also include a Reason header field in the "headers"
component of an hi-targeted-to-uri containing the URI of a request
that was retargeted as a result of internal retargeting.
If additional Reason header field parameters are defined in the
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future per [RFC3326], the use of these Reason header field parameters
for the History-Info header field MUST follow the same rules as
described above.
10.3. Indexing in the History-Info Header Field
In order to maintain ordering and accurately reflect the retargeting
of the request, the SIP entity MUST add a hi-index to each hi-entry.
Per the syntax in Section 5, the hi-index consists of a series of
nonnegative integer separated by dots (e.g., 1.1.2). Each dot
reflects a SIP forwarding hop. The nonnegative integer following
each dot reflects the order in which a request was retargeted at the
hop. The highest nonnegative integer at each hop reflects the number
of entities to which the request has been retargeted at the specific
hop (i.e., the number of branches) at the time that the request
represented by this hi-entry was generated. Thus, the indexing
results in a logical tree representation for the history of the
request and the hi-entries are given in the preorder of the tree.
The first index in a series of History-Info entries MUST be set to 1.
In the case that a SIP entity (intermediary or UAS) adds a first hi-
entry on behalf of the previous hop, the hi-index MUST be set to 1.
For each forward hop (i.e., each new level of indexing), the last
integers of the hi-indexes of the new requests MUST be generated
starting at 1 and incrementing by 1 for each additional request.
The basic rules for adding the hi-index are summarized as follows:
1. Forwarding a request without changing the target: In the case of
a request that is being forwarded without changing the target,
the hi-index reflects the increasing length of the branch. In
this case, the SIP entity MUST read the value from the History-
Info header field in the received request and MUST add another
level of indexing by appending the dot delimiter followed by an
initial value of 1 for the new level. For example, if the hi-
index in the last History-Info header field in the received
request is 1.1, a proxy would add a hi-entry with an hi-index of
1.1.1 and forward the request.
2. Retargeting within a processing entity - 1st instance: For the
first instance of retargeting within a processing entity, the SIP
entity MUST calculate the hi-index as prescribed for basic
forwarding.
3. Retargeting within a processing entity - subsequent instance: For
each subsequent retargeting of a request by the same SIP entity,
the SIP entity MUST calculate and add the hi-index for each new
branch by incrementing the rightmost value from the hi-index in
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the last hi-entry. Per the example above, the hi-index in the
next request forwarded by this same SIP entity 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 SIP entity MUST calculate
the hi-index calculated per rule 3. That is, the rightmost value
of the hi-index MUST be incremented (i.e., a new branch is
created). For example, if the hi-index in the History-Info
header field of the sent request is 1.2 and the response to the
request is a 302, then the hi-index in the History-Info header
field for the new hi-targeted-to-URI would be 1.3.
5. Forking requests: If the request forwarding is done in multiple
forks (sequentially or in parallel), the SIP entity MUST set the
hi-index for each hi-entry for each forked request per the rules
above, with each new request having a unique index. Each index
MUST be sequentially assigned. For example, if the index in the
last History-Info header field in the received request is 1.1,
this processing entity would initialize its index to 1.1.1 for
the first fork, 1.1.2 for the second, and so forth (see Figure 1
for an example). Note, that in the case of parallel forking,
only the hi-entry corresponding to the fork is included in the
request because no response can yet have been received for any of
the parallel forked requests.
6. Missing entry: If the request clearly has a gap in the hi-entry
(i.e., the last hi-entry and Request-URI differ), the entity
adding an hi-entry MUST add a single index with a value of "0"
(i.e., the non-negative integer zero) prior to adding the
appropriate index for the action to be taken. For example, if
the index of the last hi-entry in the request received was 1.1.2
and there was a missing hi-entry and the request was being
forwarded to the next hop, the resulting index will be 1.1.2.0.1.
In the case of requests which are forked by a proxy that does not
support History-Info, it is possible for hi-entries generated by
different entities to have the same index - i.e., each entity
supporting History-Info would receive a forked request with the
same hi-index to which they would add the value of ".0" prior to
adding the appropriate index. Thus, in the previous example,
each of the next hop entities would generate an hi-index of
1.1.2.0.1.
10.4. Mechanism for Target Determination in the History-Info Header
Field
This specification defines three header field parameters, "rc", "mp"
and "np". The header field parameters "rc" and "mp" indicate the
mechanism by which a new target for a request is determined. The
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header field "np" reflects that the target has not changed. All
parameters contain an index whose value is the hi-index of the hi-
entry with an hi-targeted-to-uri that represents the Request-URI that
was retargeted.
The SIP entity MUST determine the specific parameter field to be
included in the hi-target-param, in the History-Info header field, as
the targets are added to the target set per the procedures in section
16.5 of [RFC3261] or per section 8.1.3.4 [RFC3261] in the case of
retargeting to a contact URI received in a 3xx response. In the
latter case, the specific header field parameter in the Contact
header field becomes the header field parameter that is used in the
hi-entry when the request is retargeted. If the Contact header field
does not contain an "rc" or "mp" header field parameter, then the SIP
entity MUST NOT include an "rc" or "mp" header field parameter in the
hi-target-param in the hi-entry when the request is retargeted to a
contact URI received in a 3xx response. This is because the redirect
server is the only element with any knowledge on how the target was
determined. Note, that the "np" header field parameter is not
applicable in the case of redirection.
The SIP entity (intermediary or redirect server) determines the
specific header field parameter ("rc", "mp" or "np") to be used based
on the following criteria:
o "rc": The Request-URI has changed while retaining the target user
associated with the original Request-URI prior to retargeting.
o "mp": The target was determined based on a mapping to a user other
than the target user associated with the Request-URI being
retargeted.
o "np": The target hasn't changed and the associated Request-URI
remained the same.
Note that there are two scenarios by which the "mp" header field
parameter can be derived.
o The mapping was done by the receiving entity on its own authority,
in which case the mp-value is the parent index of the hi-entry's
index.
o The mapping was done due to receiving a 3xx response, in which
case the mp-value is an earlier sibling or descendant of an
earlier sibling of the hi-entry's index, that of the downstream
request which received the 3xx response.
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11. Application Considerations
History-Info provides a very flexible building block that can be used
by intermediaries and UAs for a variety of services. Prior to any
application usage of the History-Info header field parameters, the
SIP entity that processes the hi-entries MUST evaluate the hi-
entries. The SIP entity MUST be prepared to process effectively
messages whose hi-entries show evidence of "gaps", that is,
situations that reveal that not all of the forks of the request have
been recorded in the hi-entries. Gaps are possible if the request is
forwarded through intermediaries that do not support the History-Info
header field and are reflected by the existence of hi-entries with a
nonnegative integer of "0" e.g. "1.1.0.1". Gaps are also possible in
the case of parallel forking if there is an outstanding request at
the time the SIP entity sends a message. In addition, gaps may
introduce the possibility of duplicate values for the hi-index in the
case that a proxy that does not support History-Info forks a request.
If gaps are detected, the SIP entity MUST NOT treat this as an error,
but SHOULD indicate to any applications that there are gaps. The
interpretation of the information in the History-Info header field
depends upon the specific application; an application might need to
provide special handling in some cases where there are gaps.
The following describes some categories of information that
applications can use:
1. Complete history information - e.g., for debug or other
operational and management aspects, optimization of determining
targets to avoid retargeting to the same URI, etc. This
information is relevant to proxies, UACs and UASs.
2. Hi-entry with the index that matches the value of the "rc" header
field parameter in the last hi-entry with a "rc" header field
parameter in the Request received by a UAS - i.e., the last AOR
that was retargeted to a contact based on an AOR-to-contact
binding.
3. Hi-entry with the index that matches the value of the "mp" header
field parameter in the last hi-entry with a "mp" header field
parameter in the hi-target-param in the Request received by a UAS
- i.e., the last Request URI that was mapped to reach the
destination.
4. Hi-entry with the index that matches the value of the "rc" header
field parameter in the first hi-entry with a "rc" header field
parameter in the Request received by a UAS. Note, this would be
the original AoR if all the entities involved support the
History-Info header field and there is absence of an "mp" header
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field parameter prior to the "rc" header field parameter in the
hi-target-param in the History-Info header field. However, there
is no guarantee that all entities will support History-Info, thus
the hi-entry that matches the value of the "rc" header field
parameter of the first hi-entry with an "rc" header field
parameter in the hi-target-param within the domain associated
with the target URI at the destination is more likely to be
useful.
5. Hi-entry with the index that matches the value of "mp" header
field parameter in the first hi-entry with an "mp" header field
parameter in the Request received by a UAS. Note, this would be
the original mapped URI if all entities supported the History-
Info header field. However, there is no guarantee that all
entities will support History-Info, thus the hi-entry that
matches the value of the "mp" header field parameter of the first
hi-entry with an "mp" header field parameter within the domain
associated with the target URI at the destination is more likely
to be useful.
In many cases, applications are most interested in the information
within a particular domain(s), thus only a subset of the information
is required.
Some applications may use multiple types of information. For
example, an Automatic Call Distribution (ACD)/Call center application
that utilizes the hi-entry which index matches the value of the "mp"
header field parameter of the first hi-entry with an "mp" header
field parameter, may also display other agents, reflected by other
hi-entries prior to entries with hi-target value of "rc" header field
parameter, to whom the call was targeted prior to its arrival at the
current agent. This could allow the agent the ability to decide how
they might forward or reroute the call if necessary (avoiding agents
that were not previously available for whatever reason, etc.).
Since support for History-Info header field is optional, a service
MUST define default behavior for requests and responses not
containing History-Info header fields. For example, an entity may
receive an incomplete set of hi-entries or hi-entries which are not
tagged appropriately with an hi-target-param in the case of entries
added by entities that are only compliant to RFC4244. This may not
impact some applications (e.g., debug), however, it could require
some applications to make some default assumptions in this case. For
example, in an ACD scenario, the application could select the oldest
hi-entry with the domain associated with the ACD system and display
that as the original called party. Depending upon how and where the
request may have been retargeted, the complete list of agents to whom
the call was targeted may not be available.
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12. Application Specific Usage
The following are possible (non-normative) application-specific
usages of History-Info.
12.1. PBX Voicemail
A voicemail system typically requires the original called party
information to determine the appropriate mailbox so an appropriate
greeting can be provided and the appropriate party notified of the
message.
The original target is determined by finding the first hi-entry
tagged with "rc" and using the hi-entry referenced by the index of
"rc" header field parameter as the target for determining the
appropriate mailbox. This hi-entry is used to populate the "target"
URI parameter as defined in [RFC4458] The VMS can look at the last
hi-entry and find the target of the mailbox by looking at the URI
entry in the "target" URI parameter in the hi-entry.
This example usage does not work properly in the presence of
forwarding that takes place before the call reaches the company in
that case not the first hi-entry with an rc value, but the first hi-
entry with an rc value following an mp entry needs to be picked.
Further detail for this example can be found in the call flow
entitled "PBX Voicemail Example" in
[I-D.ietf-sipcore-rfc4244bis-callflows].
Note that in the case where there is no entry tagged with "rc", a VMS
can follow the procedures, as defined in [RFC4458], for the
"Interaction with Request History Information".
12.2. Consumer Voicemail
The voicemail system in these environment typically requires the last
called party information to determine the appropriate mailbox so an
appropriate greeting can be provided and the appropriate party
notified of the message.
The last target is determined by finding the hi-entry referenced by
the index of last hi-entry tagged with "rc" for determining the
appropriate mailbox. This hi-entry is used to populate the "target"
URI parameter as defined in [RFC4458]. The VMS can look at the last
hi-entry and find the target of the mailbox by looking for the
"target" URI parameter in the hi-entry. Further detail for this
example can be found in the call flow entitled "Consumer Voicemail
Example" in [I-D.ietf-sipcore-rfc4244bis-callflows].
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In the case where there is no entry tagged with "rc", a VMS can
follow the procedures, as defined in [RFC4458], for the "Interaction
with Request History Information".
13. Security Considerations
The security requirements for this specification are specified in
Appendix A.1.
This document defines a header field for SIP. The use of the
Transport Layer Security (TLS) protocol [RFC5246] as a mechanism to
ensure the overall confidentiality of the History-Info header fields
(SEC-req-4) is strongly RECOMMENDED. If TLS is NOT used, the
intermediary MUST ensure that the messages are only sent within an
environment that is secured by other means or that the messages don't
leave the intermediary's domain. 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 header fields are
no less, nor no more, secure than other SIP header fields, which
generally have even more impact on the subsequent processing of SIP
sessions than the History-Info header field.
Note that while using the SIPS scheme (as per [RFC5630]) 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.
In terms of ensuring the privacy of hi-entries, the same security
considerations as those described in [RFC3323] apply. The privacy
service that's defined in [RFC3323] MUST also support the new privacy
header field priv-value of "history" and anonymize hi-entries in the
case of a priv-value of "header" as described in Section 10.1.2.
14. IANA Considerations
This document requires several IANA registrations detailed in the
following sections.
This document obsoletes [RFC4244] but uses the same SIP header field
name, Privacy header field and Option tag. The IANA registry needs
to update the references to [RFC4244] with [RFC XXXX], where XXXX is
the RFC number for this document.
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14.1. Registration of New SIP History-Info Header Field
This document defines a SIP header field name: History-Info and an
option tag: histinfo. The following updates have been made to
http:///www.iana.org/assignments/sip-parameters.
The following row has been updated in the header field section:
Header Name Compact Form Reference
----------- ------------ ---------
History-Info none [RFC XXXX]
The following has been updated in the Options Tags section:
Name Description Reference
---- ----------- ---------
histinfo When used with the Supported header field, [RFC XXXX]
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.
14.2. Registration of "history" for SIP Privacy Header Field
This document defines a priv-value for the SIP Privacy header field:
history. The following updates have been made to
http://www.iana.org/assignments/sip-priv-values. The following has
been updated in the registration for the SIP Privacy header field:
Name Description Registrant Reference
---- ----------- ---------- ---------
history Privacy requested for Mary Barnes [RFC XXXX]
History-Info header mary.ietf.barnes@gmail.com
fields(s)
Note to RFC Editor: Please replace RFC XXXX with the RFC number of
this specification.
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14.3. Registration of Header Field Parameters
This specification defines the following new SIP header field
parameters in the SIP Header Field parameter sub-registry in the SIP
Parameter Registry, http:/www.iana.org/assignments/sip-parameters.
Header Field Parameter Name Predefined Reference
Values
____________________________________________________________________
History-Info mp No [RFC xxxx]
History-Info rc No [RFC xxxx]
History-Info np No [RFC xxxx]
Contact mp No [RFC xxxx]
Contact rc No [RFC xxxx]
Contact np No [RFC xxxx]
Note to RFC Editor: Please replace RFC XXXX with the RFC number of
this specification.
15. Acknowledgements
Jonathan Rosenberg et al produced the document that provided
additional use cases precipitating the requirement for the new header
parameters to capture the method by which a Request URI is
determined. The authors would like to acknowledge the constructive
feedback provided by Ian Elz, Paul Kyzivat, John Elwell, Hadriel
Kaplan, Marianne Mohali, Brett Tate, and Dale Worley. John Elwell
also provided excellent suggestions in terms of document structure.
Dan Romascanu performed the Gen-ART review.
Mark Watson, Cullen Jennings and Jon Peterson provided significant
input into the initial work that resulted in the development of of
[RFC4244]. 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.
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16. Changes from RFC 4244
This RFC replaces [RFC4244].
Deployment experience with [RFC4244] over the years has shown a
number of issues, warranting an update:
o In order to make [RFC4244] work in "real life", one needs to make
"assumptions" on how History-Info is used. For example, many
implementations filter out many entries, and only leave specific
entries corresponding, for example, to first and last redirection.
Since vendors uses different rules, it causes significant
interoperability issues.
o [RFC4244] is overly permissive and evasive about recording
entries, causing interoperability issues.
o The examples in the call flows had errors, and confusing because
they often assume "loose routing".
o [RFC4244] has lots of repetitive and unclear text due to the
combination of requirements with solution.
o [RFC4244] gratuitously mandates the use of TLS on every hop. No
existing implementation enforces this rule, and instead, the use
of TLS or not is a general SIP issue, not an [RFC4244] issue per
se.
o [RFC4244] does not include clear procedures on how to deliver
current target URI information to the UAS when the Request-URI is
replaced with a contact.
o [RFC4244] does not allow for marking History-Info entries for easy
processing by User Agents.
The following summarizes the functional changes between this
specification and [RFC4244]:
1. Added header field parameters to capture the specific method by
which a target is determined to facilitate processing by users of
the History-Info header field entries. A specific header field
parameter is captured for each of the target URIs as the target
set is determined (per section 16.5 of [RFC3261]). The header
field parameter is used in both the History-Info and the Contact
header fields.
2. Added a way to indicate a gap in History-Info by adding a non-
negative integer of "0".
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3. Rather than recommending that entries be removed in the case of
certain values of the Privacy header field, the entries are
anonymized.
4. Updated the security section to be equivalent to the security
recommendations for other SIP header fields inserted by
intermediaries.
5. Removed Appendix B since a separate call flow document is being
published as a companion to this document.
The first 2 changes are intended to facilitate application usage of
the History-Info header field and eliminate the need to make
assumptions based upon the order of the entries and ensure that the
most complete set of information is available to the applications.
In addition, editorial changes were done to both condense and clarify
the text, moving the requirements to an appendix and removing the
inline references to the requirements. The examples were simplified
and updated to reflect the protocol changes. Several of the call
flows in the appendix were removed and put into a separate document
that includes additional use cases that require the new header field
parameters.
16.1. Backwards compatibility
This specification is backwards compatible since [RFC4244] allows for
the addition of new optional parameters. This specification adds an
optional SIP header field parameter to the History-Info and Contact
header fields. Entities that have not implemented this specification
will ignore these parameters, however, per [RFC4244] an entity will
not remove these parameters from an hi-entry. While entities
compliant to this document and [RFC4244] must be able to recognize
gaps in the hi-entries, this document requires that an index of "0"
be used in this case. Whereas [RFC4244] recommended (but did not
require) the use of "1". However, since the ABNF in [RFC4244]
defines the index as a DIGIT, "0" would be a valid value, thus an
[RFC4244] implementation should not have an issue if it receives hi-
entries added by intermediaries compliant to this document.
As for the behavior of the UACs, UASs and intermediaries, the
following additional normative changes have been made:
UAC behavior
1. Inclusion of option tag by UAC has changed from SHOULD to MUST.
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2. Inclusion of hi-target-entry along with hi-index has changed from
MAY/RECOMMEND to MUST/MUST.
3. Behavior surrounding the addition of hi-target-entry based on 3xx
response has changed from MAY/SHOULD to MUST.
None of the behavior changes would cause any backward or forward
compatibility issues.
UAS behavior
1. Inclusion of hi-entry in response has changed from SHOULD to
MUST.
As the entity receiving response with hi-entry expected it with
SHOULD, this change will not cause any backward compatibility issues.
Proxy/Redirect Server behavior
1. Inclusion of H-I as forwarding the request has changed from
SHOULD to MUST.
2. Association of Reason with time-out/internal reason has changed
from MAY to MUST.
3. Inclusion of hi-index has changed from RECOMMENDED to MUST.
4. Inclusion of hi-entries in response has changed from SHOULD to
MUST.
None of above behavior changes impact backwards compatibility since
they only strengthen normative behavior to improve interoperability.
In cases where an entity that is compliant to this document, receives
a request that contains hi-entries compliant only to RFC4244 (i.e,
the hi-entries do not contain any of the new header field
parameters), the entity MUST NOT add any of the new header field
parameters to the hi-entries. The hi-entries MUST be cached and
forwarded as any other entries are as specified in Section 9.1. As
with RFC4244 compliant entities, applications must be able to
function in cases of missing information, as specified in Section 11.
17. References
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17.1. 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.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[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.
17.2. Informative References
[RFC5627] Rosenberg, J., "Obtaining and Using Globally Routable User
Agent URIs (GRUUs) in the Session Initiation Protocol
(SIP)", RFC 5627, October 2009.
[RFC5630] Audet, F., "The Use of the SIPS URI Scheme in the Session
Initiation Protocol (SIP)", RFC 5630, October 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.
[RFC3966] Schulzrinne, H., "The tel URI for Telephone Numbers",
RFC 3966, December 2004.
[RFC4458] Jennings, C., Audet, F., and J. Elwell, "Session
Initiation Protocol (SIP) URIs for Applications such as
Voicemail and Interactive Voice Response (IVR)", RFC 4458,
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April 2006.
[I-D.ietf-sipcore-rfc4244bis-callflows]
Barnes, M., Audet, F., Schubert, S., Elburg, H., and C.
Holmberg, "Session Initiation Protocol (SIP) History-Info
Header Call Flow Examples",
draft-ietf-sipcore-rfc4244bis-callflows-06 (work in
progress), July 2013.
Appendix A. 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.
A. In some scenarios, it might be possible for more than one
instance of retargeting to occur within the same proxy. A
proxy MUST also generate Request History information for the
'internal retargeting'.
B. An entity (UA or proxy) retargeting in response to a redirect
or REFER MUST include any Request History information from
the redirect/REFER in the new request.
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 shall include the following:
A. The new URI or address to which the request is in the process
of being retargeted,
B. The URI or address from which the request was retargeted, and
whether the retarget URI was an AOR
C. The mechanism by which the new URI or address was determined,
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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 early or 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.
A.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-Info
entry either by adding an additional hi-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.
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.
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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.
A.2. Privacy Requirements
Since the Request-URI that is captured could inadvertently reveal
information about the originator, there are general privacy
requirements that MUST be met:
1. PRIV-req-1: The entity retargeting the Request must ensure that
it maintains the network-provided privacy (as described in
[RFC3323]) associated with the Request as it is retargeted.
2. PRIV-req-2: The entity receiving the Request History must
maintain the privacy associated with the information. In
addition, local policy at a proxy may identify privacy
requirements associated with the Request-URI being captured in
the Request History information.
3. PRIV-req-3: Request History information subject to privacy shall
not be included in out going messages unless it is protected as
described in [RFC3323].
Authors' Addresses
Mary Barnes
Polycom
TX
US
Email: mary.ietf.barnes@gmail.com
Francois Audet
Skype
Email: francois.audet@skype.net
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Shida Schubert
NTT
Email: shida@ntt-at.com
Hans Erik van Elburg
Detecon International Gmbh
Sternengasse 14-16
Cologne,
Germany
Email: ietf.hanserik@gmail.com
Christer Holmberg
Ericsson
Hirsalantie 11, Jorvas
Finland
Email: christer.holmberg@ericsson.com
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