Network Working Group M. Barnes
Internet-Draft Nortel
Obsoletes: RFC4244 F. Audet
(if approved) Skype
Intended status: Standards Track S. Schubert
Expires: August 17, 2010 NTT
J. van Elburg
Detecon International Gmbh
C. Holmberg
Ericsson
February 13, 2010
An Extension to the Session Initiation Protocol (SIP) for Request
History Information
draft-ietf-sipcore-rfc4244bis-00.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 call arrives at a specific
application or user. This document defines an optional SIP header,
History-Info, for capturing the history information in requests. A
SIP/SIPS URI parameter is defined to tag information necessary to
populate the History-Info header. In addition, this document defines
a value for the Privacy header specific to the History-Info header.
Status of this Memo
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 4
3. Overview of Operations . . . . . . . . . . . . . . . . . . . . 5
4. General User Agent Behavior . . . . . . . . . . . . . . . . . 9
4.1. User Agent Client (UAC) Behavior . . . . . . . . . . . . . 9
4.2. User Agent Server (UAS) Behavior . . . . . . . . . . . . . 10
4.3. Redirect Server Behavior . . . . . . . . . . . . . . . . . 10
5. Proxy Behavior . . . . . . . . . . . . . . . . . . . . . . . . 10
5.1. Adding the History-Info Header to Requests . . . . . . . . 10
5.1.1. Initial Request . . . . . . . . . . . . . . . . . . . 11
5.1.2. Re-sending based on failure response . . . . . . . . . 12
5.1.3. Re-sending based on redirection response . . . . . . . 13
5.2. Sending History-Info in Responses . . . . . . . . . . . . 13
6. The History-Info header field . . . . . . . . . . . . . . . . 13
6.1. Definition . . . . . . . . . . . . . . . . . . . . . . . . 13
6.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 16
6.3. Procedures . . . . . . . . . . . . . . . . . . . . . . . . 16
6.3.1. SIP/SIPS URI target parameter for History-Info
Header . . . . . . . . . . . . . . . . . . . . . . . . 16
6.3.2. Privacy in the History-Info Header . . . . . . . . . . 17
6.3.3. Reason in the History-Info Header . . . . . . . . . . 18
6.3.4. Indexing in the History-Info Header . . . . . . . . . 18
6.3.5. Request Target in the History-Info Header . . . . . . 20
7. Application Considerations . . . . . . . . . . . . . . . . . . 20
8. Security Considerations . . . . . . . . . . . . . . . . . . . 21
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
9.1. Registration of New SIP History-Info Header . . . . . . . 21
9.2. Registration of "history" for SIP Privacy Header . . . . . 22
9.3. Registration of "hit" SIP/SIPS URI Parameter . . . . . . . 22
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 23
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 23
12. Changes from RFC 4244 . . . . . . . . . . . . . . . . . . . . 23
12.1. Backwards compatibility . . . . . . . . . . . . . . . . . 25
13. Changes since last Version . . . . . . . . . . . . . . . . . . 25
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28
14.1. Normative References . . . . . . . . . . . . . . . . . . . 28
14.2. Informative References . . . . . . . . . . . . . . . . . . 29
Appendix A. Request History Requirements . . . . . . . . . . . . 29
A.1. Security Requirements . . . . . . . . . . . . . . . . . . 31
A.2. Privacy Requirements . . . . . . . . . . . . . . . . . . . 31
Appendix B. Detailed call flows . . . . . . . . . . . . . . . . . 32
B.1. Sequentially Forking (History-Info in Response) . . . . . 32
B.2. Voicemail . . . . . . . . . . . . . . . . . . . . . . . . 39
B.3. Automatic Call Distribution . . . . . . . . . . . . . . . 41
B.4. History-Info with Privacy Header . . . . . . . . . . . . . 43
B.5. Privacy Header for a Specific History-Info Entry . . . . . 44
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B.6. Determining the Alias used. . . . . . . . . . . . . . . . 46
B.7. GRUU . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
B.8. Limited Use Address . . . . . . . . . . . . . . . . . . . 50
B.9. Sub-Address . . . . . . . . . . . . . . . . . . . . . . . 52
B.10. Service Invocation . . . . . . . . . . . . . . . . . . . . 56
B.11. Toll Free Number . . . . . . . . . . . . . . . . . . . . . 57
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 59
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1. Introduction
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 a need for a standard
mechanism within SIP for communicating the retargeting 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. A SIP/
SIPS URI parameter is defined to tag information necessary to
populate the History-Info header. In addition, this document defines
a value for the Privacy header specific to the History-Info header.
The History-Info header provides a building block for development of
SIP based applications and services. The requirements for the
solution described in this document are included in Appendix A.
Example scenarios using the History-Info header are included in
Appendix B.
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 both to the
process of a Proxy Server/User Agent Client (UAC) changing a Uniform
Resource Identifier (URI) in a request based on the rules for
determining request targets as described in Section 16.5 of [RFC3261]
and the subsequent forwarding of that request as described in section
16.6 of [RFC3261].
The term "forward" is used consistent with the terminology in
[RFC3261]. Noting that [RFC3261] 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.
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However, the context of the usage is sufficient to differentiate the
slightly different meanings.
The terms "location service", "redirect" and "AOR" are used
consistent with the terminology in [RFC3261].
3. Overview of Operations
SIP implicitly provides retargeting capabilities that enable calls 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 call is retargeted to process the call 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 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:
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 home proxy upon receipt
of the initial request.
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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.
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, see Appendix A). The solution is to capture the
Request-URIs as a request is retargeted, in a SIP header: History-
Info (CONTENT-req, see Appendix A). 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 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, see
Appendix A) and any valid response to these requests (ISSUER-req, see
Appendix A).
This specification defines parameters detailed in Section 6.1 for
carrying the following information in the History-Info header:
o Targeted-to-URI: The targeted-to-URI entry captures the Request-
URI for the specific request as it is forwarded.
o Index: The index reflects the chronological order of the
information, indexed to also reflect the forking and nesting of
requests.
o Reason: Reason describes why an entry was retargeted.
o Privacy: Privacy is used to request that an entry be anonymized in
the case of a request that is retargeted to a domain for which the
retargeting entity is not responsible.
o Target: The target parameter indicates whether the Targeted-to-URI
is a registered contact ("rc") for or another user mapped ("mp")
from the Request-URI in the incoming request that was retargeted.
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This specification also defines the "hit" SIP/SIPS URI Parameter.
This parameter is added to URIs as they are added to the target list
for a request based on the same criteria as the target parameter
described above. This URI parameter is used to determine the value
for the target parameter. Further detail is provided in
Section 6.3.1.
In addition, this specification defines a value for the Privacy
header, "history", that applies to all the History-Info header
entries in a Request or to a specific History-Info header entry as
described above. Further detailed is provided in Section 6.3.2.
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 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 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 target information, including any
parameters in the request URI. Bob can now recover that information
by locating the first entry just prior to the last hi-entry marked as
"rc", which is one level up in indexing from the last hi-entry -
i.e., the sip:bob@biloxi.example.com entry with index=1.1.
The formatting in this scenario 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 6.2 for the proper formatting. Additional detailed
scenarios are available in the Appendix B.
Note: This example uses loose routing procedures.
Alice atlanta.example.com biloxi.example.com Bob@pc Bob@phone
| | | | |
| INVITE sip:bob@biloxi.example.com;p=x | |
|--------------->| | | |
| Supported: histinfo | | |
| | | | |
| | INVITE sip:bob@biloxi.example.com;p=x
| |--------------->| | |
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| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1
| 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
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1.1
| History-Info: <sip:bob@192.0.2.3>;index=1.1.1;rc
| | | | |
| | | 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>;index=1.1
| History-Info: <sip:bob@192.0.2.7>;index=1.1.2;rc
| | | 200 | |
| | |<---------------| |
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1.1
| History-Info: <sip:bob@192.0.2.3>;index=1.1.1;rc
| | | | |
| | |<===Proxy cancels INVITE==>|
| | 200 | | |
| |<---------------| | |
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1.1
| History-Info: <sip:bob@192.0.2.3>;index=1.1.1;rc
| History-Info: <sip:bob@192.0.2.7?Reason=SIP;cause=487>;\
| index=1.1.2;rc
| | | | |
| 200 | | | |
|<---------------| | | |
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1.1
| History-Info: <sip:bob@192.0.2.3;index=1.1.1;rc
| History-Info: <sip:bob@192.0.2.7?Reason=SIP;cause=487>;\
| index=1.1.2;rc
| | | | |
| ACK | | | |
|--------------->| ACK | | |
| |--------------->| ACK | |
| | |--------------->| |
Figure 1: Basic Call
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4. General User Agent Behavior
This section describes the processing specific to UAs for the
History-Info header.
4.1. 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 at least know 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 main reason it is
allowed is for B2BUAs who are performing proxy-like functions such as
routing.
A UAC that does not want an hi-entry added due to privacy
considerations MUST include a Privacy header with a priv-value(s) of
"header" or "history." A UAC that wants to ensure that privacy not
be applied to its identity MUST include a Privacy header with a priv-
value of "none."
In the case where a UAC receives a 3xx response with a Contact header
and sends a new request in response to it, the UAC MAY include in the
outgoing request the previous hi-entry(s) received in the response.
In this case, the reason header MUST be associated with the hi-
targeted-to-uri in the previous (last) hi-entry, as described in
Section 6.3.3. A new hi-entry MUST then be added for the URI from
the Contact header (which becomes the new Request-URI). An index
MUST be added to the hi-entry. The value for the index is determined
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 6.3.4. If the URI in the
Contact header contains a "hit" URI parameter, the UAC MUST add a
target parameter to the hi-entry and MUST remove the URI parameter as
described in Section 6.3.5.
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.
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4.2. User Agent Server (UAS) Behavior
Once the request terminates at the UAS, 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. Some examples are included in
Appendix B.
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. If privacy is required, entries MUST be anonymized using
[RFC3323]. The UAS MUST follow the rules for a redirect server per
Section 4.3 in generating a 3xx response.
The processing of History-Info in responses follows the methodology
described in Section 16.7 of [RFC3261], with the processing of
History-Info headers adding an additional step, just before Step 9,
"Forwarding the Response".
4.3. Redirect Server Behavior
A redirect server MUST include the History-Info headers received in
the request in the 3XX response that it sends. A redirect server
MUST NOT add any new History-Info entries. In order to provide the
necessary information to populate the target parameter for the new
History-Info entries as a request is redirected, the redirect server
MUST add a "hit" URI parameter to the URIs in the contact header.
The appropriate values for this parameter are described in
Section 6.3.1.
5. Proxy Behavior
The specific processing by proxies for adding the History-Info
headers in SIP requests and responses is described in this section.
5.1. Adding the History-Info Header to Requests
This section describes the process of adding the History-Info header
to requests for the following cases:
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o Forwarding of initial request (see Section 5.1.1)
o Resending based on failure response (see Section 5.1.2)
o Resending based on redirection response (see Section 5.1.3)
Retargeting is an iterative process, i.e., a proxy may redirect
"internally " more than one time. A typical example would be a proxy
that redirects a request first to a different user (i.e., it maps to
a different AOR), and then forwards to a registered contact bound to
that new AOR. A proxy that uses such mechanism SHOULD add multiple
hi-entry fields (e.g., bob@example.com to office@example.com to
office@192.0.2.5) to provide a logical description of the retargeting
process. A Reason MAY be associated with the hi-targeted-to-uri that
has been retargeted as shown in the example in Appendix B.1.
5.1.1. Initial Request
Upon receipt of an initial request for a dialog, or a standalone
request, a proxy forwarding the request MUST perform the following
steps. Note that those steps below do not apply if the request is
being re-sent as a result of failure (i.e., timeout, reception of an
error response), or redirection caused by receipt of a 3XX message).
Step 1: Adding Entries on Behalf of Previous Hops
If an incoming request does not already have a History-Info header
field (e.g., the UAC does not include any History-Info header and
no proxies in between support History-Info), or if the Request-URI
of the incoming request does not match the last hi-entry (e.g.,
the last proxy does not support History-Info), the proxy MUST
insert an hi-entry. The proxy MUST set the hi-targeted-to-uri
based to the value of Request-URI in the incoming request, unless
privacy is required. If privacy is required, the procedures of
Section 6.3.2 MUST be used. The proxy MUST NOT include a hi-
target attribute. The proxy MUST include an hi-index attribute as
described in Section 6.3.4.
Step 2: Tagging URIs in Target Set with "hit" Parameter
The proxy then proceeds to determining the request targets as per
16.5/[RFC3261]. The proxy MUST add a "hit" SIP/SIPS URI parameter
for the target URI that are determined based on either of the two
mechanisms as described in Section 6.3.1.
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Step 3: Generating New Entries for Each Outgoing Request
The proxy then proceeds to request forwarding as per 16.6/
[RFC3261]. The proxy MUST add a separate hi-entry in each
separate outgoing request for each of the current (outgoing)
targets in the target set. The proxy MUST set the hi-targeted-to-
uri in those separate hi-entry(s) to the value of the Request-URI
of the current (outgoing) request, unless privacy is required. If
privacy is required, the procedures of Section 6.3.2 MUST be used.
The proxy MUST include an hi-index for each of the separate hi-
entry(s) as described in Section 6.3.4. If the Request-URI
contains a "hit" SIP/SIPS URI parameter, the proxy MUST include a
hi-target attribute for each of the separate entry(s) as described
in Section 6.3.5. The proxy MUST remove the "hit" URI parameter
from the Request-URI.
5.1.2. Re-sending based on failure response
When re-sending a request as a result of retargeting because of
failure (i.e., either reception of error responses or a timeout which
is considered to be an implicit 487 error response), the proxy MUST
perform the following steps:
Step 1: Including the Entries from Error Responses & Timeouts
The proxy MUST build the History-Info header field(s) sent in the
outgoing request using the aggregate information associated with
the received error responses(s) and timeout(s) for all the
branches that are generating failures, including the header
entries in the order indicated by the indexing (see
Section 6.3.4). If the received error response did not include
any History-Info header fields, the proxy MUST use the same
History-Info header fields that were sent in the outgoing request
that failed to build the outgoing request.
Step 2: Tagging the Last Entries
The proxy then examines the last hi-entry of the History-Info that
was just generated in Step 1 for each one of the branches that
generated failures or timeouts and MUST add a Reason header for
each one of those entries as per the procedures of Section 6.3.3.
Step 3: Generating New Entries for Each Outgoing Requests
Same as per Step 3 above for the normal forwarding case
Section 5.1.1.
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5.1.3. Re-sending based on redirection response
When re-sending a request as a result of retargeting because of
redirection (i.e., receipt of a 3XX response), the following steps
apply:
Step 1: Including Previous Entries
The proxy MUST include the History-Info header fields that were
sent in the outgoing request that is being redirected.
Step 2: Tagging the Last Entry
The proxy then examines the last hi-entry of the History-Info that
was just generated in Step 1 and MUST add a Reason header this
entry as per the procedures of Section 6.3.3.
Step 3: Generating New Entries for Each Outgoing Requests
Same as per Step 3 for the normal forwarding case Section 5.1.1.
5.2. Sending History-Info in Responses
A proxy that receives a request with the "histinfo" option tag in the
Supported header, SHOULD forward captured History-Info in subsequent,
provisional, and final responses to the request sent by the ultimate
UAS (see Section 4.2).
A proxy MAY anonymize any hi-entry whose domain corresponds to a
domain for which it is responsible (as per [RFC3323]). For example,
a proxy could require that such entries be anonymized when a response
is forwarded to a domain for which the proxy is not responsible.
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".
6. The History-Info header field
6.1. Definition
History-Info is a header field as defined by [RFC3261]. "It may
appear in any initial request for a dialog, standalone request or
responses associated with these requests. For example, History-Info
may appear in INVITE, REGISTER, MESSAGE, REFER, OPTIONS, SUBSCRIBE,
and PUBLISH and any valid responses, plus NOTIFY requests that
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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 5.1), including the index and securing the
header, the ordering of the History-Info headers in the request is
assured (SEC-req-2, see Appendix A.1). 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 included for the
hi-targeted-to-uri that was retargeted as opposed to the hi-
targeted-to-uri to which it was retargeted.
o Privacy: An optional parameter for History-Info, reflected in the
History-Info header field values by including the Privacy Header
[RFC3323] escaped in the hi- targeted-to-uri or by adding the
Privacy header to the request. The latter case indicates that the
History-Info entries for the domain MUST be anonymized prior to
forwarding, whereas the use of the Privacy header escaped in the
hi-targeted-to-uri means that a specific hi-entry MUST be
anonymized.
o Target (hi-target): An optional parameter for the History-Info
header. This parameter is added if the URI to which the outgoing
request is targeted contains a "hit" URI parameter Section 6.3.1.
The hi-target is added for a hi-entry when it is first added in a
History-Info header field, and only one value is permitted. Upon
receipt of a request or response containing the History-Info
header, a UA can determine the mechanism by which the target was
determined. The following attributes are defined for this
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parameter derived from the values of the "hit" URI parameter:
* "rc": The hi-target is set to "rc" if the "hit" URI parameter
is set to a value of "rc".
* "mp": The hi-target is set to "mp" if the "hit" URI parameter
is set to a value of "mp".The "mp" attribute in the hi-target
parameter includes the index parameter for the hi-targeted-to-
uri that was retargeted, thus identifying the "mapped from"
target.
o Extension (hi-extension): A 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-param)
hi-targeted-to-uri = name-addr
hi-param = hi-index / hi-target / hi-extension
hi-index = "index" EQUAL 1*DIGIT *("." 1*DIGIT)
hi-target = "rc" / mp-param
mp-param = "mp" EQUAL 1*DIGIT *("." 1*DIGIT)
hi-extension = generic-param
The following rules apply:
o There MUST be exactly one hi-index parameter per hi-entry.
o There MUST be no more than one hi-target parameter.
o There MAY be any number of hi-extension parameters.
o The ABNF definitions for "generic-param" and "name-addr" are from
[RFC3261].
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6.2. Examples
The following provides some examples of the History-Info header.
Note that the backslash and CRLF between the fields in the examples
below are for readability purposes only.
History-Info: <sip:UserA@ims.example.com>;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
6.3. Procedures
The following sections define procedures for processing of the
History-Info header and the "hit" SIP/SIPS URI parameter and Privacy
header. These procedures may be applicable to processing entities
such as Proxies, Redirect Servers or User Agents.
6.3.1. SIP/SIPS URI target parameter for History-Info Header
This specification defines a new SIP/SIPS URI Parameter indicating
the mechanism by which a new target for a request is determined.
This parameter is added to the SIP/SIPS URIs as they are added to the
target set per the procedures of 16.5 [RFC3261]] or by a redirect
server as it populates the Contact header for a 3xx response. This
parameter is used to populate the hi-target parameter Section 6.3.5
when a Request-URI is first added in a hi-entry in the History-Info
header field. This parameter MUST be removed from the URI when the
hi-entry is constructed.
The following two values are defined for this URI parameter:
o "rc": The Request-URI is a contact that is bound to an AOR in an
abstract location service. The AOR-to-contact binding has been
placed into the location service by a SIP Registrar that received
a SIP REGISTER request.
o "mp": The Request-URI is a URI that represents another user. This
occurs when a request is to be statically or dynamically
retargeted to another user.
The following defines the ABNF for the "hit" URI parameter:
hit-param = "hit=" ("rc" / "mp")
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6.3.2. Privacy in the History-Info Header
The privacy requirements for this document are described in
Appendix A.2.
The History-Info header can inadvertently reveal information about
the requestor as described in [RFC3323]. The Privacy header is used
to ensure the privacy requirements are satisfied for both the
History-Info entries received by the intermediary in the incoming
request (per PRIV-req-2 in Appendix A.2) and the History-Info entries
that are added by the intermediary as the request is retargeted per
PRIV-req-1 in Appendix A.2. If the requestor has indicated a priv-
value of "session" or "header" in the request, all History-Info
entries MUST be anonymized when the request leaves a domain for which
the intermediary is responsible.
Privacy can also be associated with a specific History-Info entry,
and any entry that corresponds to that same user rather than all
History-Info entries in a request. For example, if Alice sends a
request to Bob without any privacy, and Bob redirects to Carol with
privacy setup for himself, Carol should receive a request where
Alice's history information is present, but Bob's has been
anonymized. This is accomplished by adding a new priv-value,
history, to the Privacy header [RFC3323] indicating that a specific
History-Info header entry can not be forwarded outside the domain.
In addition, the History-Info header can reveal general routing
information which may be viewed by a specific intermediary or
network. Thus, a proxy can use local policy to determine whether the
History-Info header entries for it's whole domain are private or not
when exiting the domain through retargeting (PRIV-req-3).
It is recognized that satisfying the privacy requirements can impact
the functionality of this solution by overriding the request to
generate the information. Thus, the following recommendations are
made to ensure optimal functionality without compromising privacy:
If there is a Privacy header in the request with a priv-value of
"session", "header", or "history", an hi-entry SHOULD be added if
the request is being retargeted to a URI associated with a domain
for which the processing entity is responsible. If there is no
Privacy header, but the processing entity's local policies
indicate that the hi-entry(s) cannot be forwarded beyond the
domain for which this intermediary is responsible, then a Privacy
header with a priv-value of "history" SHOULD be associated with
each hi-entry added by the proxy as the request is forwarded
within the domain.
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If a request is being retargeted to a URI associated with a domain
for which the processing identity is not responsible and there is
a Privacy header in the request with a priv-value of "session",
"header", or "history", the processing entity MUST anonymize hi-
entry(s) as per [RFC3323] prior to forwarding, unless the
processing entity knows a priori that it can rely on a downstream
processing entity within its domain to apply the requested privacy
or local policy allows the forwarding.
6.3.3. 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 (see [RFC3326]), 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 Reason header for a protocol
that is not SIP (e.g., Q.850), it MUST be captured as an additional
Reason associated with the hi-targeted-to-uri that has been
retargeted, along with the SIP Response Code. If the Reason header
is a SIP reason, then it MUST be used as the Reason associated with
the hi-targeted-to-uri rather than the SIP response code.
If a request has timed out (instead of being explicitly rejected), it
SHOULD be treated as if a 487 "Request Terminated" error response
code was received.
6.3.4. 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 6, 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 first entry MUST be set to 1.
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 sub-level of
indexing since the depth/length of the branch is increasing. To
accomplish this, the processing entity reads the value from the
History-Info header in the received request, if available, and
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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 processing entity - 1st instance: For the
first instance of retargeting within a processing entity, the
calculation of the index follows that prescribed for basic
forwarding.
3. Retargeting within a processing entity - subsequent instance: For
each subsequent retargeting of a request by the same processing
entity, 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 processing entity, following 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. Forking requests: If the request forwarding is done in multiple
forks (sequentially or in parallel), the index MUST be captured
for each forked request per the rules above, with each new
request having a unique index. Each index are 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 for each individual fork, only the entry corresponding
that that fork is included (e.g., the entry for fork 1.1.1 is not
included in the request sent to fork 1.1.2, and vice-versa).
6. When a response is built and it represents the aggregate of
multiple forks (e.g., multiple forks that fail), the processing
entity builds the subsequent response using the aggregated
information associated with each of those forks and including the
header entries in the order indicated by the indexing. For
example, if a procesing entity received failure responses for
forks 1.1.1 and 1.1.2, it would forward both the 1.1.1 and 1.1.2
entries to 1.1. See Appendix B.1 for an example. Responses are
processed as described in Section 16.7 of [RFC3261] with the
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aggregated History-Info entries processed similar to Step 7
"Aggregate Authentication Header Field Values".
6.3.5. Request Target in the History-Info Header
The hi-target attribute MUST be added to the History-Info header if
the target to which the request is being forwarded contains a "hit"
URI parameter as defined in Section 6.3.1.
If the value of the "hit" parameter is "mp", then the index of the
entry corresponding to the original target (i.e., the "mapped-from"
target) MUST be added as a parameter to "mp".
7. Application Considerations
As seen by the example scenarios in the Appendix B, History-Info
provides a very flexible building block that can be used by
intermediaries and UAs for a variety of services. As such, any
services making use of History-Info must be designed with the
following considerations:
1. History-Info is optional; thus, a service MUST define default
behavior for requests and responses not containing History-Info
headers.
2. History-Info may be impacted by privacy considerations.
Applications requiring History-Info need to be aware that if
Header-, Session-, or History-level privacy is requested by a UA
(or imposed by an intermediary) that History-Info may not be
available in a request or response. This would be addressed by
an application in the same manner as the previous consideration
by ensuring there is reasonable default behavior should the
information not be available.
3. History-Info may be impacted by local policy. Each application
making use of the History-Info header SHOULD address the impacts
of the local policies on the specific application (e.g., what
specification of local policy is optimally required for a
specific application and any potential limitations imposed by
local policy decisions). Note that this is related to the
optionality and privacy considerations identified in 1 and 2
above, but goes beyond that. For example, due to the optionality
and privacy considerations, an entity may receive only partial
History-Info entries; will this suffice? Note that this would be
a limitation for debugging purposes, but might be perfectly
satisfactory for some models whereby only the information from a
specific intermediary is required.
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8. Security Considerations
The security requirements for this document are specified in
Appendix A.1.
This document defines a 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
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 [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.
9. IANA Considerations
This document requires several IANA registrations detailed in the
following sections.
This document updates [RFC4244] but uses the same SIP header field
name and option tag. The IANA registry needs to update the
references to [RFC4244] with [RFCXXXX].
9.1. Registration of New SIP History-Info Header
This document defines a SIP header field name: History-Info and an
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:.
The following row has been added to the header field section:
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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.
9.2. Registration of "history" for SIP Privacy Header
This document defines a 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.
9.3. Registration of "hit" SIP/SIPS URI Parameter
This specification adds a new value to the IANA registration in the
"SIP/SIPS URI Parameters" registry, http:/www.iana.org/assignments/
sip-parameters, as defined in [RFC3969].
Parameter Name Predefined Values Reference
____________________________________________
hit Yes ("rc"/"mp") [RFCxxxx]
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Note to RFC Editor: Please replace RFC XXXX with the RFC number of
this specification.
10. Contributors
Cullen Jennings, Mark Watson, and Jon Peterson contributed to the
development of the initial requirements for [RFC4244].
Jonathan Rosenberg et al produced the document that provided
additional use cases precipating the requirement for the new "target"
parameter in the History-Info header and the new SIP/SIPS URI
parameter.
11. 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.
Thanks to Ian Elz for his feedback on privacy for this specification.
12. 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 isssues.
o [RFC4244] is overly permissive and evasive about recording
entries, causing interoperability issues.
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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
o [RFC4244] gratuitly 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 a parameter, "target", to the History-Info header and
defined a SIP/SIPS URI parameter indicating targets that are
determined by a registered contact or based on mapping the
incoming Request-URI to another user to facilitate processing at
the UAS. The URI parameter is added to the target URIs as the
target set is determined (per section 16.5 of [RFC3261]) and
removed when the "target" parameter is populated, using the URI
parameter value, in the History-Info header (per section 16.6 of
[RFC3261]).
2. Rather than recommending that entries be removed in the case of
certain values of the privacy header, recommend that the entries
are anonymized.
3. Updated the security section to be equivalent to the security
recommendations for other SIP headers inserted by intermediaries.
The first 2 changes are intended to facilitate application usage of
the History-Info header 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 and examples were simplified and updated to reflect the
protocol changes.
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12.1. Backwards compatibility
This specification is backwards compatible since [RFC4244] allows for
the addition of new optional parameters. This specification adds an
optional parameter "target" to the History-Info header. Entities
that have not implemented this specification should ignore this
parameter, however, per [RFC4244] an entity MUST not remove this
parameter from an hi-entry. This specification defines a SIP/SIPS
URI parameter, "hit". An entity that does not understand the "hit"
URI parameter SHOULD ignore the parameter and MAY remove the
parameter from the URI as it is used as the target for a request.
13. Changes since last Version
NOTE TO THE RFC-Editor: Please remove this section prior to
publication as an RFC.
Changes from (individual) barnes-sipcore-4244bis-03 to (WG) ietf-
sipcore-4244bis-00:
1. Added a new SIP/SIPS URI parameter to tag the URIs as they are
added to the target list and those returned in the contact header
in a 3xx response.
2. Updated description of "target" parameter to use the new URI
parameter value in setting the value for the parameter.
3. Clarified privacy.
4. Changed handling at redirect server to include the use of the new
URI parameter and to remove the functionality of adding the
History-Info entries (basically reverting to core 4244
processing).
5. Additional text to clarify that a service such as voicemail can
be done in multiple ways.
6. Editorial changes including removal of some vestiges of tagging
all entries (including the "aor" tag).
Changes from barnes-sipcore-4244bis-02 to 03:
1. Fixed problem with indices in example in Appendix B.2.
2. Removed oc and rt from the Hi-target parameter.
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3. Removed aor tag
4. Added index parameter to "mp"
5. Added use-cases and call-flows from target-uri into appendix.
Changes from barnes-sipcore-4244bis-01 to 02:
1. Added hi-aor parameter that gets marked on the "incoming" hi-
entry.
2. Hi-target parameter defined to be either rc, oc, mp, rt, and now
gets included when adding an entry.
3. Added section on backwards compatibility, as well as added the
recognition and handling of requests that do not support this
specification in the appropriate sections.
4. Updated redirect server/3xx handling to support the new
parameters - i.e., the redirecting entity must add the new entry
since the proxy does not have access to the information as to how
the Contact was determined.
5. Added section on normative differences between this document and
RFC 4244.
6. Restructuring of document to be more in line with current IETF
practices.
7. Moved Requirements section into an Appendix.
8. Fixed ABNF to remove unintended ordering requirement on hi-index
that was introduced in attempting to illustrate it was a
mandatory parameter.
Changes from barnes-sipcore-4244bis-00 to 01 :
1. Clarified "retarget" definition.
2. Removed privacy discussion from optionality section - just refer
to privacy section.
3. Removed extraneous text from target-parameter (leftover from sip-
4244bis). Changed the terminology from the "reason" to the
"mechanism" to avoid ambiguity with parameter.
4. Various changes to clarify some of the text around privacy.
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5. Reverted proxy response handling text to previous form - just
changing the privacy aspects to anonymize, rather than remove.
6. Other editorial changes to condense and simplify.
7. Moved Privacy examples to Appendix.
8. Added forking to Basic call example.
Changes from barnes-sip-4244bis-00 to barnes-sipcore-4244bis-00:
1. Added tags for each type of retargeting including proxy hops,
etc. - i.e., a tag is defined for each specific mechanism by
which the new Request-URI is determined. Note, this is
extremely helpful in terms of backwards compatibility.
2. Fixed all the examples. Made sure loose routing was used in all
of them.
3. Removed example where a proxy using strict routing is using
History-Info for avoiding trying same route twice.
4. Remove redundant Redirect Server example.
5. Index are now mandated to start at "1" instead of recommended.
6. 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.)
7. Removed lots of ambiguity by making many "MAYs" into "SHOULDs"
and "some "SHOULDs" into "MUSTs".
8. Privacy is now recommended to be done by anonymizing entries as
per RFC 3323 instead of by removing or omitting hi-entry(s).
9. Requirement for TLS is now same level as per RFC 3261.
10. Clarified behavior for "Privacy" (i.e., that Privacy is for Hi-
entries, not headers).
11. Removed "OPTIONALITY" as specific requirements, since it's
rather superflous.
12. Other editorial changes to remove redundant text/sections.
Changes from RFC4244 to barnes-sip-4244bis-00:
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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.
14. References
14.1. 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.
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14.2. 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.
[RFC5039] Rosenberg, J. and C. Jennings, "The Session Initiation
Protocol (SIP) and Spam", RFC 5039, January 2008.
[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,
April 2006.
[RFC3761] Faltstrom, P. and M. Mealling, "The E.164 to Uniform
Resource Identifiers (URI) Dynamic Delegation Discovery
System (DDDS) Application (ENUM)", RFC 3761, April 2004.
[RFC4769] Livingood, J. and R. Shockey, "IANA Registration for an
Enumservice Containing Public Switched Telephone Network
(PSTN) Signaling Information", RFC 4769, November 2006.
[RFC3969] Camarillo, G., "The Internet Assigned Number Authority
(IANA) Uniform Resource Identifier (URI) Parameter
Registry for the Session Initiation Protocol (SIP)",
BCP 99, RFC 3969, December 2004.
[I-D.ietf-enum-cnam]
Shockey, R., "IANA Registration for an Enumservice Calling
Name Delivery (CNAM) Information and IANA Registration for
URI type 'pstndata'", draft-ietf-enum-cnam-08 (work in
progress), September 2008.
Appendix A. Request History Requirements
The following list constitutes a set of requirements for a "Request
History" capability.
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1. CAPABILITY-req: The "Request History" capability provides a
capability to inform proxies and UAs involved in processing a
request about the history/progress of that request. 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 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.
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
wether the retarget URI was an AOR
C. The mechanism by which the new URI or address was determined,
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.
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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 entry
either by adding an additional entry as a result of retargeting
or entering invalid information.
2. A rogue application could re-arrange the Request History
information to change the nature of the end application or to
mislead the receiver of the information.
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.
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:
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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 ougoing messages unless it is protected as
described in [RFC3323].
Appendix B. 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.
B.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 addresses 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
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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.
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 | |
|----------->| |
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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 -->
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
History-Info: <sip:bob@192.0.2.4>;index=1.1;rc
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
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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
History-Info: <sip:bob@192.0.2.4>;index=1.1;rc
Contact: <sip:office@example.com;hit=mp>
Content-Length: 0
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
History-Info: <sip:bob@192.0.2.4?Reason=SIP;cause=302>;\
index=1.1;rc
History-Info: <sip:office@example.com>;index=1.2;mp=1
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>
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<!-- SDP Not Shown -->
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
History-Info: <sip:bob@192.0.2.4?Reason=SIP;cause=302>;\
index=1.1;rc
History-Info: <sip:office@example.com>;index=1.2;mp=1
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
History-Info: <sip:bob@192.0.2.4?Reason=SIP;cause=302>;\
index=1.1;rc
History-Info: <sip:office@example.com>;index=1.2;mp=1
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
History-Info: <sip:bob@192.0.2.4?Reason=SIP;cause=302>;\
index=1.1;rc
History-Info: <sip:office@example.com>;index=1.2;mp=1
History-Info: <sip:office@192.0.2.5?Reason=SIP;cause=480>;\
index=1.2.1>;index=1.2.1
History-Info: <sip:home@example.com>;index=1.3;mp=1.2
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
History-Info: <sip:bob@192.0.2.4?Reason=SIP;cause=302>;\
index=1.1;rc
History-Info: <sip:office@example.com>;index=1.2;mp=1
History-Info: <sip:office@192.0.2.5?Reason=SIP;cause=480>;\
index=1.2.1>;index=1.2.1
History-Info: <sip:home@example.com>;index=1.3;mp=1.2
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
History-Info: <sip:bob@192.0.2.4?Reason=SIP;cause=302>;\
index=1.1;rc
History-Info: <sip:office@example.com>;index=1.2;mp=1
History-Info: <sip:office@192.0.2.5?Reason=SIP;cause=480>;\
index=1.2.1>;index=1.2.1
History-Info: <sip:home@example.com>;index=1.3;mp=1.2
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
B.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 can use.
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. An
example policy would be forwarding the request to the mailbox for the
first hi-targeted-to-uri in the History-Info header within the domain
for which the processing entity is responsible (e.g., in a PBX
environment). Whereas another policy might be to forward the request
to the mailbox for the last hi-targeted-to-uri tagged with "mp" in
the History-Info header (e.g., in a customer service environment).
Alice example.com Bob Carol VM
| INVITE sip:bob@example.com | | |
|------------->| | | |
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| | INVITE sip:bob@192.0.2.3 | |
| |------------->| | |
History-Info: <sip:bob@example.com>;index=1
History-Info: <sip:bob@192.0.2.3>;index=1.1;rc
| | | | |
| 100 Trying | | | |
|<-------------| 302 Moved Temporarily | |
| |<-------------| | |
History-Info: <sip:bob@example.com>;index=1
History-Info: <sip:bob@192.0.2.3?Reason=SIP;cause=302>;\
index=1.1;rc
| | | | |
| | INVITE sip:Carol@192.0.2.4 | |
| |--------------------------->| |
History-Info: <sip:bob@example.com>;index=1
History-Info: <sip:bob@192.0.2.3?Reason=SIP;cause=302>;\
index=1.1;rc
History-Info: <sip:carol@example.com>;index=1.2;mp=1
History-Info: <sip:carol@192.0.2.4>;index=1.2.1;rc
| | | | |
| | 180 Ringing | |
| |<---------------------------| |
History-Info: <sip:bob@example.com>;index=1
History-Info: <sip:bob@192.0.2.3?Reason=SIP;cause=302>;\
index=1.1;rc
History-Info: <sip:carol@example.com>;index=1.2;mp=1
History-Info: <sip:carol@192.0.2.4>;index=1.2.1;rc
| | | | |
| 180 Ringing | | | |
|<-------------| | | |
| | | | |
| . . . | | | |
| | (timeout) | |
| | | | |
| | INVITE sip:vm@192.0.2.5 |
| |-------------------------------------->|
History-Info: <sip:bob@example.com>;index=1
History-Info: <sip:bob@192.0.2.3?Reason=SIP;cause=302>;\
index=1.1;rc
History-Info: <sip:carol@example.com>;index=1.2;mp=1
History-Info: <sip:carol@192.0.2.4>;index=1.2.1;rc
History-Info: <sip:vm@example.com>;index=1.3;mp=1.2
History-Info: <sip:vm@192.0.2.5>;index=1.3.1
| | | | |
| | 200 OK |
| |<--------------------------------------|
History-Info: <sip:bob@example.com>;index=1
History-Info: <sip:bob@192.0.2.3?Reason=SIP;cause=302>;\
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index=1.1;rc
History-Info: <sip:carol@example.com>;index=1.2;mp=1
History-Info: <sip:carol@192.0.2.4>;index=1.2.1;rc
History-Info: <sip:vm@example.com>;index=1.3;mp=1.2
History-Info: <sip:vm@192.0.2.5>;index=1.3.1
| 200 OK | | | |
|<-------------| | | |
| | | | |
| ACK | | | |
|------------->| ACK |
| |-------------------------------------->|
B.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
| | | | |
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| | INVITE sip:Gold@example.com |
| |------------->| | |
History-Info: <sip:Gold@example.com>;index=1
History-Info: <sip:Gold@gold.example.com>;index=1.1
| | | | |
| | 302 Moved Temporarily | |
| |<-------------| | |
History-Info: <sip:Gold@example.com>;index=1
History-Info: <sip:Gold@gold.example.com?Reason=SIP;cause=302>;\
index=1.1
Contact: <sip:Silver@example.com>
| | | |
| | INVITE sip:Silver@example.com |
| |--------------------------->| |
History-Info: <sip:Gold@example.com>;index=1
History-Info: <sip:Gold@gold.example.com?Reason=SIP;cause=302>;\
index=1.1
History-Info: <sip:Silver@example.com>;index=2;mp=1
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
History-Info: <sip:Gold@gold.example.com?Reason=SIP;cause=302>;\
index=1.1
History-Info: <sip:Silver@example.com>;index=2;mp=1
History-Info: <sip:Silver@silver.example.com>;index=2.1
History-Info: <sip:Silver@192.0.2.7>;index=2.1.1;rc
| | | | |
| | | | 200 OK |
| | | |<-----------|
History-Info: <sip:Gold@example.com>;index=1
History-Info: <sip:Gold@gold.example.com?Reason=SIP;cause=302>;\
index=1.1
History-Info: <sip:Silver@example.com>;index=2;mp=1
History-Info: <sip:Silver@silver.example.com>;index=2.1
History-Info: <sip:Silver@192.0.2.7>;index=2.1.1;rc
| | | | |
| | 200 OK | |
| |<---------------------------| |
History-Info: <sip:Gold@example.com>;index=1
History-Info: <sip:Gold@gold.example.com?Reason=SIP;cause=302>;\
index=1.1
History-Info: <sip:Silver@example.com>;index=2;mp=1
History-Info: <sip:Silver@silver.example.com>;index=2.1
History-Info: <sip:Silver@192.0.2.7>;index=2.1.1;rc
| | | | |
200 OK | | | |
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|<-------------| | | |
| | | | |
| ACK | | | |
|------------->| ACK |
| |---------------------------------------->|
B.4. History-Info with Privacy Header
This example provides a basic call scenario such as the one in
Figure 1 but without forking, 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
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.
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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
| 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
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1.1
| History-Info: <sip:bob@192.0.2.3>;index=1.1.1;rc
| | | |
| | | 200 |
| | |<---------------|
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1.1
| History-Info: <sip:bob@192.0.2.3>;index=1.1.1;rc
| | | |
| | 200 | |
| |<---------------| |
| History-Info: <sip:anonymous@anonymous.invalid>;index=1
| History-Info: <sip:anonymous@anonymous.invalid>;index=1.1
| History-Info: <sip:anonymous@anonymous.invalid>;index=1.1.1;rc
| | | |
| 200 | | |
|<---------------| | |
| History-Info: <sip:anonymous@anonymous.invalid>;index=1
| History-Info: <sip:anonymous@anonymous.invalid>;index=1.1
| History-Info: <sip:anonymous@anonymous.invalid>;index=1.1.1;rc
| | | |
| ACK | | |
|--------------->| ACK | |
| |--------------->| ACK |
| | |--------------->|
Figure 2: Example with Privacy Header
B.5. Privacy Header for a Specific History-Info Entry
This example also provides a basic call scenario such as the one in
Figure 1 but without forking, 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
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providing Alice with some information about the history of the
request, but anonymizing Bob's local URI.
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
| 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
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1.1
| History-Info: <sip:bob@192.0.2.3?Privacy=history>;index=1.1.1;rc
| | | |
| | | 200 |
| | |<---------------|
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1.1
| History-Info: <sip:bob@192.0.2.3?Privacy=history>;index=1.1.1;rc
| | | |
| | 200 | |
| |<---------------| |
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1.1
| History-Info: <sip:anonymous@anynymous.invalid>;index=1.1.1;rc
| | | |
| 200 | | |
|<---------------| | |
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1.1
| History-Info: <sip:anonymous@anynymous.invalid>;index=1.1.1;rc
| | | |
| ACK | | |
|--------------->| ACK | |
| |--------------->| ACK |
| | |--------------->|
Figure 3: Example with Privacy Header for Specific URI
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B.6. Determining the Alias used.
SIP user agents are associated with an address-of-record (AOR). It
is possible for a single UA to actually have multiple AOR associated
with it. One common usage for this is aliases. For example, a user
might have an AOR of sip:john@example.com but also have the AORs
sip:john.smith@example.com and sip:jsmith@example.com. Rather than
registering against each of these AORs individually, the user would
register against just one of them, and the home proxy would
automatically accept incoming calls for any of the aliases, treating
them identically and ultimately forwarding them towards the UA. This
is common practice in the Internet Multimedia Subsystem (IMS), where
it is called implicit registrations and each alias is called a public
identity.
It is a common requirement for a UAS, on receipt of a call, to know
which of its aliases was used to reach it. This knowledge can be
used to choose ringtones to play, determine call treatment, and so
on. For example, a user might give out one alias to friends and
family only, resulting in a special ring that alerts the user to the
importance of the call.
Following call-flow and example messages show how History-Info can be
used to find out the alias used to reach the callee.
UAS can see which alias was used in the call by looking at the hi-
entry prior to the last hi-entry with the "rc" tag.
Alice Example.com John
| | REGISTER F1 |
| |<--------------------|
| | 200 OK F2 |
| |-------------------->|
| INVITE F3 | |
|-------------------->| |
| | INVITE F4 |
| |-------------------->|
* Rest of flow not shown *
F1 REGISTER John -> Example.com
REGISTER sip:example.com SIP/2.0
Via: SIP/2.0/UDP 192.0.2.1;branch=z9hG4bKnashds7
Max-Forwards: 70
From: John <sip:john@example.com>;tag=a73kszlfl
To: John <sip:john@example.com>
Call-ID: 1j9FpLxk3uxtm8tn@192.0.2.1
CSeq: 1 REGISTER
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Contact: <sip:john@192.0.2.1>
Content-Length: 0
F2 200 OK Example.com -> John
SIP/2.0 200 OK
Via: SIP/2.0/UDP 192.0.2.1;branch=z9hG4bKnashds7
From: John <sip:john@example.com>;tag=a73kszlfl
To: John <sip:john@example.com>
Call-ID: 1j9FpLxk3uxtm8tn@192.0.2.1
CSeq: 1 REGISTER
Contact: <sip:john@192.0.2.1>;expires=3600
Content-Length: 0
F3 INVITE Alice -> Example.com
INVITE sip:john.smith@example.com SIP/2.0
Via: SIP/2.0/TCP 192.0.2.3:5060;branch=232sxxeserg
From: Alice <sip:alice@example.com>
To: John <sip:john.smith@example.com>
Supported: histinfo
Call-Id: 12345600@example.com
CSeq: 1 INVITE
History-Info: <sip:john.smith@example.com>;index=1;
Contact: Alice <sip:alice@192.0.2.3>
Content-Type: application/sdp
Content-Length: <appropriate value>
[SDP Not Shown]
F4 INVITE Example.com -> Bob
INVITE sip:john@192.0.2.1 SIP/2.0
Via: SIP/2.0/TCP proxy.example.com:5060;branch=as2334se
Via: SIP/2.0/TCP 192.0.2.3:5060;branch=232sxxeserg
From: Alice <sip:alice@example.com>
To: John <sip:john.smith@example.com>
Supported: histinfo
Call-Id: 12345600@example.com
CSeq: 1 INVITE
Record-Route: <sip:proxy.example.com;lr>
History-Info: <sip:john.smith@example.com>;index=1;
History-Info: <sip:john@192.0.2.1>;index=1.1;rc
Contact: Alice <sip:alice@192.0.2.3>
Content-Type: application/sdp
Content-Length: <appropriate value>
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[SDP Not Shown]
Figure 4: Alias Example
B.7. GRUU
A variation on the problem in Appendix B.6 occurs with Globally
Routable User Agent URI (GRUU) [RFC5627]. A GRUU is a URI assigned
to a UA instance which has many of the same properties as the AOR,
but causes requests to be routed only to that specific instance. It
is desirable for a UA to know whether it was reached because a
correspondent sent a request to its GRUU or to its AOR. This can be
used to drive differing authorization policies on whether the request
should be accepted or rejected, for example. However, like the AOR
itself, the GRUU is lost in translation at the home proxy. Thus, the
UAS cannot know whether it was contacted via the GRUU or its AOR.
Following call-flow and example messages show how History-Info can be
used to find out the GRUU used to reach the callee.
GRUU is merely an AoR with a URI parameter that distinguishes the
target instance, and as any URI parameters are preserved in history-
info as Request-URI is trasnlated, UA can see if the request was
addressed to a specific instance (gruu) by evaluating the presence of
"gr" parameter in the hi-entry prior to the last hi-entry with the
"rc" tag.
Alice Example.com John
| | REGISTER F1 |
| |<--------------------|
| | 200 OK F2 |
| |-------------------->|
| INVITE F3 | |
|-------------------->| |
| | INVITE F4 |
| |-------------------->|
* Rest of flow not shown *
F1 REGISTER John -> Example.com
REGISTER sip:example.com SIP/2.0
Via: SIP/2.0/UDP 192.0.2.1;branch=z9hG4bKnashds7
Max-Forwards: 70
From: John <sip:John@example.com>;tag=a73kszlfl
Supported: gruu
To: John <sip:john@example.com>
Call-ID: 1j9FpLxk3uxtm8tn@192.0.2.1
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CSeq: 1 REGISTER
Contact: <sip:john@192.0.2.1>
;+sip.instance="<urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6>"
Content-Length: 0
F2 200 OK Example.com -> John
SIP/2.0 200 OK
Via: SIP/2.0/UDP 192.0.2.1;branch=z9hG4bKnashds7
From: John <sip:john@example.com>;tag=a73kszlfl
To: John <sip:john@example.com> ;tag=b88sn
Call-ID: 1j9FpLxk3uxtm8tn@192.0.2.1
CSeq: 1 REGISTER
Contact: <sip:john@192.0.2.1>
;pub-gruu="sip:john@example.com
;gr=urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6"
;temp-gruu=
"sip:tgruu.7hs==jd7vnzga5w7fajsc7-ajd6fabz0f8g5@example.com;gr"
;+sip.instance="<urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6>"
;expires=3600
Content-Length: 0
Assuming Alice has a knowledge of a gruu either through
prior communication or through other means such as presence
places a call to John's gruu.
F3 INVITE Alice -> Example.com
INVITE sip:john@example.com
;gr=urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6 SIP/2.0
Via: SIP/2.0/TCP 192.0.2.3:5060;branch=232sxxeserg
From: Alice <sip:alice@example.com>;tag=kkaz-
To: <sip:john@example.com
;gr=urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6>
Supported: gruu, histinfo
Call-Id: 12345600@example.com
CSeq: 1 INVITE
History-Info: <sip:john@example.com
;gr=urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6>;index=1
Contact: Alice <sip:alice@192.0.2.3>
Content-Length: <appropriate value>
F4 INVITE Example.com -> John
INVITE sip:john@192.0.2.1 SIP/2.0
Via: SIP/2.0/TCP proxy.example.com:5060;branch=as2334se
Via: SIP/2.0/TCP 192.0.2.3:5060;branch=232sxxeserg
From: Alice <sip:alice@example.com>;tag=kkaz-
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To: John <sip:john@example.com>
Supported: gruu, histinfo
Call-Id: 12345600@example.com
CSeq: 1 INVITE
Record-Route: <sip:proxy.example.com;lr>
History-Info: <sip:john@example.com
;gr=urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6>;index=1
History-Info: <sip:john@192.0.2.1>;index=1.1;rc
Contact: Alice <sip:alice@192.0.2.3>
Content-Type: application/sdp
Content-Length: <appropriate value>
Figure 5: GRUU Example
B.8. Limited Use Address
A limited use address is a SIP URI that is minted on-demand, and
passed out to a small number (usually one) remote correspondent.
Incoming calls targeted to that limited use address are accepted as
long as the UA still desires communications from the remote target.
Should they no longer wish to be bothered by that remote
correspondent, the URI is invalidated so that future requests
targeted to it are rejected.
Limited use addresses are used in battling voice spam [RFC5039]. The
easiest way to provide them would be for a UA to be able to take its
AOR, and "mint" a limited use address by appending additional
parameters to the URI. It could then give out the URI to a
particular correspondent, and remember that URI locally. When an
incoming call arrives, the UAS would examine the parameter in the URI
and determine whether or not the call should be accepted.
Alternatively, the UA could push authorization rules into the
network, so that it need not even see incoming requests that are to
be rejected.
This approach, especially when executed on the UA, requires that
parameters attached to the AOR, but not used by the home proxy in
processing the request, will survive the translation at the home
proxy and be presented to the UA. This will not be the case with the
logic in RFC 3261, since the Request-URI is replaced by the
registered contact, and any such parameters are lost.
Using the history-info John's UA can easily see if the call was
addressed to its AoR, GRUU or a temp-gruu and treat the call
accordingly by looking at the hi-entry prior to the last hi-entry
with the "rc" tag.
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Alice Example.com John
| | REGISTER F1 |
| |<--------------------|
| | 200 OK F2 |
| |-------------------->|
| INVITE F3 | |
|-------------------->| |
| | INVITE F4 |
| |-------------------->|
* Rest of flow not shown *
F1 REGISTER John -> Example.com
REGISTER sip:example.com SIP/2.0
Via: SIP/2.0/UDP 192.0.2.1;branch=z9hG4bKnashds7
Max-Forwards: 70
From: John <sip:John@example.com>;tag=a73kszlfl
Supported: gruu
To: John <sip:john@example.com>
Call-ID: 1j9FpLxk3uxtm8tn@192.0.2.1
CSeq: 1 REGISTER
Contact: <sip:john@192.0.2.1>
;+sip.instance="<urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6>"
Content-Length: 0
F2 200 OK Example.com -> John
SIP/2.0 200 OK
Via: SIP/2.0/UDP 192.0.2.1;branch=z9hG4bKnashds7
From: John <sip:john@example.com>;tag=a73kszlfl
To: John <sip:john@example.com> ;tag=b88sn
Call-ID: 1j9FpLxk3uxtm8tn@192.0.2.1
CSeq: 1 REGISTER
Contact: <sip:john@192.0.2.1>
;pub-gruu="sip:john@example.com
;gr=urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6"
;temp-gruu=
"sip:tgruu.7hs==jd7vnzga5w7fajsc7-ajd6fabz0f8g5@example.com;gr"
;+sip.instance="<urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6>"
;expires=3600
Content-Length: 0
Assuming Alice has a knowledge of a temp-gruu, she places a
call to the temp-gruu.
F3 INVITE Alice -> Example.com
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INVITE sip:tgruu.7hs==jd7vnzga5w7fajsc7-ajd6fabz0f8g5@example.com
;gr SIP/2.0
Via: SIP/2.0/TCP 192.0.2.3:5060;branch=232sxxeserg
From: Alice <sip:alice@example.com>;tag=kkaz-
To: <sip:sip:tgruu.7hs==jd7vnzga5w7fajsc7-ajd6fabz0f8g5@example.com
;gr>
Supported: gruu, histinfo
Call-Id: 12345600@example.com
CSeq: 1 INVITE
History-Info:
<sip:tgruu.7hs==jd7vnzga5w7fajsc7-ajd6fabz0f8g5@example.com;gr>
;index=1
Contact: Alice <sip:alice@192.0.2.3>
Content-Length: <appropriate value>
F4 INVITE Example.com -> John
INVITE sip:john@192.0.2.1 SIP/2.0
Via: SIP/2.0/TCP proxy.example.com:5060;branch=as2334se
Via: SIP/2.0/TCP 192.0.2.3:5060;branch=232sxxeserg
From: Alice <sip:alice@example.com>;tag=kkaz-
To: John <sip:john@example.com>
Supported: gruu, histinfo
Call-Id: 12345600@example.com
CSeq: 1 INVITE
Record-Route: <sip:proxy.example.com;lr>
History-Info:
<sip:tgruu.7hs==jd7vnzga5w7fajsc7-ajd6fabz0f8g5@example.com;gr>
;index=1
History-Info: <sip:john@192.0.2.1>;index=1.1;rc
Contact: Alice <sip:alice@192.0.2.3>
Content-Type: application/sdp
Content-Length: <appropriate value>
Figure 6: Limited Use Address Example
B.9. Sub-Address
Sub-Addressing is very similar to limited use addresses. Sub-
addresses are addresses within a subdomain that are multiplexed into
a single address within a parent domain. The concept is best
illustrated by example. Consider a VoIP service provided to
consumers. A consumer obtains a single address from its provider,
say sip:family@example.com. However, Joe is the patriarch of a
family with four members, and would like to be able to have a
separate identifier for each member of his family. One way to do
that, without requiring Joe to purchase new addresses for each member
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from the provider, is for Joe to mint additional URI by adding a
parameter to the AOR. For example, his wife Judy with have the URI
sip:family@example.com;member=judy, and Joe himself would have the
URI sip:family@example.com;member=joe. The SIP server provider would
receive requests to these URI, and ignoring the unknown parameters
(as required by [RFC3261]) route the request to the registered
contact, which corresponds to a SIP server in Joes home. That
server, in turn, can examine the URI parameters and determine which
phone in the home to route the call to.
This feature is not specific to VoIP, and has existing in Integrated
Services Digital Networking (ISDN) for some time. It is particularly
useful for small enterprises, in addition to families. It is also
similar in spirit (though not mechanism) to the ubiquitous home
routers used by consumers, which allow multiple computers in the home
to "hide" behind the single IP address provided by the service
provider, by using the TCP and UDP port as a sub-address.
The sub-addressing feature is not currently feasible in SIP because
of the fact that any SIP URI parameter used to convey the sub-address
would be lost at the home proxy, due to the fact that the Request-URI
is rewritten there.
Call-flow and example messages below show the how History-Info can be
used to deliver the sub-address. UAS or Proxy can determine the sub-
address by looking at the hi-entry prior to the last hi-entry with
the "rc" tag.
Alice Example.com John's Home Judy John
| | REGISTER F1 | | |
| |<-------------| | |
| | 200 OK F2 | | |
| |------------->| | |
| | | REGISTER F3 | |
| | |<-------------| |
| | | 200 OK F4 | |
| | |------------->| |
| | | | REGISTER F5 |
| | |<----------------------------|
| | | | 200 OK F6 |
| | |---------------------------->|
| INVITE F7 | | | |
|----------->| | | |
| | INVITE F8 | | |
| |------------->| | |
| | | INVITE F9 | |
| | |------------->| |
* Rest of flow not shown *
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F1 REGISTER John's Home Server -> Example.com
REGISTER sip:example.com SIP/2.0
Via: SIP/2.0/UDP 192.0.2.1;branch=z9hG4bKnashds7
Max-Forwards: 70
From: John <sip:johnhome@example.com>;tag=a73kszlfl
To: John <sip:johnhome@example.com>
Call-ID: 1j9FpLxk3uxtm8tn@192.0.2.1
CSeq: 1 REGISTER
Contact: <sip:johnhome@192.0.2.1>
Content-Length: 0
F2 200 OK Example.com -> John's Home Server
SIP/2.0 200 OK
Via: SIP/2.0/UDP 192.0.2.1;branch=z9hG4bKnashds7
From: John <sip:johnhome@example.com>;tag=a73kszlfl
To: John <sip:johnhome@example.com> ;tag=b88sn
Call-ID: 1j9FpLxk3uxtm8tn@192.0.2.1
CSeq: 1 REGISTER
Contact: <sip:johnhome@192.0.2.1>;expires=3600
Content-Length: 0
We assume that John's server acts as a proxy allowing
each of the device in the house to register.
F3 REGISTER Judy's phone -> John's Home Server
REGISTER sip:192.168.1.1 SIP/2.0
Via: SIP/2.0/UDP 192.168.1.2;branch=z9hG4bKnasdds
Max-Forwards: 70
From: Judy <sip:judy@192.168.1.1>;tag=a73kszlfl
To: Judy <sip:judy@192.168.1.1>
Call-ID: 12345pLxk3uxtm8tn@192.168.1.2
CSeq: 1 REGISTER
Contact: <sip:judy@192.168.1.2>
Content-Length: 0
F4 200 OK John's Home Server -> Judy's phone
SIP/2.0 200 OK
Via: SIP/2.0/UDP 192.168.1.2;branch=z9hG4bKnashds7
From: Judy <sip:judy@192.168.1.1>;tag=a73kszlfl
To: Judy <sip:judy@192.168.1.1>tag=b88sn
Call-ID: 12345pLxk3uxtm8tn@192.168.1.2
CSeq: 1 REGISTER
Contact: <sip:judy@192.168.1.2>;expires=3600
Content-Length: 0
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F5 REGISTER John's phone -> John's Home Server
REGISTER sip:192.168.1.1 SIP/2.0
Via: SIP/2.0/UDP 192.168.1.3;branch=z9hG4bKnasdds
Max-Forwards: 70
From: Judy <sip:john@192.168.1.1>;tag=a73kszlfl
To: Judy <sip:john@192.168.1.1>
Call-ID: 12346pLxk3uxtm8tn@192.168.1.3
CSeq: 1 REGISTER
Contact: <sip:john@192.168.1.3>
Content-Length: 0
F6 200 OK John's Home Server -> John's phone
SIP/2.0 200 OK
Via: SIP/2.0/UDP 192.168.1.3;branch=z9hG4bKnashds7
From: John <sip:john@192.168.1.1>;tag=a73kszlfl
To: John <sip:john@192.168.1.1> ;tag=b88sn
Call-ID: 12346pLxk3uxtm8tn@192.168.1.3
CSeq: 1 REGISTER
Contact: <sip:john@192.168.1.3>;expires=3600
Content-Length: 0
F7 INVITE Alice -> Example.com
INVITE sip:johnhome@example.com;member=judy SIP/2.0
Via: SIP/2.0/TCP 192.0.2.3:5060;branch=232sxxeserg
From: Alice <sip:alice@example.com>
To: Judy <sip:johnhome@example.com;member=judy>
Supported: histinfo
Call-Id: 12345600@example.com
CSeq: 1 INVITE
History-Info: <sip:johnhome@example.com;member=judy>;index=1;
Contact: Alice <sip:alice@192.0.2.3>
Content-Type: application/sdp
Content-Length: <appropriate value>
[SDP Not Shown]
F8 INVITE Example.com -> John's Home
INVITE sip:johnhome@192.0.2.1 SIP/2.0
Via: SIP/2.0/TCP proxy.example.com:5060;branch=as2334se
Via: SIP/2.0/TCP 192.0.2.3:5060;branch=232sxxeserg
From: Alice <sip:alice@example.com>
To: Judy <sip:johnhome@example.com;member=judy>
Supported: histinfo
Call-Id: 12345600@example.com
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CSeq: 1 INVITE
Record-Route: <sip:proxy.example.com;lr>
History-Info: <sip:johnhome@example.com;member=judy>;index=1;
History-Info: <sip:john@192.0.2.1>;index=1.1;rc
Contact: Alice <sip:alice@192.0.2.3>
Content-Type: application/sdp
Content-Length: <appropriate value>
[SDP Not Shown]
John's Home server can see that the call was addressed to
Judy by evaluating the entry prior to the last entry with the
"rc" tag and forwards the call accordingly.
F9 INVITE John's Home -> Judy
INVITE sip:judy@192.168.1.2 SIP/2.0
Via: SIP/2.0/TCP 192.168.1.1:5060;branch=abc2334se
Via: SIP/2.0/TCP proxy.example.com:5060;branch=as2334se
Via: SIP/2.0/TCP 192.0.2.3:5060;branch=232sxxeserg
From: Alice <sip:alice@example.com>
To: Judy <sip:johnhome@example.com;member=judy>
Supported: histinfo
Call-Id: 12345600@example.com
CSeq: 1 INVITE
Record-Route: <sip:proxy.example.com;lr>
History-Info: <sip:johnhome@example.com;member=judy>;index=1;
History-Info: <sip:john@192.0.2.1>;index=1.1;rc
History-Info: <sip:judy@192.168.1.1>;index=1.1.1;mp=1.1
History-Info: <sip:judy@192.168.1.2>;index=1.1.1.1;rc
Contact: Alice <sip:alice@192.0.2.3>
Content-Type: application/sdp
Content-Length: <appropriate value>
[SDP Not Shown]
Figure 7: Sub-Address Example
B.10. Service Invocation
Several SIP specifications have been developed which make use of
complex URIs to address services within the network rather than
subscribers. The URIs are complex because they contain numerous
parameters that control the behavior of the service. Examples of
this include the specification which first introduced the concept,
[RFC3087], control of network announcements and IVR with SIP URI
[RFC4240], and control of voicemail access with SIP URI [RFC4458].
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A common problem with all of these mechanisms is that once a proxy
has decided to rewrite the Request-URI to point to the service, it
cannot be sure that the Request-URI will not be destroyed by a
downstream proxy which decides to forward the request in some way,
and does so by rewriting the Request-URI.
Section on voicemail (Appendix B.2) shows how History-Info can be
used to invocate a service.
B.11. Toll Free Number
Toll free numbers, also known as 800 or 8xx numbers in the United
States, are telephone numbers that are free for users to call.
In the telephone network, toll free numbers are just aliases to
actual numbers which are used for routing of the call. In order to
process the call in the PSTN, a switch will perform a query (using a
protocol called TCAP), which will return either a phone number or the
identity of a carrier which can handle the call.
There has been recent work on allowing such PSTN translation services
to be accessed by SIP proxy servers through IP querying mechanisms.
ENUM, for example [RFC3761] has already been proposed as a mechanism
for performing Local Number Portability (LNP) queries [RFC4769], and
recently been proposed for performing calling name queries
[I-D.ietf-enum-cnam]. Using it for 8xx number translations is a
logical next-step.
Once such a translation has been performed, the call needs to be
routed towards the target of the request. Normally, this would
happen by selecting a PSTN gateway which is a good route towards the
translated number. However, one can imagine all-IP systems where the
8xx numbers are SIP endpoints on an IP network, in which case the
translation of the 8xx number would actually be a SIP URI and not a
phone number. Assuming for the moment it is a PSTN connected entity,
the call would be routed towards a PSTN gateway. Proper treatment of
the call in the PSTN (and in particular, correct reconciliation of
billing records) requires that the call be marked with both the
original 8xx number AND the target number for the call. However, in
our example here, since the translation was performed by a SIP proxy
upstream from the gateway, the original 8xx number would have been
lost, and the call will not interwork properly with the PSTN.
Furthermore, even if the translation of the 8xx number was a SIP URI,
the enterprise or user who utilize the 8xx service would like to know
whether the call came in via 8xx number in order to treat the call
differently (for example to play a special announcement..) but if the
original R-URI is lost through translation, there is no way to tell
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if the call came in via 8xx number.
Similar problems arise with other "special" numbers and services used
in the PSTN, such as operator services, pay numbers (9xx numbers in
the U.S), and short service codes such as 311.
To find the service number, the UAS can look at the hi-entry prior to
the first hi-entry with "mp" tag. Technically call can be forwarded
to these "special" numbers from non "special" numbers, but with the
way these services authorize trasnlation, it is not common.
Alice Toll Free Service Atlanta.com John
| | | |
| INVITE F1 | | |
|--------------->| INVITE F2 | |
| |------------->| |
| | | INVITE F3 |
| | |------------------>|
* Rest of flow not shown *
F1: INVITE 192.0.2.1 -> proxy.example.com
INVITE sip:+18005551002@example.com;user=phone SIP/2.0
Via: SIP/2.0/TCP 192.0.2.1:5060;branch=z9hG4bK-74bf9
From: Alice <sip:+15551001@example.com;user=phone>;tag=9fxced76sl
To: sip:+18005551002@example.com;user=phone
Call-ID: c3x842276298220188511
CSeq: 1 INVITE
Max-Forwards: 70
Supported: histinfo
History-Info: <sip:+18005551002@example.com;user=phone >;index=1
Contact: <sip:alice@192.0.2.1>
Content-Type: application/sdp
Content-Length: <appropriate value>
[SDP Not Shown]
F2: INVITE proxy.example.com -> atlanta.com
INVITE sip:+15555551002@atlanta.com SIP/2.0
Via: SIP/2.0/TCP 192.0.2.4:5060;branch=z9hG4bK-ik80k7g-1
Via: SIP/2.0/TCP 192.0.2.1:5060;branch=z9hG4bK-74bf9
From: Alice <sip:+15551001@example.com;user=phone>;tag=9fxced76sl
To: sip:+18005551002@example.com;user=phone
Call-ID: c3x842276298220188511
CSeq: 1 INVITE
Max-Forwards: 70
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Supported: histinfo
History-Info: <sip:+18005551002@example.com;user=phone >;index=1,
<sip:+15555551002@atlanta.com>;index=1.1;mp=1
Contact: <sip:alice@192.0.2.1>
Content-Type: application/sdp
Content-Length: <appropriate value>
[SDP Not Shown]
F3: INVITE atlanta.com -> Joe
INVITE sip:joe@192.168.1.2 SIP/2.0
Via: SIP/2.0/TCP 192.168.1.1:5060;branch=z9hG4bK-pxk7g-3
Via: SIP/2.0/TCP 192.0.2.4:5060;branch=z9hG4bK-ik80k7g-1
Via: SIP/2.0/TCP 192.0.2.1:5060;branch=z9hG4bK-74bf9
From: Alice <sip:+15551001@example.com;user=phone>;tag=9fxced76sl
To: sip:+18005551002@example.com;user=phone
Call-ID: c3x842276298220188511
CSeq: 1 INVITE
Max-Forwards: 70
Supported: histinfo
History-Info: <sip:+18005551002@example.com;user=phone >;index=1,
<sip:+15555551002@atlanta.com>;index=1.1;mp=1,
<sip:joe@atlanta.com>;index=1.1.1;mp=1.1,
<sip:joe@192.168.1.2>;index=1.1.2;rc
Contact: <sip:alice@192.0.2.1>
Content-Type: application/sdp
Content-Length: <appropriate value>
[SDP Not Shown]
Figure 8: Service Number Example
Authors' Addresses
Mary Barnes
Nortel
Richardson, TX
Email: mary.ietf.barnes@gmail.com
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Francois Audet
Skype
Email: francois.audet@skype.net
Shida Schubert
NTT
Email: shida@agnada.com
Hans Erik van Elburg
Detecon International Gmbh
Oberkasseler str. 2
Bonn,
Germany
Email: ietf.hanserik@gmail.com
Christer Holmberg
Ericsson
Hirsalantie 11, Jorvas
Finland
Email: christer.holmberg@ericsson.com
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