One document matched: draft-ietf-sipcore-rfc4244bis-12.xml
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<rfc category="std" docName="draft-ietf-sipcore-rfc4244bis-12.txt"
ipr="pre5378Trust200902" obsoletes="4244">
<front>
<title abbrev="History-Info ">An Extension to the Session Initiation
Protocol (SIP) for Request History Information</title>
<author fullname="Mary Barnes" initials="M." surname="Barnes">
<organization>Polycom</organization>
<address>
<postal>
<street></street>
<city></city>
<region>TX</region>
<code></code>
<country>US</country>
</postal>
<email>mary.ietf.barnes@gmail.com</email>
</address>
</author>
<author fullname="Francois Audet" initials="F." surname="Audet">
<organization>Skype</organization>
<address>
<postal>
<street></street>
<city></city>
<region></region>
<code></code>
<country></country>
</postal>
<email>francois.audet@skype.net</email>
</address>
</author>
<author fullname="Shida Schubert" initials="S.S." surname="Schubert">
<organization>NTT</organization>
<address>
<postal>
<street></street>
<city></city>
<region></region>
<country></country>
</postal>
<email>shida@ntt-at.com</email>
</address>
</author>
<author fullname="Hans Erik van Elburg" initials="J.F.J."
surname="van Elburg">
<organization>
Detecon International Gmbh
</organization>
<address>
<postal>
<street>
Sternengasse 14-16
</street>
<city>
Cologne
</city>
<region></region>
<country>
Germany
</country>
</postal>
<email>ietf.hanserik@gmail.com</email>
</address>
</author>
<author fullname="Christer Holmberg" initials="C.H." surname="Holmberg">
<organization>Ericsson</organization>
<address>
<postal>
<street></street>
<city>Hirsalantie 11</city>
<region>Jorvas</region>
<country>Finland</country>
</postal>
<email>christer.holmberg@ericsson.com</email>
</address>
</author>
<date month="Oct" year="2013"/>
<abstract>
<t>This document defines a standard mechanism for capturing the history
information associated with a Session Initiation Protocol (SIP) request.
This capability enables many enhanced services by providing the
information as to how and why a SIP request arrives at a specific application
or user. This document defines an optional SIP header field, History-Info, for
capturing the history information in requests. The document also
defines SIP header field parameters
for the History-Info and Contact header fields
to tag the method by which the target of a request is determined.
In addition, this specification defines a value for the Privacy header field
that
directs the anonymization of values in the History-Info header field.
This document obsoletes RFC 4244.
</t>
</abstract>
</front>
<middle>
<section anchor="intro" title="Introduction">
<t>Many services that SIP is anticipated to support require the ability
to determine why and how a SIP request arrived at a specific application.
Examples of such services include (but are not limited to) sessions
initiated to call centers via "click to talk" SIP Uniform Resource
Locators (URLs) on a web page, "call history/logging" style services
within intelligent "call management" software for SIP User Agents (UAs),
and calls to voicemail servers. Although SIP implicitly provides the
retarget capabilities that enable SIP requests to be routed to chosen
applications, there is a need for a standard mechanism within SIP for
communicating the retargeting history of the requests. This "request
history" information allows the receiving application to obtain information
about how and why the SIP request arrived at the application/user.</t>
<t>
This document defines a SIP header field, History-Info, to provide a
standard mechanism for capturing the request history information to
enable a wide variety of services for networks and end-users.
SIP header field parameters
are defined for the History-Info and Contact header fields
to tag the method by which the target of a request is determined.
This specification also
defines a value, "history", for the Privacy header field. In addition
a SIP option tag, "histinfo", is defined.</t>
<t>
The
History-Info header field provides a building block for development of
SIP based applications and services. The requirements for the solution described
in this specification are included in <xref
target="requirements"></xref>. Example scenarios using
the History-Info header field are available in
<xref target="I-D.ietf-sipcore-rfc4244bis-callflows"/>. </t>
</section>
<section title="Conventions and Terminology">
<t>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 <xref
target="RFC2119"></xref>.</t>
<t>The term "retarget" is used in this specification to refer to the
process of a SIP entity changing the request-URI [RFC3261, section
7.1] in a request based on the rules for
determining request targets as described in Section 16.5 of <xref
target="RFC3261"></xref> and of the subsequent forwarding of that request
as described in step 2 in section 16.6 of <xref target="RFC3261"></xref>.
This includes changing the Request-URI due to a location service lookup and
redirect processing. This also includes internal (to a Proxy/SIP intermediary) changes
of the URI prior to forwarding of the request.
</t>
<t>The terms "location service", "forward", "redirect" and "AOR" are used consistently with
the terminology in <xref target="RFC3261"></xref>. </t>
<t>The terms "target user" is used in this specification as the human user
associated with particular AoR or AoRs (in case the human user has multiple alias). </t>
<t> The references to "domain for which the
SIP entity/Proxy/Intermediary is responsible" are consistent with and intended to
convey the same context as the usage of that terminology in <xref target="RFC3261"></xref>.
The applicability of History-Info to architectures or models outside the context of
<xref target="RFC3261"></xref> is outside the scope of this specification.</t>
</section>
<section anchor="Background" title="Background">
<t>SIP implicitly provides retargeting capabilities that enable SIP requests to
be routed to specific applications as defined in <xref
target="RFC3261"></xref>. The motivation for capturing the request
history is that in the process of retargeting a request, old routing
information can be forever lost. This lost information may be important
history that allows elements to which the request is retargeted to process
the request in a locally defined, application-specific manner. This
document defines a mechanism for transporting the request history.
Application-specific behavior is outside the scope of this
specification.</t>
<t>Current network applications for other protocols provide the ability for elements
involved with the request to obtain additional information relating to
how and why the request was routed to a particular destination. The
following are examples of such applications:</t>
<t><list style="numbers">
<t>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</t>
<t>Email relaying whereby the recipient obtains a detailed "trace
of the path" of the message from originator to receiver, including
the time of each relay.</t>
<t>Traditional telephony services such as voicemail, call-center
"automatic call distribution", and "follow-me" style services</t>
</list></t>
<t>Several of the aforementioned applications currently define
application-specific mechanisms through which it is possible to obtain
the necessary history information.</t>
<t>In addition, request history information could be used to enhance
basic SIP functionality by providing the following: <list
style="symbols">
<t>Some diagnostic information for debugging SIP requests. </t>
<t>Capturing aliases and Globally Routable User Agent URIs (GRUUs)
<xref target="RFC5627"></xref>, which can be overwritten by a registrar or a "home proxy" (a proxy serving as the terminal point for routing an address-of-record) upon receipt of the initial request.</t>
<t>Facilitating the use of limited use addresses (minted on demand)
and sub-addressing.</t>
<t>Preserving service specific URIs that can be overwritten by a
downstream proxy, such as those defined in <xref
target="RFC3087"></xref>, and control of network announcements and
IVR with SIP URI <xref target="RFC4240"></xref>.</t>
</list></t>
</section>
<!--end background-->
<section anchor="overview" title="Overview">
<t>The fundamental functionality provided by the request history
information is the ability to inform proxies and user agents (UAs) involved in
processing a request about the history or progress of that request.
The solution
is to capture the Request-URIs as a request is retargeted, in a
SIP header field: History-Info. This allows for the capturing of the
history of a request that would be lost with the normal SIP processing
involved in the subsequent retargeting of the request. </t>
<t> The History-Info header field is added to a Request when a new request is
created by a user agent client (UAC) or forwarded by a Proxy, or when the target of a
request is changed. It
is possible for the target of a request to be changed by the same
proxy/SIP intermediary multiple times (referred to as 'internal retargeting').
A SIP entity
changing the target of a request in response to a redirect
also propagates any History-Info header field from the initial
request in the new request. The ABNF and detailed description of the History-Info
header field parameters along with examples, is provided in
<xref target="definitionhi"/>. <xref target="ua"/>, <xref target="proxy"/> and
<xref target="redirect"/> provide the
detailed handling of the History-Info
header field by SIP User Agents, Proxies and Redirect Servers respectively.</t>
<t> This specification also defines three new SIP header field parameters, "rc",
"mp" and "np", for the History-Info and Contact header fields,
to tag the method by which the target of a request is determined.
Further detail on the use of these header field parameters is provided in
<xref target="definitionhi"/>. </t>
<t> This specification also defines a priv-value for the Privacy
header, "history", that requires anonymization of
all the History-Info header field entries in a Request or to
a specific History-Info header field
hi-entry as described above. Further detail is provided in
<xref target="privacyhi"></xref>.
</t>
<t> In addition a SIP option tag, "histinfo", is defined. The use of this option
tag is described in <xref target="uac"></xref>.</t>
</section>
<!--end overview-->
<section anchor="definitionhi" title="History-Info Header Field Protocol Structure">
<t>The History-Info header field defined in this specification defines the usage in out-of-dialog requests or initial requests for a dialog (e.g., INVITE, REGISTER, MESSAGE, REFER and OPTIONS, PUBLISH and SUBSCRIBE, etc.) and any non-100 provisional or final responses to these requests.</t>
<t>The following
provides details for the information that is captured in the
History-Info header field
entries for each target used for forwarding a request:</t>
<t><list style="symbols">
<t>hi-targeted-to-uri: A mandatory parameter for
capturing the Request-URI for the specific request as it is
forwarded.</t>
<t>hi-index: A mandatory parameter for History-Info
reflecting the chronological order of the information, indexed to
reflect the forking and retargeting of requests. The format for
this parameter is a sequence of non-negative integers, separated by dots to
indicate the number of forward hops and retargets. This results in
a tree representation of the history of the request, with the
lowest-level index reflecting a leaf. By adding the
new entries in chronological order (i.e., following existing entries per the
details in <xref target="indexhi"></xref>), including the index and
sending the messages using a secure transport, the ordering of the
History-Info header fields in
the request is assured. In addition, applications may extract a
variety of metrics (total number of retargets, total number of
retargets from a specific branch, etc.) based upon the index
values. </t>
<t>hi-target-param: An optional parameter reflecting the mechanism by which the Request URI
captured in the hi-targeted-to-uri in the History-Info header field value (hi-entry)
was determined.
This parameter is either an "rc", "mp"
or "np" header field parameter, which is interpreted as follows:
<list style="hanging">
<t>"rc": The hi-targeted-to-URI represents a change in
Request-URI while the target user remains the same. This occurs
for example when user has multiple AoRs as an alias.
The "rc" header field parameter contains the value of the hi-index
in the hi-entry with an hi-targeted-to-uri that reflects the
Request-URI that was retargeted</t>
<t> "mp": The hi-targeted-to-URI represents a user other
than the target user associated with the Request-URI in the incoming
request that was retargeted.
This occurs when a request is statically or dynamically
retargeted to another user represented by an AoR unassociated with
the AoR of the original target user. The "mp" header field parameter
contains the value of the hi-index
in the hi-entry with an hi-targeted-to-uri that reflects the
Request-URI that was retargeted, thus identifying the "mapped from"
target.
</t>
<t> "np": The hi-targeted-to-URI represents that there was no change
in Request-URI. This would apply for example when a proxy merely
forwards a request to a next hop proxy and loose routing is used.
The "np" header field parameter contains the
value of the hi-index in the hi-entry with an hi-targeted-to-
uri that reflects the Request-URI that was copied unchanged
into the request represented by this hi-entry. That value will
usually be the hi-index of the parent hi-entry of this hi-
entry.
</t>
</list>
</t>
<t>Extension (hi-extension): A parameter to allow for future
optional extensions. As per <xref target="RFC3261"></xref>, any
implementation not understanding an extension MUST ignore
it.</t>
</list></t>
<t>The ABNF syntax
<xref target="RFC5234"></xref>
for the History-Info header field and header field parameters is as follows:</t>
<figure>
<artwork><![CDATA[
History-Info = "History-Info" HCOLON hi-entry *(COMMA hi-entry)
hi-entry = hi-targeted-to-uri *(SEMI hi-param)
hi-targeted-to-uri = name-addr
hi-param = hi-index / hi-target-param / hi-extension
hi-index = "index" EQUAL index-val
index-val = number *("." number)
number = [ %31-39 *DIGIT ] DIGIT
hi-target-param = rc-param / mp-param / np-param
rc-param = "rc" EQUAL index-val
mp-param = "mp" EQUAL index-val
np-param = "np" EQUAL index-val
hi-extension = generic-param
]]></artwork>
</figure>
<t>The ABNF definitions for "generic-param", "name-addr", "HCOLON", "COMMA",
"SEMI" and "EQUAL" are from <xref target="RFC3261"></xref>.</t>
<t> This document also extends the "contact-params" for the Contact header field as
defined in <xref target="RFC3261"/> with the "rc", "mp" and "np" header field parameters defined above.</t>
<t> In addition to the parameters defined by the ABNF, an hi-entry may also
include a Reason header field and/or a Privacy header field, which are both
included in the "headers" component of the hi-targeted-to-uri as described below:</t>
<t>
<list style="symbols">
<t>Reason: An optional parameter for History-Info, reflected in
the History-Info header field by including the Reason header field <xref
target="RFC3326"></xref> included in the hi-targeted-to-uri. A reason is
included in the hi-targeted-to-uri of an hi-entry to reflect information
received in a response to the request sent to that URI.</t>
<t>Privacy: An optional parameter for History-Info, reflected in the
History-Info header field values by including the Privacy Header
<xref target="RFC3323"></xref> with a priv-value of "history", as defined in this document,
included in the hi- targeted-to-uri or by adding the
Privacy header field with a priv-value of "history" to the request. The latter case indicates
that the History-Info entries for all History-Info entries whose
hi-targeted-to-uri has the same domain as the domain for which the
SIP entity processing the message is responsible MUST be
anonymized prior to forwarding, whereas the use of the Privacy
header field included in the hi-targeted-to-uri means that a
specific hi-entry MUST be anonymized.
</t>
</list>
</t>
<t> Note that since both the Reason and Privacy parameters
are included in the hi-targeted-to-uri, these
fields will not be available in the case that the hi-targeted-to-uri is a Tel-URI
<xref target="RFC3966"></xref>.</t>
<t>The following provides examples of the format for the History-Info
header field. Note that the backslash, CRLF and whitespace between
the lines in the examples below are inserted for readability purposes
only. Note, however, that History-Info can be broken into multiple lines due to the
SWS (sep whitespace) that is part of HCOLON, COMMA and SEMI, and there can be multiple
History-Info header fields due to the rule of section 7.3 <xref target="RFC3261"/>.
Additional detailed examples are available in <xref target="I-D.ietf-sipcore-rfc4244bis-callflows"/>.
</t>
<t>
<figure>
<artwork><![CDATA[
History-Info: <sip:UserA@ims.example.com>;index=1;foo=bar
History-Info: <sip:UserA@ims.example.com?Reason=SIP%3B\
cause%3D302>;index=1.1,\
<sip:UserB@example.com?Privacy=history&Reason=SIP%3B\
cause%3D486>;index=1.2;mp=1.1,\
<sip:45432@192.168.0.3>;index=1.3;rc=1.2 ]]></artwork>
</figure>
</t>
<section anchor="example" title="History-Info Header Field Example Scenario">
<t>The following is an illustrative example of usage of
History-Info. </t>
<t>In this example, Alice (sip:alice@atlanta.example.com) calls Bob
(sip:bob@biloxi.example.com). Alice's proxy in her home domain
(sip:atlanta.example.com) forwards the request to Bob's proxy
(sip:biloxi.example.com). When the request arrives at
sip:biloxi.example.com, it does a location service lookup for
bob@biloxi.example.com and changes the target of the request to Bob's
Contact URIs provided as part of normal SIP registration. In this
example, Bob is simultaneously contacted on a PC client and on a phone,
and Bob answers on the PC client.</t>
<t>
One important thing illustrated by this call flow is that without
History-Info, Bob would "lose" the original target information or the
initial request-URI, including any parameters in the request URI.
Bob can recover that information by locating the last hi-entry with
an "rc" header field parameter. This "rc" header field parameter
contains the index of the hi-entry containing the lost target
information - i.e., the sip:bob@biloxi.example.com hi-entry with
index=1.1. Note that in the 200 response to Alice, an hi-entry is
not included for the fork to sip:bob@192.0.2.7 (index 1.1.1) since
biloxi.example.com had not received a response from that fork at the
time it sent the 200 OK that ultimately reached Alice.</t>
<t> Additional detailed examples are available in
<xref target="I-D.ietf-sipcore-rfc4244bis-callflows"/>.</t>
<t><list style="empty">
<t>Note: This example uses loose routing procedures.</t>
</list></t>
<figure anchor="basicFlow" title="Basic Call">
<artwork><![CDATA[
Alice atlanta.example.com biloxi.example.com Bob@pc Bob@phone
| | | | |
| INVITE sip:bob@biloxi.example.com;p=x | |
|--------------->| | | |
| Supported: histinfo | | |
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1 |
| | | | |
| | INVITE sip:bob@biloxi.example.com;p=x |
| |--------------->| | |
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1 |
| History-Info: <sip:bob@biloxi.example.com;p=x>;np=1;index=1.1
| | | | |
| | | INVITE sip:bob@192.0.2.3|
| | |--------------->| |
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1
| History-Info: <sip:bob@biloxi.example.com;p=x>;np=1;index=1.1
| History-Info: <sip:bob@192.0.2.3>;index=1.1.1;rc=1.1
| | | | |
| | | INVITE sip:bob@192.0.2.7|
| | |-------------------------->|
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1
| History-Info: <sip:bob@biloxi.example.com;p=x>;np=1;index=1.1
| History-Info: <sip:bob@192.0.2.7>;index=1.1.2;rc=1.1
| | | 200 | |
| | |<---------------| |
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1
| History-Info: <sip:bob@biloxi.example.com;p=x>;np=1;index=1.1
| History-Info: <sip:bob@192.0.2.3>;index=1.1.1;rc=1.1
| | | | |
| | 200 | | |
| |<---------------| | |
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1
| History-Info: <sip:bob@biloxi.example.com;p=x>;np=1;index=1.1
| History-Info: <sip:bob@192.0.2.3>;index=1.1.1;rc=1.1
| | | | |
| | | Proxy Cancels INVITE |
| | |<=========================>|
| | | | |
| 200 | | | |
|<---------------| | | |
| History-Info: <sip:bob@biloxi.example.com;p=x>;index=1
| History-Info: <sip:bob@biloxi.example.com;p=x>;np=1;index=1.1
| History-Info: <sip:bob@192.0.2.3>;index=1.1.1;rc=1.1
| | | | |
| ACK | | | |
|--------------->| ACK | | |
| |--------------->| ACK | |
| | |--------------->| |
]]></artwork>
</figure>
</section>
<!--end example-->
</section>
<!--end hidefinition-->
<section anchor="ua" title="User Agent Handling of the History-Info Header Field">
<t> This section describes the processing specific to UAs(UACs, UASs and B2BUAs)
for the History-Info header."</t>
<section anchor="uac" title="User Agent Client (UAC) Behavior">
<t>The UAC MUST include the "histinfo" option tag in the Supported
header field in any out-of-dialog requests or initial requests for a dialog for
which the UAC would like the History-Info header field in the response. When
issuing a request, the UAC MUST follow the procedures in <xref target="sendReq"/>.
In the case of an initial request, except where the UAC is part of a B2BUA, there is no cache of hi-
entries with which to populate the History-Info header field and the hi-index is set to 1 per
<xref target="indexhi"/>.
When receiving a response the UAC MUST follow the procedures in <xref target="receiveResponse"/>.
</t>
<t>
If the UAC generates further forks of the initial request (either due
to acting on a 3xx response or internally-directed forking to
multiple destinations), the successive requests will add hi-entries
with hi-indexes of 2, 3, etc.</t>
</section>
<!--end uac-->
<section anchor="uas" title="User Agent Server (UAS) Behavior">
<t> When receiving a request, a UAS MUST follow the procedures defined in
<xref target="sendReq"/>. When sending a response other than a 3xx response, a
UAS MUST follows the procedures as defined in <xref target="hiresponse"/>.
When sending a 3xx response, the UAS MUST follow the procedures defined for a
redirect server per <xref target="redirect"/>. An application at the UAS can make
use of the cached hi-entries as described in
<xref target="application"/>.
</t>
</section>
<!--end uas-->
<section anchor="b2bua" title="Back-2-Back User Agent (B2BUA) Behavior">
<t>A back-to-back user agent (B2BUA) MAY
follow the behavior of a SIP intermediary, per <xref target="proxy"/>, as an alternative to
following the behavior of a user agent server (UAS) per <xref target="uas"/> and a UAC per
<xref target="uac"/>. In behaving as an intermediary, a B2BUA carries forward
hi-entries received in requests at the UAS to requests being forwarded
by the UAC, as well as carrying forward hi-entries in responses received at the UAC to
the responses forwarded by the UAS, subject to privacy considerations
per <xref target="privacyhi"/>.
</t>
</section>
<!-- end B2BUA -->
</section>
<!-- end UAs-->
<section anchor="proxy" title="Proxy/Intermediary Handling of History-Info Header Fields">
<t>
This section describes the procedures for proxies and other SIP intermediaries
for the handling of the History-Info header fields for each of the following scenarios:</t>
<t>
<list style="hanging">
<t hangText="Receiving a Request:"> An intermediary MUST
follow the procedures in <xref target="receiveReq"/> for the handling of
hi-entries in incoming SIP requests. </t>
<t hangText="Sending a Request:">
For each outgoing request relating to a target in the target
set, the intermediary MUST follow the procedures of <xref target="sendReq"/>. </t>
<t hangText="Receiving a Response or Timeout:"> An intermediary MUST follow
the procedures of <xref target="receiveResponse"/> when a SIP
response is received or a request times out.</t>
<t hangText="Sending a Response:"> An intermediary MUST follow the
procedures of <xref target="hiresponse"/> for
the handling of the hi-entries when sending a SIP response. </t>
</list>
</t>
<t>
In some cases, an intermediary may retarget a request more than
once before forwarding - i.e., a request is retargeted to a SIP entity that is
"internal" to the intermediary before the same intermediary retargets the
request to an external target .
A typical example would be a proxy
that retargets a request first to a different user (i.e., it maps to a
different AOR) and then forwards to a registered contact bound to the same
AOR. In this case, the intermediary MUST
add a hi-entry for (each of) the internal target(s) per the procedures in
<xref target="sendReq"/>. The intermediary MAY include a Reason header field in the
hi-entry with
the hi-targeted-to-uri that has been retargeted. Note, that this is shown in the
INVITE (F6) in
the example entitled "Sequentially Forking (History-Info in Response)"
in <xref target="I-D.ietf-sipcore-rfc4244bis-callflows"/>.
</t>
</section>
<section anchor="redirect" title="Redirect Server Handling of History-Info Header Fields">
<t>A redirect server MUST follow the procedures in <xref target="receiveReq"/> when
it receives a SIP Request. A redirect server MUST follow
the procedures in <xref target="hiresponse"/> when it sends a
SIP Response. When
generating the Contact header field in a
3xx response, the redirect server MUST add the appropriate "mp", "np" or "rc"
header field parameter to
each Contact header field as described in
<xref target="targethi"/>, if applicable.
</t>
</section>
<!-- end redirect-->
<section anchor="commonhi" title="Handling of History-Info Header Fields in Requests and Responses">
<t>
This section describes the procedures for SIP entities for the handling
of the History-Info header field in SIP requests and responses.
</t>
<section anchor="receiveReq" title="Receiving a Request">
<t> When receiving a request, a SIP entity MUST keep a copy of
the hi-entries from the incoming request. This document describes
this copy in terms of a cache containing
the hi-entries associated with the request. The hi-entries MUST be added
to the cache in the order in which they were received in the request. </t>
<t>
If the Request-URI of the incoming request
does not match the hi-targeted-to-uri in the last hi-entry (i.e., the previous
SIP entity that sent the request did not include a History-Info header field), the SIP entity
MUST add a hi-entry to end of the cache, on behalf of the previous
SIP entity before proceeding to <xref target="sendReq" />, as follows:</t>
<t>
<list>
<t> The
SIP entity MUST set the hi-targeted-to-uri to the value of the
Request-URI in the incoming request. If the Request-URI is a Tel-URI, it SHOULD be transformed into a SIP URI
per section 19.1.6 of [RFC3261] before being added as a hi-targted-to-uri.
</t>
<t> If privacy is required, the SIP entity MUST follow the procedures of <xref target="privacyhi"></xref>.</t>
<t> The SIP entity MUST set the hi-index parameter as described in <xref
target="indexhi"></xref>.</t>
<t> The SIP entity MUST NOT
include an "rc", "mp" or "np" header field parameter. </t>
</list>
</t>
</section>
<section anchor="sendReq" title="Sending a Request with History-Info">
<t> When sending a request, a SIP entity MUST include all the hi-entries from
the cache that was created per <xref target="receiveReq" />.
In addition, the SIP entity MUST add a new hi-entry to the outgoing request,
but the SIP entity MUST NOT add the hi-entry to the cache at this time.
The hi-entries in the outgoing
request's History-Info header field is the preorder of the tree of
hi-entries, that is, by the lexicographic ordering of the hi-indexes.
The new hi-entry is populated as follows:</t>
<t>
<list style="hanging">
<t hangText="hi-targeted-to-uri:"> The hi-targeted-to-uri MUST be set
to the value of the Request-URI of the current
(outgoing) request.</t>
<t hangText="privacy:"> If privacy is required, the procedures of <xref
target="privacyhi"></xref> MUST be followed.</t>
<t hangText="hi-index:"> The SIP entity MUST include an hi-index
for the hi-entry as described in <xref
target="indexhi"></xref>. </t>
<t hangText="rc/mp/np:"> The SIP entity MUST include
an "rc", "mp" or "np" header field parameter in the hi-entry, if applicable,
per the procedures in <xref
target="targethi"></xref>. </t>
</list>
</t>
</section>
<section anchor="receiveResponse" title="Receiving a Response with History-Info or Request Timeouts">
<t> When a SIP entity receives a non-100 response or a request times out, the SIP entity performs
the following steps:</t>
<t><list style="hanging">
<t hangText="Step 1:">Add hi-entry to cache</t>
<t hangText=""> The SIP entity
MUST add the hi-entry that was added to the request that
received the non-100 response or timed out to the cache, if
it was not already cached.
The hi-entry MUST be added to the cache
in ascending order as indicated by the
values in the hi-index parameters of the hi-entries (e.g., 1.2.1
comes after 1.2 but before 1.2.2 or 1.3). </t>
<t hangText="Step 2:"> Add Reason header field</t>
<t hangText=""> If the response is not a 100 or 2xx response, the SIP entity adds one or
more Reason header fields to the hi-targeted-to-uri in the (newly)
cached hi-entry
reflecting the SIP response code in the non-100 or non-2xx response,
per the procedures of
<xref target="reasonhi"></xref>.</t>
<t hangText="Step 3:">Add additional hi-entries</t>
<t hangText="">The SIP entity MUST also add to the cache any hi-entries
received in the response that are not already in the cache. This situation
can occur when the entity that generated the non-100 response retargeted the
request before generating the response. As per Step 1, the hi-entries
MUST be added to the cache
in ascending order as indicated by the
values in the hi-index parameters of the hi-entries</t>
</list></t>
<t> It is important to note that the cache (and the request or response) does not contain
hi-entries for requests that
have not yet received a non-100 response, so there can be gaps in indices (e.g., 1.2 and
1.4 could be present but not 1.3). </t>
</section>
<section anchor="hiresponse" title="Sending History-Info in Responses">
<t> When sending a response other than a 100, a SIP entity MUST include all the cached
hi-entries in the response, subject to the privacy consideration in <xref target="applyingprivacy"></xref>, and with the following exception: If the received request contained
no hi-entries and there is no "histinfo" option tag in the Supported header field,
the SIP entity MUST NOT include History-Info in the response.</t>
</section>
<!-- end responses -->
</section>
<!-- end common -->
<section title="Processing the History-Info Header Field">
<t>The following sections describe the procedures for processing
the History-Info header field. These procedures are applicable to
SIP entities such as Proxies/Intermediaries, Redirect Servers or User
Agents.</t>
<section anchor="privacyhi" title="Privacy in the History-Info Header Field">
<t>The privacy requirements for this document are described in <xref
target="privacyreq"></xref>. <xref target="settingprivacy"> </xref> describes the insertion of
the Privacy header field defined in
<xref target="RFC3323"></xref> to indicate the privacy to be applied to the History-Info header field
entries. <xref target="applyingprivacy"> </xref> describes how to apply privacy to a request or response that is being forwarded, based on the presence of the Privacy header field.
</t>
<section anchor="settingprivacy" title="Indicating Privacy">
<t>As with other SIP headers described in
<xref target="RFC3323"></xref>, the hi-targeted-to-uris in the
History-Info header field can inadvertently reveal
information about the initiator of the request. Thus, the UAC needs a mechanism to
indicate that the hi-targeted-to-uris in the hi-entries need
to be privacy protected. The Privacy header field is used by the UAC to indicate
that privacy is to be applied to all the hi-entries in the request as follows:
<list style="symbols">
<t> If the UAC is including a Privacy
header field with a priv-value of "header" in the request, then
the UAC SHOULD NOT include a priv-value of "history" in the Privacy header field in the
Request.</t>
<t> If the UAC is including any priv-values other than "header"
in the Privacy header field,
then the UAC MUST also include
a priv-value of "history" in the
Privacy header field in the Request.</t>
<t> If the UAC is not including any priv-values in the
Privacy header field in the request, then
the UAC MUST add a Privacy header field, with
a priv-value of "history", to the request. The UAC MUST NOT include a priv-value of "critical"
in the Privacy header field in the Request in this case. </t>
</list>
</t>
<t> In addition, the History-Info header field can reveal general routing
and diverting information within an intermediary, which the
intermediary wants to privacy protect. In this case, the
intermediary MUST construct a Privacy header field with the single
priv-value of "history" and include the Privacy header field in the
hi-targeted-to-uri, for each new hi-entry created by the intermediary
whose hi-targeted-to-uri it wishes to privacy protect. Note that the
priv-value in the Privacy header for the incoming request does not
necessarily influence whether the intermediary includes a Privacy
header field in the hi-entries. For example, even if the Privacy
header for the incoming request contained a priv-value of "none", the
Proxy can still set a priv-value of "history" in the Privacy header
field included in the hi-targeted-to-uri.</t>
<t>Finally, the UAS may not want to reveal the final reached target to the originator. In this case,
the UAS MUST include a Privacy header field with a priv-value of "history"
in the hi-targeted-to-uri in the last
hi-entry, in the response. As noted above, the UAS of the request MUST NOT use
any other priv-values in the Privacy header field included in the hi-entry.</t>
</section>
<!-- end set privacy-->
<section anchor="applyingprivacy" title="Applying Privacy">
<t> When a SIP message is
forwarded to a domain for which the SIP intermediary is not
responsible, a Privacy
Service at the boundary of the domain applies the appropriate privacy based
on the value of the Privacy header field in the message header or in the
"headers" component of the hi-targeted-to-uri in the
individual hi-entries.</t>
<t>If there is a Privacy header field in the message header of a request
or response, with a priv-value of "header" or "history", then all the
hi-targeted-to-uris in the hi-entries, associated with the domain for
which the SIP intermediary is responsible, are anonymized by the
Privacy Service. The Privacy Service MUST change any hi-targeted-to-
uris in these hi-entries that have not been anonymized (evidenced by
their domain not being "anonymous.invalid") to anonymous URIs
containing a domain of anonymous.invalid as recommended in
section 4.1.1.3 of <xref target="RFC3323"/>.
As defined in section 4.1.1.2 of <xref target="RFC3323"/>
the recommendations of <xref target="RFC3261"/> for anonymyzing the
URI Username SHOULD be followed (i.e., "anonymous" in the
user portion of the URI).
If there is a Privacy header field in
the "headers" component of the hi-targeted-to-uri in the hi-entries,
then the Privacy header field value MUST be removed from the hi-
entry. Once all the appropriate hi-entries have been anonymized, the
Privacy Service MUST remove the priv-value of "history" from the
Privacy header field in the message header of the request or
response. If there are no remaining priv-values in the Privacy
header field, the Privacy Service MUST remove the Privacy header
field from the request or response per <xref target="RFC3323"/>. </t>
<t>
If there is not a Privacy header field in the message header of the request or response
that is being forwarded, but there is a Privacy header field with a priv-value of
"history" in the "headers" component in any of the hi-targeted-uris in the hi-entries
associated with the
domain for which a SIP intermediary is responsible, then the Privacy Service MUST update those hi-targeted-to-uris as described
above. Any other priv-values in the Privacy header field in the
"headers" component of the hi-targeted-to-uris in the hi-entries MUST be ignored.
In any case, the Privacy Service MUST remove
the Privacy header field from the "headers" compenent of the hi-targeted-to-uris in the
hi-entries prior to
forwarding.</t>
</section>
<!-- end apply privacy -->
</section>
<!-- end privacy -->
<section anchor="reasonhi" title="Reason in the History-Info Header Field">
<t> A Reason header field is added to the "headers" component in an hi-
targeted-to-uri when the hi-entry is added to the cache based upon
the receipt of a SIP response that is neither a 100 nor a 2xx response,
as described in <xref target="receiveResponse"/>.
If the Reason header field is being added due to receipt of an
explicit SIP response and
the response contains any Reason header fields (see <xref
target="RFC3326"></xref>), then the SIP entity MUST include
the Reason header fields in the "headers" component of
the hi-targeted-to-uri in the last hi-entry added to the cache,
unless the hi-targeted-to-uri is a Tel-URI.
If the SIP response does not contain a Reason header field,
the SIP entity MUST include a Reason header
field, containing the SIP Response Code, in the "headers" component of
the hi-targeted-to-uri in the last hi-entry added to the cache,
unless the hi-targeted-to-uri is a Tel-URI.</t>
<t>If a request has timed out (instead of being explicitly rejected),
the SIP entity MUST update the cache as if the request received a SIP
error response code of 408 "Request Timeout".</t>
<t>A request can receive multiple responses, that are neither 100 nor 2xx responses, which carry
or imply (for responses without Reason headers, and for timeouts)
multiple, possibly duplicated, reason-values to be applied to an hi-
targeted-to-uri. In these situations, the SIP entity creating
History-Info header value would choose the appropriate Reason header
field value. </t>
<t> A SIP entity MAY also include a Reason header field in the
"headers" component of an
hi-targeted-to-uri containing the URI of a request that was retargeted
as a result of internal retargeting. </t>
<t> If additional Reason header field parameters are defined in the
future per <xref target="RFC3326"></xref>, the use of these Reason header field parameters
for the History-Info header field MUST follow the same rules as
described above.</t>
</section>
<!-- end reason -->
<section anchor="indexhi" title="Indexing in the History-Info Header Field">
<t>In order to maintain ordering and accurately reflect the retargeting of the request,
the SIP entity MUST add a hi-index to each
hi-entry.
Per the syntax in <xref target="definitionhi"></xref>, the hi-index consists of a series of nonnegative integer separated by dots (e.g., 1.1.2). Each dot
reflects a SIP forwarding hop. The nonnegative integer following
each dot reflects the order in which a request was retargeted at the
hop. The highest nonnegative integer at each hop reflects the number
of entities to which the request has been retargeted at the specific
hop (i.e., the number of branches) at the time that the request
represented by this hi-entry was generated. Thus, the indexing
results in a logical tree representation for the history of the
request and the hi-entries are given in the preorder of the tree.
</t>
<t>The first index in a series of History-Info entries MUST be set to 1.
In the case that a SIP entity (intermediary or UAS) adds a first hi-
entry on behalf of the previous hop, the hi-index MUST be set to 1.
For each forward hop (i.e., each new level of indexing), the last
integers of the hi-indexes of the new requests MUST be generated
starting at 1 and incrementing by 1 for each additional request.
</t>
<t>The basic rules for adding the hi-index are summarized as follows:
<list style="numbers">
<t>Forwarding a request without changing the target: In the case of a request that is being
forwarded without changing the target, the hi-index reflects the increasing length of the branch.
In this case, the SIP entity MUST read the value from
the History-Info header field in the received request
and MUST add another level of indexing by appending the dot
delimiter followed by an initial value of 1 for the new level.
For example, if the hi-index in the last History-Info header field
in the received request is 1.1, a proxy would add a hi-entry with an
hi-index of 1.1.1 and forward the request.</t>
<t>Retargeting within a processing entity - 1st instance: For
the first instance of retargeting within a processing entity, the
SIP entity
MUST calculate the hi-index as prescribed for basic
forwarding.</t>
<t>Retargeting within a processing entity - subsequent instance:
For each subsequent retargeting of a request by the same
SIP entity, the SIP entity MUST calculate and add the hi-index for
each new branch by incrementing the rightmost value from the hi-index in the last hi-entry.
Per the example above, the hi-index in the next request forwarded by
this same SIP entity would
be 1.1.2.</t>
<t>Retargeting based upon a Response: In the case of retargeting
due to a specific response (e.g., 302), the SIP entity MUST calculate
the hi-index
calculated per rule 3. That is, the rightmost value of the
hi-index MUST be incremented (i.e., a new branch is created).
For example, if the hi-index in the History-Info
header field of the sent request is 1.2 and the response to the request
is a 302,
then the hi-index in the
History-Info header field for the new hi-targeted-to-URI would
be 1.3.</t>
<t>Forking requests: If the request forwarding is done in
multiple forks (sequentially or in parallel), the SIP entity MUST
set the hi-index for each hi-entry for
each forked request per the rules above, with each
new request having a unique index. Each index MUST be sequentially
assigned. For example, if the index in the last History-Info
header field in the received request is 1.1, this processing
entity would initialize its index to 1.1.1 for the first fork,
1.1.2 for the second, and so forth (see <xref
target="basicFlow"></xref> for an example). Note, that
in the case of parallel forking, only the hi-entry corresponding to
the fork is included in the request because no response can yet have been received
for any of the parallel forked requests.</t>
<t>Missing entry: If the request clearly has a gap in the
hi-entry (i.e., the last hi-entry and Request-URI differ), the entity adding
an hi-entry MUST add a single index with a value of "0" (i.e., the non-negative
integer zero)
prior to adding the appropriate index
for the action to be taken.
For example, if the index of the last hi-entry in the request received was 1.1.2
and there was a missing hi-entry and the request was being forwarded to
the next hop, the resulting index will be 1.1.2.0.1. In the case of requests which
are forked by a proxy that does not support History-Info,
it is possible for hi-entries generated by different entities
to have the same index - i.e., each entity supporting History-Info would receive a
forked request with the same hi-index to which they would add the value of ".0" prior
to adding the appropriate index. Thus, in the previous example, each of the next hop
entities would generate an hi-index of 1.1.2.0.1. </t>
</list></t>
</section>
<!-- index -->
<section anchor="targethi" title="Mechanism for Target Determination in the History-Info Header Field">
<t>
This specification defines three header field parameters, "rc", "mp" and
"np". The header field parameters
"rc" and "mp" indicate the mechanism by which a new target
for a request is determined. The header field "np" reflects that
the target has not changed. All parameters contain an index whose value is the
hi-index of the hi-entry with an hi-targeted-to-uri that represents
the Request-URI that was
retargeted.</t>
<t> The SIP entity MUST determine the specific parameter field to be included
in the hi-target-param, in the History-Info header field,
as the targets are
added to the target set per the procedures in section 16.5 of <xref target="RFC3261"/>
or per section 8.1.3.4 <xref target="RFC3261"/> in the case of
retargeting to a contact URI received in a 3xx response.
In the latter case, the specific header field parameter in the
Contact header field becomes the header field parameter that is
used in the hi-entry when the request is retargeted.
If the Contact header field does not contain an
"rc" or "mp" header field parameter, then the SIP entity
MUST NOT include an "rc" or "mp" header field parameter
in the hi-target-param in the hi-entry when the request is
retargeted to a contact URI received in a 3xx response.
This is because the redirect server is the only element with any
knowledge on how the target was determined. Note, that the "np"
header field parameter is not applicable in the case of
redirection. </t>
<t> The SIP entity (intermediary or redirect server) determines the specific header
field parameter ("rc", "mp" or "np") to be used
based on the following criteria:</t>
<t>
<list style="symbols">
<t>
"rc": The Request-URI has changed while retaining the target user
associated with the original Request-URI prior to retargeting.
</t>
<t>
"mp": The target was determined based on a mapping to a user other
than the target user associated with the Request-URI being retargeted.
</t>
<t>
"np": The target hasn't changed and the associated Request-URI remained
the same.
</t>
</list>
</t>
<t> Note that there are two scenarios by which the "mp" header field parameter can be
derived. </t>
<t>
<list style="symbols">
<t> The mapping was done by the receiving entity on its own authority, in which case
the mp-value is the parent index of the hi-entry's index.</t>
<t> The mapping was done due to receiving a 3xx response, in which case the
mp-value is an earlier sibling or descendant of an earlier sibling of the hi-entry's index, that of the
downstream request which received the 3xx response. </t>
</list>
</t>
</section>
<!-- end target -->
</section>
<!-- end header field parameters -->
<section anchor="application" title="Application Considerations">
<t> History-Info provides a very flexible building block that can be used
by intermediaries and UAs for a variety of services. Prior to any
application usage of the History-Info header field parameters, the
SIP entity that processes the hi-entries MUST evaluate the hi-
entries. The SIP entity MUST be prepared to process effectively
messages whose hi-entries show evidence of "gaps", that is,
situations that reveal that not all of the forks of the request have
been recorded in the hi-entries. Gaps are possible if the request is
forwarded through intermediaries that do not support the History-Info
header field and are reflected by the existence of hi-entries with a
nonnegative integer of "0" e.g. "1.1.0.1". Gaps are also possible in
the case of parallel forking if there is an outstanding request at
the time the SIP entity sends a message. In addition, gaps may introduce
the possibility of duplicate values for the hi-index in the case that
a proxy that does not support History-Info forks a request.
If gaps are detected,
the SIP entity MUST NOT treat this as an error, but SHOULD indicate
to any applications that there are gaps.
The interpretation of the
information in the History-Info header field depends upon the
specific application; an application might need to provide special
handling in some cases where there are gaps. </t>
<t> The following describes some categories of information that applications can
use:</t>
<t>
<list style="numbers">
<t> Complete history information - e.g., for debug or other
operational and management aspects, optimization of determining targets to
avoid retargeting to the same URI, etc. This information is relevant
to proxies, UACs and UASs.</t>
<t> Hi-entry with the index that matches the value of the "rc" header field parameter
in the last hi-entry with a "rc" header field parameter
in the Request received by a UAS - i.e., the last AOR that was
retargeted to a contact based on an AOR-to-contact binding. </t>
<t> Hi-entry with the index that matches the value of the "mp" header field parameter
in the last hi-entry with a "mp" header field parameter in the hi-target-param
in the Request received by a UAS - i.e., the last Request URI that was mapped to reach the destination.</t>
<t> Hi-entry with the index that matches the value of the "rc" header field parameter
in the first hi-entry with a "rc" header field parameter
in the Request received by a UAS. Note, this would be the original AoR if all the entities involved
support the History-Info header field and there is absence of an "mp"
header field parameter prior to the "rc" header field parameter in the hi-target-param in
the History-Info header field.
However, there is no guarantee that all entities will support History-Info,
thus the hi-entry that matches the value of the "rc" header field parameter of the
first hi-entry with an "rc" header field parameter in the hi-target-param
within the domain associated with the target URI at the destination is more likely to be
useful. </t>
<t> Hi-entry with the index that matches the value of "mp" header field parameter
in the first hi-entry with an "mp" header field parameter
in the Request received by a UAS.
Note, this would be the original mapped URI if all entities
supported the History-Info header field.
However, there is no guarantee that all entities will support History-Info,
thus the hi-entry that matches the value of the "mp" header
field parameter of the first hi-entry with an "mp" header field parameter
within the domain associated with the target URI at the destination is more likely to be
useful. </t>
</list>
</t>
<t> In many cases, applications are most interested in the information within a particular domain(s),
thus only a subset of the information is required. </t>
<t> Some applications may use multiple types of information.
For example, an Automatic Call Distribution (ACD)/Call
center application that utilizes the hi-entry which index matches
the value of the "mp" header field parameter of the first
hi-entry with an "mp" header field parameter,
may also display other agents, reflected by other hi-entries prior to entries
with hi-target value of "rc" header field parameter,
to whom the call was targeted prior to its arrival at the current agent.
This could allow the agent the
ability to decide how they might forward or reroute the call if necessary
(avoiding agents that were
not previously available for whatever reason, etc.).
</t>
<t> Since support for History-Info header field is optional, a service
MUST define default
behavior for requests and responses not containing History-Info
header fields. For example, an entity may receive an incomplete set of hi-entries
or hi-entries which are not tagged appropriately with an hi-target-param in the
case of entries added by entities that are only compliant to RFC4244.
This may not impact some applications (e.g., debug), however, it could require
some applications to make some default assumptions in this case. For example, in an ACD
scenario, the application could select the oldest hi-entry with the domain
associated with the ACD
system and display that as the original called party. Depending upon how and
where the request may have
been retargeted, the complete list of agents to whom the call was targeted may not be available.
</t>
</section>
<section anchor="application_specific" title="Application Specific Usage">
<t>The following are possible (non-normative) application-specific usages of
History-Info.</t>
<section anchor="pbx_vm" title="PBX Voicemail">
<t>A voicemail system typically requires the original called
party information to determine the appropriate mailbox so an
appropriate greeting can be provided and the appropriate party
notified of the message.
</t>
<t>The original target is determined by finding the first
hi-entry tagged with "rc" and using the hi-entry referenced by the
index of "rc" header field parameter as the target for determining
the appropriate mailbox. This hi-entry is used to populate the
"target" URI parameter as defined in <xref target="RFC4458"></xref>
The VMS can look at the last hi-entry and find the target of the
mailbox by looking at the URI entry in the "target" URI parameter in
the hi-entry.
</t>
<t>This example usage does not work properly in the presence of forwarding that takes place before the call reaches the company in that case not the first hi-entry with an rc value, but the first hi-entry with an rc value following an mp entry needs to be picked. Further detail for this example can be
found in the call flow entitled "PBX Voicemail Example"
in <xref target="I-D.ietf-sipcore-rfc4244bis-callflows"/>.
</t>
<t> Note that in the case where there is no entry tagged with "rc", a VMS can
follow the procedures, as defined in <xref target="RFC4458"></xref>,
for the "Interaction with Request History Information".</t>
</section>
<section anchor="consumer_vm" title="Consumer Voicemail">
<t>The voicemail system in these
environment typically requires the last called party information to
determine the appropriate mailbox so an appropriate greeting can be
provided and the appropriate party notified of the message.
</t>
<t>The last target is determined by finding the hi-entry referenced by the index
of last hi-entry tagged with "rc" for determining the appropriate
mailbox. This hi-entry is used to populate the "target" URI
parameter as defined in <xref target="RFC4458"></xref>.
The VMS can look at the last hi-entry and find the target of the
mailbox by looking for the "target" URI parameter in the hi-entry.
Further detail for this example can be
found in the call flow entitled "Consumer Voicemail Example"
in <xref target="I-D.ietf-sipcore-rfc4244bis-callflows"/>.
</t>
<t> In the case where there is no entry tagged with "rc", a VMS can
follow the procedures, as defined in <xref target="RFC4458"></xref>,
for the "Interaction with Request History Information".</t>
</section>
</section>
<section anchor="security" title="Security Considerations">
<t>The security requirements for this specification are specified in <xref
target="secreq"></xref>.</t>
<t>This document defines a header field for SIP. The use of the Transport
Layer Security (TLS) protocol <xref target="RFC5246"></xref> as a
mechanism to ensure the overall confidentiality of the History-Info
header fields (SEC-req-4) is strongly RECOMMENDED. If TLS is NOT used, the
intermediary MUST ensure that the messages are only sent within an environment
that is secured by other means or that the messages don't leave the
intermediary's domain. This results in
History-Info having at least the same level of security as other headers
in SIP that are inserted by intermediaries. With TLS, History-Info
header fields are no less, nor no more, secure than other SIP header fields, which
generally have even more impact on the subsequent processing of SIP
sessions than the History-Info header field.</t>
<t>Note that while using the SIPS scheme (as per <xref
target="RFC5630"></xref>) 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.</t>
<t>In terms of ensuring the privacy of hi-entries, the same security considerations
as those described in <xref target="RFC3323"/> apply.
The privacy service that's defined in <xref target="RFC3323"/>
MUST also support the new privacy header field
priv-value of "history" and anonymize hi-entries in the case of a priv-value of "header"
as described in <xref target="applyingprivacy"/>. </t>
</section>
<section anchor="iana" title="IANA Considerations">
<t>This document requires several IANA registrations detailed in the
following sections.</t>
<t>This document obsoletes <xref target="RFC4244"></xref> but uses the
same SIP header field name, Privacy header field and Option tag. The IANA registry needs to
update the references to <xref target="RFC4244"></xref> with
[RFC XXXX], where XXXX is the RFC number for this document.</t>
<section anchor="header"
title="Registration of New SIP History-Info Header Field">
<t>This document defines a SIP header field name: History-Info and an
option tag: histinfo. The following updates have been made to
http:///www.iana.org/assignments/sip-parameters. </t>
<t>The following row has been updated in the header field section:</t>
<figure>
<artwork><![CDATA[
Header Name Compact Form Reference
----------- ------------ ---------
History-Info none [RFC XXXX]
]]></artwork>
</figure>
<t>The following has been updated in the Options Tags section:</t>
<figure>
<artwork><![CDATA[
Name Description Reference
---- ----------- ---------
histinfo When used with the Supported header field, [RFC XXXX]
this option tag indicates the UAC
supports the History Information to be
captured for requests and returned in
subsequent responses. This tag is not
used in a Proxy-Require or Require
header field since support of
History-Info is optional.
]]></artwork>
</figure>
<t>Note to RFC Editor: Please replace RFC XXXX with the RFC number of
this specification.</t>
</section>
<section title="Registration of "history" for SIP Privacy Header Field">
<t>This document defines a priv-value for the SIP Privacy header field:
history. The following updates have been made to
http://www.iana.org/assignments/sip-priv-values. The following has been
updated in the registration for the SIP Privacy header field:</t>
<figure>
<artwork><![CDATA[
Name Description Registrant Reference
---- ----------- ---------- ---------
history Privacy requested for Mary Barnes [RFC XXXX]
History-Info header mary.ietf.barnes@gmail.com
fields(s)
]]></artwork>
</figure>
<t>Note to RFC Editor: Please replace RFC XXXX with the RFC number of
this specification.</t>
</section>
<section title="Registration of Header Field Parameters">
<t>This specification defines the following new
SIP header field parameters in
the SIP Header Field parameter sub-registry in the SIP Parameter Registry,
http:/www.iana.org/assignments/sip-parameters.</t>
<figure>
<artwork><![CDATA[
Header Field Parameter Name Predefined Reference
Values
____________________________________________________________________
History-Info mp No [RFC xxxx]
History-Info rc No [RFC xxxx]
History-Info np No [RFC xxxx]
Contact mp No [RFC xxxx]
Contact rc No [RFC xxxx]
Contact np No [RFC xxxx]
]]></artwork>
</figure>
<t>Note to RFC Editor: Please replace RFC XXXX with the RFC number of
this specification.</t>
</section>
</section>
<section title="Acknowledgements">
<t>Jonathan Rosenberg et al produced the document that provided
additional use cases precipitating the requirement for the
new header parameters to capture the method by which a Request URI
is determined. The authors would like to acknowledge the constructive feedback
provided by Ian Elz, Paul Kyzivat, John Elwell, Hadriel Kaplan, Marianne Mohali,
Brett Tate,
and Dale Worley. John Elwell also provided excellent suggestions in
terms of document structure. Dan Romascanu performed the Gen-ART review.</t>
<t>
Mark Watson, Cullen Jennings and Jon Peterson provided significant input
into the initial work that resulted in the development of of <xref target="RFC4244"></xref>.
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 <xref target="RFC4244"></xref>.
</t>
<t> The editor would like to
acknowledge the significant input from Rohan Mahy on some of the
normative aspects of the ABNF for <xref target="RFC4244"></xref>,
particularly around the need for and format of the index and around the
security aspects.
</t>
</section>
<section title="Changes from RFC 4244">
<t>This RFC replaces <xref target="RFC4244"></xref>.</t>
<t>Deployment experience with <xref target="RFC4244"></xref> over the
years has shown a number of issues, warranting an update:</t>
<t><list style="symbols">
<t>In order to make <xref target="RFC4244"></xref> work in "real
life", one needs to make "assumptions" on how History-Info is used.
For example, many implementations filter out many entries, and only
leave specific entries corresponding, for example, to first and last
redirection. Since vendors uses different rules, it causes
significant interoperability issues.</t>
<t><xref target="RFC4244"></xref> is overly permissive and evasive
about recording entries, causing interoperability issues.</t>
<t>The examples in the call flows had errors, and confusing because
they often assume "loose routing". </t>
<t><xref target="RFC4244"></xref> has lots of repetitive and unclear
text due to the combination of requirements with solution. </t>
<t><xref target="RFC4244"></xref> gratuitously mandates the use of TLS
on every hop. No existing implementation enforces this rule, and
instead, the use of TLS or not is a general SIP issue, not an <xref
target="RFC4244"></xref> issue per se.</t>
<t><xref target="RFC4244"></xref> 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.</t>
<t><xref target="RFC4244"></xref> does not allow for marking
History-Info entries for easy processing by User Agents.</t>
</list></t>
<t> The following summarizes the functional
changes between this specification and
<xref target="RFC4244"></xref>:</t>
<t><list style="numbers">
<t>Added header field parameters to capture the specific method by
which a target is determined to facilitate
processing by users of the History-Info header field
entries.
A specific header field parameter is captured for each
of the target
URIs as the target set is determined (per section 16.5
of <xref target="RFC3261"/>). The header field
parameter is used in both the History-Info and
the Contact header fields.
</t>
<t>Added a way to indicate a gap in History-Info by adding a
non-negative integer of "0".</t>
<t>Rather than recommending that entries be removed in the case of
certain values of the Privacy header field, the entries are
anonymized.</t>
<t>Updated the security section to be equivalent to the security
recommendations for other SIP header fields inserted by
intermediaries.</t>
<t>Removed Appendix B since a separate call flow document is being
published as a companion to this document. </t>
</list></t>
<t>The first 2 changes are intended to facilitate application usage of
the History-Info header field and eliminate the need to make assumptions based
upon the order of the entries and ensure that the most complete set of
information is available to the applications.</t>
<t>In addition, editorial changes were done to both condense and clarify
the text, moving the requirements to an appendix and removing the inline references
to the requirements. The
examples were simplified and updated to reflect the
protocol changes. Several of the call flows in the appendix were removed
and put into a separate document that includes additional use cases
that require the new header field parameters. </t>
<section title="Backwards compatibility">
<t>This specification is backwards compatible since
<xref target="RFC4244"></xref>
allows for the addition of new optional parameters.
This specification adds an optional SIP header field parameter
to the History-Info and Contact header fields.
Entities that
have not implemented this specification will ignore these parameters,
however, per <xref target="RFC4244"/>
an entity will not remove these
parameters from an hi-entry.
While entities compliant to this document and <xref target="RFC4244"/> must be
able to recognize gaps in the hi-entries, this
document requires that an index of "0" be used in this case. Whereas
<xref target="RFC4244"/> recommended (but did not require)
the use of "1". However,
since the ABNF in <xref target="RFC4244"/> defines the index as a DIGIT,
"0" would be a valid value, thus an <xref target="RFC4244"/> implementation should
not have an issue if it receives hi-entries added by intermediaries compliant
to this document.
</t>
<t>As for the behavior of the UACs, UASs and intermediaries, the following
additional normative
changes have been made: </t>
<t>UAC behavior</t>
<t>
<list style="numbers">
<t>Inclusion of option tag by UAC has changed from SHOULD to MUST.</t>
<t>Inclusion of hi-target-entry along with hi-index has changed from MAY/RECOMMEND to MUST/MUST.</t>
<t>Behavior surrounding the addition of hi-target-entry based on 3xx response has changed from MAY/SHOULD to MUST.</t>
</list>
</t>
<t>None of the behavior changes would cause any backward or forward compatibility issues.</t>
<t>UAS behavior</t>
<t>
<list style="numbers">
<t>Inclusion of hi-entry in response has changed from SHOULD to MUST.</t>
</list>
</t>
<t>As the entity receiving response with hi-entry expected it with SHOULD, this
change will not cause any backward compatibility issues.</t>
<t>Proxy/Redirect Server behavior</t>
<t>
<list style="numbers">
<t>Inclusion of H-I as forwarding the request has changed from SHOULD to MUST.</t>
<t>Association of Reason with time-out/internal reason has changed from MAY to MUST.</t>
<t>Inclusion of hi-index has changed from RECOMMENDED to MUST.</t>
<t>Inclusion of hi-entries in response has changed from SHOULD to MUST.</t>
</list>
</t>
<t>
None of above behavior changes impact backwards compatibility since
they only strengthen normative behavior to improve interoperability.</t>
<t> In cases where an entity that is compliant to this document, receives
a request that contains hi-entries compliant only to RFC4244 (i.e,
the hi-entries do not contain any of the new header field
parameters), the entity MUST NOT add
any of the new header field parameters to the hi-entries.
The hi-entries MUST be cached and forwarded as any other
entries are as specified in <xref target="receiveReq"/>.
As with RFC4244 compliant entities, applications must
be able to function in cases of missing information, as specified in <xref target="application"/>.
</t>
</section>
</section>
</middle>
<back>
<references title="Normative References">
&rfc3261;
&rfc3326;
&rfc3323;
&rfc2119;
&rfc5234;
&RFC4458;
&rfc4244;
</references>
<references title="Informative References">
&rfc5627;
&rfc5630;
&rfc3087;
&rfc4240;
&rfc3966;
&rfc4458;
&I-D.ietf-sipcore-rfc4244bis-callflows;
</references>
<section anchor="requirements" title="Request History Requirements">
<t>The following list constitutes a set of requirements for a "Request
History" capability.</t>
<t><list style="numbers">
<t>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.</t>
<t>GENERATION-req: "Request History" information is generated when
the request is retargeted. <list style="letters">
<t>In some scenarios, it might be possible for more than one
instance of retargeting to occur within the same proxy. A proxy
MUST also generate Request History information for the
'internal retargeting'.</t>
<t>An entity (UA or proxy) retargeting in response to a redirect
or REFER MUST include any Request History information from the
redirect/REFER in the new request.</t>
</list></t>
<t>ISSUER-req: "Request History" information can be generated by a
UA or proxy. It can be passed in both requests and responses.</t>
<t>CONTENT-req: The "Request History" information for each
occurrence of retargeting shall include the following:<list
style="letters">
<t>The new URI or address to which the request is in the process
of being retargeted,</t>
<t>The URI or address from which the request was retargeted, and
whether the retarget URI was an AOR</t>
<t>The mechanism by which the new URI or address was
determined,</t>
<t>The reason for the Request-URI or address modification,</t>
<t>Chronological ordering of the Request History
information.</t>
</list></t>
<t>REQUEST-VALIDITY-req: Request History is applicable to requests
not sent within an early or established dialog (e.g., INVITE, REGISTER,
MESSAGE, and OPTIONS).</t>
<t>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.</t>
<t>FORWARDS-req: Request History information may also be included by
the generating entity in the request, if it is forwarded
onwards.</t>
</list></t>
<section anchor="secreq" title="Security Requirements">
<t>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.</t>
<t>The potential security problems include the following: <list
style="numbers">
<t>A rogue application could insert a bogus Request History-Info entry
either by adding an additional hi-entry as a result of retargeting or
entering invalid information.</t>
<t>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.</t>
<t>A rogue application could delete some or all of the Request
History information.</t>
</list></t>
<t>Thus, a security solution for "Request History" must meet the
following requirements: <list style="numbers">
<t>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.</t>
<t>SEC-req-2: The ordering of the Request History information must
be preserved at each instance of retargeting.</t>
<t>SEC-req-3: The entity receiving the information conveyed by the
Request History must be able to authenticate the entity providing
the request.</t>
<t>SEC-req-4: To ensure the confidentiality of the Request History
information, only entities that process the request SHOULD have
visibility to the information.</t>
</list></t>
<t>It should be noted that these security requirements apply to any
entity making use of the Request History information.</t>
</section>
<section anchor="privacyreq" title="Privacy Requirements">
<t>Since the Request-URI that is captured could inadvertently reveal
information about the originator, there are general privacy
requirements that MUST be met: <list style="numbers">
<t>PRIV-req-1: The entity retargeting the Request must ensure that
it maintains the network-provided privacy (as described in <xref
target="RFC3323"></xref>) associated with the Request as it is
retargeted.</t>
<t>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.</t>
<t>PRIV-req-3: Request History information subject to privacy
shall not be included in out going messages unless it is protected
as described in <xref target="RFC3323"></xref>.</t>
</list></t>
</section>
</section>
</back>
</rfc>| PAFTECH AB 2003-2026 | 2026-04-24 04:24:25 |