Internet Draft M. Barnes
Document: draft-ietf-sip-history-info-02.txt Editor
Category: Standards Track Nortel Networks
Expires: August, 2004 February, 2004
An Extension to the Session Initiation Protocol for Request History
Information
Status of this Memo
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Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This draft defines a standard mechanism for capturing the history
information associated with a SIP request. This capability enables
many enhanced services by providing the information as to how and why
a call arrives at a specific application or user. This draft defines
a new optional SIP header, History-Info, for capturing the history
information in requests. A new option tag, Histinfo, to be included
in the Supported header, is defined to allow UAs to indicate whether
the History-Info should be returned in responses to a request which
has captured the history information.
Table of Contents
1.Background: Why define a Generic "Request History" capability?.3
2. "Request History" Requirements.................................4
2.1 Security Requirements.........................................6
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2.2 Privacy Requirements.......................................6
3. Request History Information Description........................7
3.1 Optionality of History-Info................................8
3.2 Securing History-Info......................................8
3.3 Ensuring the Privacy of History-Info.......................9
4 Request History Information Protocol Details....................9
4.1 Protocol Structure of History-Info.........................9
4.2 Protocol Examples.........................................11
4.3 Protocol usage............................................11
4.4 Security for History-Info.................................15
4.5 Example Applications using History-Info...................16
5. Application Considerations....................................17
6. Security Considerations.......................................18
7. IANA Considerations...........................................18
Normative References.............................................21
Informational References.........................................22
Appendix A Forking Scenarios....................................23
A.1 Sequentially forking (History-Info in Response)...........23
A.2 Sequential Forking (with Success).........................24
Appendix B Voicemail............................................25
Appendix C Automatic Call Distribution Example..................30
Full Copyright Statement.........................................32
Overview
Many services that SIP is anticipated to support require the ability
to determine why and how the call arrived at a specific application.
Examples of such services include (but are not limited to) sessions
initiated to call centers via "click to talk" SIP URLs on a web page,
"call history/logging" style services within intelligent "call
management" software for SIP UAs and calls to voicemail servers and
call centers. While SIP implicitly provides the redirect/retarget
capabilities that enable calls to be routed to chosen applications,
there is currently no standard mechanism within SIP for communicating
the history of such a request. This "request history" information
allows the receiving application to determine hints about how and why
the call arrived at the application/user. This draft defines a new
SIP header, History-Info, to provide a standard mechanism for
capturing the request history information to enable a wide variety of
services for networks and end users. The History-Info header
provides a building block for development of new services.
Section 1 provides additional background motivation for the Request
History capability. Section 2 identifies the requirements for a
solution, with Section 3 providing an overall description of the
solution.
Section 4 provides the details of the additions to the SIP protocol.
An example use of the new header is included in Section 4.5, with
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additional scenarios included in the Appendix. It is anticipated that
these would be moved and progressed in a general Service examples
draft such as [SIPSVCEX] or individual informational drafts
describing these specific services, since the History-Info header is
just one of the building blocks for implementing these services.
Individual drafts would be particularly useful for documenting
services for which there are multiple solutions, as it is not the
intent, nor is it within the scope, of this draft to prescribe a
complete solution for any of these applications.
Section 5 summarizes the application considerations identified in the
previous sections. Section 6 summarizes the security solution as
described in section 4.4.
Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
In order to provide a cross reference of the solution description to
the requirements without reiterating the entirety of the requirements
inline, the requirements are referenced as [REQNAME-req] following
the text or paragraph which explicitly satisfies the requirement.
1.Background: Why define a Generic "Request History" capability?
SIP implicitly provides redirect/retarget capabilities that enable
calls to be routed to specific applications as defined in [RFC3261].
The term retarget will be used henceforth in this draft to refer to
the process of a Proxy Server/UAC changing a URI in a request and
thus changing the target of the request. This term is chosen to
avoid associating this request history only with the specific SIP
Redirect Server capability that provides for a response to be sent
back to a UAC requesting that the UAC should retarget the original
request to an alternate URI. The rules for determining request
targets as described in section 16.5 of [RFC3261] are consistent with
the use of the retarget term in this draft.
The motivation for the request history is that in the process of
retargeting old routing information can be forever lost. This lost
information may be important history that allows elements to which
the call is retargeted to process the call in a locally defined,
application specific manner. The proposal in this draft is to provide
a mechanism for transporting the request history. It is not
proposing any application specific behavior for a Proxy or UA upon
receipt of the information. Indeed, such behavior should be a local
decision for the recipient application.
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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 which will receive
some "referral" commission for generating this traffic,
2. Email forwarding whereby the forwarded-to user obtains a "history"
of who sent the email to whom and at what time
3. Traditional telephony services such as Voicemail, call-center
"automatic call distribution", and "follow-me" style services.
Several of the aforementioned applications currently define
application specific mechanisms through which it is possible to
obtain the necessary history information.
In addition, request history information could be used to enhance
basic SIP functionality by providing the following:
4. Some diagnostic information for debugging SIP requests.
5. A stronger security solution for SIP. A side effect is that each
proxy which captures the "request history" information in a secure
manner provides an additional means (without requiring signed keys)
for the original requestor to be assured that the request was
properly retargeted.
2. "Request History" Requirements
The following list constitutes a set of requirements for a "Request
History" capability.
1) CAPABILITY-req: The "Request History" capability provides a
capability to inform proxies and UAs involved in processing a request
about the history/progress of that request. While this is inherently
provided when the retarget is in response to a SIP redirect, it is
deemed useful for non-redirect retargeting scenarios, as well.
2) OPTIONALITY-req: The "Request History" information is optional.
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2.1) In many cases, it is anticipated that whether the history is
added to the Request would be a local policy decision enforced by the
specific application, thus no specific protocol element is needed.
2.2) Due to the capability being "optional" from the SIP protocol
perspective, the impact to an application of not having the "Request
History" must be described. Applicability guidelines to be addressed
by applications using this capability must be provided as part of the
solution to these requirements.
3) GENERATION-req: "Request History" information is generated when
the request is retargeted.
3.1) In some scenarios, it might be possible for more than one
instance of retargeting to occur within the same Proxy. A proxy
should also generate Request History information for the 'internal
retargeting'.
3.2) An entity (UA or proxy) retargeting in response to a redirect or
REFER should include any Request History information from the
redirect/REFER in the new request.
4) ISSUER-req: "Request History" information can be generated by a UA
or proxy. It can be passed in both requests and responses.
5) CONTENT-req: The "Request History" information for each
occurrence of retargeting, shall include the following:
5.1) The new URI or address to which the request is in the process
of being retargeted,
5.2) The URI or address from which the request was retargeted,
5.3) The reason for the Request-URI or address modification,
5.4) Chronological ordering of the Request History information.
6) REQUEST-VALIDITY-req: Request-History is applicable to requests
not sent within an established dialog. (i.e. INVITE, REGISTER,
MESSAGE, and OPTIONS).
7) BACKWARDS-req: Request-History information may be passed from the
generating entity backwards towards the UAC. This is needed to enable
services that inform the calling party about the dialog establishment
attempts.
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8) FORWARDS-req: Request-History information may also be included by
the generating entity in the request, if it is forwarded onwards.
2.1 Security Requirements
The Request History information is being inserted by a network
element retargeting a Request, resulting in a slightly different
problem than the basic SIP header problem, thus requiring specific
consideration. It is recognized that these security requirements can
be generalized to a basic requirement of being able to secure
information that is inserted by proxies.
The potential security problems include the following:
1) A rogue application could insert a bogus Request History entry
either by adding an additional entry as a result of retargeting or
entering invalid information.
2) A rogue application could re-arrange the Request History
information to change the nature of the end application or to mislead
the receiver of the information.
Thus, a security solution for "Request History" must meet the
following requirements:
1) SEC-req-1: The entity receiving the Request History must be able
to determine whether any of the previously added Request History
content has been altered.
2) SEC-req-2: The ordering of the Request History information must be
preserved at each instance of retargeting.
3) SEC-req-3: The entity receiving the information conveyed by the
Request History must be able to authenticate the source of the
information.
4) SEC-req-4: To ensure the confidentiality of the Request History
information, only entities which process the request should have
visibility to the information.
It should be noted that these security requirements apply to any
entity making use of the Request History information, either by
retargeting and capturing the information, or as an application
making use of the information received in either a Request or
Response.
2.2 Privacy Requirements
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Since the Request URI that is captured could inadvertently reveal
information about the originator, there are general privacy
requirements that MUST be met:
1) PRIV-req-1: The entity retargeting the Request must ensure that it
maintains the network-provided privacy (as described in [4])
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
requirements shall not be included in outgoing messages unless it is
protected as described in [RFC3323].
3. Request History Information Description
The fundamental functionality provided by the request history
information is the ability to inform proxies and UAs involved in
processing a request about the history or progress of that request
[CAPABILITY-req]. The solution is to capture the Request-URIs as a
request is forwarded in a new header for SIP messages: History-Info
[CONTENT-req]. This allows for the capturing of the history of a
request that would be lost with the normal SIP processing involved in
the subsequent forwarding of the request. This solution proposes no
changes in the fundamental determination of request targets or in the
request forwarding as defined in sections 16.5 and 16.6 of the SIP
protocol specification [RFC3261].
The History-Info header can appear in any request not associated with
an established dialog, which includes INVITE, REGISTER, MESSAGE,
REFER and OPTIONS [REQUEST-VALIDITY-req] and any valid response to
these requests.[ISSUER-req]
The History-Info header is added to a Request when a new request is
created by a UAC or Proxy, or when the target of a request is
changed. The term 'retarget' is introduced to refer to this changing
of the target of a request and the subsequent forwarding of that
request. It should be noted that retargeting only occurs when the
Request-URI indicates a domain for which the processing entity is
responsible. In terms of the SIP protocol, the processing associated
with retargeting is described in sections 16.5, and 16.6 of
[RFC3261]. As described in section 16.5 of [RFC3261], it is possible
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for the target of a request to be changed by the same proxy multiple
times (referred to as 'internal retargeting' in section 2), as the
proxy MAY add targets to the target set after beginning Request
Forwarding. Section 16.6 of [RFC3261] describes Request Forwarding.
It is during this process of Request Forwarding, that the History
Information is captured as an optional, additional header field.
Thus, the addition of the History-Info header does not impact
fundamental SIP Request Forwarding. An entity (UA or proxy) changing
the target of a request in response to a redirect or REFER SHOULD
also propagate any History-Info header from the initial Request in
the new request [GENERATION-req, FORWARDS-req].
3.1 Optionality of History-Info
The History-Info header is optional in that neither UAs nor Proxies
are required to support it. A new Supported header, Histinfo, is
included in the Request to indicate whether the History-Info header
is returned in Responses [BACKWARDS-req]. In addition to the Histinfo
Supported header, local policy determines whether or not the header
is added to any request, or for a specific Request-URI, being
retargeted. It is possible that this could restrict the applicability
of services which make use of the Request History Information to be
limited to retargeting within domain(s) controlled by the same local
policy, or between domain(s) which negotiate policies with other
domains to ensure support of the given policy, or services for which
"complete" History Information isn't required to provide the service.
[OPTIONALITY-req] All applications making use of the History-info
header MUST clearly define the impact of the information not being
available and specify the processing of such a request.
3.2 Securing History-Info
This draft defines a new header for SIP. The draft does RECOMMEND the
use of a secure transport mechanism such as TLS to ensure the overall
confidentiality of the History-Info headers[SEC-req-4]. However, the
problem is slightly different than the hop by hop security problem
solved by TLS, as each hop is not required to add the History-Info
header. Since the History-Info header is being inserted by an entity
as it targets and forwards a Request, the resulting security
requirements also introduce a slightly different problem than the
basic SIP header or Identity [SIPATHID] problems, which are focused
on securing the information in the initial request end to end.
However, the requirements for the security solution are similar to
the Via and Record-Route headers. For the History-Info header, the
general requirement is to secure a header that is inserted by an
intermediary and then subsequently referenced, by other
intermediaries to build the next header entry, or by an end
application using the information to provide a service. Thus, the
general requirement takes the form of a middle to middle and middle
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to end security solution, which is addressed in a separate document
[SIPIISEC]. The use of the middle-to-end security solution discussed
in [SIPIISEC] allows the integrity of the History-Info to be
ascertained as it traverses the intermediaries. Thus, including the
History-Info header in SIP Requests and securing in this manner adds
an additional level of security end to end, assuring the initiator of
a Request that it has indeed reached the intended recipient. Further
discussion of the security mechanism for History-Info is provided in
section 2.4.
3.3 Ensuring the Privacy of History-Info
Since the History-Info header can inadvertently reveal information
about the requestor as described in [RFC3323], the Privacy header
SHOULD be used to determine whether an intermediary can include the
History-Info header in a Request that it receives and forwards [PRIV-
req-2] or that it retargets [PRIV-req-1]. Thus, the History-Info
header SHOULD not be included in Requests where the requestor has
indicated a priv-value of Session or Header level privacy.
In addition, the History-Info header can reveal general routing
information, which may be viewed by a specific intermediary or
network, to be subject to privacy restrictions. Thus, local policy
MAY also be used to determine whether to include the History-Info
header at all, whether to capture a specific Request-URI in the
header, or whether it be included only in the Request as it is
retargeted within a specific domain. [PRIV-req-3]
[Issue-1: It has been proposed on the mailing list that there is a
protocol requirement to support this functionality. It has been
suggested that adding an additional field to the History-Info header
(or extending the priv-values defined in RFC 3323) would facilitate
the implementation of this functionality.]
It is recognized that satisfying the privacy requirements can impact
the functionality of this solution by overriding the request to
generate the information. As with the optionality and security
requirements, applications making use of History-Info SHOULD address
any impact this may have.
4 Request History Information Protocol Details
This section contains the details and usage of the proposed new SIP
protocol elements. It also discusses the security aspects of the
solution and provides some examples.
4.1 Protocol Structure of History-Info
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History-Info is a header field as defined by [RFC3261]. It can
appear in any request or response not associated with a dialog or
which starts a dialog. For example, History-Info can appear in
INVITE, REGISTER, MESSAGE, REFER and OPTIONS and any valid responses,
plus NOTIFY requests which initiate a dialog .
The History-Info header carries the following information:
o Targeted-to-URI: the Request URI captured as the Request is
forwarded.
o 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 including the
index and securing the header, the ordering of the History-info
headers in the request is assured.[SEC-req-2]
o Reason: An optional parameter for History-info. The reason for
the retargeting is captured by including the Reason Header
[RFC3326] associated with the Request URI being retargeted.
Thus, a reason is not included for a Request URI when it is
first added in a History-info header, but rather is added when
that particular Request-URI is retargeted. Note, that this does
appear to complicate the security problem, however, retargeting
only occurs when the Request-URI indicates a domain for which
the processing entity is responsible, thus it would be the same
processing entity that initially added the Request-URI to the
header that would be updating it with the Reason.
The following summarizes the syntax of the History-Info header, based
upon the standard SIP syntax [RFC3261]:
History-Info = "History-Info" HCOLON
hist-info *(COMMA hist-info)
hist-info = hi-targeted-to-uri *( SEMI hi-param )
hi-targeted-to-uri= name-addr
hi-param = hi-index / hi-extension
hi-index = "index" EQUAL 1*DIGIT *(DOT 1*DIGIT)
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hi-extension = generic-param
4.2 Protocol Examples
The following provides some examples of the History-Info header. Note
that the backslash, CRLF, and spacing between the fields in the
examples below are for readability purposes only.
History-Info:<sip:UserA@ims.nortelnetworks.com?Reason=SIP;\
cause=302;text="Moved Temporarily">; index=1; foo=bar
History-Info: <sip:UserA@ims.nortelnetworks.com?Reason=SIP;\
cause=302; text="Moved Temporarily">; index=1.1,
<sip:UserB@nortelnetworks.com? Reason=SIP;cause=486;\
text="Busy Here">;index=1.2,
<sip:45432@vm.nortelnetworks.com> ; index=1.3
[Editor's note: need to insert row for Table 2].
4.3 Protocol usage
This section describes the processing specific to UAs and Proxies for
the History-Info header and the Histinfo option tag. As discussed in
section 1, the fundamental objective is to capture the target
Request-URIs as a request is forwarded. This allows for the
capturing of the history of a request that would be lost due to
subsequent (re)targeting and forwarding. To accomplish this for the
entire history of a request, either the UAC must capture the Request-
URI in the initial request or a proxy must add History-Info headers
for both the Request-URI in the initial request and the target
Request-URI as the request is forwarded. The basic processing is for
each entity forwarding a request to add a History-Info header for the
target Request-URI, updating the index and adding the Reason as
appropriate for any retargeted Request-URI.
[Editor's note: Once the Security solution is fully fleshed out, it
may be reasonable to move this section 4.3 after section 4.4 and
provide the detailed security related processing prior to this
section, so that security aspects can be detailed in this section, as
well.]
4.3.1 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 in the Response. In
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addition, the UAC SHOULD initiate the capturing of the History
Information by adding a History-Info header using the Request-URI of
the request as the hi-targeted-to-uri and initializing the index to 1
in the History-Info header
The processing of the History-Info header received in the Response is
application specific and outside the scope of this draft. However,
the validity of the information SHOULD be ensured prior to any
application usage. [Editor's note: Further detail to be provided once
the security solution is available.]
4.3.2 UAS Behavior
The processing of the History-Info header by a UAS in a Request
depends upon local policy and specific applications at the UAS which
might make use of the information. Prior to any application usage of
the information, the validity SHOULD be ascertained. [Editor's note:
Further detail to be provided once the security solution is
available.]
If the Histinfo option tag is received in a request, the UAS should
include any History-Info received in the request in the subsequent
response.
4.3.3 Proxy Behavior
The inclusion of the History-Info header in a Request does not alter
the fundamental processing of proxies for determining request targets
as defined in section 16.5 of [RFC3261]. Whether a proxy adds the
the History-Info header as it forwards a Request depends upon local
policy, with the following being considerations in the definition of
that policy:
o Whether the Request contains the Histinfo option tag in the
Supported header.
o Whether the proxy supports the History-Info header.
o Whether any History-Info header added for a proxy/domain
should go outside that domain. An example being the use of
the History-Info header within the specific domain in which
it is retargeted, however, policies (for privacy, user and
network security, etc.) prohibit the exposure of that
information outside that domain. An example of such an
application is provided in Appendix C.
o Whether the History-Info header is added for a specific
Request URI due to local privacy policy considerations.
o Within a given domain, whether there is a limit on the number
of History-Info entries and the mechanism for applying the
limit. [Issue-2: It has been highlighted that messages
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carrying History-Info entries can become quite large in cases
where there is a lot of retargeting. It seems that a
reasonable recommendation could be provided for pruning the
entries (albeit only entries added by that intermediary MAY
be removed)].
An example policy would be a proxy that only adds the History-Info
header if the Histinfo option tag is in the Supported header. Other
proxies may have a policy that they always add the header, but never
forward it outside a particular domain.
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).
Consistent with basic SIP processing of optional headers, proxies
SHOULD maintain History-Info headers, received in messages being
forwarded, independent of whether local policy supports History-Info.
The specific processing by proxies for adding the History-Info
headers in Requests and Responses is described in detail in the
following sections.
4.3.3.1 Adding the History-Info header to Requests
If the proxy supports the History-Info header, the proxy SHOULD add a
History-Info header as it forwards a Request. Section 16.6 of [4]
defines the steps to be followed as the proxy forwards a Request.
Step 5 prescribes the addition of optional headers. Although, this
would seem the appropriate step for adding the History-info header,
the interaction with Step 6 "Postprocess routing information" and the
impact of a strict route in the Route header could result in the
Request-URI being changed, thus adding the History-info header
between steps 8 (adding Via header) and 9 (adding Content-Length) is
RECOMMENDED. Note, that in the case of loose routing, the Request-URI
does not change during the forwarding of a Request, thus the
capturing of History-Info for such a request would result in
duplicate Request-URIs with different indices. The History-Info
header SHOULD be added following any History-Info header received in
the request being forwarded. Additionally, if a request is received
that doesn't include a History-Info header, the proxy MAY add an
additional History-Info header preceding the one being added for the
current request being forwarded. The index for this entry is
RECOMMENDED to start at 1.
For retargets that are the result of an explicit SIP response, the
SIP Response Code that triggered the retargeting MUST be included in
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the Reason header field of the Request URI that has been retargeted.
For retargets as a result of timeouts or internal events, a Reason
MAY be included in the Reason header field of the Request URI that
has been retargeted.
In order to maintain ordering and accurately reflect the nesting and
retargeting of the request, an index MUST be included along with the
Targeted-to-URI being captured. Per the ABNF in section 4.1, the
index consists of a dot delimited series of digits (e.g. 1.1.2), with
each dot reflecting the number of hops or level of nesting of the
request. Thus, the indexing results in a logical tree representation
for the history of the Request. It is recommended that for each level
of indexing, the index start at 1. For retargets within a proxy, the
proxy MUST maintain the current level of nesting by incrementing the
lowest/last digit of the index for each instance of retargeting, thus
reflecting the number of retargets within the proxy.
The basic rules for adding the index are summarized as follows:
1. If the Request-URI in the original request indicates a resource
for which this proxy is responsible, then the proxy reads the value
from the History-Info header in the received request, if available,
and adds another level of indexing by appending the DOT delimiter
followed by an initial index for the new level of 1. For example,
if the index in the last History-Info header field in the received
request is 1.1, this proxy would initialize its index to 1.1.1.
For each subsequent target that is forwarded by the same proxy,
theindex is calculated by incrementing the last/lowest digit at the
current level.
2. If the Request-URI indicates a resource that this proxy is not
responsible for, then the lowest/last digit of the index is
incremented (i.e. a new level is not created). 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 added by this proxy
would be 1.3.
If the request forwarding is done in parallel, the proxy MUST capture
each of the Request-URIs to which the Request is forwarded in the
manner previously described per rule 1 above. The index MUST be
captured for each forked request per the rules above, with each new
Request having a unique index. The proxy builds the subsequent
requests and responses using the amalgamated information associated
with each of those requests and including the header entries in the
order indicated by the indexing. Section 4.5 provides an example of
a parallel request scenario, highlighting this indexing mechanism.
4.3.3.2 Processing History-Info in Responses
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A proxy that receives a Request with the Histinfo option tag in the
Supported header, and depending upon a local policy supporting the
capture of History-Info, SHOULD return captured History-Info in
subsequent, provisional and final responses to the Request.
It should be noted that local policy considerations, for network and
intermediary privacy, MAY restrict the sending of the History-Info
headers added by the intermediary in subsequent responses. Thus, in
such cases, the proxy MAY remove from these responses the History-
Info headers which it inserted in the original forwarded request.
4.3.4 Redirect Server Behavior
A redirect server SHOULD NOT add any new History-Info, as that would
be done by the entity receiving the 3xx response. However, a redirect
server MAY include History-Info in responses by adding any History-
Info headers received in a request to a subsequent response.
4.4 Security for History-Info
As discussed in Section 1, the security requirements are partially
met by recommending the use of TLS (a basic SIP requirement per
[RFC3261]) for hop by hop security. In addition, the use of the
middle-to-end security solution discussed in [SIPIISEC] allows the
integrity of the History-Info to be ascertained as it traverses the
intermediaries.
For the History-Info header, the general requirement is to secure a
header that is inserted by an intermediary and then subsequently
referenced, by other intermediaries to build the next header entry or
by an end application using the information to provide a service. In
terms of exactly what is being secured, it is primarily the captured
Request-URIs that are the security concern, since they can reflect
some aspect of a user's identity and service routing. However, the
indices are also important in that they can be used to determine if
specific Request-URIs have been removed from the header. Thus, the
primary objective of the security solution is to ensure that the
entire History-Info header is protected from being accessed or
manipulated by non-authorized entities, with the fundamental
assumption that retargeting entities are implicitly authorized.
The security associated with the Request History Information is
optional and depends upon local policy and the impact on specific
applications of having the information compromised. Since, the
Request History Information itself is also optional and it has been
recommended that applications document the impact of the information
not being available, it is also suggested that the impact of not
supporting the security recommendations also be documented by the
application to ensure that the impacts have been sufficiently
addressed by the application.
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4.4.1 Security examples
[Editor's Note: Need to add some protocol details for protecting
History-Info once [SIPIISEC] is further along].
4.5 Example Applications using History-Info
This scenario highlights an example where the History-Info in the
response is primarily of use in not retrying routes that have already
been tried by another proxy. Note, that this is just an example and
that there may be valid reasons why a Proxy would want to retry the
routes and thus, this would likely be a local proxy or even user
specific policy.
UA 1 sends a call to "Bob" to proxy 1. Proxy 1 forwards the request
to Proxy 2. Proxy 2 sends the requests in parallel and tries several
places (UA2, UA3 and UA4) before sending a response to Proxy 1 that
all the places are busy. Proxy 1, without the History-Info, would
try several of the same places (UA3 and UA4) based upon registered
contacts for "Bob", before completing at UA5. However, with the
History-Info, Proxy 1 determines that UA3 and UA4 have already
received the invite, thus the INVITE goes directly to UA5.
UA1 Proxy1 Proxy2 UA2 UA3 UA4 UA5
| | | | | | |
|--INVITE -->| | | | | |
| |-INVITE->| | | | |
Supported: Histinfo
History-Info: <sip:Bob@P1>;index=1,
<sip:Bob@P2>; index=2
| | | | | | |
| | |-INVITE>| | | |
History-Info: <sip:Bob@P1>;index=1,
<sip:Bob@P2>; index=2,
<sip:User2@UA2>; index=2.1
| | | | | | |
| | |-----INVITE ---->| | |
History-Info: <sip:Bob@P1>;index=1,
<sip:Bob@P2 >; index=2,
<sip:User3@UA3>; index=2.2
| | | | | | |
| | |-------INVITE------------>| |
History-Info: <sip:Bob@P1>;index=1,
<sip:Bob@P2 >; index=2,
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<sip:User4@UA4 >; index=2.3
/* All Responses from the INVITEs indicate non-success/non-
availability*/
| | | | | | |
| |<-480 ---| | | | |
History-Info: <sip:Bob@P1>;index=1,
<sip:Bob@P2>; index=2,
<sip:User2@UA2?Reason:SIP;\
cause=408;text="RequestTimeout">;index=2.1,
<sip:User3@UA3?Reason:SIP; \
cause=487;text="Request Terminated">; index=2.2,
<sip:User4@UA4?Reason:SIP;\
cause=603;text="Decline">; index=2.3
| | | | | | |
/* Upon receipt of the response, P1 determines another route for the
INVITE, but finds that it matches some routes already attempted
(e.g. UA2 and UA3, thus the INVITE is only forwarded to UA5, where
the session is successfully established */
| | | | | | |
| |----------------INVITE --------------------->|
History-Info: <sip:Bob@P1>;index=1,
<sip:Bob@P2>; index=2,
<sip:User2@UA2?Reason:SIP;cause=408;\
text="RequestTimeout">;index=2.1,
<sip:User3@UA3?Reason:SIP;cause=487;\
text="Request Terminated">; index=2.2,
<sip:User4@UA4?Reason:SIP;cause=603;\
text="Decline">; index=2.3
<sip:User5@UA5>;index=1.1
| | | | | | |
| |<-----200 OK---------------------------------|
|<--200 OK---| | | | | |
| | | | | | |
|--ACK --------------------------------------------------->|
Additional detailed scenarios are available in the appendix.
5. Application Considerations
As seen by the example scenarios in the appendix, History-Info
provides a very flexible building block that can be used by
intermediaries and UAs for a variety of services. As such, any
services making use of History-Info must be designed with the
following considerations:
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1) History-Info is optional, thus a service should 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 or Session level privacy is requested by a UA (or imposed
by an intermediary) that History-Info may not be available in a
request or response. This would be addressed by an application
in the same manner as the previous consideration by ensuring
there is reasonable default behavior should the information not
be available.
3) History-Info may be impacted by local policy. Each application
making use of the History-Info header SHOULD address the impacts
of the local policies on the specific application (e.g. what
specification of local policy is optimally required for a
specific application and any potential limitations imposed by
local policy decisions). Note, that this is related to the
optionality and privacy considerations identified in 1 and 2
above, but goes beyond that. For example, due to the optionality
and privacy considerations, an entity may receive only partial
History-Info entries; will this suffice? Note, that this would be
a limitation for debugging purposes, but might be perfectly
satisfactory for some models whereby only the information from a
specific intermediary is required.
4) The security associated with the Request History Information is
optional. Whether there is security applied to the entries
depends upon local policy. The impact of lack of having the
information compromised depends upon the nature of the specific
application (e.g. is the information something that appears on a
display or is it processed by automata which could have negative
impacts on the subsequent processing of a request?). It is
suggested that the impact of an intermediary not supporting the
security recommendations should be evaluated by the application
to ensure that the impacts have been sufficiently addressed by
the application. For the display example, a visual indicator
could be applied highlighting that the information has not been,
or could not be, validated.
6. Security Considerations
This draft provides a proposal in sections 3.2 and 4.4 for addressing
the Security requirements identified in section 2.1 by proposing the
use of TLS between entities, and by securing the History-Info headers
added by proxies as described in [SIPIISEC].
7. IANA Considerations
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(Note to RFC Editor: Please fill in all occurrences of XXXX in this
section with the RFC number of this specification).
This document defines a new SIP header field name: History-Info and a
new option tag: Histinfo.
The following changes should be made to
http:///www.iana.org/assignments/sip-parameters
The following row should be added to the header field section:
Header Name Compact Form Reference
History-Info none [RFCXXXX]
The following should be added to the Options Tags section:
Name Description Reference
Histinfo When used with the Supported header, [RFCXXXX]
this option tag indicates support
for the History Information to be
captured for requests and returned in
subsequent responses. This tag is not
used in a Proxy-Require or Require
header field since support of
History-Info is optional.
Open Issues
The following summarizes the current open issues in this document:
o Issue-1: Privacy indication for specific History-Info entries.
It has been proposed on the mailing list that there is a
requirement beyond the basic Header or Session privacy provided
by RFC 3323 for History-Info entries in terms of supporting
local policy based privacy requirements. It has been suggested
that adding an additional field to the History-Info header (or
extending the priv-values defined in RFC 3323) would facilitate
the implementation of this functionality. Adding such
information to the HI entries would impact the protocol
structure in section 4.1 and processing in 4.3.3 (and 4.3.3.1
and 4.3.3.2)
o Issue-2: Bounding the History-Info entries and a mechanism for
applying the limit. It has been highlighted by developers that
messages carrying History-Info entries can become quite large
in cases where there is a lot of retargeting. It seems that a
reasonable recommendation could be provided for pruning the
entries (albeit only entries added by that intermediary should
be removed). For example:
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. Keeping only the first and last entries
. Keeping only the last leaf of each of the branches.
. Restricting the breadth and depth of the History-Info
tree.
Such bounding would require normative processing guidelines
in section 4.3.3 and introduce an additional application
consideration in section 5.
Changes since last version
Changes from the û01 to the û02 version:
o Merged the SIPPING WG requirements draft into this document.
Note that this increments the section references in the
remainder of the document by 2 (and by 3 for Security and IANA
considerations due to new section added). Also, removed
redirect server from ISSUER-req since the solution identified
this as not being required (or desirable).
o Added an explicit privacy requirement (PRIV-req-3) for the
proxy's role in recognizing and maintaining privacy associated
with a Request-URI being captured in History-Info due to local
policy. (Note, that the text was already there, it just wasn't
highlighted as an explicit requirement).
o Clarified the use of CRLF and spacing in the example headers in
section 4.2.
o Removed the compact form for the header since unknown headers
with multiple entries would not be recognized (i.e. this may
cause parsing problems).
o Added a summary of Application Considerations to address
concerns about the optional usage of History-Info.
o Converted the references from numbers to labels to avoid the
continual problem of renumbering.
o Minor editorial changes (per NITS highlighted by Rohan and Eric
and some minor rewording for clarity).
Changes from the û00 to the û01 version:
o Attempted to be more explicit about the fundamental processing
associated with the header. Removed definitions of new terms,
only referencing the terms from the requirements in the context
of the fundamental SIP processing implied by the terms.
o Attempted to clarify the Index and the related processing.
o Added more detail addressing the privacy requirements.
o Added a bit more detail on security. The security solution
remains in a separate document and this document will need
updating once that is completed.
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o Updated the examples (in section 2.5 and appendix) and clarified
the definition and the maintenance of the Index in sections 2.1
and 2.3.3.1.
o Clarified the Reason description in section 2.1. There had been
an error in the description of the processing that was a remnant
of the change to include only a single URI for each History-Info
header.
o Miscellaneous editorial changes (i.e. HistInfo -> Histinfo,
etc.)
Changes from individual draft-barnes-sipping-history-info-02 to the û
00 WG version:
o Updated references and added reference to Security solution
draft.
o Removed appendix D which included background on analysis of
solution options.
o Cleaned up the document format per rfc2223bis.
o Strengthened the inclusion of the INDEX as a MUST (per
discussion at IETF-56).
o Added text around the capturing of the Reason (SHOULD be
captured for SIP responses and MAY be captured for other things
such as timeouts).
o Clarified the response processing 2.3.3.2 to include
provisional responses and the sending of a 183 to convey
History-Info.
o Added section 2.3.4 to address Redirect Server behavior.
Normative References
[RFC3261] J. Rosenberg et al, "SIP: Session initiation protocol," RFC
3261, June, 2002.
[RFC3326] H. Schulzrinne, D. Oran, G. Camarillo, "The Reason Header
Field for the Session Initiation Protocol", RFC 3326, December, 2002.
[RFC3323] J. Peterson, "A Privacy Mechanism for the Session
Initiation Protocol (SIP)", RFC 3323, November, 2002.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[SIPIISEC] M. Barnes, "A Mechanism to Secure SIP Headers Inserted by
Intermediaries", draft-barnes-sipping-inserted-info-01.txt, October,
2003.
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Informational References
[SIPSVCEX] A. Johnson, "SIP Service Examples", draft-ietf-sipping-
service-examples-05.txt, November, 2002.
[SIPATHID] J. Peterson, "Enhancements for Authenticated Identity
Management in the Session Initiation Protocol (SIP)", draft-ietf-sip-
identity-01.txt, February, 2003.
Acknowledgements
The editor would like to acknowledge the constructive feedback
provided by Robert Sparks, Paul Kyzivat, Scott Orton, John Elwell,
Nir Chen, Francois Audet, Palash Jain, Brian Stucker, Norma Ng,
Anthony Brown, Jayshree Bharatia, Jonathan Rosenberg and Eric Burger.
The editor would like to acknowledge the significant input from
Rohan Mahy on some of the normative aspects of the ABNF, particularly
around the need for and format of the index and around the enhanced
SIP security aspects enabled by this draft.
Contributors' Addresses
Cullen, Mark and Jon contributed to the development of the initial
requirements.
Cullen and Mark provided substantial input in the form of email
discussion in the development of the initial version of the
individual solution document.
Cullen Jennings
Cisco Systems
170 West Tasman Dr
MS: SJC-21/3
Tel: +1 408 527 9132
Email: fluffy@cisco.com
Jon Peterson
NeuStar, Inc.
1800 Sutter Street, Suite 570
Concord, CA 94520
USA
Phone: +1 925-363-8720
EMail: Jon.Peterson@NeuStar.biz
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Mark Watson
Nortel Networks (UK)
Maidenhead Office Park (Bray House)
Westacott Way
Maidenhead,
Berkshire
England
Tel: +44 (0)1628-434456
Email: mwatson@nortelnetworks.com
Author's Address
Mary Barnes
Nortel Networks
2380 Performance Drive
Richardson, TX USA
Phone: 1-972-684-5432
Email: mary.barnes@nortelnetworks.com
Appendix A Forking Scenarios
A.1 Sequentially forking (History-Info in Response)
This scenario highlights an example where the History-Info in the
response is useful to an application or user that originated the
request.
UA 1 sends a call to "Bob" via proxy 1. Proxy 1 sequentially tries
several places (UA2, UA3 and UA4) unsuccessfully before sending a
response to UA1.
This scenario is provided to show that by providing the History-Info
to UA1, the end user or an application at UA1 could make a decision
on how best to attempt finding "Bob". Without this mechanism UA1
might well attempt UA3 (and thus UA4) and then re-attempt UA4 on a
third manual attempt at reaching "Bob". With this mechanism, either
the end user or application could know that "Bob" is busy on his home
phone and is physically not in the office. If there were an
alternative address for "Bob" known to this end user or application,
that hasn't been attempted, then either the application or the end
user could attempt that. The intent here is to highlight an example
of the flexibility of this mechanism that enables applications well
beyond SIP as it is certainly well beyond the scope of this draft to
prescribe detailed applications.
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UA1 Proxy1 UA2 UA3 UA4
| | | | |
|--INVITE -->| | | |
| | | | |
| |--INVITE -------->| | |
|<--100 -----| | | |
| |<-302 ------------| | |
| | | | |
| |-------INVITE ------------>| |
| | | | |
| |<-------180 ---------------| |
|<---180 ----| | | |
| . . |-------INVITE------------->| |
| | timeout | | |
| | | | |
| |------INVITE ---------------------->|
|<--100 -----| | | |
| | | | |
| |<-486 ------------------------------|
| | | | |
| |-- ACK ---------------------------->|
|<--486------| | | |
| | | | |
|--ACK ----->| | | |
| | | | |
[Editor's Note: Need to detail the message flow.]
A.2 Sequential Forking (with Success)
This scenario highlights an example where the History-Info in the
request is primarily of use in not retrying routes that have already
been tried by another proxy. Note, that this is just an example and
that there may be valid reasons why a Proxy would want to retry the
routes and thus, this would like be a local proxy or even user
specific policy.
UA 1 sends a call to "Bob" to proxy 1. Proxy 1 sequentially tries
several places (UA2, UA3 and UA4) before retargeting the call to
Proxy 2. Proxy 2, without the History-Info, would try several of the
same places (UA3 and UA4)based upon registered contacts for "Bob",
before completing at UA5. However, with the History-Info, Proxy 2
determines that UA3 and UA4 have already received the invite, thus
the INVITE goes directly to UA5.
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UA1 Proxy1 Proxy2 UA2 UA3 UA4 UA5
| | | | | | |
|--INVITE -->| | | | | |
| | | | | | |
| |--INVITE -------->| | | |
|<--100 -----| | | | | |
| |<-302 ------------| | | |
| | | | | | |
| |-------INVITE ------------>| | |
| | | | | | |
| |<-------180 ---------------| | |
|<---180 ----| | | | | |
| . . |-------INVITE------------->| | |
| | timeout | | | |
| | | | | | |
| |------INVITE ---------------------->| |
|<--100 -----| | | | | |
| |<-302 ------------------------------| |
| | | | | | |
| |-INVITE->| | | | |
| | | | | | |
| | | | | | |
| | |------INVITE --------------------->|
| | | | | | |
| | |<-----200 OK---------------------->|
|<--200 OK-------------| | | | |
| | | | | | |
|--ACK --------------------------------------------------->|
[Editor's Note: Need to add the details of the messages here.]
Appendix B Voicemail
This scenario highlights an example where the History-Info in the
request is primarily of use by an edge service (e.g. Voicemail
Server). It should be noted that this isn't intended to be a complete
specification for this specific edge service as it is quite likely
that additional information is need by the edge service. History-Info
is just one building block that this service makes use of.
UA 1 called UA A which had been forwarded to UA B which forwarded to
a UA VM (voicemail server). Based upon the retargeted URIs and
Reasons (and other information) in the INVITE, the VM server makes a
policy decision about what mailbox to use, which greeting to play
etc.
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UA1 Proxy UA-A UA-B UA-VM
| | | | |
|--INVITE F1-->| | | |
| | | | |
| |--INVITE F2-->| | |
|<--100 F3-----| | | |
| |<-302 F4------| | |
| | | | |
| |--------INVITE F5---------->| |
| | | | |
| |<--------180 F6-------------| |
|<---180 F7----| | | |
| . . . | | | |
| |------retransmit INVITE---->| |
| . . . | | | |
| | (timeout) | |
| | | | |
| |-------INVITE F8---------------------->|
| | | | |
| |<-200 F9-------------------------------|
| | | | |
|<-200 F10-----| | | |
| | | | |
|--ACK F11-------------------------------------------->|
Message Details
INVITE F1 UA1->Proxy
INVITE sip:UserA@nortelnetworks.com SIP/2.0
Via: SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@nortelnetworks.com>
Call-Id: 12345600@here.com
CSeq: 1 INVITE
Contact: BigGuy <sip:User1@here.com>
Content-Type: application/sdp
Content-Length: <appropriate value>
v=0
o=UserA 2890844526 2890844526 IN IP4 client.here.com
s=Session SDP
c=IN IP4 100.101.102.103
t=0 0
m=audio 49170 RTP/AVP 0
a=rtpmap:0 PCMU/8000
/*Client for UA1 prepares to receive data on port 49170
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from the network. */
INVITE F2 Proxy->UA-A
INVITE sip:UserA@ims.nortelnetworks.com SIP/2.0
Via: SIP/2.0/UDPims.nortelnetworks.com:5060;branch=1
Via: SIP/2.0/UDP here.com:5060
Record-Route: <sip:UserA@nortelnetworks.com>
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@nortelnetworks.com>
Call-Id: 12345600@here.com
CSeq: 1 INVITE
History-Info: <sip:UserA@ims.nortelnetworks.com>; index=1
Contact: BigGuy <sip:User1@here.com>
Content-Type: application/sdp
Content-Length: <appropriate value>
v=0
o=UserA 2890844526 2890844526 IN IP4 client.here.com
s=Session SDP
c=IN IP4 100.101.102.103
t=0 0
m=audio 49170 RTP/AVP 0
a=rtpmap:0 PCMU/8000
100 Trying F3 Proxy->UA1
SIP/2.0 100 Trying
Via: SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@nortelnetworks.com>
Call-Id: 12345600@here.com
CSeq: 1 INVITE
Content-Length: 0
302 Moved Temporarily F4 UserA->Proxy
SIP/2.0 302 Moved Temporarily
Via: SIP/2.0/UDP ims.nortelnetworks.com:5060;branch=1
Via: SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@nortelnetworks.com>;tag=3
Call-Id: 12345600@here.com
CSeq: 1 INVITE
Contact: <sip:UserB@nortelnetworks.com>
Content-Length: 0
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INVITE F5 Proxy-> UA-B
INVITE sip:UserB@nortelnetworks.com SIP/2.0
Via: SIP/2.0/UDP ims.nortelnetworks.com:5060;branch=2
Via: SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@nortelnetworks.com>
Call-Id: 12345600@here.com
History-Info: <sip:UserA@ims.nortelnetworks.com?Reason=SIP;\
cause=302; text="Moved Temporarily">; index=1,
<sip:UserB@nortelnetworks.com>;index=2
CSeq: 1 INVITE
Contact: BigGuy <sip:User1@here.com>
Content-Type: application/sdp
Content-Length: <appropriate value>
v=0
o=User1 2890844526 2890844526 IN IP4 client.here.com
s=Session SDP
c=IN IP4 100.101.102.103
t=0 0
m=audio 49170 RTP/AVP 0
a=rtpmap:0 PCMU/8000
180 Ringing F6 UA-B ->Proxy
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP there.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@nortelnetworks.com>;tag=5
Call-ID: 12345600@here.com
CSeq: 1 INVITE
Content-Length: 0
180 Ringing F7 Proxy-> UA1
SIP/2.0 180 Ringing
SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@nortelnetworks.com>
Call-Id: 12345600@here.com
CSeq: 1 INVITE
Content-Length: 0
/* User B is not available. INVITE is sent multiple
times until it times out. */
/* The proxy forwards the INVITE to UA-VM after adding the
additional History Information entry. */
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INVITE F8 Proxy-> UA-VM
INVITE sip:VM@nortelnetworks.com SIP/2.0
Via: SIP/2.0/UDP ims.nortelnetworks.com:5060;branch=3
Via: SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@nortelnetworks.com>
Call-Id: 12345600@here.com
History-Info:<sip:UserA@ims.nortelnetworks.com?Reason=SIP;\
cause=302; text="Moved Temporarily">;index=1,
<sip:UserB@nortelnetworks.com?Reason=SIP;cause=480;\
text="Temporarily Unavailable" >;index=2,
<sip:VM@nortelnetworks.com>;index=3
CSeq: 1 INVITE
Contact: BigGuy <sip:User1@here.com>
Content-Type: application/sdp
Content-Length: <appropriate value>
v=0
o=User1 2890844526 2890844526 IN IP4 client.here.com
s=Session SDP
c=IN IP4 100.101.102.103
t=0 0
m=audio 49170 RTP/AVP 0
a=rtpmap:0 PCMU/8000
200 OK F9
SIP/2.0 200 OK UA-VM->Proxy
Via: SIP/2.0/UDP ims.nortelnetworks.com:5060;branch=3
Via: SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@nortelnetworks.com>;tag=3
Call-Id: 12345600@here.com
CSeq: 1 INVITE
Contact: TheVoiceMail <sip:VM@nortelnetworks.com>
Content-Type: application/sdp
Content-Length: <appropriate value>
v=0
o=UserA 2890844527 2890844527 IN IP4 vm.nortelnetworks.com
s=Session SDP
c=IN IP4 110.111.112.114
t=0 0
m=audio 3456 RTP/AVP 0
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a=rtpmap:0 PCMU/8000
200 OK F10 Proxy->UA1
SIP/2.0 200 OK
Via: SIP/2.0/UDP ims.nortelnetworks.com:5060;branch=3
Via: SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy <sip:UserA@nortelnetworks.com>;tag=3
Call-Id: 12345600@here.com
CSeq: 1 INVITE
Contact: TheVoiceMail <sip:VM@nortelnetworks.com>
Content-Type: application/sdp
Content-Length: <appropriate value>
v=0
o=UserA 2890844527 2890844527 IN IP4 vm.nortelnetworks.com
s=Session SDP
c=IN IP4 110.111.112.114
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000
ACK F11 UA1-> UA-VM
ACK sip:VM@nortelnetworks.com SIP/2.0
Via: SIP/2.0/UDP here.com:5060
From: BigGuy <sip:User1@here.com>
To: LittleGuy<sip:UserA@nortelnetworks.com>;tag=3
Call-Id: 12345600@here.com
CSeq: 1 ACK
Content-Length: 0
/* RTP streams are established between UA1 and
UA-VM. UA-VM starts announcement for UA1 */
Appendix C Automatic Call Distribution Example
This scenario highlights an example of an Automatic Call Distribution
service, where the agents are divided into groups based upon the type
of customers they handle. In this example, the Gold customers are
given higher priority than Silver customers, so a Gold call would get
serviced even if all the agents servicing the Gold group (ACDGRP1)
were busy, by retargeting the request to the Silver Group. Upon
receipt of the call at the agent assigned to handle the incoming
call, based upon the History-Info header in the message, the
application at the agent can provide an indication that this is a
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SIP Request History Information February 2004
Gold call, from how many groups it might have overflowed before
reaching the agent, etc. and thus can be handled appropriately by the
agent.
For scenarios whereby calls might overflow from the Silver to the
Gold, clearly the alternate group identification, internal routing or
actual agent that handles the call SHOULD not be sent to UA1, thus
for this scenario, one would expect that the Proxy would not support
the sending of the History-Info in the response, even if requested by
the calling UA.
As with the other examples, this is not prescriptive of how one would
do this type of service but an example of a subset of processing that
might be associated with such a service. In addition, this example
is not addressing any aspects of Agent availability, which might also
be done via a SIP interface.
UA1 Proxy ACDGRP1 Svr ACDGRP2 Svr UA2-ACDGRP2
| | | | |
|--INVITE F1-->| | | |
Supported:Histinfo
| | | | |
| |--INVITE F2-->| | |
Supported:Histinfo
History-Info: <sip:Gold@ACD.com>; index=1
History-Info: <sip:ACDGRP1@ACD.com>; index=1.1
| | | | |
| |<-302 F3------| | |
Contact: <sip:ACDGRP2@ACD.com>
| | | | |
| |--------INVITE F4---------->| |
History-Info: <sip:Gold@ACD.com>; index=1
History-Info: <sip:ACDGRP1@ACD.com>; index=1.1
History-Info: <sip:ACDGRP2@ACD.com>; index=1.2
| | | | |
| | | | |
| | | |INVITE F5>|
History-Info: <sip:Gold@ACD.com>; index=1
History-Info: <sip:ACDGRP1@ACD.com>; index=1.1
History-Info: <sip:ACDGRP2@ACD.com>; index=1.2
| | | | |
| | | |<-200 F6--|
| | | | |
| |<-200 F7--------------------| |
History-Info: <sip:Gold@ACD.com>; index=1
History-Info: <sip:ACDGRP1@ACD.com>; index=1.1
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SIP Request History Information February 2004
History-Info: <sip:ACDGRP2@ACD.com>; index=1.2
|<-200 F8------| | | |
No History-Info included in the response due to Local Policy>
| | | | |
|--ACK F9--------------------------------------------->|
Message Details
[To be completed]
Full Copyright Statement
Copyright (C) The Internet Society (2004). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English. The limited permissions granted above are perpetual and
will not be revoked by the Internet Society or its successors or
assigns. This document and the information contained herein is
provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE
INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."
Barnes Expires August 2004 [Page 32]
