SIPPING S. Olson
Internet-Draft O. Levin
Expires: August 16, 2004 Microsoft Corporation
February 16, 2004
Extended-REFER framework and other REFER extensions
draft-olson-sipping-refer-extensions-01
Status of this Memo
This document is an Internet-Draft and is in full conformance with
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Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This document proposes to generalize and extend REFER method for
facilitating various advanced functionalities within SIP systems. The
new extensions are explicitly signaled by inclusion of new option
tags in the Require header of REFER.
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Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1 The Extended REFER Framework . . . . . . . . . . . . . . . . 6
4.2 Additional REFER Extensions and Behaviors . . . . . . . . . 7
5. Preventing Forking of REFER Requests . . . . . . . . . . . . 8
6. Replacing Refer-To URI Syntax with a MIME Body . . . . . . . 9
7. Using Arbitrary Event Packages with REFER . . . . . . . . . 11
8. Suppressing the REFER Implicit Subscription . . . . . . . . 17
9. Applying REFER to SIP Response Codes . . . . . . . . . . . . 19
10. Adding callid and tag Parameters to Refer-To Header . . . . 27
11. Using of isfocus Feature Parameter with REFER . . . . . . . 28
12. REFER with a Referred-By Header with aib . . . . . . . . . . 29
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . 30
13.1 extended-refer Option Tag Registration . . . . . . . . . . . 30
13.2 norefersub Option Tag Registration . . . . . . . . . . . . . 30
13.3 refer-response Option Tag Registration . . . . . . . . . . . 30
14. Security Considerations . . . . . . . . . . . . . . . . . . 31
15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 32
References . . . . . . . . . . . . . . . . . . . . . . . . . 33
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 34
Intellectual Property and Copyright Statements . . . . . . . 35
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1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1].
To simplify discussions of the REFER method and its extensions, three
new terms are being used throughout the document:
o REFER-Issuer: the UA issuing the REFER request
o REFER-Recipient: the UA receiving the REFER request
o REFER-Target: the UA designated in the Refer-To URI
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2. Introduction
The REFER [3] extension to SIP [2] defines a basis for remote call
control that is useful for implementing features such as call
transfer. In fact, originally the REFER was created by the SIP WG as
a generic request to ask another UA to perform an operation on your
behalf, which is much more powerful than just the phone-like transfer
feature.)
REFER has a few limitations with respect to implementing more
advanced features in conjunction with the dialog info event package
[7]. These limitations derive in part from the limited information
available in the message/sipfrag [4] content of the associated
NOTIFY. Another limiting factor is the requirement to compress the
semantics of the referred request in the Refer-To URI by encoding the
desired headers as parameters of that URI. Finally, there are
situations where the party issuing the REFER request does not need
the NOTIFY associated with the REFER, perhaps because that agent is
already subscribed to the appropriate package outside of the REFER
request. This represents additional unnecessary traffic and state in
the REFER-Issuer and REFER-Recipient.
This document proposes to generalize and extend REFER method for
facilitating various advanced functionalities within SIP systems. The
new extensions are explicitly signaled by inclusion of new option
tags in the Require header of REFER.
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3. Requirements
Forking prevention: Prevent forking of a REFER request and allow
targeting of that REFER request to a specific device or class of
device.
Watching period: Allow the REFER-Issuer to watch the progress of the
operation triggered by REFER for the whole duration of the
requested operation. For example: Beyond the end of the INVITE
transaction and for the duration of the remotely established
dialog.
Richness of the retrieved information: Expose rich information about
the requested operation. For example: Expose the dialog
information, caller preferences, and user defined headers of the
dialog established at the REFER-Recipient as a result of the
REFER.
Operation efficiency: Reduce the number of messages exchanged to
perform a REFER operation. For example, suppress the implicit
subscription when the information is known by other means.
Operation abstraction: Reduce the amount of detailed knowledge about
the remote party that is required from the REFER-Issuer in order
to perform a REFER. For example, for remote-cc applications as
described in [11].
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4. Overview
4.1 The Extended REFER Framework
The extended REFER behavior is signaled by inclusion of
"extended-refer" option tag in the Require header of REFER. If the
REFER-Recipient does not understand or does not support the
"extended-refer" functionality defined in this specification, it MUST
return a 420 (Unsupported Extension) response to the REFER request
(as per baseline SIP behavior [2]). The REFER-Issuer SHOULD re-issue
the REFER request using URI escaping and only the Refer-To: URI to
convey the same information if possible.
Support for this extension can be queried in advance using a standard
OPTIONS request.
This extension defines the following normative functionality for
extended REFER method which differs from the basic REFER
specification:
o Refer-To header contains cid which points to the information
placed in the REFER body in MIME form.
o The actual format and the meaning of this information are
specified by the value of the Content-Type header of REFER.
o Additional application documents MAY introduce more complicate
behavior logic and MAY require to use multipart MIME body in order
to implement this logic. In these cases, the Content-Type header
can not provide enough information to specify this logic. In these
cases, the application template logic MUST be signaled by
additional means such as by inclusion of a new dedicated
"disposition type" in the Content-Disposition header of REFER. It
is expected that new disposition types will be defined and
registered with IANA per application for being used with extended
REFER.
o The REFER-Issuer MAY specify the request for subscription to any
event package by including its MIME type in an Accept header.
REFER-Recipient SHOULD maintain the subscription till the
operation, requested in REFER, is completed.
o REFER-Issuer MAY suppress the implicit refer subscription (by
using the norefersub extension) and subscribe to any event
package(s) of its interest independently from issuing the REFER.
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4.2 Additional REFER Extensions and Behaviors
Additional REFER extensions and behaviors are defined by this
document. Although they are orthogonal to the extended-refer
framework, many times they will be used together in advanced SIP
applications:
o "norefersub" feature tag suppresses implicit REFER subscription.
In this case no dialog is established upon issuing REFER and
REFER-Issuer MUST ensure that no forking will be applied to REFER
in the network.
o "refer-response" feature tag allows for injecting responses into
remote dialogs.
o "isfocus" feature parameter being used with REFER allows for
conveying conferencing information to remote parties.
For examples of the extended REFER framework usage and additional
REFER extensions, please, refer to "SIP Remote CC" [11] and "Multiple
REFER" [10].
The following sections discuss the need and specify the mechanism for
each of the extended REFER features.
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5. Preventing Forking of REFER Requests
The REFER specification allows for the possibility of forking a REFER
request which is sent outside of an existing dialog. In many
situation, especially in conjunction with the extended-refer
mechanism, forking a REFER may result in absolutely incorrect
behavior. This is especially true when the REFER is intended to
target a specific device, perhaps with specific capabilities.
The REFER-Issuer can ensure that REFER doesnÆt get forked by
specifying the REFER-Recipient as GRUU according to mechanism defined
in [12]. No extension is required.
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6. Replacing Refer-To URI Syntax with a MIME Body
In the original REFER specification, much of the semantics of the
REFER request is encapsulated in the Refer-To URI. This URI will
commonly encode the method, From, To, Call-ID, Accept-Disposition,
Accept-Contact [9], and other headers all in a properly escaped URI.
Such a URI can become long, difficult to debug, and prone to URI
escaping errors in SIP implementations. The situation becomes more
complex if the method is itself a REFER complete with a Refer-To
which must contain URI-escaped characters. This double escaping
obfuscates things even more and increases the chances of improperly
escaping/unescaping of the Refer-To URI.
This specification makes use of the currently unused REFER body to
encapsulate all the information about the requested operation (and
that is placed and potentially escaped in the refer-To URI according
to the original specification). The possible information includes the
method, headers, and body of the request which is desired to be
created by the REFER-Recipient. One obvious candidate for this is the
message/sipfrag MIME type. This MIME type can express all of these:
the method, Request-URI, headers, and body.
Use of additional REFER MIME bodies MAY be defined in separate
application specifications.
According to this specification, a cid URI [6] is placed in the
Refer-To header to reference the MIME content in the body of the
REFER.
In the example below, the body of the extended REFER is of type
message/sipfrag.
According to the basic REFER specification:
REFER sip:b@tradewind.com SIP/2.0
Via: SIP/2.0/TCP issuer.tradewind.com;branch=z9hG4bK-a-1
From: <sip:a@tradewind.com>;tag=1a
To: <sip:b@tradewind.com>
Call-ID: 1@issuer.tradewind.com
CSeq: 234234 REFER
Max-Forwards: 70
Refer-To: <sip:c@tradewind.com;method=INVITE;response=200?Call-ID=1%40target.tradewind.com&
From=b%40tradewind.com;tag=2b&To=c%40tradewind.com;tag=1c>
Accept: application/dialog-info+xml;q=0.5, message/sipfrag;q=0.1
Contact: sip:a@issuer.tradewind.com
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Content-Length: 0
According to this extended REFER specification:
REFER sip:b@tradewind.com SIP/2.0
Via: SIP/2.0/TCP issuer.tradewind.com;branch=z9hG4bK-a-1
From: <sip:a@tradewind.com>;tag=1a
To: <sip:b@tradewind.com>
Call-ID: 1@issuer.tradewind.com
Supported: gruu
CSeq: 234234 REFER
Max-Forwards: 70
Refer-To: cid:1239103912039@issuer.tradewind.com
Accept: application/dialog-info+xml;q=0.5, message/sipfrag;q=0.1
Require: extended-refer
Contact: sip:a@issuer.tradewind.com
Content-Type: message/sipfrag
Content-Id: <1239103912039@issuer.tradewind.com>
Content-Length: ...
SIP/2.0 200 OK
Call-ID: 1@target.tradewind.com
From: b@tradewind.com;tag=2b
To: c@tradewind.com;tag=1c
If the REFER-Recipient does not understand or doesnÆt support the
extended-refer option tag, it MUST return a 420 (Unsupported
Extension) response to the REFER request (as per baseline SIP
behavior [2]). The REFER-Issuer SHOULD re-issue the REFER request
using URI escaping and only the Refer-To: URI to convey the same
information if possible.
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7. Using Arbitrary Event Packages with REFER
The REFER specification [3] mandates the use of the message/sipfrag
[4] MIME type for NOTIFYs of the refer event package. These NOTIFYs
are sent as part of the implicit subscription created by the REFER.
The purpose of the NOTIFY is to communicate the state of the
transaction between the REFER-Recipient and the REFER-Target that is
created as a result of the REFER
Where the purpose of sending the REFER is actually to ask to perform
an operation, for example through an INVITE, the derivative state of
interest is actually the progress and the result of this operation.
While in some cases this may be inferred from the contents of the
message/sipfrag body this information is neither general (abstract)
nor sufficient.
To address this shortcoming, this specification extends REFER to
allow the use of any event package format. (Furthermore, subscription
to the event package(s) MAY be decoupled from issuing the REFER. This
is done by suppressing the implicit subscription as defined later in
this document).
The REFER-Issuer MAY specify the request for subscription to a
specific package by including the MIME type in an Accept header.
REFER-Recipient SHOULD maintain the subscription till the completion
of the requested operation. For example, in case of method=INVITE,
for the duration of the resultant (INVITE) dialog and RECOMMENDED
that the subscription be maintained at least until the dialog is in
"confirmed" state.
In the INVITE example, two things that are generally lacking from the
message/sipfrag content are the dialog identifier (Call-ID plus local
and remote tags) and the state of the dialog. Not coincidentally,
this is the same information available in the application/
dialog-info+xml MIME type [7] used for the dialog event package.
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Figure 1: Example of using application/dialog-info+xml
REFER-Issuer REFER-Recipient REFER-Target
| | |
| M1 REFER (INVITE) | |
|--------------------------->| |
| M2 202 Accepted | |
|<---------------------------| |
| M3 NOTIFY | |
|<---------------------------| |
| M4 200 OK | |
|--------------------------->| |
| | M5 INVITE |
| |----------------------->|
| M6 NOTIFY | |
|<---------------------------| |
| M7 200 OK | |
|--------------------------->| |
| | M8 180 Ringing |
| |<-----------------------|
| M9 NOTIFY | |
|<---------------------------| |
| M10 200 OK | |
|--------------------------->| |
| | M11 200 OK |
| |<-----------------------|
| M12 NOTIFY | |
|<---------------------------| |
| M13 200 OK | |
|--------------------------->| M14 ACK |
| |----------------------->|
Message flow:
M1: The REFER-Issuer creates a REFER, specifying support for
extended-refer and expressing its interest in the application/
dialog-info+xml MIME type.
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REFER sip:b@tradewind.com SIP/2.0
Via: SIP/2.0/TCP issuer.tradewind.com;branch=z9hG4bK-a-1
From: <sip:a@tradewind.com>;tag=1ab
To: <sip:b@tradewind.com>
Call-ID: 1@issuer.tradewind.com
Supported: gruu
CSeq: 234234 REFER
Max-Forwards: 70
Refer-To: cid:1239103912039@issuer.tradewind.com
Accept: application/dialog-info+xml
Require: extended-refer
Contact: sip:a@issuer.tradewind.com
Content-Type: message/sipfrag
Content-Id: <1239103912039@issuer.tradewind.com>
Content-Length: ...
M5: The REFER-Recipient creates an appropriate INVITE based on the
REFER and sends it to the REFER-Target.
INVITE sip:c@tradewind.com SIP/2.0
Via: SIP/2.0/TCP recipient.tradewind.com;branch=z9hG4bK-b-1
From: <sip:b@tradewind.com>;tag=1bc
To: <sip:c@tradewind.com>
Call-ID: 1@recipient.tradewind.com
CSeq: 1234567 INVITE
Max-Forwards: 70
Contact: sip:b@recipient.tradewind.com
Content-Length: ...
<SDP for audio call>
M6: The REFER-Recipient sends a NOTIFY triggered by the INVITE being
sent to the REFER-Target. The body of the NOTIFY contains the
dialog identifier and current state ("trying").
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NOTIFY sip:a@issuer.tradewind.com SIP/2.0
Via: SIP/2.0/TCP recipient.tradewind.com;branch=z9hG4bK-b-2
From: <sip:a@tradewind.com>;tag=1ab
To: <sip:b@tradewind.com>;tag=1ba
Call-ID: 1@issuer.tradewind.com
CSeq: 1278784 NOTIFY
Max-Forwards: 70
Event: refer;id=234234
Subscription-State: active;expires=3600
Contact: sip:b@recipient.tradewind.com
Content-Type: application/dialog-info+xml
Content-Length: ...
<?xml version="1.0" ?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
version="1"
state="partial"
entity="sip:b@tradewind.com">
<dialog id="2" call-id="1@recipient.tradewind.com"
local-tag="1bc"
direction="initiator">
<state>trying</state>
</dialog>
</dialog-info>
M9: The REFER-Recipient sends a NOTIFY triggered by the 180 Ringing
received from the REFER-Target. The body of the NOTIFY contains
the dialog identifier and current state ("early").
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NOTIFY sip:a@issuer.tradewind.com SIP/2.0
Via: SIP/2.0/TCP recipient.tradewind.com;branch=z9hG4bK-b-3
From: <sip:a@tradewind.com>;tag=1ab
To: <sip:b@tradewind.com>;tag=1ba
Call-ID: 1@issuer.tradewind.com
CSeq: 1278785 NOTIFY
Max-Forwards: 70
Event: refer;id=234234
Subscription-State: active;expires=3600
Contact: sip:b@recipient.tradewind.com
Content-Type: application/dialog-info+xml
Content-Length: ...
<?xml version="1.0" ?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
version="2"
state="partial"
entity="sip:b@tradewind.com">
<dialog id="2" call-id="1@recipient.tradewind.com"
local-tag="1bc" remote-tag="1cb"
direction="initiator">
<state>early</state>
</dialog>
</dialog-info>
M12: The REFER-Recipient sends a NOTIFY triggered by the 200 OK
received from the REFER-Target. The body of the NOTIFY contains
the dialog identifier and current state ("confirmed").
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NOTIFY sip:a@issuer.tradewind.com SIP/2.0
Via: SIP/2.0/TCP recipient.tradewind.com;branch=z9hG4bK-b-4
From: <sip:a@tradewind.com>;tag=1ab
To: <sip:b@tradewind.com>;tag=1ba
Call-ID: 1@issuer.tradewind.com
CSeq: 1278786 NOTIFY
Max-Forwards: 70
Event: refer;id=234234
Subscription-State: active;expires=3600
Contact: sip:b@recipient.tradewind.com
Content-Type: application/dialog-info+xml
Content-Length: ...
<?xml version="1.0" ?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
version="3"
state="partial"
entity="sip:b@tradewind.com">
<dialog id="2" call-id="1@recipient.tradewind.com"
local-tag="1bc" remote-tag="1cb"
direction="initiator">
<state>confirmed</state>
</dialog>
</dialog-info>
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8. Suppressing the REFER Implicit Subscription
The REFER specification mandates that every REFER creates an implicit
subscription between the REFER-Issuer and the REFER-Recipient. This
subscription results in at least one NOTIFY being sent from the
REFER-Recipient to the REFER-Issuer. The REFER-Recipient may choose
to cancel the implicit subscription with this NOTIFY. The
REFER-Issuer may choose to cancel this implicit subscription with an
explicit SUBSCRIBE (Expires: 0) after receipt of the initial NOTIFY
or by sending a 481 response to this initial NOTIFY request.
The purpose of requiring the implicit subscription and initial NOTIFY
is to allow for the situation where the REFER request gets forked and
the REFER-Issuer needs a way to see the multiple dialogs that may be
established as a result of the forked REFER. This is the same
approach used to handle forking of SUBSCRIBE [5] requests. Where the
REFER-Issuer explicitly specifies that forking not occur, the
requirement that an implicit subscription be established is
unnecessary.
Another purpose of the NOTIFY is to inform the REFER-Issuer of the
progress of the SIP transaction that results from the REFER at the
REFER-Recipient. In the case where the REFER-Issuer is already aware
of the progress of the requested operation, such as when the
REFER-Issuer has an explicit subscription to the dialog event package
at the REFER-Recipient, the implicit subscription and resultant
NOTIFY traffic related to the REFER is superfluous and unnecessary
network overhead.
To avoid this unnecessary overhead, this document defines a new
option tag, norefersub, which specifies that an implicit subscription
for event package refer should not be created as a result of
accepting this REFER request. Consequently, no dialog is created as
the result of sending REFER with Require header containing the
norefersub option tag.
This MUST be used by the REFER-Issuer only when the REFER-Issuer can
be certain that the REFER request will not be forked. The
REFER-Recipient MUST signal support for this extension by inserting a
Supported: norefersub header in the 2xx response to the REFER
request.
Example of extended REFER which suppresses the implicit subscription
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REFER sip:b@tradewind.com SIP/2.0
Via: SIP/2.0/TCP issuer.tradewind.com;branch=z9hG4bK-a-1
From: <sip:a@tradewind.com>;tag=1a
To: <sip:b@tradewind.com>
Call-ID: 1@issuer.tradewind.com
Supported: gruu
CSeq: 234234 REFER
Max-Forwards: 70
Refer-To: <sip:c@tradewind.com;method=INVITE>
Require: extended-refer; norefersub
Accept-Contact: *;audio;require
Contact: sip:a@issuer.tradewind.com
Content-Type: message/sipfrag
Content-Id: <1239103912039@issuer.tradewind.com>
Content-Length: ...
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9. Applying REFER to SIP Response Codes
The original REFER is defined to trigger the sending of a request
from the REFER-Recipient to the REFER-Target. The intention is most
often to initiate a dialog from the REFER-Recipient to the
REFER-Target. This is an excellent way to generate an action at the
REFER-Recipient based on an event or action that takes places at the
REFER-Issuer. The classic example is call transfer as a result of a
user at the REFER-Issuer taking some action.
With the use of the dialog event package, it is possible for one UA
to monitor events at another UA related to a dialog, such as the
receipt of an INVITE to establish a new dialog. What is lacking is a
way for the watcher to indicate what should be the response to such
an INVITE request. For example, the dialog watcher would like the
recipient of the session initiation request to accept the initiation
(send a 200 OK response to the INVITE request). One motivating
scenario for this is a set of co-operating User Agents (devices) that
belong to the same user. The user, while using one SIP device, wishes
to answer a call that is being received on another of that user's SIP
devices. This gives the user a single UI focus for control while
allowing multiple devices with differing capabilities.
To enable such a scenario, this document defines an extension to the
SIP(S) URI syntax as defined in SIP [2]. The extension is analogous
to the "method" uri-parameter that currently exists to communicate a
method for use in the Refer-To header. A new uri-parameter,
"response", is proposed that is used in conjunction with the "method"
uri-parameter and associated call-id, local tag, and remote tag to
request that the REFER-Recipient send a response within the
identified SIP transaction to the REFER-Target.
TBD: Generalize the discussion of the "response" uri-parameter to be
used with methods other than REFER.
The REFER-Issuer MUST specify a "method" parameter in addition to the
"response" parameter. The REFER-Issuer MUST also include the
appropriate local-uri, local-tag, remote-uri, and remote-tag encoded
as From and To headers in the Refer-To URI (or using a message/
sipfrag body when used in conjunction with the extended-refer
mechanism). Note that in order to satisfy this requirement, the
REFER-Issuer must have access to this information. In particular, it
is assumed that the REFER-Issuer receives the local-uri and
remote-uri in the NOTIFY for the dialog event package from the
REFER-Recipient. These elements are optional in the XML schema. It is
anticipated that User Agents that support these REFER extensions will
also include these optional elements in the application/
dialog-info+xml payload (as privacy concerns allow).
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To ensure the REFER-Recipient conformant with RFC3515 does not
misinterpret this as a REFER to send a request of the specified
method, the REFER-Issuer MUST also include a Require: refer-response
header in the REFER request. REFER-Recipients which do not understand
this extension will return a 420 response. The REFER-Target does not
need to understand this extension for this to work. Support for this
extension can be queried in advance using a standard OPTIONS request.
The REFER-Issuer MUST request the use of the application/
dialog-info+xml MIME type in NOTIFYs associated with a REFER request
which uses the "refer-response" extension.
Note that, although it is RECOMMENDED to use the "refer-response"
extension in conjunction to the "extended-refer" framework, the
extensions are orthogonal to each other. The extended REFER framework
does not include the "refer-response" behavior by default. The
"refer-response" extension can be used both with the original REFER
mechanism and with the extended REFER framework.
uri-parameters = *( ";" uri-parameter)
uri-parameter = transport-param / user-param / method-param
/ ttl-param / maddr-param / lr-param / response-param / other-param
response-param = "response=" 1*3DIGIT
An example call flow follows:
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Figure 2: Example of using the "response" uri-parameter in the
Refer-To header
REFER-Issuer REFER-Recipient REFER-Target
| | |
| N1 SUBSCRIBE (dialog) | |
|--------------------------->| |
| N2 202 Accepted | |
|<---------------------------| |
| N3 NOTIFY | |
|<---------------------------| |
| N4 200 OK | |
|--------------------------->| |
| | N5 INVITE |
| |<-----------------------|
| N6 NOTIFY | |
|<---------------------------| |
| N7 200 OK | |
|--------------------------->| |
| | N8 180 Trying |
| |----------------------->|
| N9 NOTIFY | |
|<---------------------------| |
| N10 200 OK | |
|--------------------------->| |
| | |
| N11 REFER (200) | |
|--------------------------->| |
| N12 200 OK | |
|<---------------------------| N13 200 |
| |----------------------->|
| N14 NOTIFY | |
|<---------------------------| |
| N15 200 OK | |
|--------------------------->| |
Message flow:
N1: The REFER-Issuer subscribes to the dialog event package at the
REFER-Recipient.
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SUBSCRIBE sip:b@tradewind.com SIP/2.0
Via: SIP/2.0/TCP issuer.tradewind.com;branch=z9hG4bK-a-1
From: <sip:a@tradewind.com>;tag=1ab
To: <sip:b@tradewind.com>
Call-ID: 1@issuer.tradewind.com
CSeq: 234234 SUBSCRIBE
Max-Forwards: 70
Event: dialog
Accept: application/dialog-info+xml
Contact: sip:a@issuer.tradewind.com
Content-Length: 0
N5: The REFER-Recipient receives an INVITE from the REFER-Target to
start a new call.
INVITE sip:b@tradewind.com SIP/2.0
Via: SIP/2.0/TCP target.tradewind.com;branch=z9hG4bK-c-1
From: <sip:c@tradewind.com>;tag=1cb
To: <sip:b@tradewind.com>
Call-ID: 1@target.tradewind.com
CSeq: 1234567 INVITE
Max-Forwards: 70
Contact: sip:c@target.tradewind.com
Content-Length: ...
<SDP for an audio call>
N6: The REFER-Recipient sends a NOTIFY triggered by the INVITE
received from the REFER-Target. The body of the NOTIFY contains
the dialog identifier and current state ("trying").
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NOTIFY sip:a@issuer.tradewind.com SIP/2.0
Via: SIP/2.0/TCP recipient.tradewind.com;branch=z9hG4bK-b-2
From: <sip:a@tradewind.com>;tag=1ab
To: <sip:b@tradewind.com>;tag=1ba
Call-ID: 1@issuer.tradewind.com
CSeq: 454545 NOTIFY
Max-Forwards: 70
Event: dialog;id=234234
Subscription-State: active;expires=3600
Contact: sip:b@recipient.tradewind.com
Content-Type: application/dialog-info+xml
Content-Length: ...
<?xml version="1.0" ?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
version="1"
state="partial"
entity="sip:b@tradewind.com">
<dialog id="2" call-id="1@target.tradewind.com"
remote-tag="1cb"
direction="recipient">
<local-uri>b@tradewind.com</local-uri>
<remote-uri>c@tradewind.com</remote-uri>
<state>trying</state>
</dialog>
</dialog-info>
N8: The REFER-Recipient sends a 180 Ringing response to the
REFER-Target.
SIP/2.0 180 Ringing
Via: SIP/2.0/TCP target.tradewind.com;branch=z9hG4bK-b-3
From: <sip:c@tradewind.com>;tag=1cb
To: <sip:b@tradewind.com>;tag=1bc
Call-ID: 1@target.tradewind.com
CSeq: 1234567 INVITE
Contact: sip:b@recipient.tradewind.com
Content-Length: 0
N9: The REFER-Recipient sends a NOTIFY triggered by the 180 Ringing
sent to the REFER-Target. The body of the NOTIFY contains the
dialog identifier and current state ("early").
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NOTIFY sip:a@issuer.tradewind.com SIP/2.0
Via: SIP/2.0/TCP recipient.tradewind.com;branch=z9hG4bK-b-4
From: <sip:a@tradewind.com>;tag=1ab
To: <sip:b@tradewind.com>;tag=1ba
Call-ID: 1@issuer.tradewind.com
CSeq: 454546 NOTIFY
Max-Forwards: 70
Event: dialog;id=234234
Subscription-State: active;expires=3600
Contact: sip:b@recipient.tradewind.com
Content-Type: application/dialog-info+xml
Content-Length: ...
<?xml version="1.0" ?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
version="2"
state="partial"
entity="sip:b@tradewind.com">
<dialog id="2" call-id="1@target.tradewind.com"
local-tag="1bc" remote-tag="1cb"
direction="recipient">
<local-uri>b@tradewind.com</local-uri>
<remote-uri>c@tradewind.com</remote-uri>
<state event="1xx-tag">early</state>
</dialog>
</dialog-info>
N11: The REFER-Issuer creates a REFER, specifying that the
REFER-Recipient should send a 200 OK to accept the session
invitation. The From and To headers of the 200 OK are encoded in
the Refer-To URI. The local and remote tags for this are
determined from the information provided in the NOTIFY for the
dialog package. This allows the REFER-Issuer to specify a
particular dialog. Combined with the "method" parameter, this
identifies a specific transaction within the dialog.
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REFER sip:b@tradewind.com SIP/2.0
Via: SIP/2.0/TCP issuer.tradewind.com;branch=z9hG4bK-a-2
From: <sip:a@tradewind.com>;tag=1ab
To: <sip:b@tradewind.com>
Call-ID: 2@issuer.tradewind.com
CSeq: 818181 REFER
Max-Forwards: 70
Accept: application/dialog-info+xml;q=0.5, message/sipfrag;q=0.1
Require: refer-response
Refer-To: <sip:c@tradewind.com;method=INVITE;response=200?Call-ID=1%40target.tradewind.com&
To=b%40tradewind.com;tag=1bc&From=c%40tradewind.com;tag=1cb>
Contact: sip:a@issuer.tradewind.com
Content-Length: 0
N13: The REFER-Recipient sends a 200 OK to the REFER-Target
constructed using the information in the Refer-To header.
SIP/2.0 200 OK
Via: SIP/2.0/TCP target.tradewind.com;branch=z9hG4bK-c-1
From: <sip:c@tradewind.com>;tag=1cb
To: <sip:b@tradewind.com>;tag=1bc
Call-ID: 1@target.tradewind.com
Supported: refer-response
CSeq: 1234567 INVITE
Contact: sip:b@recipient.tradewind.com
Content-Length: 0
N14: The REFER-Recipient sends a NOTIFY triggered by the 200 OK sent
to the REFER-Target. The body of the NOTIFY contains the dialog
identifier and current state ("confirmed").
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NOTIFY sip:a@issuer.tradewind.com SIP/2.0
Via: SIP/2.0/TCP recipient.tradewind.com;branch=z9hG4bK-b-4
From: <sip:a@tradewind.com>;tag=1ab
To: <sip:b@tradewind.com>;tag=1ba
Call-ID: 1@issuer.tradewind.com
CSeq: 454547 NOTIFY
Max-Forwards: 70
Event: dialog;id=234234
Subscription-State: active;expires=3600
Contact: sip:b@recipient.tradewind.com
Content-Type: application/dialog-info+xml
Content-Length: ...
<?xml version="1.0" ?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
version="3"
state="partial"
entity="sip:b@tradewind.com">
<dialog id="2" call-id="1@target.tradewind.com"
local-tag="1bc" remote-tag="1cb"
direction="recipient">
<local-uri>b@tradewind.com</local-uri>
<remote-uri>c@tradewind.com</remote-uri>
<state event="2xx">confirmed</state>
</dialog>
</dialog-info>
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10. Adding callid and tag Parameters to Refer-To Header
TBD: Motivation and examples.
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11. Using of isfocus Feature Parameter with REFER
This specification allows for using of isfocus feature parameter
defined in [8] with REFER.
TBD: Motivation and examples.
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12. REFER with a Referred-By Header with aib
REFER with a Referred-By header with an authenticated identity body
(aib) with multipart MIME.
TBD: Mechanism and examples.
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13. IANA Considerations
13.1 extended-refer Option Tag Registration
This document defines a new option tag, extended-refer, which
specifies that the recipient of the REFER request is expected to
understand and act upon the extended REFER framework as specified in
this document. This option tag is only meaningful for the REFER
request defined in RFC3515.
13.2 norefersub Option Tag Registration
This document defines a new option tag, norefersub, which specifies
that an implicit subscription for event package refer should not be
created as a result of accepting this REFER request. This option tag
is only meaningful for the REFER request defined in RFC3515.
13.3 refer-response Option Tag Registration
This document defines a new option tag, refer-response, which
specifies that the recipient of the REFER request is expected to
issue a response for the SIP transaction requested within the REFER.
This option tag is only meaningful for the REFER request defined in
RFC3515.
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14. Security Considerations
Security considerations regarding inclusion of sensitive information
inside the REFER body in MIME format will be addressed in the next
version of this document.
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15. Acknowledgements
The authors would like to thank Rohan Mahy, Gonzallo Camarillo, and
Franois Audet for their insightful comments and inputs. The authors
would also like to thank Sriram Parameswar for his ideas being
originally presented in draft-parameswar-sipping-norefersub-00 and
incorporated in this document.
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References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002.
[3] Sparks, R., "The Session Initiation Protocol (SIP) Refer
Method", RFC 3515, April 2003.
[4] Sparks, R., "Internet Media Type message/sipfrag", RFC 3420,
November 2002.
[5] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.
[6] Levinson, E., "Content-ID and Message-ID Uniform Resource
Locators", RFC 2392, August 1998.
[7] Rosenberg, J. and H. Schulzrinne, "An INVITE Inititiated Dialog
Event Package for the Session Initiation Protocol (SIP)",
draft-ietf-sipping-dialog-package-03 (work in progress),
October 2003.
[8] Rosenberg, J., "Indicating User Agent Capabilities in the
Session Initiation Protocol (SIP)",
draft-ietf-sip-callee-caps-03 (work in progress), January 2004.
[9] Rosenberg, J., Schulzrinne, H. and P. Kyzivat, "Caller
Preferences for the Session Initiation Protocol (SIP)",
draft-ietf-sip-callerprefs-10 (work in progress), October 2003.
[10] Camarillo, G., "Refering to Multiple Resources in the Session
Initiation Protocol (SIP)",
draft-camarillo-sipping-multiple-refer-00 (work in progress),
February 2004.
[11] Mahy, R., "Remote Call Control in SIP using the REFER method
and the session-oriented dialog package",
draft-mahy-sip-remote-cc-01 (work in progress), February 2004.
[12] Rosenberg, J., "Obtaining and Using Globally Routable User
Agent (UA) URIs (GRUU) in the Session Initiation Protocol
(SIP)", draft-ietf-sip-gruu-00 (work in progress), January
2004.
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Authors' Addresses
Sean Olson
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
USA
Phone: +1-425-707-2846
EMail: seanol@microsoft.com
Orit Levin
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
USA
Phone: +1-425-722-2225
EMail: oritl@microsoft.com
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HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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