SIPPING S. Olson Internet-Draft Microsoft Expires: December 19, 2003 June 20, 2003 Extensions to the REFER mechanism for Third Party Call Control draft-olson-sipping-refer-extensions-00 Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http:// www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on December 19, 2003. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract This document proposes a number of extensions to the REFER method used by the Session Initiation Protocol (SIP) for the purpose of third party call control. Olson Expires December 19, 2003 [Page 1] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 Table of Contents 1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Use of the application/dialog-info+xml MIME type with REFER . 6 5. Extending REFER to SIP response codes . . . . . . . . . . . . 11 6. Supressing forking of REFER requests . . . . . . . . . . . . . 18 7. Supressing the NOTIFY associated with a REFER . . . . . . . . 19 8. Replacing complex Refer-To URIs with a MIME body . . . . . . . 21 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24 9.1 norefersub option tag registration . . . . . . . . . . . . . . 24 9.2 refer-response option tag registration . . . . . . . . . . . . 24 10. Security Considerations . . . . . . . . . . . . . . . . . . . 25 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 26 References . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Author's Address . . . . . . . . . . . . . . . . . . . . . . . 27 Intellectual Property and Copyright Statements . . . . . . . . 28 Olson Expires December 19, 2003 [Page 2] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 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 will be defined: REFER-Issuer: the UA issuing the REFER request REFER-Recipient: the UA receiving the REFER request REFER-Target: the UA designated in the Refer-To URI Olson Expires December 19, 2003 [Page 3] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 2. Introduction The REFER [3] extension to SIP [2] defines a basis for third party call control that is useful for implementing features such as call transfer. 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 dialog package outside of the REFER request. This represents additional unnecessary traffic and state in the REFER-Issuer and REFER-recipient. Olson Expires December 19, 2003 [Page 4] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 3. Requirements Requirement 1: Allow the REFER-Issuer to watch the progress of a REFER beyond the end of the INVITE transaction and for the duration of the dialog Requirement 2: Expose the dialog information of the dialog established at the REFER-Recipient as a result of the REFER Requirement 3: Allow specification of much richer detail of the request that is generated at the REFER-Recipient as a result of the REFER beyond just the method and Request-URI. Examples include caller preferences, portions of the SDP, and user defined headers. Requirement 4: Allow one user agent to specify that another user agent answer an incoming call Requirement 5: Prevent forking of a REFER request and allow targeting of that REFER request to a specific device or class of device. Requirement 6: Reduce the number of messages exchanged to perform a REFER when the REFER-Issuer and REFER-Recipient support richer call control primitives such as the dialog and conference event packages. Olson Expires December 19, 2003 [Page 5] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 4. Use of the application/dialog-info+xml MIME type 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 establish a dialog, for example through an INVITE in the Refer-To, the derivative state of interest is actually the dialog state. While this may be inferred from the contents of the message/sipfrag body it is a bit clumsy and in many cases the REFER-Recipient will omit important details of the dialog in the message/sipfrag body. 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. To address this shortcoming, it is proposed to extend REFER to allow the (optional) use of the application/dialog-info+xml MIME type in place of message/sipfrag. The REFER-Issuer specifies support for this by including this MIME type in an Accept header. The REFER-Issuer MUST also support message/sipfrag for compatibility with strictly RFC3515 compliant implementations. If the REFER-Recipient supports this extension, it may choose to honor the request or default to using message/sipfrag dependent on local policy. It is OPTIONAL for the REFER-Recipient to maintain the subscription for the duration of the resultant (INVITE) dialog and RECOMMENDED that the subscription be maintained at least until the dialog is in "confirmed" state. 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 | | |----------------------->| Olson Expires December 19, 2003 [Page 6] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 | 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 a preference for the application/dialog-info+xml MIME type. REFER sip:b@tradewind.com SIP/2.0 Via: SIP/2.0/TCP issuer.tradewind.com;branch=z9hG4bK-a-1 From: ;tag=1ab To: Call-ID: 1@issuer.tradewind.com CSeq: 234234 REFER Max-Forwards: 70 Refer-To: sip:c@tradewind.com;method=INVITE Accept: application/dialog-info+xml;q=0.5, message/sipfrag;q=0.1 Contact: sip:a@issuer.tradewind.com Content-Length: 0 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 Olson Expires December 19, 2003 [Page 7] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 From: ;tag=1bc To: Call-ID: 1@recipient.tradewind.com CSeq: 1234567 INVITE Max-Forwards: 70 Contact: sip:b@recipient.tradewind.com Content-Length: ... 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"). NOTIFY sip:a@issuer.tradewind.com SIP/2.0 Via: SIP/2.0/TCP recipient.tradewind.com;branch=z9hG4bK-b-2 From: ;tag=1ab To: ;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: ... trying 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"). Olson Expires December 19, 2003 [Page 8] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 NOTIFY sip:a@issuer.tradewind.com SIP/2.0 Via: SIP/2.0/TCP recipient.tradewind.com;branch=z9hG4bK-b-3 From: ;tag=1ab To: ;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: ... early 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"). NOTIFY sip:a@issuer.tradewind.com SIP/2.0 Via: SIP/2.0/TCP recipient.tradewind.com;branch=z9hG4bK-b-4 From: ;tag=1ab To: ;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: ... Olson Expires December 19, 2003 [Page 9] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 confirmed Olson Expires December 19, 2003 [Page 10] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 5. Extending REFER to SIP response codes REFER is currently 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 proposes 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. 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 as defined later in this document). 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). To ensure the REFER-Recipient conformant with RFC3515 does not misintepret this as a REFER to send a request of the specified method, the REFER-Issuer MUST also include a Require: refer-response Olson Expires December 19, 2003 [Page 11] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 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 this "response" extension. The proposed syntax modification follows 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: 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 | | |--------------------------->| | | | | Olson Expires December 19, 2003 [Page 12] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 | 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. SUBSCRIBE sip:b@tradewind.com SIP/2.0 Via: SIP/2.0/TCP issuer.tradewind.com;branch=z9hG4bK-a-1 From: ;tag=1ab To: 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: ;tag=1cb To: Call-ID: 1@target.tradewind.com CSeq: 1234567 INVITE Max-Forwards: 70 Contact: sip:c@target.tradewind.com Content-Length: ... Olson Expires December 19, 2003 [Page 13] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 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"). NOTIFY sip:a@issuer.tradewind.com SIP/2.0 Via: SIP/2.0/TCP recipient.tradewind.com;branch=z9hG4bK-b-2 From: ;tag=1ab To: ;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: ... b@tradewind.com c@tradewind.com trying 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: ;tag=1cb To: ;tag=1bc Olson Expires December 19, 2003 [Page 14] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 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"). NOTIFY sip:a@issuer.tradewind.com SIP/2.0 Via: SIP/2.0/TCP recipient.tradewind.com;branch=z9hG4bK-b-4 From: ;tag=1ab To: ;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: ... b@tradewind.com c@tradewind.com early 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 Olson Expires December 19, 2003 [Page 15] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 identifies a specific transaction within the dialog. REFER sip:b@tradewind.com SIP/2.0 Via: SIP/2.0/TCP issuer.tradewind.com;branch=z9hG4bK-a-2 From: ;tag=1ab To: 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: ;tag=1cb To: ;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"). NOTIFY sip:a@issuer.tradewind.com SIP/2.0 Via: SIP/2.0/TCP recipient.tradewind.com;branch=z9hG4bK-b-4 From: ;tag=1ab To: ;tag=1ba Olson Expires December 19, 2003 [Page 16] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 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: ... b@tradewind.com c@tradewind.com confirmed Olson Expires December 19, 2003 [Page 17] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 6. Supressing 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 some situations 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. Fortunately, there is already a mechanism which can address the need to indicate that a REFER should NOT be forked. The caller preferences extension [8] defines both a way to indicate a request not be forked and a means to target a specific device with the desired capabilities. No further extension is required. An example of the usage of caller preferences in conjunction with REFER is shown below. Example of REFER using Caller Preferences extension REFER sip:b@tradewind.com SIP/2.0 Via: SIP/2.0/TCP issuer.tradewind.com;branch=z9hG4bK-a-1 From: ;tag=1a To: Call-ID: 1@issuer.tradewind.com CSeq: 234234 REFER Max-Forwards: 70 Refer-To: sip:c@tradewind.com;method=INVITE Require: pref Request-Dispostion: no-fork Accept-Contact: *;audio;require Reject-Contact: *;video Contact: sip:a@issuer.tradewind.com Content-Length: 0 Olson Expires December 19, 2003 [Page 18] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 7. Supressing the NOTIFY associated with a REFER The REFER specification mandates that every REFER create 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 subcription 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 via caller preferences, or implicitly does not allow for forking by sending the REFER within an existing dialog, 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 SIP transaction, 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, it is proposed that the REFER-Issuer insert a Supported: norefersub header in the REFER request to indicate to the REFER-Recipient that no implicit subscription or NOTIFY is needed with respect to this REFER request. 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 REFER which supresses the implicit subscription REFER sip:b@tradewind.com SIP/2.0 Via: SIP/2.0/TCP issuer.tradewind.com;branch=z9hG4bK-a-1 From: ;tag=1a Olson Expires December 19, 2003 [Page 19] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 To: Call-ID: 1@issuer.tradewind.com CSeq: 234234 REFER Max-Forwards: 70 Refer-To: sip:c@tradewind.com;method=INVITE Request-Dispostion: no-fork Accept-Contact: *;audio;require Supported: norefersub Contact: sip:a@issuer.tradewind.com Content-Length: 0 Olson Expires December 19, 2003 [Page 20] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 8. Replacing complex Refer-To URIs with a MIME body 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 [8], 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. The alternative that is proposed is to make use of the currently unused REFER body to encapsulate all the information that is potentially escaped in the Refer-To URI. The possible information includes the method, headers, and body of the request which is desired to be created by the REFER-Recipient. The ideal candidate for this is the message/sipfrag MIME type. This MIME type can express all of these: the method, Request-URI, headers, and body. This applies to requests as well as responses (as an extension). There are two possibilities: use a cid URI [6] in the Refer-To header to reference the message/sipfrag content in the body of the REFER or continue to place the URI of the REFER-Target in the Refer-To header and place all other facets of the request in the message/sipfrag body with the understanding that the presence of the body implies its usage for this purpose. A few examples should illuminate things. Before REFER sip:b@tradewind.com SIP/2.0 Via: SIP/2.0/TCP issuer.tradewind.com;branch=z9hG4bK-a-1 From: ;tag=1a To: 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 Require: refer-response Contact: sip:a@issuer.tradewind.com Content-Length: 0 Olson Expires December 19, 2003 [Page 21] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 After (placing the REFER-Target in the Refer-To) REFER sip:b@tradewind.com SIP/2.0 Via: SIP/2.0/TCP issuer.tradewind.com;branch=z9hG4bK-a-1 From: ;tag=1a To: Call-ID: 1@issuer.tradewind.com CSeq: 234234 REFER Max-Forwards: 70 Refer-To: sip:c@tradewind.com;method=INVITE Accept: application/dialog-info+xml;q=0.5, message/sipfrag;q=0.1 Require: refer-response Contact: sip:a@issuer.tradewind.com Content-Type: message/sipfrag 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 After (using a cid URI) REFER sip:b@tradewind.com SIP/2.0 Via: SIP/2.0/TCP issuer.tradewind.com;branch=z9hG4bK-a-1 From: ;tag=1a To: Call-ID: 1@issuer.tradewind.com 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: refer-response 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 Olson Expires December 19, 2003 [Page 22] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 To: c@tradewind.com;tag=1c Note that the target URI and method are still included in the Refer-To header. If the REFER-Recipient does not understand this extension, it MUST return a 4xx response to the REFER request. 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. Olson Expires December 19, 2003 [Page 23] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 9. IANA Considerations 9.1 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. 9.2 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 identified within the Refer-To URI. This option tag is only meaningful for the REFER request defined in RFC3515. Olson Expires December 19, 2003 [Page 24] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 10. Security Considerations No additional concerns above what is defined in RFC3515. Olson Expires December 19, 2003 [Page 25] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 11. Acknowledgements The author would like to thank Rohan Mahy for his insightful comments. The author would also like to thank Sriram Parameswar for his draft-parameswar-sipping-norefersub-00 proposal which is the basis for the norefersub option tag proposed in this draft. Olson Expires December 19, 2003 [Page 26] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 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-01 (work in progress), March 2003. [8] Rosenberg, J., Schulzrinne, H. and P. Kyzivat, "Caller Preferences and Callee Capabilities for the Session Initiation Protocol (SIP)", draft-ietf-sip-callerprefs-08 (work in progress), March 2003. Author's Address Sean Olson Microsoft One Microsoft Way Redmond, WA 98052 US Phone: +1-425-707-2846 EMail: seanol@microsoft.com URI: http://www.microsoft.com/rtc Olson Expires December 19, 2003 [Page 27] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. 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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 assignees. 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 Olson Expires December 19, 2003 [Page 28] Internet-Draft Extensions to the REFER mechanism for Third Party Call Control June 2003 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Olson Expires December 19, 2003 [Page 29]