draft-ietf-sipping-dialogusage-06.txt   rfc5057.txt 
Network Working Group R. Sparks Network Working Group R. Sparks
Internet-Draft Estacado Systems Request for Comments: 5057 Estacado Systems
Expires: August 20, 2007 February 16, 2007 Category: Informational November 2007
Multiple Dialog Usages in the Session Initiation Protocol Multiple Dialog Usages in the Session Initiation Protocol
draft-ietf-sipping-dialogusage-06
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Abstract Abstract
Several methods in the Session Initiation Protocol can create an Several methods in the Session Initiation Protocol (SIP) can create
association between endpoints known as a dialog. Some of these an association between endpoints known as a dialog. Some of these
methods can also create a different, but related, association within methods can also create a different, but related, association within
an existing dialog. These multiple associations, or dialog usages, an existing dialog. These multiple associations, or dialog usages,
require carefully coordinated processing as they have independent require carefully coordinated processing as they have independent
life-cycles, but share common dialog state. Processing multiple life-cycles, but share common dialog state. Processing multiple
dialog usages correctly is not completely understood. What is dialog usages correctly is not completely understood. What is
understood is difficult to implement. understood is difficult to implement.
This memo argues that multiple dialog usages should be avoided. It This memo argues that multiple dialog usages should be avoided. It
discusses alternatives to their use and clarifies essential behavior discusses alternatives to their use and clarifies essential behavior
for elements that cannot currently avoid them. for elements that cannot currently avoid them.
This is an informative document and makes no normative statements of This is an informative document and makes no normative statements of
any kind. any kind.
Table of Contents Table of Contents
1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Examples of Multiple Usages . . . . . . . . . . . . . . . . . 4 3. Examples of Multiple Usages . . . . . . . . . . . . . . . . . 4
3.1. Transfer . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1. Transfer . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Reciprocal Subscription . . . . . . . . . . . . . . . . . 7 3.2. Reciprocal Subscription . . . . . . . . . . . . . . . . . 6
4. Usage Creation and Destruction . . . . . . . . . . . . . . . . 10 4. Usage Creation and Destruction . . . . . . . . . . . . . . . . 9
4.1. Invite usages . . . . . . . . . . . . . . . . . . . . . . 10 4.1. Invite Usages . . . . . . . . . . . . . . . . . . . . . . 9
4.2. Subscribe usages . . . . . . . . . . . . . . . . . . . . . 10 4.2. Subscribe usages . . . . . . . . . . . . . . . . . . . . . 9
5. Proper Handling of Multiple Usages . . . . . . . . . . . . . . 10 5. Proper Handling of Multiple Usages . . . . . . . . . . . . . . 9
5.1. A survey of the effect of failure responses on usages 5.1. A Survey of the Effect of Failure Responses on Usages
and dialogs . . . . . . . . . . . . . . . . . . . . . . . 10 and Dialogs . . . . . . . . . . . . . . . . . . . . . . . 9
5.2. Transaction timeouts . . . . . . . . . . . . . . . . . . . 16 5.2. Transaction Timeouts . . . . . . . . . . . . . . . . . . . 15
5.3. Matching requests to usages . . . . . . . . . . . . . . . 17 5.3. Matching Requests to Usages . . . . . . . . . . . . . . . 16
5.4. Target refresh requests . . . . . . . . . . . . . . . . . 17 5.4. Target Refresh Requests . . . . . . . . . . . . . . . . . 17
5.5. Refreshing and Terminating Usages . . . . . . . . . . . . 18 5.5. Refreshing and Terminating Usages . . . . . . . . . . . . 17
5.6. Refusing new usages . . . . . . . . . . . . . . . . . . . 18 5.6. Refusing New Usages . . . . . . . . . . . . . . . . . . . 18
5.7. Replacing usages . . . . . . . . . . . . . . . . . . . . . 19 5.7. Replacing Usages . . . . . . . . . . . . . . . . . . . . . 18
6. Avoiding Multiple Usages . . . . . . . . . . . . . . . . . . . 19 6. Avoiding Multiple Usages . . . . . . . . . . . . . . . . . . . 18
7. Security Considerations . . . . . . . . . . . . . . . . . . . 24 7. Security Considerations . . . . . . . . . . . . . . . . . . . 23
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25 8. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 24
9. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 25 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 24
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 25 10. Informative References . . . . . . . . . . . . . . . . . . . . 24
11. Informative References . . . . . . . . . . . . . . . . . . . . 25
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 26
A.1. draft-ietf-05->draft-ietf-06 . . . . . . . . . . . . . . . 26
A.2. draft-ietf-04->draft-ietf-05 . . . . . . . . . . . . . . . 27
A.3. draft-ietf-03->draft-ietf-04 . . . . . . . . . . . . . . . 27
A.4. draft-ietf-02->draft-ietf-03 . . . . . . . . . . . . . . . 27
A.5. draft-ietf-01->draft-ietf-02 . . . . . . . . . . . . . . . 27
A.6. draft-ietf-00->draft-ietf-01 . . . . . . . . . . . . . . . 27
A.7. draft-sparks-01->draft-ietf-00 . . . . . . . . . . . . . . 28
A.8. draft-sparks-00->01 . . . . . . . . . . . . . . . . . . . 28
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 28
Intellectual Property and Copyright Statements . . . . . . . . . . 29
1. Overview 1. Overview
This is an informative document. It makes no normative statements of This is an informative document. It makes no normative statements of
any kind. This document refines the concept of a dialog usage in the any kind. This document refines the concept of a dialog usage in the
Session Initiation Protocol (SIP [1]), and discusses what led to its Session Initiation Protocol (SIP [1]), and discusses what led to its
existence. It explores ambiguity associated with processing multiple existence. It explores ambiguity associated with processing multiple
dialog usages that share a dialog. In particular, it surveys the dialog usages that share a dialog. In particular, it surveys the
effect of SIP failure responses on transaction, dialog usage, and effect of SIP failure responses on transaction, dialog usage, and
dialog state. This document will help the implementer understand dialog state. This document will help the implementer understand
what is required to process multiple dialog usages correctly, and what is required to process multiple dialog usages correctly, and
will inform future standards-track work clarifying RFC3261 and will provide information for future standards-track work that will
related documents. Finally, the document explores single-usage clarify RFC 3261 and other related documents. Finally, the document
dialog alternatives (using SIP extensions) to multiple dialog usages. explores single-usage dialog alternatives (using SIP extensions) to
multiple dialog usages.
2. Introduction 2. Introduction
Several methods in SIP can establish a dialog. When they do so, they Several methods in SIP can establish a dialog. When they do so, they
also establish an association between the endpoints within that also establish an association between the endpoints within that
dialog. This association has been known for some time as a "dialog dialog. This association has been known for some time as a "dialog
usage" in the developer community. A dialog initiated with an INVITE usage" in the developer community. A dialog initiated with an INVITE
request has an invite usage. A dialog initiated with a SUBSCRIBE request has an invite usage. A dialog initiated with a SUBSCRIBE
request has a subscribe usage. A dialog initiated with a REFER request has a subscribe usage. A dialog initiated with a REFER
request has a subscribe usage. request has a subscribe usage.
Dialogs with multiple usages arise when a usage-creating action Dialogs with multiple usages arise when a usage-creating action
occurs inside an existing dialog. Such actions include accepting a occurs inside an existing dialog. Such actions include accepting a
REFER or SUBSCRIBE issued inside a dialog established with an INVITE REFER or SUBSCRIBE issued inside a dialog established with an INVITE
request. Multiple REFERs within a dialog create multiple request. Multiple REFERs within a dialog create multiple
subscriptions, each of which is a new dialog usage sharing common subscriptions, each of which is a new dialog usage sharing common
dialog state. (Note that any REFER issued utilizing the dialog state. (Note that any REFER issued utilizing the
subscription-suppression mechanism specified in [8] creates no new subscription-suppression mechanism specified in [2] creates no new
usage.) Similarly, an endpoint in a dialog established with an usage.) Similarly, an endpoint in a dialog established with an
INVITE might subscribe to its peer's KPML [11] and later issue a INVITE might subscribe to its peer's Key Press Markup Language (KPML)
REFER, resulting in three dialog usages sharing common dialog state. [3] and later issue a REFER, resulting in three dialog usages sharing
common dialog state.
The common state in the dialog shared by any usages is exactly: The common state in the dialog shared by any usages is exactly:
o the Call-ID o the Call-ID
o the local Tag o the local Tag
o the remote Tag o the remote Tag
o the local CSeq o the local CSeq
o the remote CSeq o the remote CSeq
o the Route-set o the Route-set
o the local contact o the local contact
o the remote target o the remote target
o the secure flag o the secure flag
Usages have state that is not shared in the dialog. For example, a Usages have state that is not shared in the dialog. For example, a
subscription has a duration, along with other usage-specific state. subscription has a duration, along with other usage-specific state.
Multiple subscriptions in the same dialog each have their own Multiple subscriptions in the same dialog each have their own
duration. duration.
A dialog comes into existence with the creation of the first usage, A dialog comes into existence with the creation of the first usage,
and continues to exist until the last usage is terminated (reference and continues to exist until the last usage is terminated (reference
counting). Unfortunately, many of the usage management aspects of counting). Unfortunately, many of the usage management aspects of
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and some influencing the entire dialog. and some influencing the entire dialog.
The current specifications define two usages, invite and subscribe. The current specifications define two usages, invite and subscribe.
A dialog can share up to one invite usage and arbitrarily many A dialog can share up to one invite usage and arbitrarily many
subscribe usages. subscribe usages.
Because RFC3261 [1] states that user-agents should reuse Call-ID and Because RFC3261 [1] states that user-agents should reuse Call-ID and
increment CSeq across a series of registration requests (and that to- increment CSeq across a series of registration requests (and that to-
tags appear in register responses in some of the examples), some tags appear in register responses in some of the examples), some
implementations have treated REGISTER as if it were in a dialog. implementations have treated REGISTER as if it were in a dialog.
However, RFC3261 explicitly calls out that REGISTER does not create a However, RFC 3261 explicitly calls out that REGISTER does not create
dialog. A series of REGISTER requests does not create any usage or a dialog. A series of REGISTER requests does not create any usage or
dialog. Similarly, PUBLISH [10] does not create any usage or dialog. dialog. Similarly, PUBLISH [4] does not create any usage or dialog.
3. Examples of Multiple Usages 3. Examples of Multiple Usages
3.1. Transfer 3.1. Transfer
In Figure 1, Alice transfers a call she received from Bob to Carol. In Figure 1, Alice transfers a call she received from Bob to Carol.
A dialog (and an invite dialog usage) between Alice and Bob comes A dialog (and an invite dialog usage) between Alice and Bob comes
into being with the 200 OK labeled F1. A second usage (a into being with the 200 OK labeled F1. A second usage (a
subscription to event refer) comes into being with the NOTIFY labeled subscription to event refer) comes into being with the NOTIFY labeled
F2. This second usage ends when the subscription is terminated by F2. This second usage ends when the subscription is terminated by
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Figure 4 Figure 4
4. Usage Creation and Destruction 4. Usage Creation and Destruction
Dialogs come into existence along with their first usage. Dialogs Dialogs come into existence along with their first usage. Dialogs
terminate when their last usage is destroyed. The messages that terminate when their last usage is destroyed. The messages that
create and destroy usages vary per usage. This section provides a create and destroy usages vary per usage. This section provides a
high-level categorization of those messages. The section does not high-level categorization of those messages. The section does not
attempt to explore the REGISTER pseudo-dialog. attempt to explore the REGISTER pseudo-dialog.
4.1. Invite usages 4.1. Invite Usages
Created by: non-100 provisional responses to INVITE; 200 response to Created by: non-100 provisional responses to INVITE; 200 response to
INVITE INVITE
Destroyed by: 200 responses to BYE; certain failure responses to Destroyed by: 200 responses to BYE; certain failure responses to
INVITE, UPDATE, PRACK, INFO, or BYE; anything that destroys a INVITE, UPDATE, PRACK, INFO, or BYE; anything that destroys a
dialog and all its usages dialog and all its usages
4.2. Subscribe usages 4.2. Subscribe usages
Created by: 200 class responses to SUBSCRIBE; 200 class responses to Created by: 200 class responses to SUBSCRIBE; 200 class responses to
REFER; NOTIFY requests REFER; NOTIFY requests
Destroyed by: 200 class responses to NOTIFY-terminated; NOTIFY or Destroyed by: 200 class responses to NOTIFY-terminated; NOTIFY or
refresh-SUBSCRIBE request timeout; certain failure responses to refresh-SUBSCRIBE request timeout; certain failure responses to
NOTIFY or SUBSCRIBE; expiration without refresh if network issues NOTIFY or SUBSCRIBE; expiration without refresh if network issues
prevent the terminal NOTIFY from arriving; anything that destroys prevent the terminal NOTIFY from arriving; anything that destroys
a dialog and all its usages a dialog and all its usages
5. Proper Handling of Multiple Usages 5. Proper Handling of Multiple Usages
The examples in Section 3 show straightforward cases where it is The examples in Section 3 show straightforward cases where it is
fairly obvious when the dialog begins and ends. Unfortunately, there fairly obvious when the dialog begins and ends. Unfortunately, there
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5. Proper Handling of Multiple Usages 5. Proper Handling of Multiple Usages
The examples in Section 3 show straightforward cases where it is The examples in Section 3 show straightforward cases where it is
fairly obvious when the dialog begins and ends. Unfortunately, there fairly obvious when the dialog begins and ends. Unfortunately, there
are many scenarios where such clarity is not present. For instance, are many scenarios where such clarity is not present. For instance,
in Figure 1, what would it mean if the response to the NOTIFY (F2) in Figure 1, what would it mean if the response to the NOTIFY (F2)
were a 481? Does that simply terminate the refer subscription, or were a 481? Does that simply terminate the refer subscription, or
does it destroy the entire dialog? This section explores the problem does it destroy the entire dialog? This section explores the problem
areas with multiple usages that have been identified to date. areas with multiple usages that have been identified to date.
5.1. A survey of the effect of failure responses on usages and dialogs 5.1. A Survey of the Effect of Failure Responses on Usages and Dialogs
For this survey, consider a subscribe usage inside a dialog For this survey, consider a subscribe usage inside a dialog
established with an invite usage. Unless stated otherwise, we'll established with an invite usage. Unless stated otherwise, we'll
discuss the effect on each usage and the dialog when a client issuing discuss the effect on each usage and the dialog when a client issuing
a NOTIFY inside the subscribe usage receives a failure response (such a NOTIFY inside the subscribe usage receives a failure response (such
as a transferee issuing a NOTIFY to event refer). Further, unless as a transferee issuing a NOTIFY to event refer). Further, unless
otherwise stated, the conclusions apply to arbitrary multiple-usages. otherwise stated, the conclusions apply to arbitrary multiple usages.
This survey is written from the perspective of a client receiving the This survey is written from the perspective of a client receiving the
error response. The effect on dialogs and usages at the server error response. The effect on dialogs and usages at the server
issuing the response is the same. issuing the response is the same.
3xx responses: Redirection mid-dialog is not well understood in SIP, 3xx responses: Redirection mid-dialog is not well understood in SIP,
but whatever effect it has impacts the entire dialog and all of but whatever effect it has impacts the entire dialog and all of
its usages equally. In our example scenario, both the its usages equally. In our example scenario, both the
subscription and the invite usage would be redirected by this subscription and the invite usage would be redirected by this
single response. single response.
For the failure responses with code 400 and greater, there are three For the failure responses with code 400 and greater, there are three
common ways the failure can affect the transaction, usage, and dialog common ways the failure can affect the transaction, usage, and dialog
state. state.
Transaction Only The error affects only the transaction, not the Transaction Only The error affects only the transaction, not the
usage or dialog the transaction occurs in (beyond affecting the usage or dialog the transaction occurs in (beyond affecting the
local CSeq). Any other usage of the dialog is unaffected. The local CSeq). Any other usage of the dialog is unaffected. The
error is a complaint about this transaction, not the usage or error is a complaint about this transaction, not the usage or
dialog the transaction occurs in. dialog that the transaction occurs in.
Destroys Usage The error destroys the usage, but not dialog. Any Destroys Usage The error destroys the usage, but not the dialog.
other usages sharing this dialog are not affected. Any other usages sharing this dialog are not affected.
Destroys Dialog The error destroys the dialog and all usages sharing Destroys Dialog The error destroys the dialog and all usages sharing
it. it.
Table 1 and Table 2 display how the various codes affect transaction, Table 1 and Table 2 display how the various codes affect transaction,
usage, or dialog state. Response code specific comments or usage, or dialog state. Response code specific comments or
exceptions follow the table. exceptions follow the table.
+----------------------+----------------+-----------------+ +----------------------+----------------+-----------------+
| Transaction Only | Destroys Usage | Destroys Dialog | | Transaction Only | Destroys Usage | Destroys Dialog |
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| 408 | Request Timeout | Transaction | (4) | | 408 | Request Timeout | Transaction | (4) |
| 410 | Gone | Dialog | (2) | | 410 | Gone | Dialog | (2) |
| 412 | Conditional Request Failed | Transaction | | | 412 | Conditional Request Failed | Transaction | |
| 413 | Request Entity Too Large | Transaction | | | 413 | Request Entity Too Large | Transaction | |
| 414 | Request-URI Too Long | Transaction | | | 414 | Request-URI Too Long | Transaction | |
| 415 | Unsupported Media Type | Transaction | | | 415 | Unsupported Media Type | Transaction | |
| 416 | Unsupported URI Scheme | Dialog | (2) | | 416 | Unsupported URI Scheme | Dialog | (2) |
| 417 | Unknown Resource-Priority | Transaction | | | 417 | Unknown Resource-Priority | Transaction | |
| 420 | Bad Extension | Transaction | | | 420 | Bad Extension | Transaction | |
| 421 | Extension Required | Transaction | | | 421 | Extension Required | Transaction | |
| 422 | Session Interval Too Brief | Transaction | (5) | | 422 | Session Interval Too Small | Transaction | (5) |
| 423 | Interval Too Brief | Transaction | | | 423 | Interval Too Brief | Transaction | |
| 428 | Use Identity Header | Transaction | | | 428 | Use Identity Header | Transaction | |
| 429 | Provide Referrer Identity | Transaction | (6) | | 429 | Provide Referrer Identity | Transaction | (6) |
| 436 | Bad Identity-Info | Transaction | | | 436 | Bad Identity-Info | Transaction | |
| 437 | Unsupported Certificate | Transaction | | | 437 | Unsupported Certificate | Transaction | |
| 438 | Invalid Identity Header | Transaction | | | 438 | Invalid Identity Header | Transaction | |
| 480 | Temporarily Unavailable | Usage | (7) | | 480 | Temporarily Unavailable | Usage | (7) |
| 481 | Call/Transaction Does Not Exist | Usage | (8) | | 481 | Call/Transaction Does Not Exist | Usage | (8) |
| 482 | Loop Detected | Dialog | (9) | | 482 | Loop Detected | Dialog | (9) |
| 483 | Too Many Hops | Dialog | (10) | | 483 | Too Many Hops | Dialog | (10) |
| 484 | Address Incomplete | Dialog | (2) | | 484 | Address Incomplete | Dialog | (2) |
| 485 | Ambiguous | Dialog | (2) | | 485 | Ambiguous | Dialog | (2) |
| 486 | Busy Here | Transaction | (11) | | 486 | Busy Here | Transaction | (11) |
| 487 | Request Terminated | Transaction | | | 487 | Request Terminated | Transaction | |
| 488 | Not Acceptable Here | Transaction | | | 488 | Not Acceptable Here | Transaction | |
| 489 | Bad Event | Usage | (12) | | 489 | Bad Event | Usage | (12) |
| 491 | Request Pending | Transaction | | | 491 | Request Pending | Transaction | |
| 493 | Undecipherable | Transaction | | | 493 | Undecipherable | Transaction | |
| 494 | Security Agreement Required | Transaction | | | 494 | Security Agreement Required | Transaction | |
| 500/5xx | Server Internal Error | Transaction | (13) | | 500/5xx | Server Internal Error | Transaction | (13) |
| 501 | Not Implemented | Usage | (2) | | 501 | Not Implemented | Usage | (3) |
| 502 | Bad Gateway | Dialog | (14) | | 502 | Bad Gateway | Dialog | (14) |
| 503 | Service Unavailable | Transaction | (15) | | 503 | Service Unavailable | Transaction | (15) |
| 504 | Server Time-Out | Transaction | (16) | | 504 | Server Time-Out | Transaction | (16) |
| 505 | Version Not Supported | Transaction | | | 505 | Version Not Supported | Transaction | |
| 513 | Message Too Large | Transaction | | | 513 | Message Too Large | Transaction | |
| 580 | Precondition Failure | Transaction | | | 580 | Precondition Failure | Transaction | |
| 600/6xx | Busy Everywhere | Transaction | (17) | | 600/6xx | Busy Everywhere | Transaction | (17) |
| 603 | Decline | Transaction | | | 603 | Decline | Transaction | |
| 604 | Does Not Exist Anywhere | Dialog | (2) | | 604 | Does Not Exist Anywhere | Dialog | (2) |
| 606 | Not Acceptable | Transaction | | | 606 | Not Acceptable | Transaction | |
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| 604 | Does Not Exist Anywhere | Dialog | (2) | | 604 | Does Not Exist Anywhere | Dialog | (2) |
| 606 | Not Acceptable | Transaction | | | 606 | Not Acceptable | Transaction | |
+---------+---------------------------------+-------------+-------+ +---------+---------------------------------+-------------+-------+
Table 2 Table 2
(1) 402 Payment Required: This is a reserved response code. If (1) 402 Payment Required: This is a reserved response code. If
encountered, it should be treated as an unrecognized 4xx. encountered, it should be treated as an unrecognized 4xx.
(2) 404 Not Found: (2) 404 Not Found:
410 Gone: 410 Gone:
416 Unsupported URI Scheme: 416 Unsupported URI Scheme:
484 Address Incomplete: 484 Address Incomplete:
485 Ambiguous: 485 Ambiguous:
604 Does Not Exist Anywhere: 604 Does Not Exist Anywhere:
The Request-URI that is being rejected is the remote target set by The Request-URI that is being rejected is the remote target set by
the Contact provided by the peer. Getting this response means the Contact provided by the peer. Getting this response means
something has gone fundamentally wrong with the dialog state. that something has gone fundamentally wrong with the dialog state.
(3) 405 Method Not Allowed: (3) 405 Method Not Allowed:
501 Not Implemented: 501 Not Implemented:
Either of these responses would be aberrant in our example Either of these responses would be aberrant in our example
scenario since support for the NOTIFY method is required by the scenario since support for the NOTIFY method is required by the
usage. In this case, the UA knows the condition is unrecoverable usage. In this case, the UA knows the condition is unrecoverable
and should stop sending NOTIFYs on the usage. Any refresh and should stop sending NOTIFYs on the usage. Any refresh
subscriptions should be rejected. In general, these errors will subscriptions should be rejected. In general, these errors will
affect at most the usage. If the request was not integral to the affect at most the usage. If the request was not integral to the
usage (it used an unknown method, or was an INFO inside an INVITE usage (it used an unknown method, or was an INFO inside an INVITE
usage for example), only the transaction is affected. usage, for example), only the transaction will be affected.
(4) 408 Request Timeout: Receiving a 408 will have the same effect (4) 408 Request Timeout: Receiving a 408 will have the same effect
on usages and dialogs as a real transaction timeout as described on usages and dialogs as a real transaction timeout as described
in Section 5.2. in Section 5.2.
(5) 422 Session Interval Too Small: This response does not make (5) 422 Session Interval Too Small: This response does not make
sense for any mid-usage request. If it is received, an element in sense for any mid-usage request. If it is received, an element in
the path of the request is violating protocol, and the recipient the path of the request is violating protocol, and the recipient
should treat this as it would an unknown 4xx response. should treat this as it would an unknown 4xx response.
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only the usage in which the request occurs. No other usages are only the usage in which the request occurs. No other usages are
affected. If the response included a Retry-After header field, affected. If the response included a Retry-After header field,
further requests in that usage should not be sent until the further requests in that usage should not be sent until the
indicated time has past. Requests in other usages may still be indicated time has past. Requests in other usages may still be
sent at any time. sent at any time.
(8) 481 Call/Transaction Does Not Exist: This response indicates (8) 481 Call/Transaction Does Not Exist: This response indicates
that the peer has lost its copy of the dialog usage state. The that the peer has lost its copy of the dialog usage state. The
dialog itself should not be destroyed unless this was the last dialog itself should not be destroyed unless this was the last
usage. usage.
The effects of a 481 on a dialog and its usages are the most The effects of a 481 on a dialog and its usages are the most
ambiguous of any final response. There are implementations that ambiguous of any final response. There are implementations that
have chosen the meaning recommended here, and others that destroy have chosen the meaning recommended here, and others that destroy
the entire dialog without regard to the number of outstanding the entire dialog without regard to the number of outstanding
usages. Going forward with this clarification will allow those usages. Going forward with this clarification will allow those
deployed implementations that assumed only the usage was destroyed deployed implementations that assumed only the usage was destroyed
to work with a wider number of implementations. Those that made to work with a wider number of implementations. Existing
the other choice will continue to function as they do now, implementations that destroy all other usages in the dialog will
suffering at most the same extra messages needed for a peer to continue to function as they do now, except that peers following
discover that that other usages have gone away that they currently the recommendation will attempt to do things with the other usages
do. However, the necessary clarification to RFC 3261 needs to and this element will return 481s for each of them until they are
make it very clear that the ability to terminate usages all gone. However, the necessary clarification to RFC 3261 needs
to make it very clear that the ability to terminate usages
independently from the overall dialog using a 481 is not independently from the overall dialog using a 481 is not
justification for designing new applications that count on justification for designing new applications that count on
multiple usages in a dialog. multiple usages in a dialog.
The 481 response to a CANCEL request has to be treated The 481 response to a CANCEL request has to be treated
differently. For CANCEL, a 481 means the UAS can't find a differently. For CANCEL, a 481 means the UAS can't find a
matching transaction. A 481 response to a cancel affects only the matching transaction. A 481 response to a CANCEL affects only the
CANCEL transaction. The usage associated with the INVITE is not CANCEL transaction. The usage associated with the INVITE is not
affected. affected.
(9) 482 Loop Detected: This response is aberrant mid-dialog. It (9) 482 Loop Detected: This response is aberrant mid-dialog. It
will only occur if the Record-Route header field was improperly will only occur if the Record-Route header field were improperly
constructed by the proxies involved in setting up the dialog's constructed by the proxies involved in setting up the dialog's
initial usage, or if a mid-dialog request forks and merges (which initial usage, or if a mid-dialog request forks and merges (which
should never happen). Future requests using this dialog state should never happen). Future requests using this dialog state
will also fail. will also fail.
An edge condition exists during RFC3263 failover at the element An edge condition exists during RFC 3263 failover at the
sending a request where the request effectively forks to element sending a request, where the request effectively forks
multiple destinations from the client. Some implementations to multiple destinations from the client. Some implementations
increase risk entering this edge condition by trying the next increase risk entering this edge condition by trying the next
potential location as determined by RFC3263 very rapidly if the potential location as determined by RFC 3263 very rapidly if
first does not immediately respond. In any situation where a the first does not immediately respond. In any situation where
client sends the same request to more than one endpoint, it a client sends the same request to more than one endpoint, it
must be prepared to receive a response from each branch (and must be prepared to receive a response from each branch (and
should choose a "best" response to act on following the same should choose a "best" response to act on following the same
guidelines as a forking proxy). In this particular race guidelines as a forking proxy). In this particular race
condition, if multiple branches respond, all but one will most condition, if multiple branches respond, all but one will most
likely return a 482 Merged Request. The client should select likely return a 482 Merged Request. The client should select
the remaining non-482 response as the "best" response. the remaining non-482 response as the "best" response.
(10) 483 Too Many Hops: Similar to 482, receiving this mid-dialog is (10) 483 Too Many Hops: Similar to 482, receiving this mid-dialog is
aberrant. Unlike 482, recovery may be possible by increasing Max- aberrant. Unlike 482, recovery may be possible by increasing Max-
Forwards (assuming that the requester did something strange like Forwards (assuming that the requester did something strange like
using a smaller value for Max-Forwards in mid-dialog requests than using a smaller value for Max-Forwards in mid-dialog requests than
it used for an initial request). If the request isn't tried with it used for an initial request). If the request isn't tried with
an increased Max-Forwards, then the agent should follow the an increased Max-Forwards, then the agent should follow the
Destroy Dialog actions. Destroy Dialog actions.
(11) 486 Busy Here: This response is nonsensical in our example (11) 486 Busy Here: This response is nonsensical in our example
scenario, or in any scenario where this response comes inside an scenario, or in any scenario where this response comes inside an
established usage. If it occurs in that context, it should be established usage. If it occurs in that context, it should be
treated as an unknown 4xx response. treated as an unknown 4xx response.
(12) 489 Bad Event: In our example scenario, [3] declares that the (12) 489 Bad Event: In our example scenario, [5] declares that the
subscription usage in which the NOTIFY is sent is terminated. subscription usage in which the NOTIFY is sent is terminated.
This response is only valid in the context of SUBSCRIBE and This response is only valid in the context of SUBSCRIBE and
NOTIFY. UAC behavior for receiving this response to other methods NOTIFY. UAC behavior for receiving this response to other methods
is not specified, but treating it as an unknown 4xx is a is not specified, but treating it as an unknown 4xx is a
reasonable practice. reasonable practice.
(13) 500 and 5xx unrecognized responses: If the response contains a (13) 500 and 5xx unrecognized responses: If the response contains a
Retry-After header field value, the server thinks the condition is Retry-After header field value, the server thinks the condition is
temporary and the request can be retried after the indicated temporary, and the request can be retried after the indicated
interval. If the response does not contain a Retry-After header interval. If the response does not contain a Retry-After header
field value, the UA may decide to retry after an interval of its field value, the UA may decide to retry after an interval of its
choosing or attempt to gracefully terminate the usage. Whether or choosing or attempt to gracefully terminate the usage. Whether or
not to terminate other usages depends on the application. If the not to terminate other usages depends on the application. If the
UA receives a 500 (or unrecognized 5xx) in response to an attempt UA receives a 500 (or unrecognized 5xx) in response to an attempt
to gracefully terminate this usage, it can treat this usage as to gracefully terminate this usage, it can treat this usage as
terminated. If this is the last usage sharing the dialog, the terminated. If this is the last usage sharing the dialog, the
dialog is also terminated. dialog is also terminated.
(14) 502 Bad Gateway: This response is aberrant mid-dialog. It will (14) 502 Bad Gateway: This response is aberrant mid-dialog. It will
only occur if the Record-Route header field was improperly only occur if the Record-Route header field were improperly
constructed by the proxies involved in setting up the dialog's constructed by the proxies involved in setting up the dialog's
initial usage. Future requests using this dialog state will also initial usage. Future requests using this dialog state will also
fail. fail.
(15) 503 Service Unavailable: As per [2], the logic handling (15) 503 Service Unavailable: As per [6], the logic handling
locating SIP servers for transactions may handle 503 requests locating SIP servers for transactions may handle 503 requests
(effectively sequentially forking at the endpoint based on DNS (effectively, sequentially forking at the endpoint based on DNS
results). If this process does not yield a better response, a 503 results). If this process does not yield a better response, a 503
may be returned to the transaction user. Like a 500 response, the may be returned to the transaction user. Like a 500 response, the
error is a complaint about this transaction, not the usage. error is a complaint about this transaction, not the usage.
Because this response occurred in the context of an established Because this response occurred in the context of an established
usage (hence an existing dialog), the route-set has already been usage (hence an existing dialog), the route-set has already been
formed and any opportunity to try alternate servers (as formed and any opportunity to try alternate servers (as
recommended in [1]) has been exhausted by the RFC3263 logic. recommended in [1]) has been exhausted by the RFC3263 logic.
(16) 504 Server Time-out: It is not obvious under what circumstances (16) 504 Server Time-out: It is not obvious under what circumstances
this response would be returned to a request in an existing this response would be returned to a request in an existing
skipping to change at page 16, line 36 skipping to change at page 15, line 46
This usage, and any other usages sharing the dialog are This usage, and any other usages sharing the dialog are
unaffected. If the response does not contain a Retry-After header unaffected. If the response does not contain a Retry-After header
field value, the UA may decide to retry after an interval of its field value, the UA may decide to retry after an interval of its
choosing or attempt to gracefully terminate the usage. Whether or choosing or attempt to gracefully terminate the usage. Whether or
not to terminate other usages depends on the application. If the not to terminate other usages depends on the application. If the
UA receives a 600 (or unrecognized 6xx) in response to an attempt UA receives a 600 (or unrecognized 6xx) in response to an attempt
to gracefully terminate this usage, it can treat this usage as to gracefully terminate this usage, it can treat this usage as
terminated. If this is the last usage sharing the dialog, the terminated. If this is the last usage sharing the dialog, the
dialog is also terminated. dialog is also terminated.
5.2. Transaction timeouts 5.2. Transaction Timeouts
[1] states that a UAC should terminate a dialog (by sending a BYE) if [1] states that a UAC should terminate a dialog (by sending a BYE) if
no response is received for a request sent within a dialog. This no response is received for a request sent within a dialog. This
recommendation should have been limited to the invite usage instead recommendation should have been limited to the invite usage instead
of the whole dialog. [3] states that a timeout for a NOTIFY removes a of the whole dialog. [5] states that a timeout for a NOTIFY removes a
subscription, but a SUBSCRIBE that fails with anything other than a subscription, but a SUBSCRIBE that fails with anything other than a
481 does not. Given these statements, it is unclear whether a 481 does not. Given these statements, it is unclear whether a
refresh SUBSCRIBE issued in a dialog shared with an invite usage refresh SUBSCRIBE issued in a dialog shared with an invite usage
destroys either usage or the dialog if it times out. destroys either usage or the dialog if it times out.
Generally, a transaction timeout should affect only the usage in Generally, a transaction timeout should affect only the usage in
which the transaction occurred. Other uses sharing the dialog should which the transaction occurred. Other uses sharing the dialog should
not be affected. In the worst case of timeout due to total transport not be affected. In the worst case of timeout due to total transport
failure, it may require multiple failed messages to remove all usages failure, it may require multiple failed messages to remove all usages
from a dialog (at least one per usage). from a dialog (at least one per usage).
There are some mid-dialog messages that never belong to any usage. There are some mid-dialog messages that never belong to any usage.
If they timeout, they will have no effect on the dialog or its If they timeout, they will have no effect on the dialog or its
usages. usages.
5.3. Matching requests to usages 5.3. Matching Requests to Usages
For many mid-dialog requests, identifying the usage they belong to is For many mid-dialog requests, identifying the usage they belong to is
obvious. A dialog can have at most one invite usage, so any INVITE, obvious. A dialog can have at most one invite usage, so any INVITE,
UPDATE, PRACK, ACK, CANCEL, BYE, or INFO requests belong to it. The UPDATE, PRACK, ACK, CANCEL, BYE, or INFO requests belong to it. The
usage (i.e. the particular subscription) SUBSCRIBE, NOTIFY, and REFER usage (i.e. the particular subscription) SUBSCRIBE, NOTIFY, and REFER
requests belong to can be determined from the Event header field of requests belong to can be determined from the Event header field of
the request. REGISTER requests within a (pseudo)-dialog belong to the request. REGISTER requests within a (pseudo)-dialog belong to
the registration usage. (As mentioned before, implementations aren't the registration usage. (As mentioned before, implementations aren't
mixing registration usages with other usages, so this document isn't mixing registration usages with other usages, so this document isn't
exploring the consequences of that bad behavior). exploring the consequences of that bad behavior).
According to [1], "an OPTIONS request received within a dialog According to [1], "an OPTIONS request received within a dialog
generates a 200 OK response that is identical to one constructed generates a 200 OK response that is identical to one constructed
outside a dialog and does not have any impact on that dialog". Thus outside a dialog and does not have any impact on that dialog". Thus,
OPTIONS does not belong to any usage. Only those failures discussed OPTIONS does not belong to any usage. Only those failures discussed
in Section 5.1 and Section 5.2 that destroy entire dialogs will have in Section 5.1 and Section 5.2 that destroy entire dialogs will have
any effect on the usages sharing the dialog with a failed OPTIONS any effect on the usages sharing the dialog with a failed OPTIONS
request. request.
MESSAGE requests are discouraged inside a dialog. Implementations MESSAGE requests are discouraged inside a dialog. Implementations
are restricted from creating a usage for the purpose of carrying a are restricted from creating a usage for the purpose of carrying a
sequence of MESSAGE requests (though some implementations use it that sequence of MESSAGE requests (though some implementations use it that
way, against the standard recommendation). A failed MESSAGE way, against the standard recommendation). A failed MESSAGE
occurring inside an existing dialog will have similar effects on the occurring inside an existing dialog will have similar effects on the
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Mid-dialog requests with unknown methods cannot be matched with a Mid-dialog requests with unknown methods cannot be matched with a
usage. Servers will return a failure response (likely a 501). The usage. Servers will return a failure response (likely a 501). The
effect on the dialog and its usages at either the client or the effect on the dialog and its usages at either the client or the
server should be similar to that of a failed OPTIONS request. server should be similar to that of a failed OPTIONS request.
These guidelines for matching messages to usages (or determining These guidelines for matching messages to usages (or determining
there is no usage) apply equally when acting as a UAS, a UAC, or any there is no usage) apply equally when acting as a UAS, a UAC, or any
third party tracking usage and dialog state by inspecting all third party tracking usage and dialog state by inspecting all
messages between two endpoints. messages between two endpoints.
5.4. Target refresh requests 5.4. Target Refresh Requests
Target refresh requests update the remote target of a dialog when Target refresh requests update the remote target of a dialog when
they are successfully processed. The currently defined target they are successfully processed. The currently defined target
refresh requests are INVITE, UPDATE, SUBSCRIBE and NOTIFY (clarified refresh requests are INVITE, UPDATE, SUBSCRIBE, NOTIFY, and REFER
in a bug against RFC3565) and REFER (clarified in a bug against [7]).
RFC3515 [4]).
The remote target is part of the dialog state. When a target refresh The remote target is part of the dialog state. When a target refresh
request affects it, it affects it for ALL usages sharing that dialog. request affects it, it affects it for ALL usages sharing that dialog.
If a subscription and invite usage are sharing a dialog, sending a If a subscription and invite usage are sharing a dialog, sending a
refresh SUBSCRIBE with a different contact will cause reINVITEs from refresh SUBSCRIBE with a different contact will cause reINVITEs from
the peer to go to that different contact. the peer to go to that different contact.
A UAS will only update the remote target if it sends a 200 class A UAS will only update the remote target if it sends a 200 class
response to a target refresh request. A UAC will only update the response to a target refresh request. A UAC will only update the
remote target if it receives a 200 class response to a target refresh remote target if it receives a 200 class response to a target refresh
request. Again, any update to a dialog's remote target affects all request. Again, any update to a dialog's remote target affects all
usages of that dialog. usages of that dialog.
There is known ambiguity around the effects of provisional responses There is known ambiguity around the effects of provisional responses
on remote targets that future specification will attempt to clarify. on remote targets that a future specification will attempt to
Furthermore, because the remote target is part of the dialog state, clarify. Furthermore, because the remote target is part of the
not any usage state, there is ambiguity in having target refresh dialog state, not any usage state, there is ambiguity in having
requests in progress simultaneously on multiple usages in the same target refresh requests in progress simultaneously on multiple usages
dialog. Implementation designers should consider these conditions in the same dialog. Implementation designers should consider these
with care. conditions with care.
5.5. Refreshing and Terminating Usages 5.5. Refreshing and Terminating Usages
Subscription and registration usages expire over time and must be Subscription and registration usages expire over time and must be
refreshed (with a refresh SUBSCRIBE for example). This expiration is refreshed (with a refresh SUBSCRIBE, for example). This expiration
usage state, not dialog state. If several subscriptions share a is usage state, not dialog state. If several subscriptions share a
dialog, refreshing one of them has no effect on the expiration of the dialog, refreshing one of them has no effect on the expiration of the
others. others.
Normal termination of a usage has no effect on other usages sharing Normal termination of a usage has no effect on other usages sharing
the same dialog. For instance terminating a subscription with a the same dialog. For instance, terminating a subscription with a
NOTIFY/Subscription-State: terminated will not terminate an invite NOTIFY/Subscription-State: terminated will not terminate an invite
usage sharing its dialog. Likewise, ending an invite usage with a usage sharing its dialog. Likewise, ending an invite usage with a
BYE does not terminate any active Event: refer subscriptions BYE does not terminate any active Event: refer subscriptions
established on that dialog. established on that dialog.
5.6. Refusing new usages 5.6. Refusing New Usages
As the survey of the effect of failure responses shows, care must be As the survey of the effect of failure responses shows, care must be
taken when refusing a new usage inside an existing dialog. Choosing taken when refusing a new usage inside an existing dialog. Choosing
the wrong response code will terminate the dialog and all of its the wrong response code will terminate the dialog and all of its
usages. Generally, returning a 603 Decline is the safest way to usages. Generally, returning a 603 Decline is the safest way to
refuse a new usage. refuse a new usage.
5.7. Replacing usages 5.7. Replacing Usages
[6] defines a mechanism through which one usage can replace another. [8] defines a mechanism through which one usage can replace another.
It can be used, for example, to associate the two dialogs a transfer It can be used, for example, to associate the two dialogs in which a
target is involved in during an attended transfer. It is written transfer target is involved during an attended transfer. It is
using the term "dialog", but its intent was to only affect the invite written using the term "dialog", but its intent was only to affect
usage of the dialog it targets. Any other usages inside that dialog the invite usage of the dialog it targets. Any other usages inside
are unaffected. For some applications, the other usages may no that dialog are unaffected. For some applications, the other usages
longer make sense, and the application may terminate them as well. may no longer make sense, and the application may terminate them as
well.
However, the interactions between Replaces and multiple dialog usages However, the interactions between Replaces and multiple dialog usages
have not been well explored. More discussion of this topic is have not been well explored. More discussion of this topic is
needed. Implementers should avoid this scenario completely. needed. Implementers should avoid this scenario completely.
6. Avoiding Multiple Usages 6. Avoiding Multiple Usages
Processing multiple usages correctly is not completely understood. Processing multiple usages correctly is not completely understood.
What is understood is difficult to implement and is very likely to What is understood is difficult to implement and is very likely to
lead to interoperability problems. The best way to avoid the trouble lead to interoperability problems. The best way to avoid the trouble
skipping to change at page 19, line 43 skipping to change at page 18, line 52
Unfortunately, there are existing applications, like transfer, that Unfortunately, there are existing applications, like transfer, that
currently entail multiple usages, so the simple solution of "don't do currently entail multiple usages, so the simple solution of "don't do
it" will require some transitional work. This section looks at the it" will require some transitional work. This section looks at the
pressures that led to these existing multiple usages and suggests pressures that led to these existing multiple usages and suggests
alternatives. alternatives.
When executing a transfer, the transferor and transferee currently When executing a transfer, the transferor and transferee currently
share an invite usage and a subscription usage within the dialog share an invite usage and a subscription usage within the dialog
between them. This is a result of sending the REFER request within between them. This is a result of sending the REFER request within
the dialog established by the invite usage. Implementations were led the dialog established by the invite usage. Implementations were led
to this behavior by these primary pressures: to this behavior by these primary problems:
1. There was no way to ensure that a REFER on a new dialog would 1. There was no way to ensure that a REFER on a new dialog would
reach the particular endpoint involved in a transfer. Many reach the particular endpoint involved in a transfer. Many
factors, including details of implementations and changes in factors, including details of implementations and changes in
proxy routing between an INVITE and a REFER could cause the REFER proxy routing between an INVITE and a REFER could cause the REFER
to be sent to the wrong place. Sending the REFER down the to be sent to the wrong place. Sending the REFER down the
existing dialog ensured it got to the same endpoint with which existing dialog ensured it got to the same endpoint with which
the dialog was established. the dialog was established.
2. It was unclear how to associate an existing invite usage with a 2. It was unclear how to associate an existing invite usage with a
REFER arriving on a new dialog, where it was completely obvious REFER arriving on a new dialog, where it was completely obvious
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factors, including details of implementations and changes in factors, including details of implementations and changes in
proxy routing between an INVITE and a REFER could cause the REFER proxy routing between an INVITE and a REFER could cause the REFER
to be sent to the wrong place. Sending the REFER down the to be sent to the wrong place. Sending the REFER down the
existing dialog ensured it got to the same endpoint with which existing dialog ensured it got to the same endpoint with which
the dialog was established. the dialog was established.
2. It was unclear how to associate an existing invite usage with a 2. It was unclear how to associate an existing invite usage with a
REFER arriving on a new dialog, where it was completely obvious REFER arriving on a new dialog, where it was completely obvious
what the association was when the REFER came on the invite what the association was when the REFER came on the invite
usage's dialog. usage's dialog.
3. There were concerns with authorizing out-of-dialog REFERs. The 3. There were concerns with authorizing out-of-dialog REFERs. The
authorization policy for REFER in most implementations piggybacks authorization policy for REFER in most implementations piggybacks
on the authorization policy for INVITE (which is, in most cases, on the authorization policy for INVITE (which is, in most cases,
based simply on "I placed or answered this call"). based simply on "I placed or answered this call").
GRUUs [7] have been defined specifically to address problem 1 by Globally Routable User Agent (UA) URIs (GRUUs) [9] have been defined
providing a URI that will reach one specific user-agent. The Target- specifically to address problem 1 by providing a URI that will reach
Dialog header field [9] was created to address problems 2 and 3. one specific user-agent. The Target-Dialog header field [10] was
This header field allows a request to indicate the dialog identifiers created to address problems 2 and 3. This header field allows a
of some other dialog, providing association with that other dialog request to indicate the dialog identifiers of some other dialog,
that can be used in an authorization decision. providing association with the other dialog that can be used in an
authorization decision.
The Join [5] and Replaces [6] mechanisms can also be used to address The Join [11] and Replaces [8] mechanisms can also be used to address
problem 1. When using this technique, a new request is sent outside problem 1. When using this technique, a new request is sent outside
any dialog with the expectation that it will fork to possibly many any dialog with the expectation that it will fork to possibly many
endpoints, including the one we're interested in. This request endpoints, including the one we're interested in. This request
contains a header field listing the dialog identifiers of a dialog in contains a header field listing the dialog identifiers of a dialog in
progress. Only the endpoint holding a dialog matching those progress. Only the endpoint holding a dialog matching those
identifiers will accept the request. The other endpoints the request identifiers will accept the request. The other endpoints the request
may have forked to will respond with an error. This mechanism is may have forked to will respond with an error. This mechanism is
reasonably robust, failing only when the routing logic for out-of- reasonably robust, failing only when the routing logic for out-of-
dialog requests changes such that the new request does not arrive at dialog requests changes such that the new request does not arrive at
the endpoint holding the dialog of interest. the endpoint holding the dialog of interest.
The reachability aspects of using a GRUU to address problem 1 can be The reachability aspects of using a GRUU to address problem 1 can be
combined with the association-with-other-dialogs aspects of the Join/ combined with the association-with-other-dialogs aspects of the Join/
Replaces and Target-Dialog mechanisms. A REFER request sent out-of- Replaces and Target-Dialog mechanisms. A REFER request sent out-of-
dialog can be sent towards a GRUU, and identify an existing dialog as dialog can be sent towards a GRUU, and identify an existing dialog as
part of the context the receiver should use. The Target-Dialog part of the context the receiver should use. The Target-Dialog
header field can be included in the REFER listing the dialog this header field can be included in the REFER listing the dialog this
REFER is associated with. Figure 5 sketches how this could be used REFER is associated with. Figure 5 sketches how this could be used
to achieve transfer without reusing a dialog. For simplicity, the to achieve transfer without reusing a dialog. For simplicity, the
diagram and message details do not show the server at example.com diagram and message details do not show the server at example.com
that will be involved in routing the GRUU. Refer to [7] for those that will be involved in routing the GRUU. Refer to [9] for those
details. details.
Alice Bob Carol Alice Bob Carol
| | | | | |
| F1 INVITE (Bob's AOR) | | | F1 INVITE (Bob's AOR) | |
| Call-ID: (call-id one) | | | Call-ID: (call-id one) | |
| Contact: (Alice's-GRUU) | | | Contact: (Alice's-GRUU) | |
|------------------------------->| | |------------------------------->| |
| F2 200 OK | | | F2 200 OK | |
| To: <>;tag=totag1 | | | To: <>;tag=totag1 | |
skipping to change at page 23, line 24 skipping to change at page 22, line 37
SIP/2.0 200 OK SIP/2.0 200 OK
Supported: gruu Supported: gruu
To: <sip:carol@example.com>;tag=totag2 To: <sip:carol@example.com>;tag=totag2
From: <sip:bob@example.com>;tag=fromtag2 From: <sip:bob@example.com>;tag=fromtag2
Call-ID: 23rasdnfoa39i4jnasdf@bob.example.com Call-ID: 23rasdnfoa39i4jnasdf@bob.example.com
Contact: <sip:carol@example.com;gr=urn:uuid:(Carol's UA's bits)> Contact: <sip:carol@example.com;gr=urn:uuid:(Carol's UA's bits)>
After consulting Carol, Bob places her on hold and refers Alice to After consulting Carol, Bob places her on hold and refers Alice to
her using message F5. Notice that the Refer-To URI is Carol's GRUU, her using message F5. Notice that the Refer-To URI is Carol's GRUU,
and that this is on a different Call-ID than message F1. (The URI in and that this is on a different Call-ID than message F1. (The URI in
the Refer-To header is line-broken for readability in this draft, it the Refer-To header is line-broken for readability in this document;
would not be valid to break the URI this way in a real message) it would not be valid to break the URI this way in a real message.)
Message F5 (abridged, detailing pertinent fields) Message F5 (abridged, detailing pertinent fields)
REFER sip:aanewmr203raswdf@example.com SIP/2.0 REFER sip:aanewmr203raswdf@example.com SIP/2.0
Call-ID: 39fa99r0329493asdsf3n@bob.example.com Call-ID: 39fa99r0329493asdsf3n@bob.example.com
Refer-To: <sip:carol@example.com;g=urn:uid:(Carol's UA's bits) Refer-To: <sip:carol@example.com;g=urn:uid:(Carol's UA's bits)
?Replaces=23rasdnfoa39i4jnasdf@bob.example.com; ?Replaces=23rasdnfoa39i4jnasdf@bob.example.com;
to-tag=totag2;from-tag=fromtag2> to-tag=totag2;from-tag=fromtag2>
Target-Dialog: 13jfdwer230jsdw@alice.example.com; Target-Dialog: 13jfdwer230jsdw@alice.example.com;
local-tag=fromtag1;remote-tag=totag1 local-tag=fromtag1;remote-tag=totag1
skipping to change at page 23, line 38 skipping to change at page 23, line 4
REFER sip:aanewmr203raswdf@example.com SIP/2.0 REFER sip:aanewmr203raswdf@example.com SIP/2.0
Call-ID: 39fa99r0329493asdsf3n@bob.example.com Call-ID: 39fa99r0329493asdsf3n@bob.example.com
Refer-To: <sip:carol@example.com;g=urn:uid:(Carol's UA's bits) Refer-To: <sip:carol@example.com;g=urn:uid:(Carol's UA's bits)
?Replaces=23rasdnfoa39i4jnasdf@bob.example.com; ?Replaces=23rasdnfoa39i4jnasdf@bob.example.com;
to-tag=totag2;from-tag=fromtag2> to-tag=totag2;from-tag=fromtag2>
Target-Dialog: 13jfdwer230jsdw@alice.example.com; Target-Dialog: 13jfdwer230jsdw@alice.example.com;
local-tag=fromtag1;remote-tag=totag1 local-tag=fromtag1;remote-tag=totag1
Supported: gruu Supported: gruu
Contact: <sip:bob@example.com;gr=urn:uuid:(Bob's UA's bits)> Contact: <sip:bob@example.com;gr=urn:uuid:(Bob's UA's bits)>
Alice uses the information in the Target-Dialog header field to Alice uses the information in the Target-Dialog header field to
determine that this REFER is associated with the dialog she already determine that this REFER is associated with the dialog she already
has in place with Bob. Alice is now in a position to use the same has in place with Bob. Alice is now in a position to use the same
admission policy she used for in-dialog REFERs: "Do I have a call admission policy she used for in-dialog REFERs: "Do I have a call
with this person?". She accepts the REFER. sends Bob the obligatory with this person?". She accepts the REFER, sends Bob the obligatory
immediate NOTIFY, and proceeds to INVITE Carol with message F6. immediate NOTIFY, and proceeds to INVITE Carol with message F6.
Message F6 (abridged, detailing pertinent fields) Message F6 (abridged, detailing pertinent fields)
sip:carol@example.com;gr=urn:uuid:(Carol's UA's bits) sip:carol@example.com;gr=urn:uuid:(Carol's UA's bits)
\ / \ /
\ / \ /
| | | |
v v v v
INVITE SIP/2.0 INVITE SIP/2.0
Call-ID: 4zsd9f234jasdfasn3jsad@alice.example.com Call-ID: 4zsd9f234jasdfasn3jsad@alice.example.com
Replaces: 23rasdnfoa39i4jnasdf@bob.example.com; Replaces: 23rasdnfoa39i4jnasdf@bob.example.com;
to-tag=totag2;from-tag=fromtag2 to-tag=totag2;from-tag=fromtag2
Supported: gruu Supported: gruu
Contact: <sip:alice@example.com;gr=urn:uuid:(Alice's UA's bits)> Contact: <sip:alice@example.com;gr=urn:uuid:(Alice's UA's bits)>
Carol accepts Alice's invitation to replace her dialog (invite usage) Carol accepts Alice's invitation to replace her dialog (invite usage)
with Bob and notifies him that the REFERenced INVITE succeeded with with Bob, and notifies him that the REFERenced INVITE succeeded with
F7: F7:
Message F7 (abridged, detailing pertinent fields) Message F7 (abridged, detailing pertinent fields)
NOTIFY sip:boaiidfjjereis@example.com SIP/2.0 NOTIFY sip:boaiidfjjereis@example.com SIP/2.0
Subscription-State: terminated;reason=noresource Subscription-State: terminated;reason=noresource
Call-ID: 39fa99r0329493asdsf3n@bob.example.com Call-ID: 39fa99r0329493asdsf3n@bob.example.com
Contact: <sip:alice@example.com;gr=urn:uuid:(Alice's UA's bits)> Contact: <sip:alice@example.com;gr=urn:uuid:(Alice's UA's bits)>
Content-Type: message/sipfrag Content-Type: message/sipfrag
skipping to change at page 24, line 45 skipping to change at page 24, line 4
7. Security Considerations 7. Security Considerations
Handling multiple usages within a single dialog is complex and Handling multiple usages within a single dialog is complex and
introduces scenarios where the right thing to do is not clear. The introduces scenarios where the right thing to do is not clear. The
ambiguities described here can result in unexpected disruption of ambiguities described here can result in unexpected disruption of
communication if response codes are chosen carelessly. Furthermore, communication if response codes are chosen carelessly. Furthermore,
these ambiguities could be exploited, particularly by third-parties these ambiguities could be exploited, particularly by third-parties
injecting unauthenticated requests or inappropriate responses. injecting unauthenticated requests or inappropriate responses.
Implementations choosing to create or accept multiple usages within a Implementations choosing to create or accept multiple usages within a
dialog should give extra attention to the security considerations in dialog should give extra attention to the security considerations in
[1], especially those concerning authenticity of requests and [1], especially those concerning the authenticity of requests and
processing of responses. processing of responses.
Service implementations should carefully consider the effects on Service implementations should carefully consider the effects on
their service of peers making different choices in these areas of their service of peers making different choices in these areas of
ambiguity. A service that requires multiple usages needs to pay ambiguity. A service that requires multiple usages needs to pay
particular attention to the effect on service and network utilization particular attention to the effect on service and network utilization
when a client fails to destroy a dialog the service believes should when a client fails to destroy a dialog the service believes should
be destroyed. A service that disallows multiple usages should be destroyed. A service that disallows multiple usages should
consider the effect on clients that, for instance, destroy the entire consider the effect on clients that, for instance, destroy the entire
dialog when only a usage should be torn down. In the worst case of a dialog when only a usage should be torn down. In the worst case of a
service deployed into a network with a large number of misbehaving service deployed into a network with a large number of misbehaving
clients trying to create multiple usages in an automated fashion, a clients trying to create multiple usages in an automated fashion, a
retry storm similar to an avalanche restart could be induced. retry storm similar to an avalanche restart could be induced.
8. IANA Considerations 8. Conclusion
This document has no actions for IANA.
9. Conclusion
Handling multiple usages within a single dialog is complex and Handling multiple usages within a single dialog is complex and
introduces scenarios where the right thing to do is not clear. introduces scenarios where the right thing to do is not clear.
Implementations should avoid entering into multiple usages whenever Implementations should avoid entering into multiple usages whenever
possible. New applications should be designed to never introduce possible. New applications should be designed to never introduce
multiple usages. multiple usages.
There are some accepted SIP practices, including transfer, that There are some accepted SIP practices, including transfer, that
currently require multiple usages. Recent work, most notably GRUU, currently require multiple usages. Recent work, most notably GRUU,
makes those practices unnecessary. The standardization of those makes those practices unnecessary. The standardization of those
practices and the implementations should be revised as soon as practices and the implementations should be revised as soon as
possible to use only single-usage dialogs. possible to use only single-usage dialogs.
10. Acknowledgments 9. Acknowledgments
The ideas in this draft have been refined over several IETF meetings The ideas in this document have been refined over several IETF
with many participants. Significant contribution was provided by meetings with many participants. Significant contribution was
Adam Roach, Alan Johnston, Ben Campbell, Cullen Jennings, Jonathan provided by Adam Roach, Alan Johnston, Ben Campbell, Cullen Jennings,
Rosenberg, Paul Kyzivat, and Rohan Mahy. Members of the reSIProcate Jonathan Rosenberg, Paul Kyzivat, and Rohan Mahy. Members of the
project also shared their difficulties and discoveries while reSIProcate project also shared their difficulties and discoveries
implementing multiple-usage dialog handlers. while implementing multiple-usage dialog handlers.
11. Informative References 10. Informative References
[1] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., [1] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002. Session Initiation Protocol", RFC 3261, June 2002.
[2] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol [2] Levin, O., "Suppression of Session Initiation Protocol (SIP)
(SIP): Locating SIP Servers", RFC 3263, June 2002. REFER Method Implicit Subscription", RFC 4488, May 2006.
[3] Roach, A., "Session Initiation Protocol (SIP)-Specific Event [3] Burger, E. and M. Dolly, "A Session Initiation Protocol (SIP)
Event Package for Key Press Stimulus (KPML)", RFC 4730,
November 2006.
[4] Niemi, A., "Session Initiation Protocol (SIP) Extension for
Event State Publication", RFC 3903, October 2004.
[5] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002. Notification", RFC 3265, June 2002.
[4] Sparks, R., "The Session Initiation Protocol (SIP) Refer [6] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol
Method", RFC 3515, April 2003. (SIP): Locating SIP Servers", RFC 3263, June 2002.
[5] Mahy, R. and D. Petrie, "The Session Initiation Protocol (SIP) [7] Sparks, R., "The Session Initiation Protocol (SIP) Refer
"Join" Header", RFC 3911, October 2004. Method", RFC 3515, April 2003.
[6] Mahy, R., Biggs, B., and R. Dean, "The Session Initiation [8] Mahy, R., Biggs, B., and R. Dean, "The Session Initiation
Protocol (SIP) "Replaces" Header", RFC 3891, September 2004. Protocol (SIP) "Replaces" Header", RFC 3891, September 2004.
[7] Rosenberg, J., "Obtaining and Using Globally Routable User [9] Rosenberg, J., "Obtaining and Using Globally Routable User
Agent (UA) URIs (GRUU) in the Session Initiation Protocol Agent (UA) URIs (GRUU) in the Session Initiation Protocol
(SIP)", draft-ietf-sip-gruu-11 (work in progress), (SIP)", Work in Progress, June 2006.
October 2006.
[8] Levin, O., "Suppression of Session Initiation Protocol (SIP)
REFER Method Implicit Subscription", RFC 4488, May 2006.
[9] Rosenberg, J., "Request Authorization through Dialog [10] Rosenberg, J., "Request Authorization through Dialog
Identification in the Session Initiation Protocol (SIP)", Identification in the Session Initiation Protocol (SIP)",
RFC 4538, June 2006. RFC 4538, June 2006.
[10] Niemi, A., "Session Initiation Protocol (SIP) Extension for [11] Mahy, R. and D. Petrie, "The Session Initiation Protocol (SIP)
Event State Publication", RFC 3903, October 2004. "Join" Header", RFC 3911, October 2004.
[11] Dolly, M. and E. Burger, "A Session Initiation Protocol (SIP)
Event Package for Key Press Stimulus (KPML)",
draft-ietf-sipping-kpml-08 (work in progress), July 2006.
Appendix A. Change Log
RFC-EDITOR: Please remove this entire Change Log section while
formatting this document for publication.
A.1. draft-ietf-05->draft-ietf-06
o Noted that 481 to CANCEL is special and affects only the CANCEL
transaction, not any associated INVITE usage.
o Noted that certain errors to BYE can effectively terminate a usage
in the usage creation and destruction overview.
A.2. draft-ietf-04->draft-ietf-05
o Fixed the flaw with the GRUU message description text that Paul
caught.
o Integrated Paul's table and further simplified the comment/
exception text.
A.3. draft-ietf-03->draft-ietf-04
o Many minor editorial fixes addressing WGLC comments
o Aligned with changes to GRUU
o Added a short overview
o Added a table summarizing the survey of responses and removed the
description from those responses that were not exceptional.
A.4. draft-ietf-02->draft-ietf-03
o Removed discussion of the retargetting affect of provisional
responses - that is a general problem that will now be addressed
in SIP.
o Added a Security Considerations section (blush) summarizing points
from the document and the list discussion.
o Added a no-op IANA Considerations section.
A.5. draft-ietf-01->draft-ietf-02
o Incorporated editorial-fix contributions from the list
o Noted that REFERs using norefersub (RFC4488) don't create a new
subscribe usage
o Changed the affect of 403 to affect only the transaction, not the
usage. This is motivated by text in 3261 (bottom of page 87 -
pointed out by Brian Stucker) which states that a UA receiving a
non-2xx final response to a re-INVITE must leave the session
parameters unchanged as if the re-INVITE had not been issued.
There are other recommendations in this document that violate that
normative must (404,410, etc) but on review, I believe they are
correct (except for 403) and that this text in 3261 needs to be
updated to recognize the conditions under which they're sent.
o Added text concerning the race condition wherein endpoints failing
over rapidly to 3263 destinations may stimulate a merged-request
response.
o Corrected the 481 inconsistency Paul Kyzivat pointed out (by
removing the inconsistent paragraph)
A.6. draft-ietf-00->draft-ietf-01
o Changed 481 to only affect the usage the response occurred in,
closing the last open issue. Added some text justifying this
recommendation.
o Added 422 Session Interval Too Small
o Added 417 Unknown Resource-Priority
o Added 428 Use Identity Header
o Added 436 Bad Identity-Info
o Added 437 Unsupported Certificate
o Added 438 Invalid Identity header
o Added a section categorizing messages that create and destroy
usages
o Made sure all descriptions in Section 5 addressed the generic
multi-usage case.
o Clarified that the mechanics described in matching messages to
usages applied equally to UACs and UASs.
o More explicitly noted that REFER creates a subscribe-usage
A.7. draft-sparks-01->draft-ietf-00
o Draft rename
A.8. draft-sparks-00->01
o Changed 480 to affect only the usage the response occurred in.
o Closed the open issue on 482. Usages and dialogs are destroyed
even though there is an edge condition in which the response is
only stimulated by certain methods (due to method specific routing
rules).
o Closed the open issue on 483. Usages are not terminated since the
request might succeed if retried with a greater initial Max-
Forwards
o Closed the open issue on 502, accepting -00s suggestion that the
same reasoning used for 482 applies.
o Redid the transfer example to not require a GRUU per usage, but
instead leverage the target-dialog concepts common to Join and
Replaces.
Author's Address Author's Address
Robert J. Sparks Robert J. Sparks
Estacado Systems Estacado Systems
Email: RjS@estacado.net EMail: RjS@estacado.net
Full Copyright Statement Full Copyright Statement
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors contained in BCP 78, and except as set forth therein, the authors
retain all their rights. retain all their rights.
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
skipping to change at page 29, line 44 skipping to change at line 1151
attempt made to obtain a general license or permission for the use of attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at this standard. Please address the information to the IETF at
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
Acknowledgment
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
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