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RFC2976 - The SIP INFO Method

王朝other·作者佚名  2008-05-31
窄屏简体版  字體: |||超大  

Network Working Group S. Donovan

Request for Comments: 2976 dynamicsoft

Category: Standards Track October 2000

The SIP INFO Method

Status of this Memo

This document specifies an Internet standards track protocol for the

Internet community, and requests discussion and suggestions for

improvements. Please refer to the current edition of the "Internet

Official Protocol Standards" (STD 1) for the standardization state

and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2000). All Rights Reserved.

Abstract

This document proposes an extension to the Session Initiation

Protocol (SIP). This extension adds the INFO method to the SIP

protocol. The intent of the INFO method is to allow for the carrying

of session related control information that is generated during a

session. One example of sUCh session control information is ISUP and

ISDN signaling messages used to control telephony call services.

This and other example uses of the INFO method may be standardized in

the future.

Table of Contents

1 Introduction................................................2

1.1 Example Uses................................................2

2 INFO Method.................................................3

2.1 Header Field Support for INFO Method........................3

2.2 Responses to the INFO Request Method........................4

2.3 Message Body Inclusion......................................5

2.4 Behavior of SIP User Agents.................................6

2.5 Behavior of SIP Proxy and Redirect Servers..................6

2.5.1 Proxy Server................................................6

2.5.2 Forking Proxy Server........................................6

2.5.3 Redirection Server..........................................6

3. INFO Message Bodies.........................................6

4. Guidelines for extensions making use of INFO................7

5. Security Considerations.....................................7

6. References..................................................8

7. Acknowledgments.............................................8

8. Author's Address............................................8

Full Copyright Statement....................................9

1. Introduction

The SIP protocol described in [1] defines session control messages

used during the setup and tear down stages of a SIP controlled

session.

In addition, the SIP re-INVITE can be used during a session to change

the characteristics of the session. This is generally to change the

properties of media flows related to the session or to update the SIP

session timer.

However, there is no general-purpose mechanism to carry session

control information along the SIP signaling path during the session.

The purpose of the INFO message is to carry application level

information along the SIP signaling path.

The INFO method is not used to change the state of SIP calls, or the

parameters of the sessions SIP initiates. It merely sends optional

application layer information, generally related to the session.

It is necessary that the mid-session signaling information traverse

the post session setup SIP signaling path. This is the path taken by

SIP re-INVITEs, BYEs and other SIP requests that are tied to an

individual session. This allows SIP proxy servers to receive, and

potentially act on, the mid-session signaling information.

This document proposes an extension to SIP by defining the new INFO

method. The INFO method would be used for the carrying of mid-call

signaling information along the session signaling path.

1.1 Example Uses

The following are a few of the potential uses of the INFO message:

- Carrying mid-call PSTN signaling messages between PSTN

gateways.

- Carrying DTMF digits generated during a SIP session.

- Carrying wireless signal strength information in support of

wireless mobility applications.

- Carrying account balance information.

- Carrying images or other non streaming information between the

participants of a session.

These are just potential uses; this document does not specify such

uses nor does it necessarily recommend them.

It can also be envisioned that there will be other telephony and

non-telephony uses of the INFO method.

2. INFO Method

The INFO method is used for communicating mid-session signaling

information along the signaling path for the call.

The INFO method is not used to change the state of SIP calls, nor

does it change the state of sessions initiated by SIP. Rather, it

provides additional optional information which can further enhance

the application using SIP.

The signaling path for the INFO method is the signaling path

established as a result of the call setup. This can be either direct

signaling between the calling and called user agents or a signaling

path involving SIP proxy servers that were involved in the call setup

and added themselves to the Record-Route header on the initial INVITE

message.

The mid-session information can be communicated in either an INFO

message header or as part of a message body. The definition of the

message body and/or message headers used to carry the mid-session

information is outside the scope of this document.

There are no specific semantics associated with INFO. The semantics

are derived from the body or new headers defined for usage in INFO.

2.1 Header Field Support for INFO Method

Tables 1 and 2 add a column to tables 4 and 5 in the [1]. Refer

to Section 6 of [1] for a description of the content of the

tables. Note that the rules defined in the enc. and e-e columns

in tables 4 and 5 in [1] also apply to use of the headers in the

INFO request and responses to the INFO request.

2.2 Responses to the INFO Request Method

If a server receives an INFO request it MUST send a final

response.

A 200 OK response MUST be sent by a UAS for an INFO request with

no message body if the INFO request was successfully received for

an existing call. Beyond that, no additional operations are

required.

Header Where INFO

------ ----- ----

Accept R o

Accept-Encoding R o

Accept-Language R o

Allow 200 -

Allow 405 o

Authorization R o

Call-ID gc m

Contact R o

Contact 1xx -

Contact 2xx -

Contact 3xx -

Contact 485 -

Content-Encoding e o

Content-Length e o

Content-Type e *

CSeq gc m

Date g o

Encryption g o

EXPires g o

From gc m

Hide R o

Max-Forwards R o

Organization g o

Table 1 Summary of header fields, A-0

Handling of INFO messages that contain message bodies is outside

the scope of this document. The documents defining the message

bodies will also need to define the SIP protocol rules associated

with those message bodies.

A 481 Call Leg/Transaction Does Not Exist message MUST be sent by

a UAS if the INFO request does not match any existing call leg.

If a server receives an INFO request with a body it understands,

but it has no knowledge of INFO associated processing rules for

the body, the body MAY be rendered and displayed to the user. The

INFO is responded to with a 200 OK.

If the INFO request contains a body that the server does not

understand then, in the absence of INFO associated processing

rules for the body, the server MUST respond with a 415 Unsupported

Media Type message.

Header Where INFO

------ ----- ----

Priority R o

Proxy-Authenticate 407 o

Proxy-Authorization R o

Proxy-Require R o

Require R o

Retry-After R -

Retry-After 404,480,486 o

Retry-After 503 o

Retry-After 600,603 o

Response-Key R o

Record-Route R o

Record-Route 2xx o

Route R o

Server r o

Subject R o

Timestamp g o

To gc(1) m

Unsupported 420 o

User-Agent g o

Via gc(2) m

Warning r o

WWW-Authenticate 401 o

Table 2 Summary of header fields, P-Z

Bodies which imply a change in the SIP call state or the sessions

initiated by SIP MUST NOT be sent in an INFO message.

Other request failure (4xx), Server Failure (5xx) and Global

Failure (6xx) responses MAY be sent for the INFO Request.

2.3 Message Body Inclusion

The INFO request MAY contain a message body.

2.4 Behavior of SIP User Agents

Unless stated otherwise, the protocol rules for the INFO request

governing the usage of tags, Route and Record-Route,

retransmission and reliability, CSeq incrementing and message

formatting follow those in [1] as defined for the BYE request.

An INFO request MAY be cancelled. A UAS receiving a CANCEL for an

INFO request SHOULD respond to the INFO with a "487 Request

Cancelled" response if a final response has not been sent to the

INFO and then behave as if the request were never received.

However, the INFO message MUST NOT change the state of the SIP

call, or the sessions initiated by SIP.

2.5 Behavior of SIP Proxy and Redirect Servers

2.5.1 Proxy Server

Unless stated otherwise, the protocol rules for the INFO

request at a proxy are identical to those for a BYE request as

specified in [1].

2.5.2 Forking Proxy Server

Unless stated otherwise, the protocol rules for the INFO

request at a proxy are identical to those for a BYE request as

specified in [1].

2.5.3 Redirection Server

Unless stated otherwise, the protocol rules for the INFO

request at a proxy are identical to those for a BYE request as

specified in [1].

3. INFO Message Bodies

The purpose of the INFO message is to carry mid-session information

between SIP user agents. This information will generally be carried

in message bodies, although it can be carried in headers in the INFO

message.

The definition of the message bodies or any new headers created for

the INFO method is outside the scope of this document. It is

expected that separate documents will be created to address

definition of these entities.

In addition, the INFO method does not define additional mechanisms

for ensuring in-order delivery. While the CSeq header will be

incremented upon the transmission of new INFO messages, this should

not be used to determine the sequence of INFO information. This is

due to the fact that there could be gaps in the INFO message CSeq

count caused by a user agent sending re-INVITES or other SIP

messages.

4. Guidelines for extensions making use of INFO

The following are considerations that should be taken into account

when defining SIP extensions that make use of the INFO method.

- Consideration should be taken on the size of message bodies to be

carried by INFO messages. The message bodies should be kept small

due to the potential for the message to be carried over UDP and the

potential for fragmentation of larger messages.

- There is potential that INFO messages could be forked by a SIP

Proxy Server. The implications of this forking of the information

in the INFO message need to be taken into account.

- The use of multi-part message bodies may be helpful when defining

the message bodies to be carried by the INFO message.

- The extensions that use the INFO message MUST NOT rely on the

INFO message to do anything that effects the SIP call state or the

state of related sessions.

- The INFO extension defined in this document does not depend on

the use of the Require or Proxy-Require headers. Extensions using

the INFO message may need the use of these mechanisms. However,

the use of Require and Proxy-Require should be avoided, if

possible, in order to improve interoperability between SIP

entities.

5. Security Considerations

If the contents of the message body are private then end-to-end

encryption of the message body can be used to prevent unauthorized

Access to the content.

There are no other security issues specific to the INFO method.

The security requirements specified in the SIP specification apply

to the INFO method.

6. References

[1] Handley, M., Schulzrinne, H., Schooler, E. and J. Rosenberg,

"SIP: Session Initiation Protocol", RFC2543, March 1999.

7. Acknowledgements

The author would like to thank Matthew Cannon for his contributions

to this document. In addition, the author would like to thank the

members of the MMUSIC and SIP working groups, especially Jonathan

Rosenberg, for comments and suggestions on how to improve the

document.

8. Author's Address

Steve Donovan

dynamicsoft

5100 Tennyson Parkway, Suite 200

Plano, Texas 75024

Email: sdonovan@dynamicsoft.com

9. Full Copyright Statement

Copyright (C) The Internet Society (2000). All Rights Reserved.

This document and translations of it may be copied and furnished to

others, and derivative works that comment on or otherwise explain it

or assist in its implementation may be prepared, copied, published

and distributed, in whole or in part, without restriction of any

kind, provided that the above copyright notice and this paragraph are

included on all such copies and derivative works. However, this

document itself may not be modified in any way, such as by removing

the copyright notice or references to the Internet Society or other

Internet organizations, except as needed for the purpose of

developing Internet standards in which case the procedures for

copyrights defined in the Internet Standards process must be

followed, or as required to translate it into languages other than

English.

The limited permissions granted above are perpetual and will not be

revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an

"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING

TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING

BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION

HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF

MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

Funding for the RFCEditor function is currently provided by the

Internet Society.

 
 
 
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