draft-ietf-sip-reason-01.txt   rfc3326.txt 
Internet Engineering Task Force SIP WG Network Working Group H. Schulzrinne
Internet Draft H. Schulzrinne Request for Comments: 3326 Columbia University
Columbia University Category: Standards Track D. Oran
D. Oran
Cisco Cisco
G. Camarillo G. Camarillo
Ericsson Ericsson
draft-ietf-sip-reason-01.txt December 2002
May 14, 2002
Expires: August 2002
The Reason Header Field for the Session Initiation Protocol
STATUS OF THIS MEMO
This document is an Internet-Draft and is in full conformance with The Reason Header Field for the Session Initiation Protocol (SIP)
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Status of this Memo
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Internet-Drafts are draft documents valid for a maximum of six months This document specifies an Internet standards track protocol for the
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material or to cite them other than as "work in progress". Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
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Abstract Abstract
For creating services, it is often useful to know why a SIP request For creating services, it is often useful to know why a Session
was issued. This document defines a header field, Reason, that Initiation Protocol (SIP) request was issued. This document defines
provides this information. The Reason header field is also intended a header field, Reason, that provides this information. The Reason
to be used to encapsulate a final status code in a provisional header field is also intended to be used to encapsulate a final
response. This functionality is needed to resolve the "Heterogeneous status code in a provisional response. This functionality is needed
Error Response Forking Problem", or HERFP. to resolve the "Heterogeneous Error Response Forking Problem", or
HERFP.
Table of Contents Table of Contents
1 Introduction ........................................ 3 1. Introduction ............................................... 2
1.1 Terminology ......................................... 3 1.1. Terminology ................................................ 3
2 The Reason Request Header Field ..................... 3 2. The Reason Request Header Field ............................ 3
3 Examples ............................................ 5 3. Examples ................................................... 4
3.1 Call Completed Elsewhere ............................ 5 3.1. Call Completed Elsewhere ................................... 4
3.2 Refusing an Offer that Comes in a Response .......... 5 3.2. Refusing an Offer that Comes in a Response ................. 4
3.3 Third Party Call Control ............................ 5 3.3. Third Party Call Control ................................... 5
3.4 ISUP interworking ................................... 6 3.4. ISUP interworking .......................................... 5
4 IANA Considerations ................................. 6 4. IANA Considerations ........................................ 6
5 Security Considerations ............................. 7 5. Security Considerations .................................... 6
6 Acknowledgments ..................................... 7 6. Acknowledgments ............................................ 7
7 Authors' Addresses .................................. 7 7. Authors' Addresses ......................................... 7
8 Normative References ................................ 7 8. Normative References ....................................... 7
9. Full Copyright Statement ................................... 8
1 Introduction 1. Introduction
The same SIP [1] request can be issued for a variety of reasons. For The same SIP [1] request can be issued for a variety of reasons. For
example, a SIP CANCEL request can be issued if the call has completed example, a SIP CANCEL request can be issued if the call has completed
on another branch or was abandoned before answer. While the protocol on another branch or was abandoned before answer. While the protocol
and system behavior is the same in both cases, namely, alerting will and system behavior is the same in both cases, namely, alerting will
cease, the user interface may well differ. In the second case, the cease, the user interface may well differ. In the second case, the
call may be logged as a missed call, while this would not be call may be logged as a missed call, while this would not be
appropriate if the call was picked up elsewhere. appropriate if the call was picked up elsewhere.
Third party call controllers sometimes generate a SIP request upon Third party call controllers sometimes generate a SIP request upon
reception of a SIP response from another dialog. Gateways generate reception of a SIP response from another dialog. Gateways generate
SIP requests after receiving messages from a different protocol than SIP requests after receiving messages from a different protocol than
SIP. In both cases the client may be interested in knowing what SIP. In both cases the client may be interested in knowing what
triggered the SIP request. triggered the SIP request.
SIP responses already have a means of informing the user of why a SIP responses already offer a means of informing the user of why a
request failed. The simple mechanism in this draft accomplishes request failed. The simple mechanism in this document accomplishes
something roughly similar for requests. something roughly similar for requests.
An INVITE can sometimes be rejected not because the session An INVITE can sometimes be rejected not because the session
initiation was declined, but because some aspect of the request was initiation was declined, but because some aspect of the request was
not acceptable. If the INVITE forked and resulted in a rejection, the not acceptable. If the INVITE forked and resulted in a rejection,
error response may never be forwarded to the client unless all the the error response may never be forwarded to the client unless all
other branches also reject the request. This problem is known as the the other branches also reject the request. This problem is known as
"Heterogeneous Error Response Forking Problem", or HERFP. The header the "Heterogeneous Error Response Forking Problem", or HERFP. It is
field defined in this draft allows encapsulating the final error foreseen that a solution to this problem may involve encapsulating
response in a 155 (Update Requested) provisional response [2]. the final error response in a provisional response. The Reason header
field is a candidate to be used for such encapsulation.
Initially, the Reason header field defined here appears to be most Initially, the Reason header field defined here appears to be most
useful for BYE and CANCEL requests, but it can appear in any request useful for BYE and CANCEL requests, but it can appear in any request
within a dialog, in any CANCEL request and in 155 (Update Requested) within a dialog, in any CANCEL request and in any response whose
responses. status code explicitly allows the presence of this header field.
When used in requests, clients and servers are free to ignore this Note that the Reason header field is usually not needed in responses
header field. It has no impact on protocol processing. because the status code and the reason phrase already provide
sufficient information.
Clients and servers are free to ignore this header field. It has no
impact on protocol processing.
1.1 Terminology 1.1 Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED", In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in RFC 2119 [3] and and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119
indicate requirement levels for compliant SIP implementations. [2] and indicate requirement levels for compliant SIP
implementations.
2 The Reason Request Header Field 2. The Reason Header Field
The Reason header field can appear in any request within a dialog, in The Reason header field MAY appear in any request within a dialog, in
any CANCEL request and in 155 (Update Requested) responses. The any CANCEL request and in any response whose status code explicitly
syntax of the header field follows the standard SIP parameter syntax. allows the presence of this header field. The syntax of the header
field follows the standard SIP parameter syntax.
Reason = "Reason" HCOLON reason-value *(COMMA reason-value) Reason = "Reason" HCOLON reason-value *(COMMA reason-value)
reason-value = protocol *(SEMI reason-params) reason-value = protocol *(SEMI reason-params)
protocol = SIP / Q.850 / token protocol = "SIP" / "Q.850" / token
reason-params = protocol-cause / reason-text reason-params = protocol-cause / reason-text
/ reason-extension / reason-extension
protocol-cause = "cause" EQUAL cause protocol-cause = "cause" EQUAL cause
cause = 1*DIGIT cause = 1*DIGIT
reason-text = "text" EQUAL quoted-string reason-text = "text" EQUAL quoted-string
reason-extension = generic-param reason-extension = generic-param
The following values for the protocol field have been defined: The following values for the protocol field have been defined:
SIP: The cause parameter contains a SIP status code. SIP: The cause parameter contains a SIP status code.
skipping to change at page 4, line 34 skipping to change at page 4, line 16
Reason: SIP ;cause=200 ;text="Call completed elsewhere" Reason: SIP ;cause=200 ;text="Call completed elsewhere"
Reason: Q.850 ;cause=16 ;text="Terminated" Reason: Q.850 ;cause=16 ;text="Terminated"
Reason: SIP ;cause=600 ;text="Busy Everywhere" Reason: SIP ;cause=600 ;text="Busy Everywhere"
Reason: SIP ;cause=580 ;text="Precondition Failure" Reason: SIP ;cause=580 ;text="Precondition Failure"
Proxies generating a CANCEL request upon reception of a CANCEL from Proxies generating a CANCEL request upon reception of a CANCEL from
the previous hop that contains a Reason header field SHOULD copy it the previous hop that contains a Reason header field SHOULD copy it
into the new CANCEL request. into the new CANCEL request.
In normal SIP operation, a SIP status codes in a response provides In normal SIP operation, a SIP status code in a response provides the
the client with information about the request that triggered the client with information about the request that triggered the
response, the session parameters, or the user. For example, a 405 response, the session parameters, or the user. For example, a 405
(Method not allowed) response indicates that the request contained an (Method not allowed) response indicates that the request contained an
unsupported method. A 488 (Not Acceptable Here) indicates that the unsupported method. A 488 (Not Acceptable Here) indicates that the
session parameters are unacceptable and a 486 (Busy Here) provides session parameters are unacceptable and a 486 (Busy Here) provides
information about the status of the user. information about the status of the user.
Any SIP status code MAY appear in the Reason header field of a Any SIP status code MAY appear in the Reason header field of a
request. However, status codes that provide information about the request. However, status codes that provide information about the
user and about session parameters are typically useful for user and about session parameters are typically useful for
implementing services whereas status codes intended to report errors implementing services whereas status codes intended to report errors
about a request are typically useful for debugging purposes. about a request are typically useful for debugging purposes.
A SIP message MAY contain more than one Reason values (i.e., multiple A SIP message MAY contain more than one Reason value (i.e., multiple
Reason lines), but all of them MUST have different protocol values Reason lines), but all of them MUST have different protocol values
(e.g., one SIP and another Q.850). A implementation is free to ignore (e.g., one SIP and another Q.850). An implementation is free to
Reason values that it does not understand. ignore Reason values that it does not understand.
3 Examples 3. Examples
This section contains a number of examples that illustrate the use of This section contains a number of examples that illustrate the use of
the Reason header field. the Reason header field.
3.1 Call Completed Elsewhere 3.1 Call Completed Elsewhere
A proxy forks an INVITE request and one of the branches returns a 200 A proxy forks an INVITE request and one of the branches returns a 200
(OK). The forking proxy includes this status code in the CANCEL that (OK). The forking proxy includes this status code in a Reason header
it sends to the rest of the branches. field in the CANCEL request that it sends to the rest of the
branches.
3.2 Refusing an Offer that Comes in a Response 3.2 Refusing an Offer that Comes in a Response
A client sends an empty INVITE and receives an unacceptable offer in A client sends an empty INVITE and receives an unacceptable offer in
a 200 (OK) response. The client sends an ACK with a correctly a 200 (OK) response. The client sends an ACK with a correctly
formatted answer and immediately sends a BYE to terminate the formatted answer and immediately sends a BYE to terminate the
session. The client includes a 488 (Not Acceptable Here) status code session. The client includes a 488 (Not Acceptable Here) status code
in a Reason header field. in a Reason header field.
3.3 Third Party Call Control 3.3 Third Party Call Control
skipping to change at page 6, line 42 skipping to change at page 6, line 22
| |<-----------------| | |<-----------------|
| REL (16) | | | REL (16) | |
|-----------------> | | |-----------------> | |
| | CANCEL (Q.850 16)| | | CANCEL (Q.850 16)|
| |----------------->| | |----------------->|
| | 200 OK | | | 200 OK |
| |<-----------------| | |<-----------------|
Figure 2: ISUP Interworking Figure 2: ISUP Interworking
4 IANA Considerations 4. IANA Considerations
IANA registers new protocol values for the Reason header field.
IANA also registers new values for the triggered parameter. These This document defines a new SIP header field, "Reason", according to
values MUST refer to either an ITU-T Recommendation number, an IETF Section 27 of RFC 3261.
protocol name or the recognized protocol identifier from another
standardization organization.
5 Security Considerations Protocol values (and their associated protocol cause) to be used with
this header field are registered by the IANA into a new sub-registry
under http://www.iana.org/assignments/sip-parameters, labeled "Reason
Protocols". Reason protocols MUST refer to either an ITU-T
Recommendation number, an IETF protocol name or the recognized
protocol identifier from another standardization organization.
Protocol cause describes the source of the 'cause' field in the
Reason header field.
While spoofing or removing the Reason header field from a request has The only entries in the registry for the time being are:
no impact on protocol operation, the user interface may change and
end systems may provide services based on this header field. Spoofing
or removing the Reason header field from a 155 (Update Requested)
response can make impossible for a client to update properly its
previous request, making therefore session establishment impossible.
Thus, it is RECOMMENDED that this header field is protected by a
suitable integrity mechanism.
6 Acknowledgments Protocol Value Protocol Cause Reference
-------------- --------------- -----------
SIP Status code RFC 3261
Q.850 Cause value in decimal ITU-T Q.850
representation
5. Security Considerations
Spoofing or removing the Reason header field from a response in a
HERFP scenario can make it impossible for a client to update properly
its previous request, making therefore session establishment
impossible. Thus, it is RECOMMENDED that this header field is
protected by a suitable integrity mechanism.
properly its previous request, making therefore session establishment
impossible. Thus, it is RECOMMENDED that this header field is
protected by a suitable integrity mechanism.
6. Acknowledgments
Jonathan Rosenberg, Rohan Mahy and Vijay K. Gurbani provided helpful Jonathan Rosenberg, Rohan Mahy and Vijay K. Gurbani provided helpful
comments and suggestions. comments and suggestions.
7 Authors' Addresses 8. Normative References
[1] 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.
[2] Bradner, S., "Key words for use in RFCs to indicate requirement
levels," BCP 14, RFC 2119, March 1997.
7. Authors' Addresses
Henning Schulzrinne Henning Schulzrinne
Dept. of Computer Science Dept. of Computer Science
Columbia University Columbia University
1214 Amsterdam Avenue 1214 Amsterdam Avenue
New York, NY 10027 New York, NY 10027
USA USA
electronic mail: schulzrinne@cs.columbia.edu
EMail: schulzrinne@cs.columbia.edu
David R. Oran David R. Oran
Cisco Systems, Inc. Cisco Systems, Inc.
Acton, MA Acton, MA
USA USA
electronic mail: oran@cisco.com
EMail: oran@cisco.com
Gonzalo Camarillo Gonzalo Camarillo
Ericsson Ericsson
Advanced Signalling Research Lab. Advanced Signalling Research Lab.
FIN-02420 Jorvas FIN-02420 Jorvas
Finland Finland
electronic mail: Gonzalo.Camarillo@ericsson.com
8 Normative References
[1] J. Rosenberg, H. Schulzrinne, et al. , "SIP: Session initiation
protocol," Internet Draft, Internet Engineering Task Force, Feb.
2002. Work in progress.
[2] J. Rosenberg, "The SIP UPDATE method," Internet Draft, Internet
Engineering Task Force, Mar. 2002. Work in progress.
[3] S. Bradner, "Key words for use in RFCs to indicate requirement EMail: Gonzalo.Camarillo@ericsson.com
levels," RFC 2119, Internet Engineering Task Force, Mar. 1997.
Full Copyright Statement 9. Full Copyright Statement
Copyright (c) The Internet Society (2002). All Rights Reserved. Copyright (C) The Internet Society (2002). All Rights Reserved.
This document and translations of it may be copied and furnished to This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of Internet organizations, except as needed for the purpose of
skipping to change at line 320 skipping to change at page 8, line 32
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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