Reason Header in Responses June 2007
BLISS Roland Jesske
Internet Draft Deutsche Telekom
Intended Status: private
Document: draft-jesske-sipping-etsi-ngn-reason-01.txt
Expires: December 2007 June 2007
Use of the Reason header field in Session Initiation Protocol (SIP)
responses
draft-jesske-sipping-etsi-ngn-reason-01.txt
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document proposes the use of the Reason header field in SIP
responses. In addition for the interoperability wit DSS1 interworked
devices and the ISUP a Location fild is defined in addition.
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Table of Contents
1. Overview.......................................................2
2. Overall Applicability..........................................2
3. Terminology....................................................3
4. Procedures.....................................................3
4.1 Procedures at the UA.......................................3
4.2 Procedures at a SIP proxy..................................3
4.3 Procedures at an application server........................3
5. Procedures at an interworking point with ISUP..................4
6. Example........................................................4
7. Security Considerations........................................5
8. IANA Considerations............................................5
9. References.....................................................5
1. Overview
The European Telecommunication Standards Institute (ETSI) is defining
a Next Generation Network (NGN) where a substantial part of it is
based on the IP Multimedia Subsystem (IMS) defined by the Third-
Generation Partnership Project (3GPP). IMS is largely based on the
Session Initiation Protocol [1].
ETSI has developed a number of requirements draft-jesske-sipping-
tispan-requirements [5] to support the usage of SIP in Next
Generation Networks that interoperate, at the service level, with the
Public Switched Telephone Network (PSTN), the Integrated Services
Digital Network (ISDN), the 3GPP IP Multimedia Subsystem (IMS), and
SIP networks and terminals that implement the service logic.
In order to provide full support in SIP of existing services,
extensions to SIP are needed.
This document proposes the use of the Reason header field in
responses. This is needed for creating services that must be
interoperable with the PSTN/ISDN network and the interoperability of
traversing communications through SIP not using SIP-I. This fulfils
the requirement [REQ-GEN-1 in draft-jesske-sipping-tispan-
requirements [5]]
2.Overall Applicability
The SIP procedures specified in this document are foreseen for
networks providing simulation services and/or interworking to the
PSTN/ISDN.
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The document is describing the use of the Reason header in SIP
responses. These procedures are only valuable if the reason contained
in the element "protocol" is "Q.850". A inclusion of a SIP reason
(protocol="SIP") is not helpful due to the fact that the response
already provides the SIP reason. The Release Causes are described
within ETSI EN300 485 [5]
3. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119. [9].
4. Procedures
For providing services and PSTN/ISDN interoperability for SIP
networks it MUST be possible to include Reason header fields with
Q.850 Cause values in responses.
4.1 Procedures at the UA
A UA that supports the Reason header field can process the Q.850
Cause Value and display it or an equivalent text. The inclusion of a
Reason header field by UA is only for 2B2 UA interworking with the
PSTN/ISDN or providing PSTN/ISDN like services foreseen.
For a pure SIP UA the reason header will not harm if not supported
because it will not be processed. For SIP end devices the support of
the Reason header field the cause maybe an valuable hint why the call
was released by an non SIP entity.
4.2 Procedures at a SIP proxy
SIP proxies that receive a response containing a Reason header field
is forwarding the response without changing the reason.
A SIP proxy receiving a request that includes a Reason header field
can route the request to an application server for further analysis
and base services on it.
Based on network policy a Proxy can remove a Reason header field send
from a UAC.
4.3 Procedures at an application server
An application server that receives a SIP request that contains a
response including a Reason header MAY analyze the SIP Reason and
base further procedures on this analyses.
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For Example the application server could use the reason for sending a
announcement towards the originating entity of the Session.
If the application server provides a Service it can provide also
Responses include a Q.850 reason in responses.
5. Procedures at an interworking point with ISUP
For interoperability reasons the Q.850 Cause Value of a Release shall
be mapped to the Reason Header.
6. Example
Figure 1 shows the example of SIP interworking with the PSTN/ISDN
A Gateway Proxy AS
| IAM | | |
|------------------>| INVITE | |
| |----------------->| INVITE |
| | 100 Trying |----------------->|
| |<-----------------| 100 Trying |
| | |<-----------------|
| ACK SDP held | | |
|<------------------| | 603 Decline |
| | 603 Decline | Reason Q850 #87 |
| | Reason Q850 #87 | |
| REL Cause #87 | |<-----------------|
| |<-----------------| |
|<----------------- | | |
| | | |
| | | |
| | | |
Figure 1: Example of an ISDN like service executed within the SIP
domain
Figure 2 shows the example of SIP interworking with the PSTN/ISDN
where the call is traversed through the SIP network
A Gateway Gateway B
| IAM | | |
|------------------>| INVITE | |
| |----------------->| IAM |
| | 100 Trying |----------------->|
| | | REL Cause #29 |
| | 500 Server Error | |
| | Reason Q850 #29 | |
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Reason Header in Responses June 2007
| REL Cause #29 | |<-----------------|
| |<-----------------| |
|<----------------- | | |
| | | |
| | | |
Figure 1: Example of an ISDN - SIP - ISDN Call
7. Security Considerations
The presence of the Reason header in a response does not affect the
treatment of the response.
Including such a header by an untrusted entity could adulterate the
reactions of the originating entities. E.G. sending back a cause
value
"87" can cause an announcement within the PSTN/ISDN saying that the
call was rejected due to the Closed User Group service.
Therefore it is RECOMMENDED to include the Reason header only by
trusted entities as it is described within RFC3325 [8] or at least by
network entities.
8. IANA Considerations
This document describes the use of the Reason header field described
within RFC 3326 [2]. No additional SIP elements are defined within
this document. Therefore, this document does not provide any action
to IANA.
9. 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] H. Schulzrinne, D. Oran, G. Camarillo, "The Reason Header for
the Session Initiation Protocol (SIP)", RFC 3326.
[3] Jesske, R., Alexeitsev, D., Garcia-Martin, M. "Input Require-
ments for the Session Initiation Protocol (SIP) in support for
the European Telecommunications Standards Institute (ETSI) Next
Generation Network (NGN) simulation services", draft-jesske-
sipping-tispan-requirements-04.txt (work in progress), June 2007.
[4] 3GPP TS 24.229: "IP Multimedia Call Control Protocol based on SIP
and SDP".
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[5] ETSI EN 300 485: "Integrated Services Digital Network (ISDN);
Dfinition and usage of cause and location in Digital Subscriber
Signalling System No. one (DSS1) and Signalling System No. 7 (SS7)
ISDN User Part (ISUP) [ITU-T Recommendation Q.850 (1998) with
addendum modified] ".
[6] Jesske, R., Alexeitsev, D., Garcia-Martin, M. "Analysis of the
Input Requirements for the Session Initiation Protocol (SIP) in
support for the European Telecommunications Standards Institute
(ETSI) Next Generation Networks (NGN) simulation services" (work
in progress) June 2005
[8] Jennings C., Peterson J., and Watson M. "Private Extensions to
the Session Initiation Protocol (SIP) for Asserted Identity
within Trusted Networks", RFC 3325, November 2002.
[9] RFC2119 Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels," BCP 14, RFC 2119, March 1997 (TXT, HTML,
XML).
Note: The ETSI specifications can be downloaded under
http://pda.etsi.org/pda/queryform.asp free of charge.
Contributors
Denis Alexeitsev
Deutsche Telekom
Deutsche Telekom Allee1
64307 Darmstadt
Germany
Phone: +496151832130
Email: d.alexeitsev@t-com.net
Acknowledgments
The author would like to thank the members of the ETSI TISPAN WG3
for their comments to this memo.
Author's Addresses
Roland Jesske
Deutsche Telekom
Deutsche Telekom Allee1
64307 Darmstadt
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Germany
Phone: +496151835940
Email: r.jesske@t-com.net
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