One document matched: draft-jesske-sipping-etsi-ngn-reason-00.txt
Internet draft Reason header in responses July 2005
Sipping Working Group
Internet Draft Roland Jesske
Expires: January 5, 2006 Deutsche Telekom
July 2005
Use of the Reason header filed in Session Initiation Protocol (SIP)
responses
draft-jesske-sipping-etsi-ngn-reason-00.txt
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document proposes the use of the Reason header field in SIP
responses.
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Internet draft Reason header in responses July 2005
Table of Contents
1. Overview
2. Overall Applicability
3. Terminology
4. Procedures
5. Example
6. Security Considerations
7. IANA Considerations
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.
An example is the ACR services described within draft-jesske-sipping-
tispan-requirements [2]. Here it is needed to send the cause value
#24 back to the PSTN/ISDN to identify why the communication was
restricted and serve the user a correct announcement.
The described solution fulfils the requirements [REQ-GEN-1] and [REQ-
ACR-1].
2. Overall Applicability
The SIP procedures specified in this document are foreseen for
networks providing simulation services and/or interwoking to the
PSTN/ISDN.
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" or "Redirection". " Redirection"
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Internet draft Reason header in responses July 2005
is a redirecting reason as described in [7] draft-elwell-sipping-
redirection-reason-02.txt.
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 keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT,
SHOULD,SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear
in this document, are to be interpreted as described in RFC 2119
[RFC2119].
4. Procedures
For providing services and PSTN/ISDN interoperability it MUST be
possible to include Reason header fields with Q.850 Cause values or
redirecting reasons as described in [7] draft-elwell-sipping-
redirection-reason-02.txt 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 services foreseen.
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.
For Example the application server could use the reason for sending a
announcement towards the originating entity of the Session.
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Internet draft Reason header in responses July 2005
If the application server provides a Service it can provide also
Responses include a Q.850 reason or redirecting reasons as described
in [7] draft-elwell-sipping-redirection-reason-02.txt in responses.
As an example the Anonymous Communication Rejection (ACR) service
defined by ETSI Telecommunications and Internet converged Services
and Protocols for Advanced Networking (TISPAN)
5 Example
Figure 1 shows the example of the ACR service 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 #24 |
| | Reason Q850 #24 | |
| REL Cause #24 | |<-----------------|
| |<-----------------| |
|<----------------- | | |
| | | |
| | | |
| | | |
Figure 1: Third Party Call Control
6. 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 entitys. E.G. sending back a cause value
"24" can cause an announcement within the PSTN/ISDN saying that the
call was rejected due to the ACR service.
Therefore it is RECOMMENDED to include the Reason header in Responses
only by trusted entities as it is described within RFC3325 [8]
7. IANA Considerations
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Internet draft Reason header in responses July 2005
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.
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 Requirements
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-01.txt (work in progress), June 2005.
[4] 3GPP TS 24.229: "IP Multimedia Call Control Protocol based on SIP
and SDP".
[5] ETSI EN 300 485: "Integrated Services Digital Network (ISDN);
Definition 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
[7] Elwell, J., "SIP Reason header extension for indicating
redirection reasons", draft-elwell-sipping-redirection-reason-
02.txt (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.
Note: The ETSI specifications can be downloaded under
http://pda.etsi.org/pda/queryform.asp free of charge.
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Internet draft Reason header in responses July 2005
Contributors
Denis Alexeitsev
Deutsche Telekom
Am Kavalleriesand 3
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
Am Kavalleriesand 3
64307 Darmstadt
Germany
Phone: +496151835940
Email: r.jesske@t-com.net
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Internet draft Reason header in responses July 2005
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