7.1. "Preemption" Namespace Registry
RFC 4411 creates the new SIP "Reason Header" [1] protocol namespace:
"Preemption", with 4 defined cause codes:
In instances where this namespace is used to indicate preemption
at a UA, the following syntax shall be used (the reason-text is a
default string; it is not mandatory, and may be different):
Reason: preemption ;cause=1 ;text="UA Preemption"
Section 5.1 of this document describes in detail the semantics
of this cause code.
The default text above is part of a new IANA Registry for
default text strings for any new protocol namespace cause code.
See Section 7.2 for details.
In instances where this namespace is used to indicate preemption
because an RSVP ResvErr message was received at a SIP UA, the
following syntax shall be used (the reason-text is a default
string; it is not mandatory, and may be different):
Reason: preemption ;cause=2 ;text="Reserved Resources Preempted"
Section 5.2 of this document describes in detail the semantics
of this cause code.
The default text above is part of a new IANA Registry for
default text strings for any new protocol namespace cause code.
See section 7.2 for details.
In instances where this namespace is used to indicate a
generalized preemption event to the destination UA from a Proxy
that modifies the Reason value only during this last SIP hop, the
following syntax shall be used (the reason-text is a default
string; it is not mandatory, and may be different):
Reason: preemption ;cause=3 ;text="Generic Preemption"
Section 5.3 of this document describes in detail the semantics
of this cause code.
The default text above is part of a new IANA Registry for
default text strings for any new protocol namespace cause code.
See Section 7.2 for details.
In instances where this namespace is used to indicate preemption
from a non-IP portion of a call leg, a SIP Gateway shall use the
following syntax to inform the SIP infrastructure of this event
(the reason-text is a default string; it is not mandatory, and may
be different):
Reason: preemption ;cause=4 ;text=" Non-IP Preemption"
Section 5.4 of this document describes in detail the semantics
of this cause code.
The default text above is part of a new IANA Registry for
default text strings for any new protocol namespace cause code.
See Section 7.2 for details.
Additional definitions of the preemption namespace and its cause
codes MUST be defined in Standards Track documents.
7.2. Default Reason-Text IANA Registry for the SIP Reason Header
Below is a new IANA Registry for SIP Reason Header reason-text
strings, associated with their respective protocol type and Reason-
param cause values. Per RFC 3326, the Reason-text string is a quoted
default string with only human understandability meant. These
strings can be changed by local policy.
Reason-
Protocol param Reason-Text Reference
-------- ------- ------------ ---------
Preemption Cause=1 UA Preemption RFC 4411
Preemption Cause=2 Reserved Resources RFC 4411
Preempted
Preemption Cause=3 Generic Preemption RFC 4411
Preemption Cause=4 Non-IP Preemption RFC 4411
8. Contributions
The following individuals contributed to this effort:
Subhasri Dhesikan
Gonzalo Camarillo
Dave Oran
The author thanks these individuals greatly for their aid in this
effort.
9. Acknowledgements
To Haluk Keskiner for providing a valued sanity check. To Dean
Willis, Rohan Mahy, and Allison Mankin for their belief in and
backing of this effort. To Adam Roach and Arun Kumar for helpful
comments to this document.
Thanks to Mike Pierce for helpful comments and catching a flaw in
this spec late in the process (before it was too late).
10. References
10.1. Normative References
[1] Schulzrinne, H., Oran, D., and G. Camarillo, "The Reason Header
Field for the Session Initiation Protocol (SIP)", RFC 3326,
December 2002.
[2] 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.
[3] Camarillo, G., Marshall, W., and J. Rosenberg, "Integration of
Resource Management and Session Initiation Protocol (SIP)", RFC
3312, October 2002.
[4] Schulzrinne, H. and J. Polk, "Communications Resource-Priority
Header in the Session Initiation Protocol (SIP)", RFC 4412,
February 2006.
[5] ITU-T Recommendation Q.850 (1993)
[6] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[7] Braden, R., Zhang, L., Berson, S., Herzog, S., and S. Jamin,
"Resource ReSerVation Protocol (RSVP) -- Version 1 Functional
Specification", RFC 2205, September 1997.
10.2. Informative References
[8] J. Manner, G. Karagiannis, A. McDonald, S. Van den Bosch, "NSLP
for Quality-of-Service signalling", Work in Progress, September
2005.
Author Information
James M. Polk
Cisco Systems
2200 East President George Bush Turnpike
Richardson, Texas 75082 USA
EMail: jmpolk@cisco.com
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