ISUP Cause Location Parameter for the SIP Reason Header Field
draft-ietf-sipcore-reason-q850-loc-04

   The use of the location parameter is restricted to Q850 cause values
   in other cases the location, if present, MUST be silently ignored.

5.  Example

   The following example shows a SIP 404 response message containing a
   Reason header field with a [Q.850] cause value and a isup-cause-
   location value.  The 404 Response will be set up when a gateway
   receives an ISUP Release with a [Q.850] cause set to 1 meaning
   "Unallocated (unassigned) number", i.e. the number is not known in
   the PSTN.

         SIP/2.0 404 Not Found

         From: Alice <sips:alice@atlanta.example.com>;tag=1234567
         To: Bob <sips:bob@biloxi.example.com>;tag=765432
         Call-ID: 12345600@atlanta.example.com
         CSeq: 1 INVITE
         Reason: Q.850;cause=1;text="Unallocated (unassigned) number";
              location=LN
         Content-Length: 0

            Figure 2: Example Location in Reason header field.

6.  Privacy Considerations

   This document doesn't change any of the privacy considerations
   described in [RFC3326].  While the addition of the location parameter
   does provide an indicator of the entity that added the location in
   the signaling path this provides little more exposure than the
   [Q.850] cause itself.

7.  Security Considerations

   This document doesn't change any of the security considerations
   described in [RFC3326].  The addition of the location parameter does
   provide an indicator of the [Q.850] location where the call was
   released within the PSTN.  This information may be used for specific
   location driven services but does not create any additional security
   constrains.  But since the [Q.850] location is very imprecise the
   [Q.850] location value itself will not add any major security
   constraint.  The use of this parameter is not restricted to a
   specific architecture.

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8.  IANA Considerations

8.1.  Registration of location Parameter for Reason header field

   This document calls for IANA to register a new SIP header parameter
   as per the guidelines in [RFC3968], which will be added to Header
   Field Parameters sub-registry under http://www.iana.org/assignments/
   sip-parameters.

   Header Field:  Reason

   Parameter Name:  location

9.  Acknowledgments

   Thanks to Michael Kreipl, Thoams Belling, Marianne Mohali, Peter
   Daws, Paul Kyzivat, Dale Worley, Yehoshua Gev, Keith Drage for the
   comments and review.

10.  Normative References

   [Q.850]    INTERNATIONAL TELECOMMUNICATION UNION, "Usage of cause and
              location in the Digital Subscriber Signalling System No. 1
              and the Signalling System No. 7 ISDN User Part", Q 850,
              May 1998.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,
              <https://www.rfc-editor.org/info/rfc3261>.

   [RFC3326]  Schulzrinne, H., Oran, D., and G. Camarillo, "The Reason
              Header Field for the Session Initiation Protocol (SIP)",
              RFC 3326, DOI 10.17487/RFC3326, December 2002,
              <https://www.rfc-editor.org/info/rfc3326>.

   [RFC3968]  Camarillo, G., "The Internet Assigned Number Authority
              (IANA) Header Field Parameter Registry for the Session
              Initiation Protocol (SIP)", BCP 98, RFC 3968,
              DOI 10.17487/RFC3968, December 2004,
              <https://www.rfc-editor.org/info/rfc3968>.

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   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

Author's Address

   Roland Jesske
   Deutsche Telekom
   Heinrich-Hertz Str, 3-7
   Darmstadt  64295
   Germany

   Email: r.jesske@telekom.de
   URI:   www.telekom.de

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