ISUP Cause Location Parameter for the SIP Reason Header Field
draft-ietf-sipcore-reason-q850-loc-01

Sipcore                                                        R. Jesske
Internet-Draft                                          Deutsche Telekom
Updates: RFC6442 (if approved)                        September 29, 2017
Intended status: Standards Track
Expires: April 2, 2018


     ISUP Cause Location Parameter for the SIP Reason Header Field
                 draft-ietf-sipcore-reason-q850-loc-01

Abstract

   The SIP Reason header field is defined for carrying ISUP cause values
   as well as SIP response codes.  Some services in SIP networks may
   need to know the ISUP location where the call was released in the
   PSTN network to correctly interpret the reason of release.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on April 2, 2018.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Rationale . . . . . . . . . . . . . . . . . . . . . . . . . .   2
   4.  Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   5.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   4
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Registration of isup-cause-location Parameter for reason
           header field  . . . . . . . . . . . . . . . . . . . . . .   5
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   5
     10.2.  Informative References . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   The SIP Reason header field specification [RFC3326] describes a SIP
   header field that is used to indicate that a SIP request is carrying
   the reason of release.  It may be an SIP response or ISUP release
   cause as specified within [Q.850].  [RFC3326] does specify that a
   ISUP [Q.850] cause code can be carried within a SIP response.  The
   [Q.850] location information identifies the part of the ISUP network
   where the call was released.

   This document adds a location value parameter to the reason-extension
   parameter in [RFC3326] so that the [Q.850] location value can be
   interworked from the PSTN.  The interworking from PTSN needs only to
   include the location received by the interworking gateway.

2.  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 [RFC2119].

3.  Rationale

   The primary intent of the parameter defined in this specification is
   for use in IMS networks defined by 3GPP but also open to be used by
   any other network.  The purpose of this parameter is to transport the
   location of call release from the originating PSTN entity to the SIP
   entity receiving the response or BYE message containing the location
   of the call release.  The ISDN location is defined in [Q.850].




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4.  Mechanism

   As defined by [RFC3326] a Reason header field MAY appear in any
   request in a dialog, in any CANCEL request and in any response whose
   status code explicitly allows the presence of this header field.  The
   syntax of the header field follows the standard SIP parameter syntax.

   The mechanism employed adds a parameter with the ISUP location value
   defined in [Q.850] to the Reason header field that identifies the
   [Q.850] location of the call release in ISUP as defined in [Q.850] .
   The location is a 4 bit value which reflects the possible locations
   where an ISUP call is released.  Some values are spare or reserved
   for national use.  The Augmented BNF (ABNF) [RFC5234] for this
   parameter is shown in Figure 1.

   reason-extension =/ isup-cause-location
   isup-cause-location =  "location" EQUAL string

   The following values shall be used as location:
   U       for 0 0 0 0 user
   LPN     for 0 0 0 1 private network serving the local user
   LN      for 0 0 1 0 public network serving the local user
   TN      for 0 0 1 1 transit network
   RLN     for 0 1 0 0 public network serving the remote user
   RPN     for 0 1 0 1 private network serving the remote user
   LOC-6   for 0 1 1 0 spare
   INTL    for 0 1 1 1 international network
   LOC-8   for 1 0 0 0 spare
   LOC-9   for 1 0 0 1 spare
   BI      for 1 0 1 0 network beyond interworking point
   LOC-11  for 1 0 1 1 spare
   LOC-12  for 1 1 0 0 reserved for national use
   LOC-13  for 1 1 0 1 reserved for national use
   LOC-14  for 1 1 1 0 reserved for national use
   LOC-15  for 1 1 1 1 reserved for national use

                       Figure 1: isup-cause-location

   Note: These are the values defined within [Q.850] as location.  Thus
   other values are not within the scope of this document.

   Depending on the direction the UAC or UAS shall include the isup-
   cause-location when setting up the Reason header field with a [Q.850]
   cause.  This approach is only valid in cases when the ISUP [Q.850]
   location is available.






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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.


        404 Not Found

         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 isup-cause-
   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 isup-cause-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 constrain.  The use of this parameter is not restricted to a
   specific architecture.







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8.  IANA Considerations

8.1.  Registration of isup-cause-location Parameter for reason header
      field

   This document calls for IANA to register a new SIP header parameter
   as per the guidelines in [RFC3261], which will be added to header
   sub-registry under http://www.iana.org/assignments/sip-parameters.

   Header Field:  Reason

   Parameter Name:  isup-cause-location

9.  Acknowledgments

   Thanks to Michael Kreipl, Thomas Belling, Marianne Mohali, Peter
   Dawes, Paul Kyzivat and Dale Worley for the comments and review.

10.  References

10.1.  Normative References

   [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>.

   [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>.

10.2.  Informative References







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   [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.

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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