Internet DRAFT - draft-sipcore-reason-q850-loc
draft-sipcore-reason-q850-loc
Sipcore R. Jesske
Internet-Draft Deutsche Telekom
Updates: RFC6442 (if approved) May 15, 2017
Intended status: Standards Track
Expires: November 16, 2017
ISUP Cause Location Parameter for the SIP Reason Header Field
draft-sipcore-reason-q850-loc-00.txt
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
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This Internet-Draft will expire on November 16, 2017.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Rationale . . . . . . . . . . . . . . . . . . . . . . . . . . 2
4. Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 4
7. Security Considerations . . . . . . . . . . . . . . . . . . . 4
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
8.1. Registration of isup-cause-location Parameter for reason
header field . . . . . . . . . . . . . . . . . . . . . . 4
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
10.1. Normative References . . . . . . . . . . . . . . . . . . 5
10.2. Informative References . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
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 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 user
LPN for private network serving the local user
LN for public network serving the local user
TN for transit network
RLN for public network serving the remote user
RPN for private network serving the remote user
INTL for international network
BI for network beyond interworking point
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.
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.
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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.
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
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9. Acknowledgments
Thanks to Michael Kreipl, Thoams Belling, Marianne Mohali, Peter
Daws, Paul Kyzivat 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,
<http://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,
<http://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,
<http://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,
<http://www.rfc-editor.org/info/rfc5234>.
10.2. Informative 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.
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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