Internet DRAFT - draft-ietf-sipcore-reason-q850-loc
draft-ietf-sipcore-reason-q850-loc
Sipcore R. Jesske
Internet-Draft Deutsche Telekom
Updates: 3326 (if approved) March 13, 2019
Intended status: Standards Track
Expires: September 14, 2019
ISUP Cause Location Parameter for the SIP Reason Header Field
draft-ietf-sipcore-reason-q850-loc-07.txt
Abstract
The SIP Reason header field is defined for carrying ISUP (Integrated
Services Digital Network User Part) 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. This document will update
RFC3326.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on September 14, 2019.
Copyright Notice
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Rationale . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . 5
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8.1. Registration of location Parameter for Reason header
field . . . . . . . . . . . . . . . . . . . . . . . . . . 6
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
10. Normative References . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
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. The reason of release indicates why a SIP
Dialog or a PSTN call, in case where the call was interworked to the
PSTN, was terminated. This may be a normal termination or a
termination based on a failure within an entity or other reasons like
congestion. The reason may be an SIP response or ISUP release cause
as specified within [Q.850]. [RFC6432] specifies that a ISUP [Q.850]
cause code can be carried within a SIP response, but not the Q.850
location information. 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. [Q.850]
describes the definition of cause code values and locations used in
ISDN and DSS1 environment. The cause code is used for identifying
the reason of release of a call and the location identifies where the
call was released.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
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14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Rationale
The primary intent of the parameter defined in this specification is
for use in IMS (IP Multimedia Subsystem) networks defined by 3GPP but
it is also open to be used by any other network that includes ISUP
interworking gateways and uses Q.850 reason codes. 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].
4. Mechanism
As defined by [RFC6432] any SIP Response message, with the exception
of a 100 (Trying), MAY contain a Reason header field with a Q.850
[Q.850] cause code.
This specification adds a parameter with the ISUP location value
defined in [Q.850] to the Reason header field that identifies the
location of the call release in ISUP. 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.
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reason-extension =/ isup-cause-location
isup-cause-location = "location" EQUAL isup-location-value
isup-location-value =
%s"U" / ; for 0 0 0 0 user
%s"LPN" / ; for 0 0 0 1 private network serving the local user
%s"LN" / ; for 0 0 1 0 public network serving the local user
%s"TN" / ; for 0 0 1 1 transit network
%s"RLN" / ; for 0 1 0 0 public network serving the remote user
%s"RPN" / ; for 0 1 0 1 private network serving the remote user
%s"LOC-6" / ; for 0 1 1 0 spare
%s"INTL" / ; for 0 1 1 1 international network
%s"LOC-8" / ; for 1 0 0 0 spare
%s"LOC-9" / ; for 1 0 0 1 spare
%s"BI" / ; for 1 0 1 0 network beyond interworking point
%s"LOC-11" / ; for 1 0 1 1 spare
%s"LOC-12" / ; for 1 1 0 0 reserved for national use
%s"LOC-13" / ; for 1 1 0 1 reserved for national use
%s"LOC-14" / ; for 1 1 1 0 reserved for national use
%s"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 whether the message is a request or a response the UAC
or UAS SHALL include the location parameter when setting up the
Reason header field with a [Q.850] cause. This approach is only
possible in cases when the ISUP [Q.850] location is available.
The use of the location parameter is restricted to Q850 cause values.
Other values MUST be ignored if present.
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 sent 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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SIP/2.0 404 Not Found
Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bKx5st
Via: SIP/2.0/TCP 192.0.2.3:5060;branch=z9hG4bK4321
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
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.
The ISUP location value itself will not reveal the identity of the
originating or terminating party of the call. It shows only the ISUP
network location of the device that released the call. The ISUP
location does not show show the physical location of the caller or
callee.
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.
[RFC3398] describes detailed security consideration due to
interworking between ISUP and SIP. Beyond these considerations the
addition of the location does not add additional security concerns.
The location shows the network part where the call is released.
Knowing this does not increase the possibilities of extended fraud
scenarios.
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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
Predefined Values: yes
Reference: RFCXXXX
Note to RFC Editor: Please replace RFC XXXX with the RFC number of
this specification.
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>.
[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>.
[RFC3398] Camarillo, G., Roach, A., Peterson, J., and L. Ong,
"Integrated Services Digital Network (ISDN) User Part
(ISUP) to Session Initiation Protocol (SIP) Mapping",
RFC 3398, DOI 10.17487/RFC3398, December 2002,
<https://www.rfc-editor.org/info/rfc3398>.
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[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>.
[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>.
[RFC6432] Jesske, R. and L. Liess, "Carrying Q.850 Codes in Reason
Header Fields in SIP (Session Initiation Protocol)
Responses", RFC 6432, DOI 10.17487/RFC6432, November 2011,
<https://www.rfc-editor.org/info/rfc6432>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
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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