Internet Engineering Task Force (IETF) R. Jesske Request for Comments: 8606 Deutsche Telekom Updates: 3326 June 2019 Category: Standards Track ISSN: 2070-1721ISDN User Part (ISUP) Cause Location Parameter for the SIP Reason Header Field
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RFC 8606 ISUP Release Location Parameter June 2019
Table of Contents
1. Introduction
Section 3.4 of [RFC3326] describes a SIP message flow for canceling an INVITE request when a REL (release) message is received from the ISUP side. That document specifies the SIP Reason header field [RFC3326] that is used to indicate the reason of release. The reason of release indicates why a SIP Dialog or a PSTN call, in cases where the call was interworked to the PSTN, was terminated. The termination may be normal, based on a failure within an entity (e.g. temporary failure) or caused by other factors (e.g., congestion). The reason may be a SIP response or an ISUP release cause as specified within [Q.850]. [RFC6432] specifies that an 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.
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RFC 8606 ISUP Release Location Parameter June 2019 2. TerminologyThe 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 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 networks that include ISUP interworking gateways and use Q.850 reason codes. The purpose of this parameter is to hold the location of the call release so that it can be transported from the originating PSTN entity to the SIP entity via a response or BYE message. The ISDN location is defined in [Q.850].
4. Mechanism
As defined by [RFC6432], any SIP Response message, with the exception of 100 (Trying), MAY contain a Reason header field with a Q.850 [Q.850] cause code.
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RFC 8606 ISUP Release Location Parameter June 2019
isup-location-value = "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
5. Example
The following example shows a SIP 404 response message containing a Reason header field with a [Q.850] cause value and an 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. 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";
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RFC 8606 ISUP Release Location Parameter June 2019
location=LN
6. Privacy Considerations
While the addition of the location parameter provides an indicator of the entity that added the location in the signaling path, it 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 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 provides 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 constraints. Because the [Q.850] location is very imprecise, the [Q.850] location value itself will not add any major security constraints. The use of this parameter is not restricted to a specific architecture.
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RFC 8606 ISUP Release Location Parameter June 2019 8. IANA Considerations 8.1. Registration of the Location Parameter for the Reason Header FieldIANA has registered a new SIP header parameter in the "Header Field Parameters and Parameter Values" subregistry of the "Session Initiation Protocol (SIP) Parameters" registry <https://www.iana.org/assignments/sip-parameters>, per the guidelines in [RFC3968]:
9. Normative References
[Q.850] ITU-T, "Usage of cause and location in the Digital
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RFC 8606 ISUP Release Location Parameter June 2019
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax