Network Working Group D. Schwartz Internet-Draft Kayote Networks Intended status: Standards Track July 2007 Expires: January 2, 2008 No Service To This Number Reject Code draft-schwartz-sip-nsr-code-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 2, 2008. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract The Session Initiation Protocol (SIP) allows calls to both addresses of record (AORs) such as sip:alice@example.com and telephone numbers with either sip or tel schemes such as tel:+12127771234. As opposed to the AOR where the domain specifies the exact location or realm of the user and a reject code provides enough visiblity to the calling party to exit gracefully (e.g. a 404 indicates that there is no point in trying further as the requested user either does not exist or is offline with no voicemail) with telephone numbers (TNs) this is not Schwartz Expires January 2, 2008 [Page 1] Internet-Draft Termination Based Reject July 2007 the case. With more and more TNs representing actual IP endpoints there is a need to differentiate in an error code between rejecting a call due to a misdialed number (i.e. the number does not exist) and a number that is just not associated with an IP endpoint (for example in a case where there is no billing relationship and as such the rejecting proxy cannot forward to a PSTN termination provider. This specification defines a new SIP response code (No Service Reject - nsr) for this purpose. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. UAS Behavior . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. UAC Behavior . . . . . . . . . . . . . . . . . . . . . . . . . 4 5. 4XX (No Service To This Number) Definition . . . . . . . . . . 4 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4 7. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5 9.1. Normative References . . . . . . . . . . . . . . . . . . . 5 9.2. Informative References . . . . . . . . . . . . . . . . . . 5 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6 Intellectual Property and Copyright Statements . . . . . . . . . . 7 Schwartz Expires January 2, 2008 [Page 2] Internet-Draft Termination Based Reject July 2007 1. Introduction The Session Initiation Protocol (SIP) [SIP] facilitates outgoing calls to a UAS, or proxy acting on its behalf, by having the caller enter either an address of record in the form sip:user@domain, sip: telephone-number or tel:telephone-number with some additional tags (e.g. phone-context). The underlying premise behind both the AOR and TN approach is that the requested user is either served by the UAS receiving the request or that this proxy/server will find the requested user and connect the call. Any failure to complete the call is held against the UAS in the form of reduced ASR or other such metrics. While this makes perfect sense in the case where the request uri contains an AOR where the implicit assumption is that the requested user is IP enabled, in the case where the request URI contains a TN this is not always the case. More and more IP endpoints are using TNs in the form of Direct Inward Dial (DID) numbers that look and smell like ordinary numbers but in reality are actual IP termination endpoints. A service providing free termination to IP endpoints only may wish to respond to a request for an actual PSTN resource (discovered for example by dipping into a private ENUM registry and not finding the TN) with an error code other than 404 to indicate that this number was not found in the free space and perhaps should be reattempted using a different outbound proxy and that the failure should not be held against the ASR rating of this original proxy. SIP does not provide a response code that allows the UAS, or a proxy acting on its behalf, to explicitly indicate that the request was rejected because it was not an IP endpoint served by this UAS. The closest response code is 404 (Not Found), which doesn't convey a specific reason. While it is possible to include a reason phrase in a 404 response that indicates to the human user that the call was rejected because this particular UAS does not service that number, a reason phrase is not useful for automata in the form of LCR engines receiving the response. An indication that can be understood by an automaton would allow for programmatic handling, including automatic retries and proper classification of error in dynamic LCR environments. To remedy this, this specification defines the 4XX (No Service To This Number) response code. 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 RFC 2119 [TERM]. Schwartz Expires January 2, 2008 [Page 3] Internet-Draft Termination Based Reject July 2007 3. UAS Behavior A server (generally acting on behalf of the called party, though this need not be the case) MAY generate a 4XX (No Service To This Number) response when it receives a request for a TN that is not serviced by this UAS. The reasons for lack of service may be any one of the following cases: * The requested TN does not exist in the realm that this UAS is responsible for and no forwarding rules are defined * The requested TN exists however it is part of a number block that has been assigned but not activated * The requested TN exists however the caller has an assumed behavior (e.g. free calls) and the requested TN does not fulfill this assumption In all these cases the 4XX (No Service To This Number) response should be returned indicating this case. 4. UAC Behavior A UAC receiving a 4XX (No Service To This Number) MUST NOT retry the request to same UAS and SHOULD fail over to alternate User Agent Servers if these are available to try to complete the call. Receipt of a 4XX response to a mid-dialog request SHOULD NOT cause the dialog to terminate, and SHOULD NOT cause the specific usage of that dialog to terminate [MIDDIALOG]. A UAC that does not understand or care about the specific semantics of the 4XX response will treat it as a 400 response. 5. 4XX (No Service To This Number) Definition This response indicates that the server refused to fulfill the request because the resource being requested by the caller is not availble at this UAS but may be available elsewhere. Its default reason phrase is "No Service To This Number". 6. IANA Considerations This section registers a new SIP response code according to the procedures of RFC 3261. RFC Number: RFC XXXX [[NOTE TO IANA: Please replace XXXX with the RFC number of this specification]] Schwartz Expires January 2, 2008 [Page 4] Internet-Draft Termination Based Reject July 2007 Response Code Number: 4XX Default Reason Phrase: No Service To This Number 7. Security Considerations The fact that a request was rejected because it was targeted at a resource that is not available at a particular UAS does in fact reveal sensitive information about the called party - the actual numberspace served by this UAS. This information may or may not be sensitive. If it is, a UAS SHOULD reject the request with a 404 instead. 8. Acknowledgements This draft was motivated by trials at XConnect Global Networks where rejection of TN requests by participating operators led to reduced ASRs and consequential automatic removal from operator LCR tables when rejection by XConnect was due to TN being an PSTN endpoint (non-IP) and not server error or other termination failure problem justifying the reduced ASR. 9. References 9.1. Normative References [SIP] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [TERM] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. 9.2. Informative References [MIDDIALOG] Sparks, R., "Multiple Dialog Usages in the Session Initiation Protocol", draft-ietf-sipping-dialogusage-06 (work in progress), February 2007. [WARNING] Hautakorpi, J. and G. Camarillo, "Extending the Session Initiation Protocol Reason Header with Warning Codes", draft-hautakorpi-reason-header-for-warnings-00 (work in progress), October 2005. Schwartz Expires January 2, 2008 [Page 5] Internet-Draft Termination Based Reject July 2007 Author's Address David Schwartz Kayote Networks Malcha Technology Park Building # 1 Jerusalem 90961 Israel Phone: +972 52 347 4656 Email: david.schwartz@kayote.com URI: www.kayote.com Schwartz Expires January 2, 2008 [Page 6] Internet-Draft Termination Based Reject July 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). 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The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Schwartz Expires January 2, 2008 [Page 7]