INTERNET-DRAFT Randy Bush draft-ymbk-enum-trip-00.txt AT&T Research 2001.07.13 How ENUM, SIP URIs, TRIP, and Gateways Relate "49 reasons all in a line. All of them good ones, all of them lies." -- csn Copyright (C) The Internet Society (2001). All Rights Reserved. This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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. 0. Abstract The often tenuous relationships between ENUM [RFC2916], TRIP [RFC2871], SIP [RFC2543], and SIP gateways have been confusing. This document attempts to clarify them somewhat. 1. ENUM, a Simple Case ENUM DNS lookup processing takes a telephone number in E.164 format, e.g. +19733607330 [0], and returns, for example a URI SIP:randyoffice@psg.com, and the client places a SIP connection to the host which is named in the SRV record for the domain psg.com passing the SIP URI. I.e., in the above example, a client places a connection to the gateway psg.com passing the local part "randyoffice." ENUM can return a wide variety of URI types, this was a simple example. R Bush Expires 2002.01.13 [Page 1] INTERNET-DRAFT ENUM, SIP URIs, TRIP, and Gateways 2001.07.13 2. TRIP, the 'Simple' Case: Given a phone number +19733607330, SIP URI sip:+19733607330, etc., the client on the caller's host hands it to their local call server (PBX or whatever, we will use PBX). For policy reasons (perceived cost savings, whatever), the local PBX is configured to be part of one or more TRIP consortia. I.e. it has or knows one or more TRIP location servers (LSs). TRIP servers form a mesh, usually mapping business relationships and policies, in which they pass around PSTN reachability data analogously to how BGP-speakers pass IP prefix reachability data. So a TRIP server will tell the client's PBX the 'best', in terms of policy, cost, aroma, etc., destination gateway where their call can exit the Internet to the PSTN. The user's PBX will place the call to the gateway, acting as a proxy for the user. Unlike BGP-speaking routing, where the data path follows the signal path, i.e. packets follow the BGP speaker mesh, TRIP servers provide a similar signaling mesh, but the SIP signaling and data paths are independent of the TRIP mesh, using IP routing, quite possibly never touching a TRIP speaker en-route. Similarly, SIP separates signaling from data. so the SIP data path is expected to often not be congruent with the SIP servers setting up that path. 3. ENUM and TRIP Either the user's client, or their PBX acting as their proxy, might use ENUM to look up a telephone number in E.164 format, e.g. +19733607330, to get a set of URIs which might refer to many types of things. Some of these might be direct TEL URIs, e.g. direct references to PSTN gateways, or SIP URIs, or to use TRIP, or if the client itself is configured to use TRIP, TRIP location services will be used to find the gateway. 4. TRIPped Up Note that there is no specified protocol between a client, be it a desk- or lap-top or a proxy PBX, and a TRIP location server. [RFC2871] sec 10.2 blithely tells us that "There are numerous protocols that can be used in the front end to access the LS database. TRIP does not specify or restrict the possibilities for the front end." And [RFC2871] then goes on to suggest SLP, OSP, LDAP, HTTP, or TRIP itself. Some may not find this cheering. R Bush Expires 2002.01.13 [Page 2] INTERNET-DRAFT ENUM, SIP URIs, TRIP, and Gateways 2001.07.13 5. Footnote [0] - It seems worth noting, as there has been so much misunderstanding, obfuscation, and FUD generated about this, that the control of delegation of NS chains, and hence DNS content, of the E164.ARPA zone is clearly specified to be in the hands of the ITU, see [RFC2916] and [RFC3026]. 6. Security Considerations This document is merely an extremely high-level description of some relationships between current protocols. Undoubtedly these protocols each have security issues. These issues are best discussed in the relevant documents, not here. Of course, by revealing the relationships between these protocols, this document may open them to an anti-complexity attack from within the IETF community. 7. Acknowledgments Allison Mankin incited this small effort. Scott Bradner provided a lot of clue. Harald Alvestrand and Patrik F"altstr"om provided very useful tuning. 8. References [RFC2543] SIP: Session Initiation Protocol. M. Handley, H. Schulzrinne, E. Schooler, J. Rosenberg. March 1999. [RFC2871] A Framework for Telephony Routing over IP. J. Rosenberg, H. Schulzrinne. June 2000. [RFC2916] E.164 number and DNS. P. F"altstr"om. September 2000. [RFC3026] Liaison to IETF/ISOC on ENUM. R. Blane. January 2001. R Bush Expires 2002.01.13 [Page 3] INTERNET-DRAFT ENUM, SIP URIs, TRIP, and Gateways 2001.07.13 9. Author's Address Randy Bush 5147 Crystal Springs Bainbridge Island, WA US-98110 +1 206 780 0431 randy@psg.com 10. Full Copyright Statement Copyright (C) The Internet Society (1999). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. R Bush Expires 2002.01.13 [Page 4]