INTERNET-DRAFT J. Loughney Internet Engineering Task Force Nokia James Yu Issued: 14 July 2000 NeuStar Expires: 14 January 2001 Roaming Support with DNS Status of This Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC 2026. 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. Abstract This draft proposes a new service to support cellular roaming. It calls for a new service type, called 'roam' to be stored in DNS. This draft outlines the resolution of telephone numbering plans (E.214, E.212 and E.164, among others) by DNS to support cellular roaming. Considerations need to be made for scalability, reliability and performance. Internet Draft Roaming Support with DNS July 12, 2000 Abstract..............................................................1 1 Introduction........................................................3 1.1 Scope ...........................................................3 1.2 Terminology .....................................................3 2 Overview............................................................3 3 Formats.............................................................4 3.1 Storage of E.164 numbers ........................................4 3.2 NAPTR RR Format .................................................4 3.2 Lookup Format ...................................................4 4 Examples............................................................4 5 Security Considerations.............................................5 6 Scalability Concerns................................................5 7 IANA Considerations.................................................5 8 Acknowledgments.....................................................6 9 Author's Addresses..................................................6 10 References.........................................................6 Full Copyright Statement..............................................7 Loughney, Yu [Page 2] Internet Draft Roaming Support with DNS July 12, 2000 1 Introduction This document proposes a new service, called 'roam' to enable roaming in cellular systems (2G, 3G), supported by using the ENUM solution for DNS resolution of E.164 numbers. By querying DNS for the roaming service entity for the particular E.164 number, DNS can return the location of the network element that supports the cellular roaming services (i.e. - HLR, VLR, AAA server). 1.1 Scope This document introduces a new service into DNS. How roaming is provisioned by operators and service providers is outside of the scope of this document. 1.2 Terminology 2G - 2nd Generation 3G - Third Generation AAA - Authentication, Authorization and Accounting ENUM - Telephone Number Mapping GT - SS7 Global Title GTT - Global Title Translation HLR - Home Location Register SRV RR - Service Resource Record SS7 - Signaling System No. 7 VLR - Visitor Location Register 2 Overview As IP based cellular networks are being developed, there is an ongoing process of aligning PSTN and cellular networks with IP based networks. This introduces some complications for address resolution, especially when users roam outside of their home networks. Also, certain Application Protocols may carry addressing information to be used as the SS7 Global Titles. For translation selectors that use E.214, E.212 and E.164 numbering plans (translation type 0), services can be defined for each translation selector, so that ENUM can be used to retrieve the corresponding Resource Record associated with the visited/home Loughney, Yu [Page 3] Internet Draft Roaming Support with DNS July 12, 2000 network element (e.g., HLR, VLR, AAA server). The next step will involve the sending of a "roam" related application message using a specific protocol (e.g., TCP or SCTP) to the cellular network element corresponding to the domain name in the Target field of the retrieved SRV RR. This assumes a public IP network. If the network elements always use the E.164 numbers in the GT for the subsequent messages, it may be worthwhile to add IP address as another option for the roaming service entity (i.e. - HLRID, VLRID, etc.) as an enhancements to a SS7 Application Protocol, but that is outside of the scope of this document. 3 Formats 3.1 Storage of E.164 numbers The rules for storing an E.164 number in DNS are described in [E.164-DNS]. A quick overview is: Take a full E.164 number (including country & city codes), remove all non-digit characters. Insert a dot (i.e. - '.') between all the digits. Reverse the order of the digits. Append the .e164.arpa domain to the end. This is the DNS name of the E.164 number. For example: +358 40 749 9122 becomes 2.2.1.9.9.4.7.0.4.8.5.3.e164.arpa. 3.2 NAPTR RR Format Following the format given in [NAPTR], we follow the format given by the statement. ;; order pref flags serv regexp replacement IN NAPTR 100 10 "" "" "/urn:cid:.+@([^\.]+\.)(.*)$/\2/i" . The service field should be filled in with "_roam+E2R" for support of the roam service. 3.2 Lookup Format If a client wants to discover the server providing the ROAM service, using a particular transport protocol (for example TCP, SCTP) it should do a lookup of the particular E.164 number in question: x.x.x.e164.arpa where x.x.x is the processed E.164 number returned by step 1 on the ENUM service. 4 Examples Loughney, Yu [Page 4] Internet Draft Roaming Support with DNS July 12, 2000 This example shows how the 'roam' service could be used. This is only an example - any resemblance to any existing services or domains (living or dead) is purely coincidental. The use of SCTP in the example is purely for illustrative reasons. The DNS record would be: $ORIGIN 1.1.1.0.6.8.5.3.e164.arpa. IN NAPTR 10 10 "s" "roam+E2I" ""_sctp.hlr.nokia.com This indicates that the we should look up the SRV record of _sctp.hlr.nokia.com, to find the actual host(s) supporting this service. Note that there would likely be other services in the DNS record. The next step would to query _sctp.hlr.nokia.com, which could return: ;; Pref Weight Port Target _sctp.hlr.nokia.com IN SRV 0 0 1000 glc1.nokia.com IN SRV 0 0 1000 glc2.nokia.com IN SRV 0 0 1000 glc3.nokia.com This indicates that there are three hosts that actually provide the roam services. 5 Security Considerations As this service is built on top of DNS, the results from any query will not be more secure than any other DNS query. DNSSEC is therefore, is strongly recommended for securing and verifying zones. 6 Scalability Concerns This may have an impact on ENUM provisioning. "roam" is the first service where E.164 numbers are used by the telephony service providers that has nothing to do with many end-user services (e.g., e-mail, personal web page, SIP server). There are many other possible services such as calling card database, switches that serve a particular E.164 number. ENUM's existing process requires that one ANS knows all the services about a particular E.164 number. This introduces possible scalability problems. 7 IANA Considerations Cellular roaming requires three GTTs: one on E.214 (E.214 mobile global title to HLR) and the second on E.164 (E.164 number to a network element such as HLR, VLR, AuC and MSC) and the third on E.212 (E.212 to HLR) (E.212 is used by IS-41 based systems). E.214 number is similar to a E.164 number, but it is not E.164 strictly Loughney, Yu [Page 5] Internet Draft Roaming Support with DNS July 12, 2000 speaking. E.212 numbers should be located in the e214.arpa domain, which needs to be allocated. For the purpose of using ENUM, E.214 can be treated as E.164 (E.214 numbers look like E.164 numbers, but its length or number digits, may not be the same as that of the regular E.164 number. This should not be a problem because only the leading digits are required to perform the GTT. Each GTT table will require an IANA "service" to get the proper mapping if ENUM is to be used to perform the similar functions. Only one service is needed - "roam", but we need IAB to reserve e214.arpa and e212.arpa just like e164.arpa. 8 Acknowledgments The authors would like to thank Michael Mealling for his illustrative examples on the ENUM mailing list. 9 Author's Addresses John Loughney Nokia Research Center PO Box 407 FIN-00045 Nokia Group Finland Email: john.loughney@nokia.com James Yu NeuStar, Inc. 1120 Vermont Avenue, NW, Suite 550 Washington, D.C. 20005 United States Email: james.yu@neustar.com 10 References [ENUM-REQ] "ENUM Requirements" , December 1999, Work in Progress. [E.164-DNS] "E.164 number and DNS" , July 10, 2000, Work In Progress. [ENUM-OP] "ENUM Service Specific Provisioning: Principles of Operation", , April 2000, Work in Progress. Loughney, Yu [Page 6] Internet Draft Roaming Support with DNS July 12, 2000 [RFC 2782] Gulbrandsen, Vixie and Esibov, "A DNS RR for specifying the location of services (DNS SRV)" RFC 2782, February 2000. [RFC 1034] Mockapetris, P., "Domain names - concepts and Facilities", STD 13, RFC 1034, November 1987. [NAPTR] Mealling, M.; Daniel R. "The Naming Authority Pointer (NAPTR) DNS Resource Record"; ; June 24, 1999; Work in Progress. Full Copyright Statement Copyright (C) The Internet Society (2000). 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. This draft expires on 14 January 2001 Loughney, Yu [Page 7]