ENUM J. Lim Internet-Draft W. Kim Intended status: Informational C. Park Expires: October 30, 2008 NIDA L. Conroy RMRL April 28, 2008 ENUM-based Softswitch Requirement 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 October 30, 2008. Lim, et al. Expires October 30, 2008 [Page 1] Internet-Draft Softswitch ENUM Use April 2008 Abstract This document describes experiences of operational requirements and several considerations for ENUM-based softswitches concerning call routing between two Korean VoIP carriers, gained during the ENUM pre- commercial trial hosted by National Internet Development Agency of Korea (NIDA) in 2006. These experiences show that an interim solution can maintain the stability of on-going commercial softswitch system operations during the initial stage of ENUM service, where the DNS does not have sufficient data for the majority of calls. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Call Routing on Softswitch . . . . . . . . . . . . . . . . . . 4 3. Infrastructure ENUM trial in Korea . . . . . . . . . . . . . . 5 4. Requirement for ENUM-based Softswitches . . . . . . . . . . . 6 4.1. Call routing cases for DNS response codes . . . . . . . . 6 4.2. Call routing cases for domainparts . . . . . . . . . . . . 7 5. Trial Results . . . . . . . . . . . . . . . . . . . . . . . . 9 6. 'e164.arpa' considerations . . . . . . . . . . . . . . . . . . 10 7. Security Considerations . . . . . . . . . . . . . . . . . . . 11 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 10.1. Normative References . . . . . . . . . . . . . . . . . . . 14 10.2. Informative References . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16 Intellectual Property and Copyright Statements . . . . . . . . . . 17 Lim, et al. Expires October 30, 2008 [Page 2] Internet-Draft Softswitch ENUM Use April 2008 1. Introduction ENUM[RFC3761] is a mapping system based on DNS[RFC1034] [RFC1035] that converts from an E.164[E164] number to a domain name using the Naming Authority Pointer (NAPTR) [RFC3403] resource record type. ENUM is able to store different service types (such as fax, email, homepage, SIP, H.323 and so on), for every E.164 number. It originally focused on how end-users could gain access to other end- user's communications contact information through the Internet. Recently, discussion on the need to update RFC 3761 has begun, to ensure that the standard also works in the "Infrastructure ENUM" scenario, where ENUM provides routing information between carriers. This has resulted in two documents, the updated ENUM specification [draft-rfc3761bis] and an Enumservice guide [draft-enumservice-guide]. When providing VoIP service, a VoIP carrier that wants to integrate various protocols typically uses a softswitch. However, such a system is still inefficient for interconnection, number portability, and sharing protocol support information among carriers, because each softswitch does not have complete end-to-end routing information for all carriers. This information can be stored in DNS, using ENUM. Therefore, carriers can expect to gain many advantages if they use ENUM within the call routing functions of their softswitches. To confirm these benefits and to verify the performance of ENUM- enabled softswitches, NIDA cooperated with two Korean VoIP service providers for an Infrastructure ENUM trial in 2006. NIDA is a non- profit organization with a mandate to manage 2.8.e164.arpa. (representing the +82 country code of Korea). NIDA promotes and facilitates technical cooperation on a national scale between partners, and this includes ENUM. During the trial, NIDA provided a centralized ENUM DNS to each VoIP service provider for call routing. The data used in this Infrastructure trial was also accessible to the public (i.e. it was an Internet-based system, rather than a closed scheme). Lim, et al. Expires October 30, 2008 [Page 3] Internet-Draft Softswitch ENUM Use April 2008 2. Call Routing on Softswitch In the PSTN (Public Switched Telephone Network), hardware-based switches predominate in the network. A softswitch provides similar functionality, but is implemented on a computer system by software. It typically has to support various signalling protocols (such as SIP[RFC3261], H.323[H323], MGCP[RFC3435], and others), to make call connections for VoIP service, often on the boundary point between the circuit and packet network. To make a call, first of all a softswitch must discover routing information. It has to process the E.164 number that comes from a caller through its own routing table. The goal is to determine how the call can be routed towards the callee, so that either the call can be processed through the softswitch or the caller can connect to the callee directly. Today, call routing is often based on a prefix of the dialled number. This is used very widely not only for legacy PSTN switches, but also for softswitches. So, if a softswitch exclusively uses ENUM DNS for call routing, then in the beginning most of the calls queried to ENUM DNS would fail if there are only a small group of carriers provisioning data into ENUM. However a softswitch will have a higher success rate with ENUM DNS as the number of carriers grows, and so the overall percentage of numbers provisioned in ENUM increases. In short, ENUM as a long term solution has obvious benefits, but the problem lies in migrating from today's prefix based routing towards that long term ENUM-based solution. Lim, et al. Expires October 30, 2008 [Page 4] Internet-Draft Softswitch ENUM Use April 2008 3. Infrastructure ENUM trial in Korea As described in Section 1, NIDA and two VoIP Service Providers built ENUM-processing modules into their softswitches, interconnected these via the IP network, and provisioned their trial users' numbers into a centralized ENUM DNS system operated by NIDA. The carriers provisioned their E.164 numbers using EPP [RFC4114] to a centralized Registration Server (also operated by NIDA). Changes to the ENUM data were implemented and updated to the ENUM DNS instantly, using DNS Dynamic Update [RFC2136]. In the trial, the EPP-based provisioning sub-system was developed and operated separately from the carriers' main customer provisioning systems and protocols. It was not integrated as the carriers already operated their own customer provisioning systems that were totally different from the EPP-based model, and (as mission-critical components) those were not open to modification. Call routing +---------------------------------------------+ | | | | +-----+------+ +-----------------+ +------+-----+ |Softswitch A|------| ENUM DNS(+82) |------|Softswitch B| +-----+------+ | (Tier1,2) | +------+-----+ | +--------+--------+ | +-----+------+ | +------+-----+ | IP Phone A | |Dynamic update | IP Phone B | +------------+ |(RFC 2136) +------------+ | +------------+ +--------+--------+ +------------+ | EPP Client | | Registration | | EPP Client | | |------| server |------| | +------------+ +-----------------+ +------------+ Provisioning E.164 Numbers(RFC 4114) Carrier A NIDA Carrier B Figure 1: Infrastructure ENUM Trial System Topology Lim, et al. Expires October 30, 2008 [Page 5] Internet-Draft Softswitch ENUM Use April 2008 4. Requirement for ENUM-based Softswitches 4.1. Call routing cases for DNS response codes To use ENUM DNS, each softswitch needs to have an ENUM module that converts from an E.164 number to the ENUM domain name (as defined in RFC 3761) and processes a query to ENUM DNS. This ENUM module uses the algorithm specified in RFC 3761. However, in the initial stage of ENUM DNS roll-out, ENUM shares call routing information from a limited number of carriers. There is the problem that a softswitch can't find all of the call routing information it needs just using ENUM. To solve this problem, ENUM- based softswitches have to follow a consistent set of rules. In the Korean trial, the rules were: 1. The ENUM module of the softswitch converts an E.164 number coming from the VoIP subscriber to an ENUM domain name (as defined in RFC 3761). 2. The ENUM module, acting as a DNS stub resolver, sends a query to a recursive name server. 3. if the ENUM module receives a DNS answer, the call routing process may branch off in several ways, depending on the Rcode value in the DNS response message, as shown below. A. Rcode=0 (No error condition) There is, potentially, an answer to the corresponding query. The normal call routing process needs to differentiate between the following conditions: + The response includes no URI that can be used to initiate a call (such as SIP or H.323) - The call fails immediately. Note: A domain that DOES exist but DOES NOT include any supported NAPTRs was used to indicate that the telephone number could ONLY be reached by the Internet. A softswitch receiving this response meant that the call could be dropped immediately - it would fail if passed to the PSTN. + There is at least one usable URI (such as SIP and/or H.323 URIs) - The softswitch picks one based on the preference and order values in the NAPTR Resource Record Set, and routes the call using the method described in Section 4.2. Lim, et al. Expires October 30, 2008 [Page 6] Internet-Draft Softswitch ENUM Use April 2008 B. Rcode=3 (Name error), 1 (Format Error), 2 (Server Failure), 4 (Not Implemented) or 5 (Refused) There is no valid answer for the query. The softswitch has no choice but to route the call using the E.164 number with its vendor-specific method (such as a prefix-based method). In this case, it means that the call has to be delivered through the PSTN for onward call routing. It is also important to stress that the ENUM DNS servers MUST respond to all queries they receive from the softswitches. If the ENUM module in a softswitch does not receive a response, it will eventually time out, and the ENUM module will treat this as a DNS error. However, the delay involved is long in terms of the normal call setup time, and should be avoided. 4.2. Call routing cases for domainparts If the DNS response has a valid URI such as SIP or H.323, the softswitch can resolve the domain name part of that URI to route a call by searching two different sources. One is a recursive nameserver, and the other is a fixed routing table held in the softswitch, mapping from the domain name to the corresponding gateway's host name and IP address. If there are many points of interconnection, using a recursive nameserver is useful for resolving a domain name, but if there are just a few known carriers and they do not change this interconnection information frequently, a fixed (internal) routing table mapping from domain name to the corresponding gateway hostname and IP address is more efficient (rather than querying the recursive nameserver every time). In addition, carriers would like to charge an interconnection fee for all received calls, so they tend to make interconnection only with trusted carriers based on some sort of bilateral agreement between these carriers. They may agree on a specific gateway for this purpose, so the interconnection information is often private to the parties of this particular agreement. These two types of domain routing are also affected by the Rcode=0 case described in Section 4.1. There are two choices for routing. These are described and compared here: 1. Case when using a fixed routing table: A. If the domain name part of the URI is found in the internal fixed routing table, the softswitch can use it. Lim, et al. Expires October 30, 2008 [Page 7] Internet-Draft Softswitch ENUM Use April 2008 B. If the domain name part of URI does not exist in the fixed routing table, the call is forwarded to the PSTN. 2. Case when using a recursive nameserver: A. If the domain name part of the URI can be resolved via the recursive nameserver, the softswitch can use it. B. If the domain name part of the URI cannot be resolved on the recursive nameserver for any reason (such as a response with no usable resource records according to [RFC3263] and [RFC3261], or with Rcode=1, 2, 3, 4, or 5), the call must be forwarded to the PSTN. Case (1) seems inefficient because the administrator maintains two management points for numbers; the ENUM DNS and the softswitch itself. However this configuration can minimize the call routing failure ratio during the transition period of ENUM (when there are relatively few provisioned ENUM entries and so few IP-based Points Of Interconnection). Thus case (1) could reasonably be implemented on the softswitches during the trial phase, and hereafter as ENUM entries are populated, case (2) would be a reasonable choice. With these choices, the two carriers could use ENUM DNS for call routing without any impact on their on-going commercial VoIP service. Lim, et al. Expires October 30, 2008 [Page 8] Internet-Draft Softswitch ENUM Use April 2008 5. Trial Results To provide a stable commercial service, an ENUM-based softswitch must have a defined performance, in the same way as must any non-ENUM- based softswitch. The only difference between these two types of softswitch is the searching mechanism for call routing information, which can be stored in the softswitch itself or in the DNS. Therefore a similar delay time for call routing is important to guarantee quality of service. During the trial, each carrier measured this delay time when using the SIP protocol. This was based on the "Answer Delay time", defined as the elapsed time between requesting a call ('INVITE' message) and receiving a response ('200 OK' message) [RFC3261]. +------------------------+------+----------+ | Call Type | ENUM | Non-ENUM | +------------------------+------+----------+ | Carrier A->A | 2.33 | 2.28 | | | | | | Carrier A->B | 2.23 | 2.25 | | | | | | Carrier A->other(PSTN) | 4.11 | 3.79 | | | | | | Carrier B->B | 2.18 | 2.05 | | | | | | Carrier B->A | 2.19 | 2.19 | | | | | | Carrier B->other(PSTN) | 3.95 | 3.41 | +------------------------+------+----------+ Table 1: Average Answer Delay time (sec) As shown in Table 1, there is little difference in time (under a second) between the ENUM and non-ENUM cases. Therefore it is difficult for a caller with either carrier to detect the choice (ENUM or non-ENUM) as an aspect of quality when a call initiates. This means that ENUM definitely works well with softswitches on a commercial basis. To make the trial more realistic, the resolver that was used by these ENUM-based softswitches was a recursive nameserver that could be accessed publicly. This was done as it was felt that a tough condition would be better to verify the fact that an ENUM-based softswitch works as well as non-ENUM-based softswitch in providing a commercial VoIP service. Lim, et al. Expires October 30, 2008 [Page 9] Internet-Draft Softswitch ENUM Use April 2008 6. 'e164.arpa' considerations During the trial, the Infrastructure ENUM deployed in the 2.8.e164.arpa zone could be accessed via the (public) Internet. In this situation, each carrier questioned whether the centralized number management under the ENUM DNS was realistic or not. Another issue concerned responsibility for routing errors. All carriers can use the shared ENUM data to route their calls. However, if there are routing errors (due to the data being provisioned incorrectly), it is not always clear who has responsibility for these errors and who can correct the data. The errors occur in the networks of the carriers placing the calls. Unless the identity of the carrier responsible for delivering service to this telephone number is known, it is not obvious (to the carrier handling the error) who should be informed of these problems. This is a particular issue when number portability is introduced. In addition, the carriers also question whether or not Infrastructure ENUM needs to be accessible publicly. To prevent disclosure of telephone numbers, they would prefer to access the ENUM DNS privately. Therefore any ENUM module embedded in a softswitch needs to be flexible, to adopt these considerations during the interim period of ENUM, before common policies and agreements have been forged. Lim, et al. Expires October 30, 2008 [Page 10] Internet-Draft Softswitch ENUM Use April 2008 7. Security Considerations This document inherits the security considerations described in RFC 3761 and 'draft-ietf-enum-infrastructure-05.txt' [draft-enum-infrastructure], as the ENUM DNS used with softswitches in this trial could be accessed publicly. In addition, if the recursive resolvers handling ENUM queries coming from a softswitch were to be compromised by an attacker, that attacker would be able to force calls to fail or cause delay to calls. Therefore, the DNS resolvers used should allow access from the local network to which the softswitch is connected, whilst restricting access from outside, using a proper access-list policy. Lim, et al. Expires October 30, 2008 [Page 11] Internet-Draft Softswitch ENUM Use April 2008 8. IANA Considerations This document is only advisory, and does not have any IANA considerations. Lim, et al. Expires October 30, 2008 [Page 12] Internet-Draft Softswitch ENUM Use April 2008 9. Acknowledgements Thanks to Richard Shockey, Jason Livingood, Karsten Fleischhauer, Jim Reid and Otmar Lendl who helped guide the direction of this document. Lim, et al. Expires October 30, 2008 [Page 13] Internet-Draft Softswitch ENUM Use April 2008 10. References 10.1. Normative References [E164] ITU-T, "The International Public Telecommunication Number Plan", Recommendation E.164, February 2005. [RFC1034] Mockapetris, P., "DOMAIN NAMES - CONCEPTS AND FACILITIES", RFC 1034, November 1987. [RFC1035] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, November 1987. [RFC3403] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part Three: The Domain Name System (DNS) Database", RFC 3403, October 2002. [RFC3761] Faltstrom, P. and M. Mealling, "The E.164 to Uniform Resource Identifiers (URI) Dynamic Delegation Discovery System (DDDS) Application (ENUM)", RFC 3761, April 2004. 10.2. Informative References [H323] ITU-T, "Packet-based multimedia communications systems", Recommendation H.323, 2003. [RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, "Dynamic Updates in the Domain Name System (DNS UPDATE)", RFC 2136, April 1997. [RFC3261] 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. [RFC3263] Rosenberg, J., "Session Initiation Protocol (SIP): Locating SIP Servers", RFC 3263, June 2002. [RFC3435] Andreasen, F. and B. Foster, "Media Gateway Control Protocol (MGCP) Version 1.0", RFC 3435, January 2003. [RFC4114] Hollenbeck, S., "E.164 Number Mapping for the Extensible Provisioning Protocol (EPP)", RFC 4114, June 2005. [draft-enum-infrastructure] Livingood, J., Pfautz, P., and R. Stastny, "The E.164 to Uniform Resource Identifiers (URI) Dynamic Delegation Discovery System (DDDS) Application for Infrastructure Lim, et al. Expires October 30, 2008 [Page 14] Internet-Draft Softswitch ENUM Use April 2008 ENUM", draft ietf-enum-infrastructure-05.txt (work in progress), January 2007. [draft-enumservice-guide] Hoeneisen, B., Mayrhofer, A., and J. Livingood, "Guide and Template for IANA Registrations of Enumservices", draft-ietf-enum-enumservices-guide-06.txt (work in progress), November 2007. [draft-rfc3761bis] Bradner, S., Conroy, L., and K. Fujiwara, "The E.164 to Uniform Resource Identifiers (URI) Dynamic Delegation Discovery System (DDDS) Application (ENUM)", draft-ietf-enum-rfc3761bis-03.txt (work in progress), February 2008. Lim, et al. Expires October 30, 2008 [Page 15] Internet-Draft Softswitch ENUM Use April 2008 Authors' Addresses JoonHyung Lim National Internet Development Agency of Korea(NIDA) 3F. KTF B/D 1321-11, Seocho-dong, Seocho-gu Seoul Korea Phone: +82-2-2186-4548 Email: jhlim@nida.or.kr URI: http://www.nida.or.kr Weon Kim National Internet Development Agency of Korea(NIDA) 3F. KTF B/D 1321-11, Seocho-dong, Seocho-gu Seoul Korea Phone: +82-2-2186-4502 Email: wkim@nida.or.kr URI: http://www.nida.or.kr ChanKi Park National Internet Development Agency of Korea(NIDA) 3F. KTF B/D 1321-11, Seocho-dong, Seocho-gu Seoul Korea Phone: +82-2-2186-4504 Email: ckp@nida.or.kr URI: http://www.nida.or.kr Lawrence Conroy Roke Manor Research Roke Manor Old Salisbury Lane Romsey United Kingdom Phone: +44-1794-833666 Email: lconroy@insensate.co.uk URI: http://www.sienum.co.uk Lim, et al. Expires October 30, 2008 [Page 16] Internet-Draft Softswitch ENUM Use April 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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. 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