Authors: Jakob Fredriksson & Jakob Schlyter (Guide) GUIDE/NOS/NORID-ENUM-2/REPORT/001 Approved: Hilde Thunem Rev.

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1 Norid report Page 1 (16) This report is a subset of a complete ENUM report that was originally produced for Norid by Jakob Fredriksson & Jakob Schlyter, Guide Konsult Göteborg AB. This subset contains information that is assumed to be useful for anyone interested in ENUM in Norway. Among other things, it describes relevant areas of work if a more extensive field test should follow from the current test project. ENUM Report Authors: Jakob Fredriksson & Jakob Schlyter (Guide) Copyright 2003, UNINETT Norid AS Guide Konsult Göteborg AB Olof Asklunds gata 10 SE Västra Frölunda Sweden Telephone url:

2 Norid report Page 2 (16) Contents 1Introduction...3 2The Model of ENUM ENUM Roles Organizing ENUM One ENUM Registry ENUM Registry Tasks Validation Organizing Competition Organizing Registrars Supervision...7 3The ENUM Framework The Market for ENUM ENUM Customers and Users Amount of ENUM Users ENUM Registry Customers A Fair Competition Liabilities and Regulations Relations to E.164 Actors Business Models and Payment Schemes The Value of ENUM for the End Users Termination Fees The Costs of ENUM Conclusions and Recommendations Security Considerations References...16

3 Norid report Page 3 (16) 1 Introduction ENUM is best described as a protocol and a database enabling a service which translates an E.164 (PSTN) number to a URI (Uniform Resource Identifier). A URI can point to various types of resources such as a mail address (mailto:user@example.com), a web page ( or a SIP address (sip:user@example.com). The purpose is that, if you know a person s normal telephone number (the E.164 number), you should be able to look up the ways in which you can communicate with this person. This enables various ways of communication, but the focus has been on services that enables voice communication over the Internet (VoIP). One of the protocols enabling such services are SIP (Session Initiation Protocol). Even though ENUM services are fairly small in scope and easy to implement into an existing DNS service, it is a topic that arises a lot of questions and is believed to have a large impact on the cost-benefit calculations for the competitors on the PSTN market. This leaves us with a difficult problem regarding strong actors and low level on knowledge regarding ENUM. ENUM is defined in RFC 2916 and is revised in a Internet draft also known as 2916bis. The relationship between IETF and ITU was resolved at ITU-T Working Party 1/2 meeting held in Berlin, October 2000 (the liaison is documented in Liaison to IETF/ISOC on ENUM [WP1-2] and RFC3026 [RFC3026]). ENUM isn t necessarily about telephone communication over the Internet. This is a common misconception often heard from the telecom industry and leads to the misunderstanding that telecom industry will loose profits if ENUM is implemented. ENUM is just a database and a specification of how to get the data in the database. The only formal connection between the telecom industry and ENUM is that ENUM utilizes the E.164 number plan. If ENUM hadn t used that number plan, it would have been a matter only for the Internet community. But, since the E.164 number plan was chosen the telecom industry and all its regulations must be taken into account. Many people ask what application that would be envisioned as the killer application of ENUM and is indeed difficult to come up with a good answer. Most probably, ENUM will initially be used for simple E.164 number to SIP address mapping for VoIP or E.164 number to address mapping for SMS/MMS. As the usage of ENUM increases and the comprehension of how ENUM can be used grows, other applications will join the simple, but yet very useful, voice application.

4 Norid report Page 4 (16) 2 The Model of ENUM 2.1 ENUM Roles The main roles of ENUM are: Registry The entity that is responsible for operating ENUM in a country and have received the delegation of the ENUM domain corresponding to the E.164 country code (for Norway.7.4.e164.arpa) from RIPE NCC (evaluation and approval is made by ITU-T TSB). The registry ensures that reference is made to the servers in which the ENUM information is located. Registrar The party who manages the registrant s access information and ensures that it is publicly available on the Internet. Registrant The registrant is the person who makes his access information available to others through ENUM. DNS Provider The actor that operates the servers on which the ENUM information is stored and made available to the public. The actual ENUM information is stored in DNS using NAPTR records. The government It is only a country s representative in ITU-T that can request a delegation of the ENUM domain to the country s ENUM registry. The government might want to be involved in ENUM of several reasons, mainly based on the fact that telephony is a very important service to the public and that voice over IP applications (VoIP, IP telephony) is regarded as the killer application for ENUM implementations. Norway s representative in ITU-T is Postog teletilsynet ( Other actors with a direct interest in ENUM can be the number holders that have been authorized to hold a part of the country s number plan for their customers. They will perhaps be involved regarding the issue of who owns a number and the authorization of the registrant. The issue is made even more complex by the fact that a number portability scheme has been adopted. The issue of who actually owns a number is a great challenge to be resolved. 2.2 Organizing ENUM Since ENUM data is offered through DNS, it is tempting to state that ENUM should be organized in the same manner as the cctld and the subdomains are organized. Unfortunately, this is to simplify the reality too much. ENUM is not only about providing a database for access information, but will affect the communication market substantially. Depending on how ENUM will be used different issues stands out, but the following is a list of the most important issues: Operation The operation of ENUM is decisive and should be conducted as to satisfy the requirements of the users of ENUM. This might seem to be an obvious statement, but rises several important questions:

5 Norid report Page 5 (16) Should the administration of ENUM be designed to fit the telecom industry s current procedures regarding billing, registration, subscription, etc? Should ENUM be organized as to promote cooperation with current usages of means for communication, or should it be structured as to promote creation of new technologies and applications? The problem becomes practical if ENUM should be organized to fit current applications and perhaps divided into one range for fixed telephony and another for mobile phones. Competition The purpose of promoting competition could be twofold: robustness of services and adequate prices. Security ENUM depend on the quality of ENUM services (robustness, performance, etc.) and the level of security. Cost and benefits ENUM could be considered as a resource for the society as a whole, in the same manner as infrastructure is considered to be. Regulations Depending on how ENUM is organized, different measures (regulations, supervision requirements, etc.) must be taken to ensure that the goals of ENUM are fulfilled of all parts that compose the ENUM implementation in Norway One ENUM Registry As might be understood from this section s heading, we believe that there should be but one ENUM registry. Apart from that we believe that the organization of cctld s in Norway (and their subdomains) also would fit ENUM in Norway, we find reasons for a single registry when investigating cost, competence, quality and administrative issues. Since the usage of ENUM is to be defined by emerging technologies it is utterly important for the organization of ENUM not to thwart any usage of ENUM so the business opportunities can be made profitable. The organization of DNS have proven to be efficient in not preventing business opportunities that where unforeseen. DNS have also scaled far beyond it s original design in respect of size and usage. We believe that this are very good reasons to implement a similar organization for ENUM. The implementation of DNS in Norway have today a reliable and thorough tested organization which have been accepted by and earned respect from all DNS actors (ISP s, DNS operators, registry, registrars, registrants). Supervision procedures and regulations are being revised and modernized. ENUM should be organized to take advantage of the experience from the organization of DNS, and can be organized in a similar way. The only aspect that differs is that ENUM needs different means for validation of the applicant. The validation can however be defined as an independent procedure in the organization of ENUM, with a well defined interface toward the other parts of the ENUM organization. This render it possible to organize ENUM is a way that are similar to DNS, and to take advantage of the experience that have been aggregated over the years. We believe that the cost of having several ENUM registries would be larger than having a monopoly. The tasks are (or can be) very strictly defined so there are not much

6 Norid report Page 6 (16) to gain from having competition between different registries. Even more, the definition of ENUM as a database incorporated in DNS makes it impossible to implement true competition since there cannot be two registry s that answers questions about the same ENUM record (the ENUM representation of the E.164 number). In the case of several registry s, the ENUM namespace had to be divided for each of the registry s. This would lead to implications regarding how such division should be done, and could affect the pace at what emerging technologies and new applications could use ENUM. Several ENUM registries does not guarantee that the quality of the ENUM registry services are kept at the same level. It will also be harder and more costly to supervise and handle complaints. Accreditation of registrars, the administration of agreements, delegation procedures, self-supervision, and other administrative tasks would be more costly with several ENUM registries than it would be with a single one. To conclude: There are no benefits from implementing competition at the ENUM registry level. It would even be more costly and the quality of ENUM services would suffer. Several ENUM registries should lead to a complicated organization that might even oppose the emergence of new applications that uses ENUM. Several administrative tasks would be more costly to perform in the case of several ENUM registries. We strongly recommends that ENUM is organized with a single registry ENUM Registry Tasks The following items is a list of the ENUM registry tasks. DNS functions The registry provides zone files for the domain 7.4.e164.arpa. It is important to understand that the registry is not a distribution mechanism, but a provider of zone files. Registry services The registry offers registry services to ENUM registrars and DNS operators. Information The registry informs the ENUM actors about rules, regulations and administrative procedures used to manage the registry. The registry also keeps information about the requirements put on the registrars publicly available. Competition The registry manages and develops its organization is such way that all ENUM actors receives fair treatment. Accreditation of registrars The registry accredits ENUM registrars through registrar agreements Validation We believe that validation of ENUM registrations and other changes of the ENUM

7 Norid report Page 7 (16) databases should be put on the registrars (and partly on the DNS operators). This mitigates the administrative effort needed to perform validation of requests. This will however put requirements on the relation between the registrar and the registry. The registry must be able to trust that the registrar has performed the validation in a trustworthy way. The ENUM actors and potential actors must be involved in the planning of the validation procedures, since it might inflict upon their calculations of how profitable certain business opportunities are. We recommend that this issue is resolved as a part of a field test Organizing Competition As described in section 3.1.4, competition is organized (promoted) through an agreement. Since this is enough for the DNS registrar market, it should be enough for the ENUM market as well Organizing Registrars The ENUM Registrars should be organized and controlled through registrar agreements. The registrars must conclude that agreement with the registry before they are accredited as ENUM Registrars..no is using these kind of agreements today to organize and control DNS registrars (see Registraravtale [REGAVTALE]). This agreement need to be revised to be useful in the ENUM case, but is a very good starting point. We recommend that the current registrar agreement is copied and revised to be useful in the ENUM organization. We also recommend that the agreement is tested during a field test of ENUM. We have no recommendation today as to what the agreement should contain, but it should at least regulate the DNS issues and how validation should be conducted (so the registry can be assured that it is done in a trustworthy manner) Supervision As well as the organization and management of the domain.no, the organization and management of the ENUM domain 7.4.e164.arpa need supervision. The organization and management of the registry for.no is supervised by PT. The same would be appropriate for ENUM since ENUM render access to communication information possible. 3 The ENUM Framework 3.1 The Market for ENUM This section defines and discusses the actors that must be a part of the ENUM work and the actors that have an interest in the ENUM work (or non-work). It also discusses the customers to the ENUM registry and how to promote fair competition between them. Finally it estimates the usage of ENUM in Norway ENUM Customers and Users It is not obvious who the customers and users of access information derived from an ENUM database (NAPTR records) are. The person making the call might not even be

8 Norid report Page 8 (16) aware of the fact that ENUM is utilized to obtain the necessary information to reach the called person. This is the fact for PSTN (the normal telephone network) calls where routing information etc. is derived from a source of information that almost no end users of telephones are aware of. Whether the end user is the customer and/or user of ENUM is a matter of how the number plan and the number portability plan is implemented. The end users are probably the same as the subscribers of a telephone line (and number) and in a sense the user of access information derived from an ENUM database. The natural user of access information derived from ENUM is the applications in need of it. The entity that offers the services that such applications uses would therefore be the users of ENUM. The customer of ENUM is the entity providing the end user with a package of services, of which the services of ENUM might be a part. IP telephony, often put forward as the killer application for ENUM, might be a service utilizing ENUM to provide telephony services to the public. The provider of the applications that derive access information from the ENUM databases is the natural customer of ENUM. Such providers might be the current providers of telephony or Internet services. The user of ENUM is probably not the end user, but it is information about and originating from the end user that will compose the ENUM database. The providers of applications using ENUM will perhaps use ENUM to offer added value to their services. Regarding telephony, it could for example be redirection of incoming calls to the preferred application (mobile phone, stationary phone, etc.) in an order set by the end user. As you probably have understood at this point, the term user not very useful in the ENUM framework and we define it as the end user of the access information derived from an ENUM database. The term customer is mostly applicable when discussing billing. The end user is often the customer of a customer of ENUM services. For larger implementations however this is not the case. A large company or organization might want to run its own ENUM services to be able to take full advantage of ENUM. Thus, the customer of ENUM is the entity providing the user with services or applications utilizing ENUM Amount of ENUM Users The amount of ENUM users is hard to estimate and depend on several issues: Larger organizations and companys need for improved or new access applications. The cost of administering PBX/PSTN telephones at larger installations. Some Swedish organizations have already seen the possible efficiency gain by limiting the need for competence to one area: IP networking. By moving toward using IP telephony their need for resources regarding PBX/PSTN is eliminated and the IT departments skills can be utilized instead. How and at what scale the deployment of broadband VoIP telephony is implemented.

9 Norid report Page 9 (16) Norwegian telephone customers seems to be rather apt to adopt new means of making their telephone bills a bit smaller. According to Post- og teletilsynet s (PT) compilation of telecom market statistics of the first 6 months of year 2002 [TELESTAT2002], the introduction of carrier preselection was a success. Almost 25% of the fixed network telephone customers chose carrier preselection during the first years ( ). Some 25% of them have returned to Telenor since. The figures are not important as such, but shows us that Norwegian people are interested in opportunities and perhaps even new technologies. Even though the public seems to be apt to adopt the concept of carrier preselection, it is a larger step to convert to using IP telephony. In the short term it is very hard to estimate the public s interest in applications using ENUM, but in the long term we believe that ENUM will be a part of almost all access applications. The amount of users will then consequently be almost all persons that hold some means of communication. Even though an estimation of ENUM users amongst the public is far fetched, the following show that the amount of users can be very large. If about 5% of the fixed network telephone customers would move toward using IP telephony when introduced, that would result in about users of ENUM services. This figures are also unimportant since they depend on how the telecom market offers ENUM services and at what price level such offerings would be. The number of users that reside within organizations and companies is more meaningful to estimate. In Sweden the interest of IP telephony services and applications increases every time the companys or organizations PBX is to be updated or replaced. One example is Stockholm University that are in progress to migrate its about 6000 extensions to VoIP using ENUM. This example shows that the amount of ENUM users will increase in a rather abrupt way, when whole organizations are deploying ENUM. However, the amount of customers for the registry has increased by a single entity. We believe that a field test of ENUM, that we recommend should be conducted prior to public deployment, should contain activities that asks the market and potential users if they find ENUM useful and interesting. Any other estimations are pointless ENUM Registry Customers As we have defined earlier in this report, the registry only has two types of customers: the registrars and the DNS operators. The number of registry customers will therefore in both long and short term be few A Fair Competition Firstly we would like to point out that the Norwegian telecom and Internet market is dominated by a single actor: Telenor. Telenor holds (according to PT s statistics on the telecom market in Norway [TELESTAT2002]): about 75% of the market for fixed network telephones, about 60% of the market for mobile phones, 100% of the market for analog leased lines, about 50% of the Internet service provider market (60% of the broadband market, and 30% of the cable modems). It is only in the cable modems market that a competitor comes even close to the same

10 Norid report Page 10 (16) market share as Telenor. UPC holds 60% of the cable modems market. The dominant position of Telenor might lead to difficulties regarding developing practices for ENUM promoting the ENUM service and not some old legacy of the telecom market. It will be very interesting to follow how PT s project SMP (Markedsanalyser) will be received by the market. As we propose to organize ENUM in Norway, it is amongst the registrars and DNS providers that competition will take place. But, since the market for telecom in Norway is dominated by a single company, the organization of ENUM might prove to be of no significance for creating a fair competition on the markets that will use ENUM in Norway. However, what can be done should be done. The regulations that apply in the DNS market in Norway seems to us as a good model for regulating ENUM as well. As we have stated before: ENUM is information through DNS. We recommend that it is tested if the regulations that apply to the DNS market today would work for an ENUM market as well. This test should be conducted as a part of an ENUM trial period. 3.2 Liabilities and Regulations Communication security and telecommunication security has attracted attention in Norway lately. The new Nasjonal sikkerhetsmyndigheten (NSM) that were established at the beginning of 2003 is a direct consequence of the new Sikkerhetsloven. PT has been given (by the Stortinget ) the responsibility to create rules and regulations for electronic communication. These are but two examples of important actors and work in progress. During an ENUM field test, a commitment must be made to do a thorough investigation regarding regulations and liabilities, as well as the relation to the governing agencies and their work. The following list is an outline of the possible issues that should be considered and the laws and regulations that should be investigated. Laws The Norwegian Teleloven is an important law that must be examined and it s impact on ENUM identified. There are also several laws pertaining to tele communications that must be adhered, and their impact on ENUM should also be revised. Public authorities Implementation and operation of ENUM services might need support from public authorities, amongst which PT is the most important since they can enforce needed measures regarding E.164 issues that is necessary for an implementation of ENUM. PT is also Norway s representative in ITU and the authority that can request the delegation of 7.4.e164.arpa. Legislative Security Issues The new governing agency Nasjonal sikkerhetsmyndighet is an important actor regarding the security issues in Norway. It might prove that they do not embrace security issues of ENUM since ENUM might only be related to personal privacy and telecommunications. Then it is PT that is the important authority.

11 Norid report Page 11 (16) Field test We recommend that a field test of ENUM in Norway also comply of a thorough investigation of liabilities and regulations pertaining to ENUM. 3.3 Relations to E.164 Actors The primary goal must be to keep the E.164 number plan and ENUM unanimous. This means that the valid holder of a number from the E.164 number plan also shall be the end user pointed out by ENUM. This will however give rise to the question of who owns the number. In the case of domain names within the.no domain, it is only one part that can offer the ownership of a domain name (Norid). In the ENUM case it is a bit more complicated. In order to apply for delegation of the ENUM name corresponding to the E.164 number, the applicant must be the valid owner of that number. The applicant must therefore be the holder of a telephone subscription. What will happen if the subscription is ended? Will the registrant still be a valid owner of the ENUM name? These issues must be resolved prior to providing ENUM services to the public. We recommend that this discussion should be conducted during a field study since it is a matter much better discussed if it can be put into context. The issue of ownership of a number is only one of the issues that could lead to conflict between the ENUM organization at one side and the E.164 actors at the other side. We recommend that means and measures for handling conflicts regarding the relation between ENUM and E.164 actors is established as soon as possible. Otherwise will these conflicts have a potential to paralyze an implementation of ENUM. 3.4 Business Models and Payment Schemes The money issues must not overshadow the primary issue: ENUM should be an information service to the Internet community that enables business opportunities on a new market segment. ENUM is therefore an important part of the development of new telecom services and technologies. ENUM should be organized and implemented to promote fair competition at the same time as it provides business opportunities The Value of ENUM for the End Users When discussing business models, costs and payment schemes it is essential to understand that ENUM itself only is a database containing access information about end users. It does not provide the end user with an application or anything that the end user might find valuable. ENUM services must be wrapped in some product or application before the end user is willing to pay for it. The value of ENUM might be compared to the value of the SS7 routing tables. The PSTN user don t care about the routing information services that a PSTN network need to be able to route a call, but are willing to pay for the service as a whole. The difference is however that ENUM might be used for so much more than routing information Termination Fees It is also important to realize that the structure of the PSTN network, in respect of how

12 Norid report Page 12 (16) payment is realized in it, will affect the business models of ENUM implementations and how ENUM is payed for. Take into consideration the following case. 1. A call is initiated from a PSTN network to an IP telephone. 2. The call reaches the IP telephony service provider and is, in PSTN respect, terminated there. 3. The call is routed on an IP network and reaches the called number. The interesting part is that the IP telephony service provider will get the termination fee from the callers PSTN service provider. In the case of the IP telephone user calling a PSTN user, the IP telephony service provider will have to pay the termination fee. With ENUM, two IP telephony service providers can interconnect using IP without any prior relationship since all necessary call routing information can be found in DNS. The termination fees are therefore not in themselves an incentive for getting payed for ENUM services. But, if the IP telephony service can be offered to the end users for free, then the cost of the ENUM services that are needed must be covered by billing the end user for them The Costs of ENUM ENUM DNS Operators Costs ENUM, like other DNS based services, is not free, even though any user might freely implement a DNS service. The major part of the Internet community does not implement their own DNS services and will probably not do it with ENUM. An ISP often provide its customers with a DNS service as a part of the Internet connection service or as an add-on to the connection service. A potential ISP customer might even consider a solid DNS service to to be a requirement for he or she to buy the services provided by the ISP. The DNS service is regarded as a natural part of the Internet connection services. Payment for the DNS service is not specified but, as a part of the Internet connection services package, it is included. In the same way will ENUM services most likely be a natural part of an access application, e.g. IP telephony. The cost of providing ENUM services might therefore not be the object of billing and must be covered with other strategies. ENUM services be seen as a part of the basis that some other application that the end user is willing to pay for, e.g IP telephony. Registrars Costs The Registrars only has administrative costs, mainly originating from registrations and validations. To promote fair competition between large and small organizations we suggest that the validation services should be strictly regulated (to keep the cost and quality of it at the same level). The alternative is to establish some kind of public authority or governmental agency that carry out validations on a non-profit

13 Norid report Page 13 (16) basis. This will however diminish the opportunity to decrease the costs of validations through skill and optimization of number of personnel. It would also eliminate the advantage that the telecom service providers have since they already have a validation procedure for the PSTN telephone services. We recommend that this issue is discussed at length before any decision is made about the validation procedure. Registry s Costs The registry s costs are mainly administrative, if the actor responsible for it already is a registry for DNS. The administrative part might even be the same as for DNS if the validation process is placed elsewhere. The real work with ENUM is done at the registrar and DNS operator level. It is they who gets the requests, validates and runs the DNS servers containing the NAPTR records (the ENUM databases). The registrar only points out the DNS servers that holds the NAPTR record for a given number. The ENUM registry is burdened with costs that probably are at the same level as running a cctld registry. There might even be some possibilities for optimization since the services are similar in respect of organization and relations to registrars and other actors. The cost of billing might be lesser for the ENUM services than for general DNS services, since the end user most likely will not pay for the ENUM services to the registry. The registry might limit its costs for billing considerable if it where to bill the registrars and ENUM DNS operators only.

14 Norid report Page 14 (16) Conclusions and Recommendations It is far to early to draw any conclusions about which business models and payment schemes that would fit the ENUM market. We have however noted the following issues that could be worthwhile to consider when discussing such topics: Since ENUM is an enabler for emerging telecom technologies and services, any organization and implementation must not oppose the possible business opportunities utilizing ENUM. ENUM services will probably be sold to end users as a part of a service or application that the end user finds worthwhile to pay for. If this is accurate, payment for specified ENUM services will only be made by the registrars and ENUM DNS operators to the registry. The ENUM DNS operators and the registrars costs for ENUM can be covered in several ways. We have noted some aspects of which the issues of termination fees and packaging is the most important. This is however a matter that will be resolved by the commercial actors and need not be addressed in an ENUM study. Validation must however be discussed and regulated. We suggests that the procedures that is used in the PSTN services market is used for ENUM as well, provided it promotes fair competition in an acceptable way. Since the registry only takes care of the registrations and pointers to ENUM entries (NAPTR records) their costs for the ENUM registry needs not to be different from the costs of running the cctld registry.

15 Norid report Page 15 (16) 3.5 Security Considerations This section is primarily about security as in preventing security breaches and not security as a quality of service, even though many attacks have a negative impact on the quality of service. As described in the security considerations of [RFC2916bis], the security model for ENUM is basically the same as for any other DNS service. When discussing ENUM security in a VoIP context, it is also important to know what security mechanisms are in use in PSTN today and how/if these mechanisms can be mapped to Internet technologies. We recommend that the DNS security considerations are investigated further by the registry and that the ENUM application security considerations are revised during a field test. Note that DNS security and ENUM application security are different in many ways. The former should be addressed by the DNS infrastructure and the latter by the ENUM application implementors and users. Correct number validation is essential in the PSTN and also for ENUM. If validation fails, hijacking end-user communication could, as in the PSTN, become an easy task. It is therefore essential that the validation procedures for ENUM match the corresponding procedure for PSTN.

16 Norid report Page 16 (16) 4 References [TELESTAT2002 ] Det norske telemarkedet - første halvår Post- og teletilsynet publikasjoner/telestatistikk/statistikk2002/halvar/index. html [REGAVTALE ] Registraravtale. html [RFC2916 ] E.164 number and DNS. Request for comments: Patrik Fältström. September [RFC2916bis ] The E.164 to URI DDDS Application. Internet Draft, work in progress. Patrik Fältström. April drafts/ draft ietf enum rfc2916bis 05.txt. [RFC3026 ] Liaison to IETF/ISOC on ENUM. Request for comments: R. Blane. January [WP1-2 ] Liaison to IETF/ISOC on ENUM. ITU-TWorking Party 1/2, Berlin, October _rev1.html