draft-ietf-enum-operation-02.txt

bind-3.2.

 

Telephone Number Mapping                                       A. Brown
Internet Draft                                          Nortel Networks
Document: <draft-ietf-enum-operation-02.txt>             Greg Vaudreuil
                                                    Lucent Technologies
                                                      February 23, 2001
 
 
                       ENUM Service Reference Model 
 
 
    
Status of this Memo 
 
   This document is an Internet-Draft and is in full conformance with 
   all provisions of Section 10 of RFC2026 [1].  
    
   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. 
    
    
1. Abstract 
    
   This document outlines the principles for the operation of a 
   telephone number directory service.  This service provides for the 
   resolution of telephone numbers into Internet domain name addresses 
   and service specific directory discovery. 
    



















  
 
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   Table of Contents 
 
   1. Abstract........................................................1 
   2. Introduction....................................................2 
   3. Scope...........................................................2 
   4. Overview........................................................4 

   4.1 Relationship with Dynamic Services.............................4 
   4.2 Number Portability.............................................5 
   5. The ENUM Service................................................5 
   5.1 First Tier: Determining the Service Registrar..................5 
   5.2 Second Tier: Retrieving Resource records.......................6 
   5.3 Third Tier: Service-Specific Queries...........................6 
   6.  Interesting Numbering Topologies...............................8 
   6.1 Sub-addressing.................................................8 

   6.2 Default and Range-based Service Records........................9 
   6.3  Permissive dialing for dialing plan transitions...............9 
   7 Illustrative System Examples....................................10 
   7.1 Example: Hypothetical Reachme Service.........................10 
   7.2 Example: SIP Call Setup Service Request.......................11 
   8. Security Considerations........................................12 
   9. References.....................................................13 

   10. Acknowledgments...............................................13 
   11. Author's Addresses............................................13 
   12. Full Copyright Statement......................................14 
   Appendix:.........................................................15 
   Changes from draft-ietf-enum-operations-00.txt....................15 
   Changes from draft-ietf-enum-operations-01.txt....................15 
    
    
2. Introduction 
    
   This document outlines the principles for the operation of a 
   telephone number directory service.  This service provides for the 
   resolution of telephone numbers into the address of a service 
   specific directory or where applicable for a given service, directly 
   into a service-specific endpoint addresses. 
    
   This directory service uses the algorithms and methods described in 
   RFC 2916. 
     
   Please send comments on this document to the ENUM working group. 
 
3. Scope 
    
   This document defines the reference architecture behind the ENUM 
   protocols necessary to implement a telephone number-based Internet 
   directory system.  This solution enables an extensible set of 
   services to be provided for a given telephone number. Example 
   services may include IP telephony, store and forward or real-time 
   Internet Fax, VPIM voice messaging, Internet paging, geographic 
   phone location, and many others.  Each service is to be separately 
   defined and identified using a unique, registered service 
   identifier.  
    


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   This document does not specify the particulars of any telephone 
   number-based service.  In particular, it does not describe how phone 
   calls are placed, routed, or terminated or how voice, fax, pager, or 
   email messages are routed.  























































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4. Overview 
    
   This telephone number-based directory system implements a three-tier 
   information model; the first two constituting the ENUM service.  
   This abstract model is based on analysis of pre-existing 
   administrative structures, generalized service requirements, and the 
   capabilities of candidate protocols.  This model does not itself 
   specify an administrative model, but provides a reference to guide 
   implementers or conforming clients and servers. 
   The mechanics of the ENUM service are specified in [ENUM]. 
    
   The first tier is the mapping of the telephone number delegation 
   tree to the service registrar.  Conceptually, this delegated 
   authority knows nothing about service-specific information 
   associated with the telephone number but provides  a reference to 
   the service registrar that does know the specific information. Where 
   this services registrar is different from the delegated authority, a 
   query redirection from the delegated authority to the name server of 
   the service registrar for a given telephone number is necessary. 
    
    
   The second tier is the set of service records themselves.  The 
   service records indicate which of several services may be available 
   for a given telephone number.  Multiple records indicating redundant 
   or competitive service providers may be provided. The set of records 
   may be provided or modified by any number of service providers. The 
   ENUM service defines these records to be NAPTR records yielding a 
   valid URL for a potentially useful service.  It is up to the client 
   initiating the service request to sort through the set of NAPTR 
   records to determine which services are appropriate for the intended 
   action. 
    
   The service registrar is conceptually responsible for maintaining 
   the set of service records for a given telephone number. Because 
   there may be multiple service providers for a given telephone 
   number, conceptually this registrar of services assumes a role of 
   managing service registrations and arbitrating conflicts between 
   service providers. 
    
   If necessary, an additional service-specific tier of information can 
   be provided by the service provider itself. This tier provides 
   specific attributes including any necessary attributes to place a 
   call, route a message, validate capabilities, or other data 
   necessary for that service that are known only by the provider of 
   that specific service.  
    
4.1 Relationship with Dynamic Services 
    
   The telephone number delegation information changes infrequently.  
   However, when a change to this data is made, the information must be 
   rapidly propagated through the directory system.  Inconsistencies 
   between the authoritative data and cached data may result in loss of 
   service, misrouting of communications, and/or service loops.  An 
   effective ENUM service requires that DNS time-to-live fields be set 
   to an appropriate value consistent with the telephone number 
   reassignment policies and service record update intervals. 
    
   Use of the ENUM system to implement time-of-day and other highly 
   dynamic services is discouraged.  Where such a service is desired, 
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   it is recommended that itself be implemented as part of a service 
   indicated by the service records. 
    
4.2 Number Portability 
    
   The concept of number portability generally refers to the ability of 
   a subscriber to change service providers, service types, or 
   locations without changing their telephone number.  For a full 
   discussion of number portability, see [PORT].  In support of number 
   portability, the ENUM service provides mechanism at the three 
   conceptual tiers of the ENUM service. 
    
   1.      If the telephone number has been re-delegated to another 
     authority, and that authority also provides the Tier-1 ENUM 
     service, the telephone number can be re-delegated in the ENUM 
     service by changing the name server "NS" records to point to the 
     new authority.  This may be the case where numbers are re-
     delegated from the incumbent service provider to another or to a 
     portability authority.  The immediately higher delegated authority 
     coordinates the transfer. 
    
   2.      The service registrar may be reassigned.  This may be the case 
     where an individual or corporation changes telephony service 
     providers and wishes that telephony service provider to also 
     provide service registrar functions.  The new service registrar 
     would recreate the appropriate service specific NAPTR records and 
     the delegated authority would coordinate the transfer from one 
     registrar to the other. 
  
   3.      If a specific service for a given telephone number was changed 
     from one provider to another, such as switching telephone 
     answering / voice messaging providers, the NATPR record indicating 
     the specific service would change.  The service registrar would 
     coordinate the deletion of the record for the previous service 
     provider and the insertion of a record for the new service 
     provider.  
    
   It is anticipated that in the early stages of an ENUM deployment, 
   the delegated authority and the service registrar may be the same 
   entity. 
    
5. The ENUM Service 
    
5.1 First Tier: Determining the Service Registrar 
    
   The first tier is the mapping of an E.164-formatted international 
   telecommunication number into the identity of the service registrar 
   for that number. This may or may not involve more than one referral 
   in DNS.  
    
   The delegation of telephone numbers from the root authority (the 
   ITU) down to individuals is a well-established system.  While there 
   are differing Tier-1 administrative models, to a client they each 
   aim to represent in a single tree the trusted relationship between 
   the delegated carriers and subsidiary registrars; a necessary 
   precondition to ensure protection against various attacks.  The 
   delegated authority, sub-delegated authority, or individual may 
   arrange to have a third-party (e.g., a service provider) list their 

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