

Telephone Number Mapping                                       A. Brown
Internet Draft                                          Nortel Networks
Document: <draft-ietf-enum-operation-01.txt>             Greg Vaudreuil
                                                    Lucent Technologies
                                                      October  27, 2000


                    ENUM Service Specific Provisioning:
                          Principles of Operation


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........................................................3
   4.1 Relationship with Dynamic Services.............................3
   4.2 Number Portability.............................................4
   5. The ENUM Service................................................4
   5.1 First Level: Determining the Delegated Authority...............4
   5.2 Second Level: Determining the Service Registrar................5
   5.3 Third Level: Retrieving Resource records.......................6
   5.4 Service-Specific Queries.......................................6

   6.  Interesting Numbering Topologies...............................7
   6.1 Subaddressing..................................................7
   6.2 Default and Range-based Service Records........................8
   7 Illustrative System Examples.....................................9
   7.1 Example: Hypothetical Reachme Service..........................9
   7.2 Example: SIP Call Setup Service Request.......................10
   8. Security Considerations........................................11

   9. References.....................................................12
   10. Acknowledgments...............................................12
   11. Author's Addresses............................................12
   12. Full Copyright Statement......................................13
   Appendix: changes from draft-ietf-enum-operations-00.txt..........14


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 architecture and mechanics 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.

   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 four-level
   information model, the first two constituting the ENUM service
   itself.  This model is based on analysis of pre-existing
   administrative structures, generalized service requirements, and the
   capabilities of candidate protocols.

   The mechanics of the ENUM service are specified in [ENUM]

   The first level is the mapping of the telephone number delegation
   tree to the authority to which the number has been delegated.
   Conceptually, this delegated authority knows nothing about service-
   specific information associated with the telephone number but can
   provide a reference to the appropriate entity that does know the
   specific information.

   The second is the delegation from the authority to which the
   telephone number has been delegated to the service registrar.  The
   registrar is conceptually responsible for maintaining the set of
   service records for a given telephone number. 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. 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.

   The third level 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.

   If necessary, an additional service-specific level of information
   can be provided by the service provider itself. This level 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

   ED Note: Text requested discussing FAST UPDATE VS SLOW UPDATE.  WG
   decided only slow update is in scope for ENUM.  Discuss timing
   considerations for propagation of changed records at various levels.

   Illustrate how time-of-day services should be provided at the
   service-specific level.


   The telephone number delegation information changes infrequently.
   However, when a change to this data is made, the information must be
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   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

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 [portability].  In support of
   number portability, the ENUM service provides mechanism at the three
   conceptual levels of the ENUM service.

   1.      If the number has been redelegated to another authority, the
     telephone number can be redelegated in the ENUM service to that
     authority by changing the name server "NS" records to point to the
     new authority.  This may be the case where numbers are redelegated
     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.  Assuming the delegated
     authority and service registrar are separate entities, the DNAME
     or CNAME redirection records pointing to the previous service
     registrar would be changed to point to the new service registrar.
     The appropriate service specific NAPTR records would be recreated
     by the new service registrar 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 Level: Determining the Delegated Authority

   The first level 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.  From the client's perspective, this level is transparent,
   bundled within the query for the service-specific resource records
   stored at the second level.


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   The delegation of telephone numbers from the root authority (the
   ITU) down to individuals is a well-established system that can be
   utilized. These telephone number registrars have a trusted
   relationship with their delegated carriers or subsidiary registrars;
   a valuable asset to ensure protection against various attacks.  Note
   that in this model, the delegation of telephone number blocks or
   individual numbers to a corporation or to an individual can be
   administratively and technically modeled as a subdelegation to
   another carrier.  With that additional information publicly
   registered, the mapping between telephone numbers and these domain
   names can be provided by any neutral entity. The delegated
   authority, subdelegated authority, or individual may arrange to have
   a third-party (e.g., a service provider) list their information.  In
   this case the service provider's domain would be returned in the
   ENUM query.

   The Internet Domain Name System provides an ideal technology for the
   first-level directory due to its hierarchical structure, fast
   connectionless queries, and distributed administrative model.
   Earlier experimentation with the TPC.INT remote printing experiment
   has shown how the hierarchical assignment of telephone numbers can
   be mapped directly to the hierarchy of domains within the DNS.  The
   ENUM directory uses that approach to map any arbitrary telephone
   number into a single domain name.

   ITU standard E.164 defines the structure of the public telephone
   number as follows: country code, followed by nationally significant
   part, followed by subaddress.  The country code may be from one to
   three digits, and the total length may be up to 15 digits.  The
   nationally-significant portion may be arbitrarily divided on any
   number boundary.  In many countries numbering plans, the divisions
   are not uniform, that is, the "area codes" or "city codes" may be of
   varying lengths within a single country and the total number of
   digits may be variable.  Where supported by the relevant service, an
   optional subaddress of up to four digits may be utilized to
   designate an extension telephone number. Note that while sub-
   addressing is not well supported in GSTN calling, it is more widely
   supported for voice messaging.  It is important to note that the
   national long-distance access or international dialing prefix
   sequence is not part of the canonical E.164 number.

   Within this delegation flexibility, it is always the case that the
   delegation of authority is always done left-to-right. With this
   assumption, a numbering tree can be built on a digit-by-digit basis
   that can represent any arbitrary hierarchical structure.  DNS
   permits the delegation of authority on arbitrary boundaries such
   that a delegation to country code "1", "44", and "972" can all
   coexist under a single numbering plan root.  The same applies for
   "service selectors", "area codes", "city codes", "line number", or
   "additional address information " within numbering plans.

5.2 Second Level: Determining the Service Registrar


   In the event that the designated authority is not the same as the
   service registrar, the DNAME and CNAME records provide the
   redirection from the designated authority to the service registrar.
   The DNAME provides a means for reforming and re-issuing a query for
   a "non-terminal" domain name. As is standard for compliant DNS
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   resolver libraries, clients must support the CNAME record type.
   Servers that provide for substitution MAY support the DNAME record
   to provide redirection for an entire telephone number range as a DNS
   subtree.  These servers MUST provide synthesized CNAME records for
   the proper operation of older resolver libraries that have not been
   extended to understand DNAME.  Servers that redirect queries on a
   per-telephone number basis MUST support CNAMES.


   From the client's perspective, this level may be transparent based
   on the capabilities of the resolver library in use.  The client
   (with the help of a suitable DNS library) must be able interpret
   returned CNAME and should be able to resolve DNAME records into a
   new domain name.  The new domain name MUST be used to continue the
   query for the requested service records.

   It is important to ensure that DNS configurations provide only one
   path from the e164.arpa tree to a single DNS leaf-node entry.  If
   multiple paths point to the same node, the substitution string
   provided in the NAPTR may provide unintended results.  In
   particular, substitution expressions which use the original
   telephone number string may result in different URI's depending upon
   which number was used to initiate the ENUM query.

5.3 Third Level: Retrieving Resource records.

   The third level is the request for NAPTR RRs to discover the URL of
   the appropriate service-specific directory such as an LDAP directory
   server, H.323 gatekeeper, or specific endpoint addresses.

   The service registrar is responsible for ensuring that multiple
   services may be provided on behalf of a single telephone number,
   potentially by different service providers. This function includes
   an arbiter function to ensure that there is a deterministic instance
   of any given service assigned to a single telephone number.  The
   service-specific directory locator function is a new service modeled
   upon existing telcoservice provisioning models. Long-distance
   carrier selection within the United States is one well-known example
   of a service-specific registration requiring an arbiter function
   within the current network.

5.4 Service-Specific Queries

   An additional level of query may be used to a service-specific
   directory for service-specific information.  As indicated in the
   URI, such a query may include a SIP query to a designated gatekeeper
   or an LDAP query to a designated directory server.  This level is
   specific to the service and is to be described in service-specific
   documents.  The service-specific directory is expected to be
   dynamic.  It is important that as little coordination as possible be
   required between the directories of innovative and potentially
   competing service-specific providers.







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6.  Interesting Numbering Topologies

   The following numbering uses require special consideration in the
   provision and use of ENUM services.

6.1 Subaddressing

   The E.164 standard provides for subaddressing through "additional
   information" within the 16 digits of an E.164 number.  This
   information is passed through many telecommunications networks to be
   used by terminal equipment to select between alternate services or
   terminal devices.  The subaddress digits are not processed by the
   switching system and are not used by intermediate processes to
   select services or route calls.  In many cases, the network
   numbering infrastructure may be unaware of the existence or use of
   subaddressing by a given endpoint. Within ENUM, subaddressing may be
   supported in two ways.  The service registrar may explicitly
   provision NAPTR records for each subaddress, or the service
   registrar may provision default records for a range of subaddresses.

   Using common DNS server implementations, the registrar may provision
   default records for a block of subaddresses.  A combination of
   explicit entries and default entries may be provided in common DNS
   server implementations using a longest-match algorithm.  It is
   important to note that if a NAPTR or any other RR is provisioned for
   a subaddress, then all NAPTR records that are useful for that sub-
   address must also be provisioned.

   It is also important to note that numbers with optional subaddresses
   may be queried without the subaddress component.  For example, it
   may be useful to dial an address when placing a PSTN telephone call.
   The telephone number may terminate on an automated attendant
   application which can prompt for the appropriate internal extension.
   However, when placing a SIP call using IP telephony, the address
   plus the subaddress may be queried.

   The following set of records for company.com illustrate one
   configuration where a PSTN caller will be directed to the automated
   attendant application whether they dial the number or the number
   plus a subaddress, and whether the subaddress is explicitly
   provisioned or not.  Calling using SIP to the explicitly provisioned
   subaddress will result in a direct call to the intended recipient.

   Example:

   1.2.3.4.5.6.7.8.9.e164.arpa
       IN NAPTR 102 10 "u" "tel+E2U" "!^.*$!tel:+987654321!"  .
       IN NAPTR  10 10 "u" "sip+E2U" "!+(.*)!sip:AA@company.com!"  .

   *.1.2.3.4.5.6.7.8.9.e164.arpa
       IN NAPTR 102 10 "u" "tel+E2U" "!^.*$!tel:+987654321!"  .
       IN NAPTR  10 10 "u" "sip+E2U" "!+(.*)!sip:AA@company.com!"  .

   1.0.1.1.2.3.4.5.6.7.8.9.e164.arpa
       IN NAPTR  10 10 "u" "sip+E2U" "!^.*$!sip:joe@company.com!"  .
       IN NAPTR 102 10 "u" "tel+E2U" "!^.*$!tel:+987654321!"  .



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6.2 Default and Range-based Service Records

   It is envisioned that a corporation or service provider not subject
   to number portability may wish to maintain a set of default NAPTR
   records for all E.164 telephone numbers within a delegation block.
   Similar to subaddressing, a service registrar may provision a set of
   NAPTR records for a set of E.164 numbers with similar service
   requirements.

   Example:

   *.3.4.5.6.7.8.9.SvcReg.company.com
     IN NAPTR 102 10 "u" "tel+E2U" "!+(.*)!Tel:+\1"  .
     IN NAPTR  10 10 "u" "sip+E2U" "!^.*$!sip:AA@company.com!"  .
     IN NAPTR  10 10 "U" "mailto+E2U" \
                                "!+(.*)!mailto:+\1@company.com!" .

   1.0.3.4.5.6.7.8.9.SvcReg.company.com
     IN NAPTR 102 10 "u" "tel+E2U" "!^.*$!tel:+987654310!"  .
     IN NAPTR  10 10 "u" "sip+E2U" "!^.*$!sip:AA@company.com!"  .

   2.2.3.4.5.6.7.8.9.SvcReg.company.com
     IN NAPTR 102 10 "u" "tel+E2U" "!^.*$!tel:+987654322!"  .
     IN NAPTR  10 10 "u" "sip+E2U"   "!^.*$!sip:joe@company.com!"  .
     IN NAPTR  10 10 "U" "mailto+E2U" \
                                "!^.*$!tel:+987654322@company.com!" .

   In this example, mail sent to a number within the 100's block that
   does not have an explicit entry will be sent to tel#@company.com.
   Mail is not accepted at the automated attendant number as indicted
   by the lack of a mailto service record.  Because extension 22 has an
   explicit record, it must also have an explicit mailto: URL in a
   NAPTR record.


























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7 Illustrative System Examples

7.1 Example: Hypothetical Reachme Service

   The following hypothetical service enables an end-user to discover
   the various means by which she can reach a recipient represented by
   their corporate telephone number +1 613-555-1212 using the
   hypothetical "reachme" service.  This service is hosted by directly
   by the recipient's corporation.

   The telephone number is transformed into a domain name form to be
   used in a DNS query.

        2.1.2.1.5.5.5.6.1.3.1.e164.arpa

   Sample configuration file for the top level delegations from ITU:

        1.e164.arpa.      IN NS ns.NANP.phone.net. ;for NANP
        3.3.e164.arpa.    IN NS  ns.FR.phone.net. ; for France
        2.7.9.e164.arpa.  IN NS  ns.il.phone.net.  ; for Israel

   Sample configuration file for numbers delegated from the NANP node
   in the DNS tree:

        5.5.5.3.1.6.1.e164.arpa.  IN NS ns.ServiceProviderA.net.
                                          ;for +1 613 555 XXXX

   In this example, ServiceProviderA.net is the authority to which the
   telephone number has been delegated.  ServiceProviderA.net provides
   a non-terminal redirection pointer to Zcorporation, the designated
   service registrar for the block of 100 numbers +1 613 555 12XX. The
   configuration for this block of numbers is:

        2.1.5.5.5.3.1.6.1.e164.arpa.
                DNAME 2.1.5.5.3.1.6.1.Zcorporation.com.

   Zcorporation provides the following service specific record for all
   telephone numbers within it's 100 number block:

      *.2.1.5.5.5.3.1.6.1.Zcorporation.com.
            IN NAPTR 100 10 "u" "ldap+E2U"\
            "$!ldap://ldap1.Zcorporation.com/cn=\1!" .

   Assuming the resolver is using non-extended DNS, the query using
   telephone number +1 613 555 1212 for the _reachme service is as
   follows:

       QueryType: NAPTR
       QueryName: _ 2.1.2.1.5.5.5.3.1.6.1.e164.arpa.
       Response:
   IN CNAME 2.1.2.1.5.5.5.3.1.6.1.Zcorporation.com
          IN NAPTR 10 10 "u" "Reachme+E2U" \
                    "!LDAP:\\ldap1.zcorporation.com\cn=\1!" .
   The client can then apply the regular expression to yield an LDAP
   URI of LDAP:\\ldap1.zcorporation.com\cn=16135551212 and then use
   LDAP with the reachme schema to determine the set of communications
   technologies available for +1 613 555 1212.


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7.2 Example: SIP Call Setup Service Request

   This example provides resolution of a telephone number to the
   identifier for the SIP gatekeeper designated to support real-time
   calling (Sipphonecall) to 972 555 1313.  The telephone number is
   part of a block of ported telephone numbers that have been ported
   out of the donor carriers block to another carrier.

   The telephone number is transformed into a domain name form to be
   used in a DNS query.

   Sample configuration file for the top level delegations from ITU:

        1.e164.arpa.     IN NS  ns.NANP.phone.net.  ;for NANP
        3.3.e164.arpa.   IN NS  ns.FR.phone.net.  ; for France
        2.7.9.e164.arpa. IN NS  ns.il.phone.net. ; for Israel

   Sample DNS configuration file for the ported number block serviced
   by the 972 555 number portability authority delegated from the NANP
   node in the DNS tree:

       5.5.5.2.7.9.1.e164.arpa.  IN NS ns.972555Port.NANP.phone.net.
                                          ;for 972 555

   The number portability authority manages the delegation on a per-
   telephone number basis.  Logically, the ns.972555Port.NANP.phone.net
   has the following record for the telephone number.

       3.1.3.1.5.5.5.2.7.9.1.e164.arpa.  IN NS ns.ServiceProviderB.net.
                                          ;for 972 555 1313

   ServiceProviderB provides service registrar functions directly for
   the telephone number and hosts the service records directly without
   using a DNAME record.  The following configuration entry is provided
   for +1 972 555 1313.


      3.1.3.1.5.5.2.7.9.1.ServiceProviderB.net.
          IN NAPTR 10 10 "u" "sip+E2U"\
               "!^.*$!sip:19725551313@ServiceProviderB.net!" .
   The DNS Query and response using telephone number +1 972 555 1313:

        QueryType: NAPTR
        QueryName: 3.1.3.1.5.5.5.2.7.9.1.e164.arpa
        Result:
           IN NAPTR  10 10 "u" "sip+E2U" \
               "!^.*$!sip:19725551313@ServiceProviderB.net!"   .

   The client can now use the SIP protocols to contact the SIP gateway
   to initiate a phone call.









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8. Security Considerations

   The following are known security issues taken into consideration in
   the definition of this directory service.

     1.        Service provider customer information is very sensitive,
       especially in this time of local phone competition.  Service
       providers require the maximum flexibility to protect this data.

     2.        Registration of a domain name for the telephone numbers
       delegated to another carrier may result in messages being
       misdirected to the wrong carrier.  As subdelegations are
       implemented, the risk that phone numbers delegated to one
       enterprise may be incorrectly pointed at another will increase.

     3.        Service providers operate in a regulated environment where
       certain information about subscribers must not be disclosed.
       Telephony services and Voice Messaging are subject to caller-ID
       blocking restrictions, restrictions normally enforced in the
       telephony network.  No such protection is available on the
       Internet.  The protection of this data is essential, but is up
       to the individual service providers to not disclose this
       information outside of their control.




































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9. References

   [DNS1] Mockapetris, P., "Domain names - implementation and
   specification", RFC1035, Nov 1987.

   [DNS2] Mockapetris, P., "Domain names - concepts and facilities",
   RFC 1034, Nov 1987.

   [SRV] Arnt Gulbrandsen, Paul Vixie, Levon Esibov, "A DNS RR for
   specifying the location of services (DNS SRV)", Work in Progress

   [E164] ITU, "CCITT Recommendation E.164 (1991), Telephone Network
   and ISDN Operation, Numbering, Routing and  Mobile Service -
   Numbering Plan for the ISDN Era."

   [TPC1] Malamud, Carl, Rose, Marshall, "Principles of Operation for
   the TPC.INT Subdomain: Remote Printing -- Technical Procedures", RFC
   1530, October 1993.

   [VPIM2] Vaudreuil, Greg, Parsons, Glen, "Voice Profile for Internet
   Mail, Version 2", RFC 2421, September 1998.

   [SRV] Gulbrandsen, A., Vixie, P., "A DNS RR for specifying the
   location of services (DNS SRV)", RFC 2052, October 1996.

   [REQ] Brown, Anne, "ENUM Requirements", work-in-progress, November
   1999

   [ENUM] Faltstrom, Patrick, "E.164 number and DNS", RFC 2916,
   September 2000.

   [DNAME]

   [NAPTR] M. Mealling, R. Daniel _The Naming Authority Pointer (NAPTR)
   DNS Resource Record_, RFC 2915, September 2000.

   [Portability]

10. Acknowledgments

11. Author's Addresses

   Anne R. Brown
   Nortel Networks
   P.O. Box 3511, Station C
   Ottawa, ON  K1Y 4H7
   Canada
   Phone: +1-613-765-5274
   Fax: +1-613-763-2697
   Email: ARBrown@NortelNetworks.com                                                                                                         

   Gregory M. Vaudreuil
   Lucent Technologies,
   Communications Application Group
   17080 Dallas Parkway
   Dallas, TX  75248-1905
   United States
   Phone/Fax: +1-972-733-2722
   Email: GregV@IEEE.org
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12. 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











































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                        ENUM Operations               Auguest 18, 2000


Appendix: changes from draft-ietf-enum-operations-00.txt

   o Discussion of interesting numbering topologies was added

   o Retrieval of NAPTR records are now described in a separate step
   from the determination of a service registrar.

   o A new example was created to illustrate ENUM using sub-addressing.



















































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