draft-ietf-enum-operation-02.txt

bind-3.2.

 
 
   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-tier 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 sub-address.  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 sub-address 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 Tier: Retrieving Resource records. 
 
   The second tier 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 telco service 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. 
    
5.3 Third Tier: Service-Specific Queries 
 
   An additional tier of query may be used to a service-specific 
   directory for service-specific information.  As indicated in the 
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   URI, such a query may include a SIP query to a designated gatekeeper 
   or an LDAP query to a designated directory server.  This tier 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 Sub-addressing  
 
   The E.164 standard provides for sub-addressing 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 sub-address 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 
   sub-addressing by a given endpoint. Within ENUM, sub-addressing may 
   be supported in two ways.  The service registrar may explicitly 
   provision NAPTR records for each sub-address, or the service 
   registrar may provision default records for a range of sub-
   addresses. 
    
   Using common DNS server implementations, the registrar may provision 
   default records for a block of sub-addresses.  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 sub-address, 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 sub-
   addresses may be queried without the sub-address 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 that can prompt for the appropriate internal 
   extension. However, when placing a SIP call using IP telephony, the 
   address plus the sub-address 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 sub-address, and whether the sub-address is explicitly 
   provisioned or not.  Calling using SIP to the explicitly provisioned 
   sub-address 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:[phone]!"  .  
       IN NAPTR  10 10 "u" "sip+E2U" "!+(.*)!sip:[e-mail]!"  . 
    
   *.1.2.3.4.5.6.7.8.9.e164.arpa 
       IN NAPTR 102 10 "u" "tel+E2U" "!^.*$!tel:[phone]!"  . 
       IN NAPTR  10 10 "u" "sip+E2U" "!+(.*)!sip:[e-mail]!"  . 
    
   1.0.1.1.2.3.4.5.6.7.8.9.e164.arpa  
       IN NAPTR  10 10 "u" "sip+E2U" "!^.*$!sip:[e-mail]!"  . 
       IN NAPTR 102 10 "u" "tel+E2U" "!^.*$!tel:[phone]!"  . 
    

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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 sub-addressing, a service registrar may provision a set 
   of NAPTR records for a set of E.164 numbers with similar service 
   requirements.   
    
   Example: 
    
   *.3.4.5.6.7.8.9.164.arpa 
     IN NAPTR 102 10 "u" "tel+E2U" "!+(.*)!Tel:+\1"  .  
     IN NAPTR  10 10 "u" "sip+E2U" "!^.*$!sip:[e-mail]!"  . 
     IN NAPTR  10 10 "U" "mailto+E2U" \  
                                "!+(.*)!mailto:+\[e-mail]!" . 
    
   1.0.3.4.5.6.7.8.9.164.arpa 
     IN NAPTR 102 10 "u" "tel+E2U" "!^.*$!tel:[phone]!"  . 
     IN NAPTR  10 10 "u" "sip+E2U" "!^.*$!sip:[e-mail]!"  . 
    
   2.2.3.4.5.6.7.8.9.164.arpa  
     IN NAPTR 102 10 "u" "tel+E2U" "!^.*$!tel:[phone]!"  . 
     IN NAPTR  10 10 "u" "sip+E2U"   "!^.*$!sip:[e-mail]!"  . 
     IN NAPTR  10 10 "U" "mailto+E2U" \ 
                                "!^.*$!tel:[e-mail]!" . 
    
   In this example, mail sent to the phone number [phone] using 
   1.1.3.4.5.6.7.8.9.164.arpa will be sent to [e-mail].  
   Mail is explicitly not accepted at the automated attendant number as 
   indicted by the lack of a mailto service record.  Because extension 
   22 has an explicit NAPTR record for inbound calls via the tel 
   record, it must also have an explicit mailto: URL in a NAPTR record. 
    
6.3  Permissive dialing for dialing plan transitions 
    
   In the real-world environment, the telephone number hierarchy is 
   modified as necessary to prevent number exhaustion and to facilitate 
   new services.  These re-numberings either insert additional digits 
   at arbitrary parts of the previous telephone number or result in the 
   re-assignment of a sub-tree of numbers to a new prefix.  To avoid 
   the operational and social disruption involved with a _flash cut_, a 
   practice of _permissive dialing_ has been created.  Permissive 
   dialing enables and end-user to use either the previous or new 
   telephone number for a period of time.  During this time, there may 
   be two different telephone numbers pointing to the same set of 
   service records, or a duplicate set of service records for the new 
   and previous number. 
    
 









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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 [phone] 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.   
    
        2.1.2.1.5.5.5.3.1.6.1.e164.arpa 
    
   Sample configuration file for the top tier 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.Zcorporation.com.   
                                          ;for +1 613 555 XXXX 
   Zcorporation is the designated service registrar for the block of 
   100 numbers [phone]XX. 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.e164.arpa.  
            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 [phone] 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 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 [phone]. 
    









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