IANA Registration for an Enumservice Trunkgroup

ENUM (E.164 Number Mapping), RFC 3761 is a system that transforms E.164 numbers (The International Public Telecommunication Number Plan, ITU-T Recommendation E.164) into domain names and then uses the Domain Name System (DNS), RFC 1034 and Naming Authority Pointer Records (NAPTR) records in the Dynamic Delegation Discovery System (DDDS) RFC 3403 to query the services that are available for a specific domain name. This document registers an Enumservice 'trunk' according to the guidelines given in RFC 3761, to be used for provisioning a NAPTR resource record to indicate a type of connection associated with an end point and/or telephone number. The registration is defined within the DDDS (Dynamic Delegation Discovery System ) hierarchy, for use with the "E2U" DDDS Application defined in RFC 3761. The service parameters defined in RFC 3761 dictate that a 'type' and one or more 'subtype' should be specified. Within this set of specifications the convention is assumed that the 'type' (being the more generic term) defines the service and at least one of the 'subtype' may indicate the URI scheme. In this document, one type is specified, 'trunk' and two subtypes 'sip' and 'tel' corresponding to the URI scheme specified. RFC 4904 defines the general problem statement as to why sip/tel URI's need to covey trunkgroup parameters. This Enumservice solves the problem of how SIP proxies or other intermediate session routing elements can query for and utilize trunkgroup data. The design of this Enumservice was influenced by several factors: RFC 3761 has become the de facto query-response protocol of for a variety of data types associated with E.164 numbering, addressing and routing. RFC 3761 is already being used by service providers to query for data that has significant privacy or security issues associated with it. RFC 4769, for instance, describes an Enumservice that associates an E.164 number with a PSTN Local Routing Number. This Enumservice extends that functionality to another form of PSTN routing data. Communications service providers are concerned with the impact of call setup up times on the overall user experience. There is a strong desire to maintain a single query-response mechanism for data involving E.164 phone numbers and not complicate call processing applications with multiple protocol mechanisms. Were the query for trunkgroup data to require a secondary protocol mechanism such as LDAP or IRIS to retrieve the data, it could significantly impact call setup times.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

Trunking data is defined in RFC 4904 as specific circuits in the PSTN that represent a communications paths connecting two switching systems that are used in the establishment of a end to end connection.

The distribution of trunkgroup data is generally restricted to internal network operations. The NAPTR records described herein SHOULD not be part of the e164.arpa DNS tree. Distribution of this NAPTR data would be either within a service provider's internal network, or on a private basis between one or more parties using a variety of security mechanisms to prohibit general public access.

This section documents several examples of how this protocol is used for illustrative purposes only. From examples given in RFC 4904:

tel:+16305550100;tgrp=TG-1;trunk-context=+1-630 Transforming this tel URI to a sip URI yields: sip:+16305550100;tgrp=TG-1;trunk-context=+1-630@isp.example.net;user=phone In an ENUM query-response mechanism this data would be presented as follows. $ORIGIN 0.0.1.0.5.5.5.0.3.6.1.enum4.network.net NAPTR 10 100 "u" "E2U+trunk:tel" "!^.*$!tel:+16305550100;tgrp=TG-1;trunk-context=+1-630!". NAPTR 10 50 "u" "E2U+trunk:sip" "!^.*$!sip:+16305550100;tgrp=TG-1;trunk-context=+1-630@isp.example.net;user=phone!".

There may be one or more trunkgroups associated with a particular E.164 number since there may be multiple terminations strategies associated with an end-to-end connection. Since an ENUM query for trunkgroup data may return multiple responses, it is important that there be unambiguous information on which group to use or the order to which sessions should be attempted. Implementations of this Enumservice MUST be able to distinguish between the order and preference fields in the NAPTR records. It is recommended that implementers should fix the Order field to a single value (such as 100) and use the preference field to rank order the selections.

It is assumed that carriers, service providers, or other organizations that originate trunkgroup data will not publish such information in a globally visible DNS tree, such as e164.arpa. This data is strictly for internal service provider use only in highly internally cached ENUM databases, which is only able to be queried by trusted elements of their network, such as soft switches and SIP proxy servers.

The trunkgroup Enumservice defined in this document is assumed to be used in an environment where elements are trusted and where attackers are not supposed to have access to the protocol messages between those elements. Traffic protection between network elements is sometimes achieved by using IPSec and sometimes by physically protecting the underlying network. In any case, it is presumed the environment where the enum trunkgroup request-response mechanism will be used can ensure the integrity and accuracy of the data.

This document registers the 'trunk' Enumservice using the type 'trunk' and the subtypes 'sip' and 'tel' in the Enumservice registry described in the IANA considerations in RFC 3761.

Enumservice Name: "trunk" Enumservice Type: "trunk" Enumservice Subtype: "tel" URI Scheme: 'tel:' Functional Specification: This Enumservices indicate trunkgroup data, as defined in RFC 4904 necessary for a SIP proxy to make routing decisions. Security Considerations: See Section 8. Intended Usage: COMMON Authors: Richard Shockey (richard.shockey@neustar.biz) Tom Creighton (tom_creighton@cable.comcast.com)

Enumservice Name: "pstn" Enumservice Type: "pstn" Enumservice Subtype: "sip" URI Scheme: 'sip:' Functional Specification: These Enumservices indicate that the remote resource identified can be addressed by the associated URI scheme in order to initiate a telecommunication session, which may include two-way voice or other communications, to the PSTN. Security Considerations: See Section 7. Intended Usage: COMMON Authors: Richard Shockey (richard.shockey@neustar.biz) Tom Creighton (tom_creighton@cable.comcast.com) Interoperability considerations. The URI is designed to be used specifically in conjunction with systems that utilize private the RFC 3761 [ENUM] databases.