One document matched: draft-lendl-enum-sip-lr-00.txt
ENUM -- Telephone Number Mapping O. Lendl
Working Group enum.at
Internet-Draft May 2, 2008
Expires: November 3, 2008
IANA Registration for the enumservice-subtype 'sip:lr'
draft-lendl-enum-sip-lr-00
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Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract
This document requests IANA registration of an enumservice-subtype
for loose route variant for SIP, the Session Initiation Protocol.
This subtype allows for the routing of SIP messages addressed to tel:
Uniform Resource Identifiers (URIs) according to
[I-D.rosenberg-sip-ua-loose-route].
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Table of Contents
1. Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. ENUM Service Registration - sip:lr . . . . . . . . . . . . . . 4
4. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Security & Privacy Considerations . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
7. DNS Considerations . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6
Intellectual Property and Copyright Statements . . . . . . . . . . 7
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1. Preface
There is discussion in the IETF SIP working group regarding the
introduction of a distinction between "routing" and "retargeting" of
SIP calls. No consensus has been reached yet. This document is
based on one of the proposals ([I-D.rosenberg-sip-ua-loose-route]).
The purpose of this I-D is to stimulate discussion in the ENUM WG on
what the implications could be if the ua-loose-route idea is
standardized.
2. Introduction
E.164 Number Mapping (ENUM) [RFC3761] uses the Domain Name System
(DNS) [RFC1035] to refer from E.164 numbers [refs.E164] to Uniform
Resource Identifiers (URIs) [RFC3986]. Specific services to be used
with ENUM must be registered with IANA.
[I-D.ietf-enum-enumservices-guide] describes the process of such an
Enumservice registration.
The enumservice registration for SIP Addresses-of-Record [RFC3764]
defines a mapping from E.164 telephone number to a SIP AoR which can
be used by SIP devices to retarget a telephone number based call
towards a SIP AoR. INVITE messages generated by this process use the
retrieved AoR as the Request URI.
If further call routing hops are done based on the original telephone
number (TN), the ENUM entry often contains not a true AoR, but
something like sip:TN@nexthop.example.com;user=phone. The SIP proxy
at that next hop extracts the TN from the Request URI and applies his
own TN-based routing algorithm to determine the next steps.
According to [I-D.rosenberg-sip-ua-loose-route], this is a clear
example of a "routing" operation and not a "retargetting" operation,
as from a logical point of view the call is still addressed to the
same telephone number. Consequently, the Request-URI should be kept,
and only a Route header should be inserted to indicate the next SIP
hop. For backward compatibility reasons, it is necessary (Section 6,
last paragraph in [I-D.rosenberg-sip-ua-loose-route]) that the next
hop indicates that he supports loose-route.
This subtype for the "sip" enumservice does exactly that: it allows
the destination network to announce that it supports loose routing as
defined by [I-D.rosenberg-sip-ua-loose-route].
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3. ENUM Service Registration - sip:lr
The following template contains information required for the IANA
registrations of the "lr" subtype for the Enumservice "sip",
according to [I-D.ietf-enum-enumservices-guide]:
Enumservice Type: "sip"
Enumservice Subtype: "lr"
URI Schemes: "sip"
Functional Specification:
This Enumservice/subtype indicates that the resource identified is
a SIP next hop towards the endpoint identified by the telephone
number as defined by [I-D.rosenberg-sip-ua-loose-route].
Security Considerations: see Section 5
Intended Usage: COMMON
Registration Document: This document's RFC number once it is
published.
Author: Otmar Lendl <mailto:otmar.lendl@enum.at>
4. Example
An example ENUM entry indicating a SIP next hop could look like:
$ORIGIN 6.9.4.0.6.9.4.5.1.1.4.4.e164.arpa.
@ IN NAPTR ( 100 10 "u"
"E2U+sip:lr"
"!^.*$!sip:p1.example.com;lr!" .
)
To visualize the difference between how "sip" and "sip:lf" entries
are interpreted, consider the following entries:
$ORIGIN 6.9.4.0.6.9.4.5.1.1.4.4.e164.arpa.
@ IN NAPTR ( 100 10 "u"
"E2U+sip"
"!^.*$!sip:alice@example.com!" .
)
@ IN NAPTR ( 100 10 "u"
"E2U+sip:lr"
"!^.*$!sip:p1.example.com;lr!" .
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)
A SIP proxy dealing with a call to tel:+441154960496 can select
either record. The first leads to
INVITE sip:alice@example.com SIP/2.0
being sent to the proxy responsible for example.com. If the sip:lr
record is used, then
INVITE tel:+441154960496 SIP/2.0
Route: <sip:p1.example.com;lr>
is sent to p1.example.com.
5. Security & Privacy Considerations
The registration document of the "sip" enumservice ([RFC3764])
contains an extensive Security section.
The loose route subtype adds no new concerns, to the contrary: as the
SIP URI contained in such a records does not contain a (potentially
revealing) AoR, but only a hostname and port, it is less likely to
leak personal information.
On the other hand, the hostnames contained in these records may
expose information on the internal network topology.
6. IANA Considerations
This memo requests IANA to add a new "lr" Enumservice subtype to the
'Enumservice Registrations' registry entry for "sip", according to
the definitions in this document and
[I-D.ietf-enum-enumservices-guide].
The required template is contained in Section 3.
7. DNS Considerations
This is a straight forward ENUM service-type.
8. References
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8.1. Normative References
[RFC3761] Faltstrom, P. and M. Mealling, "The E.164 to Uniform
Resource Identifiers (URI) Dynamic Delegation Discovery
System (DDDS) Application (ENUM)", RFC 3761, April 2004.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC3764] Peterson, J., "enumservice registration for Session
Initiation Protocol (SIP) Addresses-of-Record", RFC 3764,
April 2004.
[I-D.ietf-enum-enumservices-guide]
Hoeneisen, B., Mayrhofer, A., and J. Livingood, "IANA
Registration of Enumservices: Guide, Template and IANA
Considerations", draft-ietf-enum-enumservices-guide-08
(work in progress), March 2008.
8.2. Informative References
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[refs.E164]
ITU-T, "The international public telecommunication
numbering plan", Recommendation E.164 (02/05), Feb 2005.
[I-D.rosenberg-sip-ua-loose-route]
Rosenberg, J., "Applying Loose Routing to Session
Initiation Protocol (SIP) User Agents (UA)",
draft-rosenberg-sip-ua-loose-route-02 (work in progress),
January 2008.
Author's Address
Otmar Lendl
enum.at GmbH
Karlsplatz 1/9
Wien A-1010
Austria
Phone: +43 1 5056416 33
Email: otmar.lendl@enum.at
URI: http://www.enum.at/
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