One document matched: draft-lawrence-dispatch-sipforum-provider-alias-00.txt
DISPATCH S. Lawrence, Ed.
Internet-Draft Avaya, Inc.
Intended status: Informational J. Elwell
Expires: September 23, 2010 Siemens Enterprise Communications
March 22, 2010
Provider Alias Numbers for Session Initiation Protocol (SIP) User Agent
Configuration
draft-lawrence-dispatch-sipforum-provider-alias-00
Abstract
This document defines procedures for how a SIP User Agent can
translate an identifier provided by a user into the SIP DNS domain
name of a service provider. The form of the user supplied identifier
is constrained to values that can be entered using only a standard 12
key telephone keypad.
This document is derived from work begun in the SIP Forum Technical
Working Group User Agent Configuration Task Group.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on September 23, 2010.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
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Internet-Draft Provider Alias Number for SIP UA Config March 2010
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Numeric Domain Alias Entry . . . . . . . . . . . . . . . . . . 4
3.1. Provider Alias Number Resolution Example . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
6. Normative References . . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
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1. Introduction
Given the problem statement:
A user gets a new SIP User Agent (UA); it may be a hardware device
or software. Some User Agents have a user interface that can
accept a username, password, and domain name. Other devices, like
Analog Telephony Adapters (ATAs), have no user interface other
than that provided by an attached analog phone. How does a non-
technical user minimally configure it so that when it is started,
something useful happens?
The [draft-sipforum-user-agent-config] "Session Initiation Protocol
(SIP) User Agent Configuration" specification provides a procedure
for how a SIP User Agent locates, retrieves, and maintains current
configuration information for a given SIP Service Provider. However,
it assumes that either:
o the UA to be configured is connected to a network whose DHCP (or
DHCPv6) service provides the DNS Name of the SIP domain for which
configuration is desired,
or:
o the UA has a means by which the user can enter that SIP domain
name.
Since some SIP UAs may have no more user interface than a standard 12
key telephone keypad (the digits 0 through 9, '*', and '#'), entry of
DNS names (see [RFC1034]), even for users comfortable with DNS names,
is inconvenient at best. This leaves the problem of configuring a UA
to obtain configuration for a SIP service provider whose domain name
is not provisioned by the local network. This specification provides
a means by which the UA can translate a value entered using only the
standard telephone keypad into the DNS name of a SIP service
provider; in the terminology of [draft-sipforum-user-agent-config],
the "Configuration Service Domain Name".
2. Terminology
The following terms are used in this document:
User Agent, UA
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As defined in [RFC3261]. Note that this includes any
implementation of a User Agent. A SIP phone is a User Agent, but
the term also encompasses any other entity that uses SIP (for
example: for a text chat, for sharing a whiteboard or for fax).
SIP Service Provider, Service Provider
An entity that provides services to User Agents using the SIP
protocol. This specification requires that a Service Provider
make configuration data and certain other information available in
order to configure User Agents.
Configuration
The set of information that establishes operational parameters for
a particular User Agent.
Configuration Service, CS
The source of Configuration for User Agents.
Configuration Service Domain
The DNS name for the service from which a Configuration is
requested.
Provider Alias Number, PAN
A string consisting of decimal digits used to identify a domain
from which configuration is to be requested.
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 [RFC2119].
3. Numeric Domain Alias Entry
A UA MAY have an interface by which a string consisting only of
decimal digits, called a Provider Alias Number (PAN), is provided by
the user. The PAN value is resolved to the Configuration Service
Domain using the S-NAPTR (Simple NAPTR) DDDS application [RFC3958].
The lookup key for the S-NAPTR request is the Provider Alias Number
concatenated with a fixed root suffix (for the purposes of this
initial draft, the value ".pan.sipforum.org." is used) to form a DNS
domain name. The UA MUST make a DNS request for NAPTR records for
that domain name. From the returned records (see next paragraph),
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the UA MUST select the record whose Service field value is
"SFUA.PAN"; the Configuration Service Domain Name is the value found
in the Replacement field of this record.
The DNS for the fixed root MUST be configured such that at most one
NAPTR record is returned for any given Provider Alias Number, and
MUST be configured to return the Flag field set to "a", an empty
Regular Expression field, and the Substitution value set to the
Configuration Service Domain Name.
3.1. Provider Alias Number Resolution Example
Through some manual process, the UA has obtained the provider alias
number "555". To obtain the Configuration Service Domain Name, the
UA constructs a DNS NAPTR request by appending the domain suffix
".pan.sipforum.org." to form the query key "555.pan.sipforum.org.",
which returns the DNS record:
NAPTR 10 10 "a" "SFUA.PAN" "" "example.net."
Figure 1: PAN NAPTR Query Result
The record with the service-field "SFUA.PAN" provides the DNS name
"example.net." for the Configuration Service Domain Name.
4. IANA Considerations
This document registers the following S-NAPTR application service tag
in the registry defined by [RFC3958] "Domain-Based Application
Service Location Using SRV RRs and the Dynamic Delegation Discovery
Service (DDDS)":
+-------------------------+----------+
| Application Service Tag | SFUA.PAN |
+-------------------------+----------+
5. Security Considerations
Because the mapping of the user-entered PAN value to Configuration
Service Domain Name relies on a potentially unsecured DNS lookup, the
UA SHOULD take steps to ensure that the correct provider has been
found.
If possible, the resulting Configuration Service Domain Name SHOULD
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be confirmed by the human user.
Following the translation (specified in
[draft-sipforum-user-agent-config]) of the Configuration Service
Domain Name to the configuration request URL, the UA makes an https
request for configuration data. Because this request is https, it is
made over TLS. As the TLS server, the CS always provides a server
certificate during the TLS handshake; if possible, the UA should
validate that certificate and confirm that it contains the DNS name
constructed from the PAN by concatenating the fixed root
("555.pan.sipforum.org" in the example in Section 3.1). While it may
not be possible to have the information needed to perform a full
validation of the CS server certificate prior to the first
configuration (for example, the UA may not have a current CA
certificate for the CA that signs the CS server certificate),
implementors are advised to provide for including that information in
configuration data so that it can be used for subsequent
reconfigurations; this narrows the window of vulnerability to the
first configuration attempt.
6. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC3958] Daigle, L. and A. Newton, "Domain-Based Application
Service Location Using SRV RRs and the Dynamic Delegation
Discovery Service (DDDS)", RFC 3958, January 2005.
[draft-sipforum-user-agent-config]
Lawrence, S., Ed. and J. Elwell, "Session Initiation
Protocol User Agent Configuration", March 2010.
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Authors' Addresses
Scott Lawrence (editor)
Avaya, Inc.
600 Technology Park
Billerica, MA 01821
USA
Phone: +1 978 288 5508
Email: xmlscott@gmail.com
John Elwell
Siemens Enterprise Communications
Phone: +44 1908 855608
Email: john.elwell@siemens-enterprise.com
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