Network Working Group O. Levin
Request for Comments: 3508 RADVISION
Category: Informational April 2003

H.323 Uniform Resource Locator (URL) Scheme Registration

Status of this Memo

This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2003). All Rights Reserved.

Abstract

ITU-T Recommendation H.323 version 4 introdUCed an H.323-specific
Uniform Resource Locator (URL). This document reproduces the H323-
URL definition found in H.323, and is published as an RFCfor ease of
Access and registration with the Internet Assigned Numbers Authority
(IANA).

Conventions used in this document

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 BCP 14, RFC2119 [2].

Table of Contents

1. Introduction...................................................2
2. URL Scheme Formal Syntax Definition and Character Encoding.....2
3. Intended Usage.................................................3
4. Applications and/or protocols, which may use H.323 URL scheme..3
5. Security Considerations........................................3
6. IANA Considerations............................................4
References........................................................4
Acknowledgments...................................................5
Author's Address..................................................5
Full Copyright Statement..........................................6

1. Introduction

ITU-T Recommendations H.323 [3] and H.225.0 [4] define a system for
multimedia communications services over packet based networks.
H.225.0 [4] defines an alias type for carrying any standard Uniform
Resource Locator (URL). H.323 version 4 [3] introduced an H.323-
specific URL, which may be used to resolve the address of a network
entity to which H.323 calls may be directed.

This document reproduces the H323-URL definition found in ITU-T
recommendation H.323 [3] and is published as an RFCfor ease of
access and IANA registration.

2. URL Scheme Formal Syntax Definition and Character Encoding

The H.323 URL is defined in ABNF as shown below. Note that it
utilizes the Core Rules specified in section 6.1 of [2].

H323-URL = "h323:" address [ url-parameters ]
address = user / "@" hostport / user "@" hostport
user = 1*(%x21-24 / %x26-3F / %x41-7F / escaped)
; The symbols "%", "@", and symbols with
; a character value below 0x21 may be
; represented as escaped sequences.
hostport = host [ ":" port]
host = hostname / IPv4address / IPv6reference
hostname = *( domainlabel "." ) toplabel [ "." ]
domainlabel = alphanum / alphanum *( alphanum / "-" ) alphanum
toplabel = ALPHA / ALPHA *( alphanum / "-" ) alphanum
IPv4address = 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT
IPv6reference = "[" IPv6address "]"
IPV6address = heXPart [ ":" IPv4address ]
hexpart = hexseq / hexseq "::" [ hexseq ] / "::" [ hexseq ]
hexseq = hex4 *( ":" hex4 )
hex4 = 1*4HEXDIG
port = 1*DIGIT
url-parameters = *( ";" url-parameter )
url-parameter = 1*(%x21-24 / %x26-3A / %x3C-7F / escaped)
; Specific parameter definitions are for
; further study.
; The symbols "%", ";", and symbols
; with a character value below 0x21 may be
; represented as escaped sequences.
alphanum = ALPHA / DIGIT
escaped = "%" HEXDIG HEXDIG

The host is case insensitive.

The "user" is a Unicode [8] string that shall be UTF-8 [7] encoded
and then escaped as necessary. In the "user" field, the characters
with a numeric value below 0x80 are case insensitive and the
characters with a numeric value above or equal to 0x80 are case
sensitive.

The character set and case sensitivity of the "url-parameter" is
specified in each parameter definition.

3. Intended Usage

The H.323 URL is intended to help an entity resolve the address of
another H.323 entity, where an "entity" may be a user, a device, or a
service. The "user" portion of the URL specifies an alias for the
entity, without carrying any information about the location of the
entity. The "hostport", on the other hand, is the domain name of an
Endpoint, Gatekeeper, Border Element, or other functional element to
which H.323 calls may be directed or for which services may be
performed.

4. Applications and/or protocols, which may use H.323 URL scheme

H.323 URLs may be carried by other protocols, such as SIP [6] or TRIP
[9]. H.323 URLs may be also contained within web pages or within XML
data, which may be utilized by H.323 entities in order to initiate
calls or perform services.

5. Security Considerations

When an H.323 URL is carried within H.225.0 [4] messages, security is
addressed by the H.235 security framework [5]. When an H.323 URL
carried within other protocols (such as SIP [6]), the security is
addressed within the corresponding protocol.

In general, security, as it relates to the usage and carriage of the
H.323 URLs, is considered as an issue that should be addressed within
scope of H.323 or other relevant protocols and is not within the
scope of this document.

6. IANA Considerations

The purpose of this document is serving as a reference point for the
purposes of registering the H.323 URL scheme with IANA.

Having the URL registered with IANA will ensure that there is no
duplication of the URL scheme "h323". This document reproduces the
exact H323-URL definition as published in ITU-T Recommendation H.323
[3].

Registration Template

URL scheme name: h323

URL scheme syntax: Section 2 of RFC3508

Character encoding considerations: Section 2 of RFC3508

Intended usage: Section 3 of RFC3508

Applications and/or protocols which use this scheme: Section 4 of
RFC3508

Interoperability considerations: None. (Section 2 of RFC3508
contains the first version of "h323" URL definition.)

Security considerations: Section 5 of RFC3508

Relevant publications: [3] and [4]

Contact: Orit Levin, orit@radvision.com

Author/Change Controller: IESG

References

[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC2119, March 1997.

[2] Crocker, D., Editor, and P. Overell "Augmented BNF for Syntax
Specifications: ABNF", RFC2234, November 1997.

[3] ITU-T Recommendation H.323v.4 "Packet-based multimedia
communications systems", November 2000.

[4] ITU-T Recommendation H.225.0 "Call signalling protocols and
media stream packetization for packet-based multimedia
communication systems", November 2000.

[5] ITU-T Recommendation H.235 "Security and Encryption for H Series
(H.323 and other H.245 based) multimedia terminals", November
2000.

[6] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:
Session Initiation Protocol", RFC3261, June 2002.

[7] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC
2279, January 1998.

[8] ISO/IEC 10646-1:1993, Information technology "Universal
Multiple-Octet Coded Character Set (USC)" Part 1: Architecture
and Basic Multilingual Plane.

[9] Rosenberg, J., Salama, H. and M. Squire, "Telephony Routing over
IP (TRIP)", RFC3219, January 2002.

Acknowledgments

This document is prepared and posted on behalf of SG-16 ITU-T. I
wish to thank Paul E. Jones, Robert Callaghan and Cullen Jennings for
their comments and active help.

Author's Address

Orit Levin
RADVISION
266 Harristown Road
Glen Rock, NJ USA

Phone: +1-201-689-6330
EMail: orit@radvision.com

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