Request for Comments: 3508
H.323 Uniform Resource Locator (URL) Scheme Registration
Status of this Memo
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Copyright © The Internet Society (2003). All Rights Reserved.
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 RFC for 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, RFC 2119 .
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
ITU-T Recommendations H.323  and H.225.0  define a system for multimedia communications services over packet based networks. H.225.0  defines an alias type for carrying any standard Uniform Resource Locator (URL). H.323 version 4  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  and is published as an RFC for 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 .
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  string that shall be UTF-8  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  or TRIP . 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  messages, security is addressed by the H.235 security framework . When an H.323 URL carried within other protocols (such as SIP ), 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 .
URL scheme name: h323
URL scheme syntax: Section 2 of RFC 3508
Character encoding considerations: Section 2 of RFC 3508
Intended usage: Section 3 of RFC 3508
Applications and/or protocols which use this scheme: Section 4 of RFC 3508
Interoperability considerations: None. (Section 2 of RFC 3508 contains the first version of "h323" URL definition.)
Security considerations: Section 5 of RFC 3508
Relevant publications:  and  Contact: Orit Levin, email@example.com Author/Change Controller: IESG
 Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.  Crocker, D., Editor, and P. Overell "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997.  ITU-T Recommendation H.323v.4 "Packet-based multimedia communications systems", November 2000.  ITU-T Recommendation H.225.0 "Call signalling protocols and media stream packetization for packet-based multimedia communication systems", November 2000.  ITU-T Recommendation H.235 "Security and Encryption for H Series (H.323 and other H.245 based) multimedia terminals", November 2000.  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.  Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC 2279, January 1998.  ISO/IEC 10646-1:1993, Information technology "Universal Multiple-Octet Coded Character Set (USC)" Part 1: Architecture and Basic Multilingual Plane.  Rosenberg, J., Salama, H. and M. Squire, "Telephony Routing over IP (TRIP)", RFC 3219, January 2002.
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.
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