draft-ietf-ecrit-service-urn-06.txt   draft-ietf-ecrit-service-urn-07.txt 
ECRIT H. Schulzrinne ECRIT H. Schulzrinne
Internet-Draft Columbia U. Internet-Draft Columbia U.
Intended status: Standards Track March 4, 2007 Intended status: Standards Track August 15, 2007
Expires: September 5, 2007 Expires: February 16, 2008
A Uniform Resource Name (URN) for Services A Uniform Resource Name (URN) for Emergency and Other Well-Known
draft-ietf-ecrit-service-urn-06 Services
draft-ietf-ecrit-service-urn-07
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
skipping to change at page 1, line 34 skipping to change at page 1, line 35
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on September 5, 2007. This Internet-Draft will expire on February 16, 2008.
Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2007).
Abstract Abstract
The content of many communication services depends on the context, The content of many communication services depends on the context,
such as the user's location. We describe a 'service' URN that allows such as the user's location. We describe a 'service' URN that allows
to identify context-dependent services that can be resolved in a to identify well-known context-dependent services that can be
distributed manner. resolved in a distributed manner. Examples include emergency
services, directory assistance and call-before-you-dig hot lines.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Registration Template . . . . . . . . . . . . . . . . . . . . 5 3. Registration Template . . . . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
4.1. New Service-Identifying Labels . . . . . . . . . . . . . . 7 4.1. New Service-Identifying Labels . . . . . . . . . . . . . . 7
4.2. Sub-Services for the 'sos' Service . . . . . . . . . . . . 8 4.2. Sub-Services for the 'sos' Service . . . . . . . . . . . . 8
4.3. Sub-Services for the 'counseling' Service . . . . . . . . 9 4.3. Sub-Services for the 'counseling' Service . . . . . . . . 9
4.4. Initial IANA Registration . . . . . . . . . . . . . . . . 9 4.4. Initial IANA Registration . . . . . . . . . . . . . . . . 9
5. Internationalization Considerations . . . . . . . . . . . . . 10 5. Internationalization Considerations . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . . 11 7.1. Normative References . . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . . 11 7.2. Informative References . . . . . . . . . . . . . . . . . . 11
Appendix A. Alternative Approaches Considered . . . . . . . . . . 12 Appendix A. Alternative Approaches Considered . . . . . . . . . . 12
Appendix B. Acknowledgments . . . . . . . . . . . . . . . . . . . 13 Appendix B. Acknowledgments . . . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14
Intellectual Property and Copyright Statements . . . . . . . . . . 15 Intellectual Property and Copyright Statements . . . . . . . . . . 15
1. Introduction 1. Introduction
In existing telecommunications systems, there are many well-known In existing telecommunications systems, there are many well-known
communication and information services that are offered by loosely communication and information services that are offered by loosely
coordinated entities across a large geographic region, with well- coordinated entities across a large geographic region, with well-
known identifiers. Some of the services are operated by governments known identifiers. Some of the services are operated by governments
or regulated monopolies, others by competing commercial enterprises. or regulated monopolies, others by competing commercial enterprises.
Examples include emergency services (reached by dialing 9-1-1 in Examples include emergency services (reached by dialing 9-1-1 in
skipping to change at page 4, line 34 skipping to change at page 4, line 34
URNs in the end host is beyond the scope of this document. These URNs in the end host is beyond the scope of this document. These
translations likely depend on the location of the caller and may be translations likely depend on the location of the caller and may be
many-to-one, i.e., several service numbers may map to one service many-to-one, i.e., several service numbers may map to one service
URN. For example, a phone for a traveler could recognize the URN. For example, a phone for a traveler could recognize the
emergency service number for both the traveler's home location and emergency service number for both the traveler's home location and
the traveler's visited location, mapping both to the same universal the traveler's visited location, mapping both to the same universal
service URN, urn:service:sos. service URN, urn:service:sos.
Since service URNs are not routable, a SIP proxy or user agent has to Since service URNs are not routable, a SIP proxy or user agent has to
translate the service URN into a routable URI for a location- translate the service URN into a routable URI for a location-
appropriate service provider, such as a SIP URL. LoST [17] is appropriate service provider, such as a SIP URL. LoST [18] is
expected to be used as a resolution system for mapping service URNs expected to be used as a resolution system for mapping service URNs
to URLs based on geographic location. In the future, there may be to URLs based on geographic location. In the future, there may be
several such protocols, possibly different ones for different several such protocols, possibly different ones for different
services. services.
Services are described by top-level service type, and may contain a Services are described by top-level service type, and may contain a
hierarchy of sub-services further describing the service, as outlined hierarchy of sub-services further describing the service, as outlined
in Section 3. in Section 3.
We discuss alternative approaches for creating service identifiers, We discuss alternative approaches for creating service identifiers,
and why they are unsatisfactory, in Appendix A. and why they are unsatisfactory, in Appendix A.
2. Terminology 2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED", In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in RFC 2119 [2]. and "OPTIONAL" are to be interpreted as described in RFC 2119 [2].
Terminology specific to emergency services is defined in [19]. Terminology specific to emergency services is defined in [20].
3. Registration Template 3. Registration Template
Below, we include the registration template for the URN scheme Below, we include the registration template for the URN scheme
according to RFC 3406 [12]. according to RFC 3406 [13].
Namespace ID: service Namespace ID: service
Registration Information: Registration version: 1; registration Registration Information: Registration version: 1; registration
date: 2006-04-02 date: 2006-04-02
Declared registrant of the namespace: Declared registrant of the namespace:
Registering organization: IETF ECRIT Working Group Registering organization: IETF
Designated contact: Henning Schulzrinne Designated contact: Henning Schulzrinne
Designated contact email: hgs@cs.columbia.edu Designated contact email: hgs@cs.columbia.edu
Declaration of syntactic structure: The URN consists of a Declaration of syntactic structure: The URN consists of a
hierarchical service identifier, with a sequence of labels hierarchical service identifier, with a sequence of labels
separated by periods. The left-most label is the most significant separated by periods. The left-most label is the most significant
one and is called 'top-level service', while names to the right one and is called 'top-level service', while names to the right
are called 'sub-services'. The set of allowable characters is the are called 'sub-services'. The set of allowable characters is the
same as that for domain names [1] and a subset of the labels same as that for domain names [1] and a subset of the labels
allowed in [5]. Labels are case-insensitive and MUST be specified allowed in [5]. Labels are case-insensitive and MUST be specified
in all lower-case. For any given service URN, service-identifiers in all lower-case. For any given service URN, service-identifiers
can be removed right-to-left and the resulting URN is still valid, can be removed right-to-left and the resulting URN is still valid,
referring a more generic service. In other words, if a service referring a more generic service. In other words, if a service
'x.y.z' exists, the URNs 'x' and 'x.y' are also valid service 'x.y.z' exists, the URNs 'x' and 'x.y' are also valid service
URNs. URNs. The ABNF [6] is shown below.
"URN:service:" service service-URN = "URN:service:" service
service = top-level *("." sub-service) service = top-level *("." sub-service)
let-dig = ALPHA / DIGIT
let-dig-hyp = let-dig / '-'
sub-service = let-dig [ *let-dig-hyp let-dig ]
top-level = let-dig [ *25let-dig-hyp let-dig ] top-level = let-dig [ *25let-dig-hyp let-dig ]
sub-service = let-dig [ *let-dig-hyp let-dig ]
let-dig-hyp = let-dig / "-"
let-dig = ALPHA / DIGIT
ALPHA = %x41-5A / %x61-7A ; A-Z / a-z
DIGIT = %x30-39 ; 0-9
Relevant ancillary documentation: None Relevant ancillary documentation: None
Community considerations: The service URN is believed to be relevant Community considerations: The service URN is believed to be relevant
to a large cross-section of Internet users, including both to a large cross-section of Internet users, including both
technical and non-technical users, on a variety of devices, but technical and non-technical users, on a variety of devices, but
particularly for mobile and nomadic users. The service URN will particularly for mobile and nomadic users. The service URN will
allow Internet users needing services to identify the service by allow Internet users needing services to identify the service by
kind, without having to determine manually who provides the kind, without having to determine manually who provides the
particular service in the user's current context, e.g., at the particular service in the user's current context, e.g., at the
skipping to change at page 6, line 16 skipping to change at page 6, line 18
having to know the emergency dial string of the visited country. having to know the emergency dial string of the visited country.
The assignment of identifiers is described in the IANA The assignment of identifiers is described in the IANA
Considerations (Section 4). The service URN does not prescribe a Considerations (Section 4). The service URN does not prescribe a
particular resolution mechanism, but it is assumed that a number particular resolution mechanism, but it is assumed that a number
of different entities could operate and offer such mechanisms. of different entities could operate and offer such mechanisms.
Namespace considerations: There do not appear to be other URN Namespace considerations: There do not appear to be other URN
namespaces that serve the same need of uniquely identifying namespaces that serve the same need of uniquely identifying
widely-available communication and information services. Unlike widely-available communication and information services. Unlike
most other currently registered URN namespaces, the service URN most other currently registered URN namespaces, the service URN
does not identify documents and protocol objects (e.g., [9], [10], does not identify documents and protocol objects (e.g., [10],
[15], [16]), types of telecommunications equipment [14], people or [11], [16], [17]), types of telecommunications equipment [15],
organizations [8]. tel URIs [13] identify telephone numbers, but people or organizations [9]. tel URIs [14] identify telephone
numbers commonly identifying services, such as 911 or 112, are numbers, but numbers commonly identifying services, such as 911 or
specific to a particular region or country. 112, are specific to a particular region or country.
Identifier uniqueness considerations: A service URN identifies a Identifier uniqueness considerations: A service URN identifies a
logical service, specified in the service registration (see IANA logical service, specified in the service registration (see IANA
Considerations (Section 4)). Resolution of the URN, if Considerations (Section 4)). Resolution of the URN, if
successful, will return a particular instance of the service, and successful, will return a particular instance of the service, and
this instance may be different even for two users making the same this instance may be different even for two users making the same
request in the same place at the same time; the logical service request in the same place at the same time; the logical service
identified by the URN, however, is persistent and unique. Service identified by the URN, however, is persistent and unique. Service
URNs MUST be unique for each unique service; this is guaranteed URNs MUST be unique for each unique service; this is guaranteed
through the registration of each service within this namespace, through the registration of each service within this namespace,
skipping to change at page 7, line 10 skipping to change at page 7, line 13
'service' URNs of that service. 'service' URNs of that service.
Rules for Lexical Equivalence: 'service' identifiers are compared Rules for Lexical Equivalence: 'service' identifiers are compared
according to case-insensitive string equality. according to case-insensitive string equality.
Conformance with URN Syntax: The BNF in the 'Declaration of Conformance with URN Syntax: The BNF in the 'Declaration of
syntactic structure' above constrains the syntax for this URN syntactic structure' above constrains the syntax for this URN
scheme. scheme.
Validation mechanism: Validation determines whether a given string Validation mechanism: Validation determines whether a given string
is currently a validly-assigned URN [12]. Due to the distributed is currently a validly-assigned URN [13]. Due to the distributed
nature of the mapping mechanism and since not all services are nature of the mapping mechanism and since not all services are
available everywhere and not all mapping servers may be configured available everywhere and not all mapping servers may be configured
with all current service registrations, validation in this sense with all current service registrations, validation in this sense
is not possible. Also, the discovery mechanism for the mapping is not possible. Also, the discovery mechanism for the mapping
mechanism may not be configured with all current top-level mechanism may not be configured with all current top-level
services. services.
Scope: The scope for this URN is public and global. Scope: The scope for this URN is public and global.
4. IANA Considerations 4. IANA Considerations
skipping to change at page 10, line 27 skipping to change at page 10, line 27
sos.mountain RFC XYZ Mountain rescue sos.mountain RFC XYZ Mountain rescue
sos.physician RFC XYZ Physician referral service sos.physician RFC XYZ Physician referral service
sos.poison RFC XYZ Poison control center sos.poison RFC XYZ Poison control center
sos.police RFC XYZ Police, law enforcement sos.police RFC XYZ Police, law enforcement
[[NOTE TO RFC-EDITOR: Please replace above 'RFC XYZ' reference with [[NOTE TO RFC-EDITOR: Please replace above 'RFC XYZ' reference with
the RFC number of this document and remove this note.]] the RFC number of this document and remove this note.]]
5. Internationalization Considerations 5. Internationalization Considerations
The service labels are protocol elements [11] and not normally seen The service labels are protocol elements [12] and not normally seen
by users. Thus, the character set for these elements is restricted, by users. Thus, the character set for these elements is restricted,
as described in Section 3. as described in Section 3.
6. Security Considerations 6. Security Considerations
As an identifier, the service URN does not appear to raise any As an identifier, the service URN does not appear to raise any
particular security issues. The services described by the URN are particular security issues. The services described by the URN are
meant to be well-known, even if the particular service instance is meant to be well-known, even if the particular service instance is
access-controlled, so privacy considerations do not apply to the URN. access-controlled, so privacy considerations do not apply to the URN.
There are likely no specific privacy issues when including a service There are likely no specific privacy issues when including a service
URN on a web page, for example. On the other hand, ferrying the URN URN on a web page, for example. On the other hand, ferrying the URN
in a signaling protocol can give attackers information on the kind of in a signaling protocol can give attackers information on the kind of
service desired by the caller. For example, this makes it easier for service desired by the caller. For example, this makes it easier for
the attacker to automatically find all calls for emergency services the attacker to automatically find all calls for emergency services
or directory assistance. Appropriate, protocol-specific security or directory assistance. Appropriate, protocol-specific security
mechanisms need to be implemented for protocols carrying service mechanisms need to be implemented for protocols carrying service
URNs. The mapping protocol needs to address a number of threats, as URNs. The mapping protocol needs to address a number of threats, as
detailed in [18]. That document also discusses the security detailed in [19]. That document also discusses the security
considerations related to the use of the service URN for emergency considerations related to the use of the service URN for emergency
services. services.
7. References 7. References
7.1. Normative References 7.1. Normative References
[1] Braden, R., "Requirements for Internet Hosts - Application and [1] Braden, R., "Requirements for Internet Hosts - Application and
Support", STD 3, RFC 1123, October 1989. Support", STD 3, RFC 1123, October 1989.
skipping to change at page 11, line 25 skipping to change at page 11, line 25
October 1998. October 1998.
[4] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., [4] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002. Session Initiation Protocol", RFC 3261, June 2002.
[5] Daigle, L. and A. Newton, "Domain-Based Application Service [5] Daigle, L. and A. Newton, "Domain-Based Application Service
Location Using SRV RRs and the Dynamic Delegation Discovery Location Using SRV RRs and the Dynamic Delegation Discovery
Service (DDDS)", RFC 3958, January 2005. Service (DDDS)", RFC 3958, January 2005.
[6] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005.
7.2. Informative References 7.2. Informative References
[6] Crocker, D., "MAILBOX NAMES FOR COMMON SERVICES, ROLES AND [7] Crocker, D., "MAILBOX NAMES FOR COMMON SERVICES, ROLES AND
FUNCTIONS", RFC 2142, May 1997. FUNCTIONS", RFC 2142, May 1997.
[7] Resnick, P., "Internet Message Format", RFC 2822, April 2001. [8] Resnick, P., "Internet Message Format", RFC 2822, April 2001.
[8] Mealling, M., "The Network Solutions Personal Internet Name [9] Mealling, M., "The Network Solutions Personal Internet Name
(PIN): A URN Namespace for People and Organizations", RFC 3043, (PIN): A URN Namespace for People and Organizations", RFC 3043,
January 2001. January 2001.
[9] Rozenfeld, S., "Using The ISSN (International Serial Standard [10] Rozenfeld, S., "Using The ISSN (International Serial Standard
Number) as URN (Uniform Resource Names) within an ISSN-URN Number) as URN (Uniform Resource Names) within an ISSN-URN
Namespace", RFC 3044, January 2001. Namespace", RFC 3044, January 2001.
[10] Hakala, J. and H. Walravens, "Using International Standard Book [11] Hakala, J. and H. Walravens, "Using International Standard Book
Numbers as Uniform Resource Names", RFC 3187, October 2001. Numbers as Uniform Resource Names", RFC 3187, October 2001.
[11] Hoffman, P., "Terminology Used in Internationalization in the [12] Hoffman, P., "Terminology Used in Internationalization in the
IETF", RFC 3536, May 2003. IETF", RFC 3536, May 2003.
[12] Daigle, L., van Gulik, D., Iannella, R., and P. Faltstrom, [13] Daigle, L., van Gulik, D., Iannella, R., and P. Faltstrom,
"Uniform Resource Names (URN) Namespace Definition Mechanisms", "Uniform Resource Names (URN) Namespace Definition Mechanisms",
BCP 66, RFC 3406, October 2002. BCP 66, RFC 3406, October 2002.
[13] Schulzrinne, H., "The tel URI for Telephone Numbers", RFC 3966, [14] Schulzrinne, H., "The tel URI for Telephone Numbers", RFC 3966,
December 2004. December 2004.
[14] Tesink, K. and R. Fox, "A Uniform Resource Name (URN) Namespace [15] Tesink, K. and R. Fox, "A Uniform Resource Name (URN) Namespace
for the Common Language Equipment Identifier (CLEI) Code", for the Common Language Equipment Identifier (CLEI) Code",
RFC 4152, August 2005. RFC 4152, August 2005.
[15] Kang, S., "Using Universal Content Identifier (UCI) as Uniform [16] Kang, S., "Using Universal Content Identifier (UCI) as Uniform
Resource Names (URN)", RFC 4179, October 2005. Resource Names (URN)", RFC 4179, October 2005.
[16] Kameyama, W., "A Uniform Resource Name (URN) Namespace for the [17] Kameyama, W., "A Uniform Resource Name (URN) Namespace for the
TV-Anytime Forum", RFC 4195, October 2005. TV-Anytime Forum", RFC 4195, October 2005.
[17] Hardie, T., "LoST: A Location-to-Service Translation Protocol", [18] Hardie, T., "LoST: A Location-to-Service Translation Protocol",
draft-ietf-ecrit-lost-04 (work in progress), February 2007. draft-ietf-ecrit-lost-06 (work in progress), August 2007.
[18] Taylor, T., "Security Threats and Requirements for Emergency [19] Taylor, T., "Security Threats and Requirements for Emergency
Call Marking and Mapping", draft-ietf-ecrit-security-threats-03 Call Marking and Mapping", draft-ietf-ecrit-security-threats-04
(work in progress), July 2006. (work in progress), April 2007.
[19] Schulzrinne, H. and R. Marshall, "Requirements for Emergency [20] Schulzrinne, H. and R. Marshall, "Requirements for Emergency
Context Resolution with Internet Technologies", Context Resolution with Internet Technologies",
draft-ietf-ecrit-requirements-12 (work in progress), draft-ietf-ecrit-requirements-13 (work in progress),
August 2006. March 2007.
Appendix A. Alternative Approaches Considered Appendix A. Alternative Approaches Considered
The discussions of ways to identify emergency calls has yielded a The discussions of ways to identify emergency calls has yielded a
number of proposals. Since these are occasionally brought up during number of proposals. Since these are occasionally brought up during
discussions, we briefly summarize why this document chose not to discussions, we briefly summarize why this document chose not to
pursue these solutions. pursue these solutions.
tel:NNN;context=+C This approach uses tel URIs [13]. Here, NNN is tel:NNN;context=+C This approach uses tel URIs [14]. Here, NNN is
the national emergency number, where the country is identified by the national emergency number, where the country is identified by
the context C. This approach is easy for user agents to implement, the context C. This approach is easy for user agents to implement,
but hard for proxies and other SIP elements to recognize, as it but hard for proxies and other SIP elements to recognize, as it
would have to know about all number-context combinations in the would have to know about all number-context combinations in the
world and track occasional changes. In addition, many of these world and track occasional changes. In addition, many of these
numbers are being used for other services. For example, the numbers are being used for other services. For example, the
emergency number in Paraguay (00) is also used to call the emergency number in Paraguay (00) is also used to call the
international operator in the United States. As another example, international operator in the United States. As another example,
A number of countries, such as Italy, use 118 as an emergency A number of countries, such as Italy, use 118 as an emergency
number, but it also connects to directory assistance in Finland. number, but it also connects to directory assistance in Finland.
tel:sos This solution avoids name conflicts, but is not a valid tel:sos This solution avoids name conflicts, but is not a valid
"tel" [13] URI. It also only works if every outbound proxy knows "tel" [14] URI. It also only works if every outbound proxy knows
how to route requests to a proxy that can reach emergency services how to route requests to a proxy that can reach emergency services
since tel URIs. The SIP URI proposed here only requires a user's since tel URIs. The SIP URI proposed here only requires a user's
home domain to be appropriately configured. home domain to be appropriately configured.
sip:sos@domain Earlier work had defined a special user identifier, sip:sos@domain Earlier work had defined a special user identifier,
sos, within the caller's home domain in a SIP URI, for example, sos, within the caller's home domain in a SIP URI, for example,
sip:sos@example.com. Such a user identifier follows the sip:sos@example.com. Such a user identifier follows the
convention of RFC 2142 [6] and the "postmaster" convention convention of RFC 2142 [7] and the "postmaster" convention
documented in RFC 2822 [7]. This approach had the advantage that documented in RFC 2822 [8]. This approach had the advantage that
dial plans in existing user agents could probably be converted to dial plans in existing user agents could probably be converted to
generate such a URI and that only the home proxy for the domain generate such a URI and that only the home proxy for the domain
has to understand the user naming convention. However, it has to understand the user naming convention. However, it
overloads the user part of the URI with specific semantics rather overloads the user part of the URI with specific semantics rather
than being opaque, makes routing by the outbound proxy a special than being opaque, makes routing by the outbound proxy a special
case that does not conform to normal SIP request-URI handling case that does not conform to normal SIP request-URI handling
rules and is SIP-specific. The mechanism also does not extend rules and is SIP-specific. The mechanism also does not extend
readily to other services. readily to other services.
SIP URI user parameter: One could create a special URI, such as SIP URI user parameter: One could create a special URI, such as
 End of changes. 36 change blocks. 
48 lines changed or deleted 55 lines changed or added

This html diff was produced by rfcdiff 1.34. The latest version is available from http://tools.ietf.org/tools/rfcdiff/