In existing telecommunications systems, there are many well-known
communication and information services that are offered by loosely
coordinated entities across a large geographic region, with well-
known identifiers. Some of the services are operated by governments
or regulated monopolies, others by competing commercial enterprises.
Examples include emergency services (reached by dialing 9-1-1 in
North America, 1-1-2 in Europe), community services and volunteer
opportunities (2-1-1 in some regions of the United States), telephone
directory and repair services (4-1-1 and 6-1-1 in the United States
and Canada), government information services (3-1-1 in some cities in
the United States), lawyer referral services (1-800-LAWYER), car
roadside assistance (automobile clubs), and pizza delivery services.
Unfortunately, almost all of them are limited in scope to a single
country or possibly a group of countries, such as those belonging to
the North American Numbering Plan or the European Union. The same
identifiers are often used for other purposes outside that region,
making access to such services difficult when users travel or use
devices produced outside their home country.
These services are characterized by long-term stability of user-
visible identifiers, decentralized administration of the underlying
service, and a well-defined resolution or mapping mechanism. For
example, there is no national coordination or call center for "9-1-1"
in the United States; rather, various local government organizations
cooperate to provide this service based on jurisdictions.
In this document, we propose a URN namespace that, together with
resolution protocols beyond the scope of this document, allows us to
define such global, well-known services, while distributing the
actual implementation across a large number of service-providing
entities. There are many ways to divide provision of such services,
such as dividing responsibility by geographic region or by the
service provider a user chooses. In addition, users can choose
different mapping service providers that in turn manage how
geographic locations are mapped to service providers.
Availability of such service identifiers allows end systems to convey
information about the desired service to other network entities. For
example, an IP phone could have a special set of short cuts, address
book entries, or buttons that invoke emergency services. When such a
service identifier is put into the outgoing Session Initiation
Protocol (SIP) [RFC3261] message, it allows SIP proxies to
unambiguously take actions, as it would not be practical to configure
them with dial strings and emergency numbers used throughout the
world. Hence, such service identifiers make it possible to delegate
routing decisions to third parties and to mark certain requests as
having special characteristics while preventing these characteristics
from being accidentally invoked.
This URN identifies services independent of the particular protocol
that is used to request or deliver the service. The URN may appear
in protocols that allow general URIs, such as the SIP [RFC3261]
request URIs, web pages, or mapping protocols.
The service URN is a protocol element and is generally not expected
to be visible to humans. For example, it is expected that callers
will still dial the emergency number '9-1-1' in the United States to
reach emergency services. In some other cases, speed dial buttons
might identify the service, as is common practice on hotel phones
today. (Speed dial buttons for summoning emergency help are
considered inappropriate by most emergency services professionals, at
least for mobile devices, as they are too prone to being triggered
The translation of service dial strings or service numbers to service
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
many-to-one, i.e., several service numbers may map to one service
URN. For example, a phone for a traveler could recognize the
emergency service number for both the traveler's home location and
the traveler's visited location, mapping both to the same universal
service URN, urn:service:sos.
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-
appropriate service provider, such as a SIP URL. A Location-to-
Service Translation Protocol (LoST) [LOST] is expected to be used as
a resolution system for mapping service URNs to URLs based on
geographic location. In the future, there may be several such
protocols, possibly different ones for different services.
Services are described by top-level service type, and may contain a
hierarchy of sub-services that further describe the service, as
outlined in Section 3.
We discuss alternative approaches for creating service identifiers,
and why they are unsatisfactory, in Appendix A.
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in RFC 2119
Terminology specific to emergency services is defined in [RFC5012].
3. Registration Template
Below, we include the registration template for the URN scheme
according to RFC 3406 [RFC3406].
Namespace ID: service
Registration version: 1
Registration date: 2006-04-02
Declared registrant of the namespace:
Registering organization: IETF
Designated contact: Henning Schulzrinne
Designated contact email: email@example.com
Declaration of syntactic structure: The URN consists of a
hierarchical service identifier, with a sequence of labels
separated by periods. The left-most label is the most significant
one and is called 'top-level service', while names to the right
are called 'sub-services'. The set of allowable characters is the
same as that for domain names [RFC1123] and a subset of the labels
allowed in [RFC3958]. Labels are case-insensitive, but MUST be
specified in all lower-case. For any given service URN, service-
identifiers can be removed right-to-left; the resulting URN is
still valid, referring to a more generic service. In other words,
if a service 'x.y.z' exists, the URNs 'x' and 'x.y' are also valid
service URNs. The ABNF [RFC4234] is shown below.
service-URN = "URN:service:" service
service = top-level *("." sub-service)
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
Community considerations: The service URN is believed to be relevant
to a large cross-section of Internet users, including both
technical and non-technical users, on a variety of devices, but
particularly for mobile and nomadic users. The service URN will
allow Internet users needing services to identify the service by
kind, without having to determine manually who provides the
particular service in the user's current context, e.g., at the
user's current location. For example, travelers will be able to
use their mobile devices to request emergency services without
having to know the emergency dial string of the visited country.
The assignment of identifiers is described in the IANA
Considerations (Section 4). The service URN does not prescribe a
particular resolution mechanism, but it is assumed that a number
of different entities could operate and offer such mechanisms.
Namespace considerations: There do not appear to be other URN
namespaces that serve the same need of uniquely identifying
widely-available communication and information services. Unlike
most other currently registered URN namespaces, the service URN
does not identify documents and protocol objects (e.g., [RFC3044],
[RFC3187], [RFC4179], and [RFC4195]), types of telecommunications
equipment [RFC4152], people, or organizations [RFC3043]. tel URIs
[RFC3966] identify telephone numbers, but numbers commonly
identifying services (such as 911 or 112) are specific to a
particular region or country.
Identifier uniqueness considerations: A service URN identifies a
logical service, specified in the service registration (see IANA
Considerations (Section 4)). Resolution of the URN, if
successful, will return a particular instance of the service, and
this instance may be different even for two users making the same
request in the same place at the same time; the logical service
identified by the URN, however, is persistent and unique. Service
URNs MUST be unique for each unique service; this is guaranteed
through the registration of each service within this namespace,
described in Section 4.
Identifier persistence considerations: The 'service' URN for the
same service is expected to be persistent, although there
naturally cannot be a guarantee that a particular service will
continue to be available globally or at all times.
Process of identifier assignment: The process of identifier
assignment is described in the IANA Considerations (Section 4).
Process for identifier resolution: There is no single global
resolution service for 'service' URNs. However, each top-level
service can provide a set of mapping protocols to be used with
'service' URNs of that service.
Rules for lexical equivalence: 'service' identifiers are compared
according to case-insensitive string equality.
Conformance with URN syntax: The BNF in the 'Declaration of
syntactic structure' above constrains the syntax for this URN
Validation mechanism: Validation determines whether a given string
is currently a validly-assigned URN [RFC3406]. Due to the
distributed nature of the mapping mechanism, and since not all
services are available everywhere and not all mapping servers may
be configured with all current service registrations, validation
in this sense is not possible. Also, the discovery mechanism for
the mapping mechanism may not be configured with all current top-
Scope: The scope for this URN is public and global.
4. IANA Considerations
This section registers a new URN scheme with the registration
template provided in Section 3.
Below, Section 4.1 details how to register new service-identifying
labels. Descriptions of sub-services for the first two services to
be registered, sos and counseling, are given in Section 4.2 and
Section 4.3, respectively. Finally, Section 4.4 contains the initial
4.1. New Service-Identifying Labels
Services and sub-services are identified by labels managed by IANA,
according to the processes outlined in [RFC2434] in a new registry
called "Service URN Labels". Thus, creating a new service requires
IANA action. The policy for adding top-level service labels is
'Standards Action'. (This document defines the top-level services
'sos' and 'counseling'.) The policy for assigning labels to sub-
services may differ for each top-level service designation and MUST
be defined by the document describing the top-level service.
Entries in the registration table have the following format:
Service Reference Description
foo RFCxyz Brief description of the 'foo' top-level service
foo.bar RFCabc Description of the 'foo.bar' service
To allow use within the constraints of S-NAPTR [RFC3958], all top-
level service names MUST NOT exceed 27 characters.
4.2. Sub-Services for the 'sos' Service
This section defines the first service registration within the IANA
registry defined in Section 4.1, using the top-level service label
The 'sos' service type describes emergency services requiring an
immediate response, typically offered by various branches of the
government or other public institutions. Additional sub-services can
be added after expert review and must be of general public interest
and have a similar emergency nature. The expert is designated by the
ECRIT working group, its successor, or, in their absence, the IESG.
The expert review should only approve emergency services that are
offered widely and in different countries, with approximately the
same caller expectation in terms of services rendered. The 'sos'
service is not meant to invoke general government, public
information, counseling, or social services.
urn:service:sos The generic 'sos' service reaches a public safety
answering point (PSAP), which in turn dispatches aid appropriate
to the emergency. It encompasses all of the services listed
urn:service:sos.ambulance This service identifier reaches an
ambulance service that provides emergency medical assistance and
urn:service:sos.animal-control Animal control typically enforces
laws and ordinances pertaining to animal control and management,
investigates cases of animal abuse, educates the community in
responsible pet ownership and wildlife care, and provides for the
housing and care of homeless animals, among other animal-related
urn:service:sos.fire The 'fire' service identifier summons the fire
service, also known as the fire brigade or fire department.
urn:service:sos.gas The 'gas' service allows the reporting of
natural gas (and other flammable gas) leaks or other natural gas
urn:service:sos.marine The 'marine' service refers to maritime
search and rescue services such as those offered by the coast
guard, lifeboat, or surf lifesavers.
urn:service:sos.mountain The 'mountain' service refers to mountain
rescue services (i.e., search and rescue activities that occur in
a mountainous environment), although the term is sometimes also
used to apply to search and rescue in other wilderness
urn:service:sos.physician The 'physician' emergency service connects
the caller to a physician referral service.
urn:service:sos.poison The 'poison' service refers to special
information centers set up to inform citizens about how to respond
to potential poisoning. These poison control centers maintain a
database of poisons and appropriate emergency treatment.
urn:service:sos.police The 'police' service refers to the police
department or other law enforcement authorities.
4.3. Sub-Services for the 'counseling' Service
The 'counseling' service type describes services where callers can
receive advice and support, often anonymous, but not requiring an
emergency response. (Naturally, such services may transfer callers
to an emergency service or summon such services if the situation
warrants.) Additional sub-services can be added after expert review
and should be of general public interest. The expert is chosen in
the same manner as described for the 'sos' service. The expert
review should take into account whether these services are offered
widely and in different countries, with approximately the same caller
expectation in terms of services rendered.
urn:service:counseling The generic 'counseling' service reaches a
call center that transfers the caller based on his or her specific
urn:service:counseling.children The 'children' service refers to
counseling and support services that are specifically tailored to
the needs of children. Such services may, for example, provide
advice to run-aways or victims of child abuse.
urn:service:counseling.mental-health The 'mental-health' service
refers to the "diagnostic, treatment, and preventive care that
helps improve how persons with mental illness feel both physically
and emotionally as well as how they interact with other persons".
(U.S. Department of Health and Human Services)
urn:service:counseling.suicide The 'suicide' service refers to the
suicide prevention hotline.
4.4. Initial IANA Registration
The following table contains the initial IANA registration for
emergency and counseling services.
Service Reference Description
counseling RFC 5031 Counseling services
counseling.children RFC 5031 Counseling for children
counseling.mental-health RFC 5031 Mental health counseling
counseling.suicide RFC 5031 Suicide prevention hotline
sos RFC 5031 Emergency services
sos.ambulance RFC 5031 Ambulance service
sos.animal-control RFC 5031 Animal control
sos.fire RFC 5031 Fire service
sos.gas RFC 5031 Gas leaks and gas emergencies
sos.marine RFC 5031 Maritime search and rescue
sos.mountain RFC 5031 Mountain rescue
sos.physician RFC 5031 Physician referral service
sos.poison RFC 5031 Poison control center
sos.police RFC 5031 Police, law enforcement
5. Internationalization Considerations
The service labels are protocol elements [RFC3536] and are not
normally seen by users. Thus, the character set for these elements
is restricted, as described in Section 3.
6. Security Considerations
As an identifier, the service URN does not appear to raise any
particular security issues. The services described by the URN are
meant to be well-known, even if the particular service instance is
access-controlled, so privacy considerations do not apply to the URN.
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
in a signaling protocol can give attackers information on the kind of
service desired by the caller. For example, this makes it easier for
the attacker to automatically find all calls for emergency services
or directory assistance. Appropriate, protocol-specific security
mechanisms need to be implemented for protocols carrying service
URNs. The mapping protocol needs to address a number of threats, as
detailed in [RFC5069]. That document also discusses the security
considerations related to the use of the service URN for emergency
7.1. Normative References
[RFC1123] Braden, R., "Requirements for Internet Hosts - Application
and Support", STD 3, RFC 1123, October 1989.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
[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.
[RFC4234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005.
7.2. Informative References
[LOST] Hardie, T., "LoST: A Location-to-Service Translation
Protocol", Work in Progress, March 2007.
[RFC2142] Crocker, D., "MAILBOX NAMES FOR COMMON SERVICES, ROLES AND
FUNCTIONS", RFC 2142, May 1997.
[RFC2822] Resnick, P., "Internet Message Format", RFC 2822,
[RFC3043] Mealling, M., "The Network Solutions Personal Internet
Name (PIN): A URN Namespace for People and Organizations",
RFC 3043, January 2001.
[RFC3044] Rozenfeld, S., "Using The ISSN (International Serial
Standard Number) as URN (Uniform Resource Names) within an
ISSN-URN Namespace", RFC 3044, January 2001.
[RFC3187] Hakala, J. and H. Walravens, "Using International Standard
Book Numbers as Uniform Resource Names", RFC 3187,
[RFC3406] Daigle, L., van Gulik, D., Iannella, R., and P. Faltstrom,
"Uniform Resource Names (URN) Namespace Definition
Mechanisms", BCP 66, RFC 3406, October 2002.
[RFC3536] Hoffman, P., "Terminology Used in Internationalization in
the IETF", RFC 3536, May 2003.
[RFC3966] Schulzrinne, H., "The tel URI for Telephone Numbers",
RFC 3966, December 2004.
[RFC4152] Tesink, K. and R. Fox, "A Uniform Resource Name (URN)
Namespace for the Common Language Equipment Identifier
(CLEI) Code", RFC 4152, August 2005.
[RFC4179] Kang, S., "Using Universal Content Identifier (UCI) as
Uniform Resource Names (URN)", RFC 4179, October 2005.
[RFC4195] Kameyama, W., "A Uniform Resource Name (URN) Namespace for
the TV-Anytime Forum", RFC 4195, October 2005.
[RFC5012] Schulzrinne, H. and R. Marshall, Ed., "Requirements for
Emergency Context Resolution with Internet Technologies",
RFC 5012, January 2008.
Appendix A. Alternative Approaches Considered
The discussions of ways to identify emergency calls has yielded a
number of proposals. Since these are occasionally brought up during
discussions, we briefly summarize why this document chose not to
pursue these solutions.
tel:NNN;context=+C This approach uses tel URIs [RFC3966]. Here, NNN
is the national emergency number, where the country is identified
by the context C. This approach is easy for user agents to
implement, but hard for proxies and other SIP elements to
recognize, as it would have to know about all number-context
combinations in the world and track occasional changes. In
addition, many of these numbers are being used for other services.
For example, the emergency number in Paraguay (00) is also used to
call the international operator in the United States. As another
example, a number of countries, such as Italy, use 118 as an
emergency number, but it also connects to directory assistance in
tel:sos This solution avoids name conflicts, but requires extending
the "tel" URI "tel" [RFC3966]. It also only works if every
outbound proxy knows how to route requests to a proxy that can
reach emergency services since tel URIs do not identify the
sip:sos@domain Earlier work had defined a special user identifier,
sos, within the caller's home domain in a SIP URI, for example,
sip:firstname.lastname@example.org. Such a user identifier follows the
convention of RFC 2142 [RFC2142] and the "postmaster" convention
documented in RFC 2822 [RFC2822]. This approach had the advantage
that dial plans in existing user agents could probably be
converted to generate such a URI and that only the home proxy for
the domain has to understand the user naming convention. However,
it overloads the user part of the URI with specific semantics
rather than being opaque, makes routing by the outbound proxy a
special case that does not conform to normal SIP request-URI
handling rules and is SIP-specific. The mechanism also does not
extend readily to other services.
SIP URI user parameter: One could create a special URI, such as
"aor-domain;user=sos". This avoids the name conflict problem, but
requires mechanism-aware user agents that are capable of emitting
this special URI. Also, the 'user' parameter is meant to describe
the format of the user part of the SIP URI, which this usage does
not do. Adding other parameters still leaves unclear what, if
any, conventions should be used for the user and domain part of
the URL. Neither solution is likely to be backward-compatible
with existing clients.
Special domain: A special domain, such as "sip:email@example.com" could
be used to identify emergency calls. This has similar properties
as the "tel:sos" URI, except that it is indeed a valid URI. To
make this usable, the special domain would have to be operational
and point to an appropriate emergency services proxy. Having a
single, if logical, emergency services proxy for the whole world
seems to have undesirable scaling and administrative properties.
Appendix B. Acknowledgments
This document is based on discussions with Jonathan Rosenberg and
benefited from the comments of Leslie Daigle, Keith Drage, Benja
Fallenstein, Paul Kyzivat, Andrew Newton, Brian Rosen, Jonathan
Rosenberg, Martin Thomson, and Hannes Tschofenig.
Department of Computer Science
450 Computer Science Building
New York, NY 10027
Phone: +1 212 939 7004
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