RFC 5031
A Uniform Resource Name (URN) for Emergency and Other Well-Known Services
RFC 5031: A Uniform Resource Name (URN) for Emergency and Other Well-Known Services 🚨✨
Okay bestie, let's start with the title block 💖. This is RFC 5031, written by H. Schulzrinne of Columbia U. 🎓 It's dated January 2008 and it's on the Standards Track 🎀, so it's an actual Internet standards track protocol doc. The title block doesn't list anything it obsoletes or updates, so no drama there 🦋. It comes from the Network Working Group too 🌸.
Status of This Memo 📜
This doc is a full-on Internet standards track protocol for the Internet community 🌈, and it's basically asking everyone to talk about it and send over suggestions for making it better 💬. If you want to know where this protocol stands in standardization, check the current edition of "Internet Official Protocol Standards" (STD 1) ✔️. Distribution of this memo is unlimited, so share away 💅.
Abstract 🌸
Okay so, a LOT of communication services depend on context, like where you are ✨. This doc describes a 'service' URN that lets us identify well-known, context-dependent services that can be resolved in a distributed way 🗺️. Think emergency services, directory assistance, and call-before-you-dig hot lines 📞. Iconic, honestly 👑.
Table of Contents 🍓
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Registration Template . . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
4.1. New Service-Identifying Labels . . . . . . . . . . . . . . 6
4.2. Sub-Services for the 'sos' Service . . . . . . . . . . . . 7
4.3. Sub-Services for the 'counseling' Service . . . . . . . . 8
4.4. Initial IANA Registration . . . . . . . . . . . . . . . . 9
5. Internationalization Considerations . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1. Normative References . . . . . . . . . . . . . . . . . . . 10
7.2. Informative References . . . . . . . . . . . . . . . . . . 11
Appendix A. Alternative Approaches Considered . . . . . . . . . . 13
Appendix B. Acknowledgments . . . . . . . . . . . . . . . . . . . 141. Introduction 🧚
Okay, so in existing telecom systems there are tons of well-known communication and information services 📱. They're offered by loosely coordinated entities across a huge geographic region, and they come with well-known identifiers 🪪. Some are run by governments or regulated monopolies, and others by competing commercial companies 🏢. Examples include emergency services (you dial 9-1-1 in North America and 1-1-2 in Europe) 🚑, community services and volunteer stuff (2-1-1 in some parts of the US) 🤝, telephone directory and repair services (4-1-1 and 6-1-1 in the US and Canada) ☎️, government info services (3-1-1 in some US cities) 🏛️, lawyer referral services (1-800-LAWYER) ⚖️, car roadside assistance (automobile clubs) 🚗, and pizza delivery 🍕. Honestly, the pizza is the real MVP.
The sad part? Almost all of them are limited to a single country, or maybe a group of countries like the North American Numbering Plan or the European Union 🌍. The same identifiers are also often used for other stuff outside that region, so it gets messy when people travel or use devices made outside their home country 😭.
These services have a few things in common: the user-visible identifiers stay stable for the long term, the admin is decentralized, and there's a well-defined resolution or mapping mechanism 🧩. For example, there's no national coordination or call center for "9-1-1" in the United States. Instead, local government organizations cooperate to provide the service based on their jurisdictions 🗽.
So in this doc, we propose a URN namespace that, together with resolution protocols that are beyond the scope of this document, lets us define these kinds of global, well-known services 🌐. The actual implementation gets spread across a large number of service-providing entities 🫶. There are lots of ways to split up provision of these services, like by geographic region or by the service provider a user picks 🗺️. Users can also choose different mapping service providers, and those providers manage how geographic locations get mapped to service providers 🧭.
Having these service identifiers lets end systems tell other network entities what service they want 📣. For example, an IP phone could have special shortcuts, address book entries, or buttons that invoke emergency services 📲. When a service identifier goes into an outgoing Session Initiation Protocol (SIP) [RFC3261] message, SIP proxies can unambiguously take action 🎯. That matters because it's not practical to configure them with every dial string and emergency number used around the world 🙈. So these identifiers make it possible to hand off routing decisions to third parties, and to mark certain requests as having special characteristics while preventing those characteristics from being accidentally invoked 🔒.
This URN identifies services without caring about which protocol is used to request or deliver them 💜. The URN may show up in protocols that allow general URIs, like SIP [RFC3261] request URIs, web pages, or mapping protocols 🕸️.
The service URN is a protocol element, so humans generally aren't expected to see it 🙈. For example, callers will still dial '9-1-1' in the United States to reach emergency services 📞. In some other cases, speed dial buttons might identify the service, which is already common on hotel phones 🏨. (Speed dial buttons for summoning emergency help are considered inappropriate by most emergency services professionals, at least for mobile devices, because they're too easy to trigger by accident 😬.)
Translating service dial strings or service numbers into service URNs on the end host is beyond the scope of this document 🧾. These translations probably depend on where the caller is, and they may be many-to-one, meaning several service numbers can 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 visited location, and map both to the same universal service URN, urn:service:sos ✈️.
Since service URNs aren't routable, a SIP proxy or user agent has to translate the service URN into a routable URI for a location-appropriate service provider, like a SIP URL 🛣️. The Location-to-Service Translation Protocol (LoST) [LOST] is expected to be used as the 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 a top-level service type, and they may contain a hierarchy of sub-services that describe the service in more detail, as outlined in Section 3 🌳.
We talk about alternative approaches for creating service identifiers, and why they're unsatisfactory, in Appendix A 🙅♀️.
2. Terminology 💜
In this doc, 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 [RFC2119] 📖. These are the words that really matter, so read them carefully 🔥.
Terminology specific to emergency services is defined in [RFC5012] 🚨.
3. Registration Template 🎀
okay so the registration template for this URN scheme follows RFC 3406 [RFC3406], and I'm obsessed with how neatly it's laid out ✨
Namespace ID: service
Registration Information: registration version 1, registered on 2006-04-02 📅
Declared registrant of the namespace: the registering organization is the IETF, and the designated contact is Henning Schulzrinne (hgs@cs.columbia.edu) 💌
Declaration of syntactic structure: the URN is a hierarchy of service labels separated by periods 🌸 The leftmost label is the most significant one and gets called the top-level service. Everything to its right is a sub-service. The allowed characters are the same as for domain names [RFC1123], and they're a subset of the labels allowed in [RFC3958]. Labels are case-insensitive, but they MUST be written in all lower-case. Here's the fun part: for any service URN you can peel off identifiers from the right, and the shorter URN is still valid and just points at a more generic service. So if x.y.z exists, then x and x.y are valid service URNs too 🧚 The ABNF [RFC4234] looks like this:
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 ; 0-9Relevant ancillary documentation: None 🙅♀️
Community considerations: ngl this one is so important 🫶 The service URN is believed to matter to a big slice of Internet users, technical and non-technical alike, on all kinds of devices, and especially for mobile and nomadic users. It lets people who need a service name it by kind, without having to work out who provides it in their current context, like their current location. Picture a traveler asking for emergency help from their phone without knowing the emergency dial string of the country they're visiting. Iconic. The assignment process is covered in the IANA Considerations (Section 4). The service URN doesn't lock in one resolution mechanism, though it's assumed that a bunch of different entities could run and offer those mechanisms 🌈
Namespace considerations: as far as anyone can tell, no other URN namespace does the same job of uniquely identifying widely available communication and information services 👑 Most other registered URN namespaces are different: the service URN doesn't 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 that commonly identify services (like 911 or 112) are specific to a particular region or country 📞
Identifier uniqueness considerations: a service URN identifies a logical service, which is specified in its service registration (see IANA Considerations (Section 4)) 💖 If resolution works, you get a particular instance of the service. That instance can differ even for two users making the same request in the same place at the same time. The logical service the URN names, though, is persistent and unique. Service URNs MUST be unique for each unique service, and the registration of each service in this namespace (described in Section 4) is what guarantees it 🔒
Identifier persistence considerations: the service URN for the same service is expected to stay persistent. There can't be a guarantee that a service will be available globally or at all times, though 🦋
Process of identifier assignment: this is described in the IANA Considerations (Section 4) 📝
Process for identifier resolution: there's no single global resolution service for service URNs 🌍 Instead, each top-level service can provide a set of mapping protocols to use with the service URNs of that service 🧭
Rules for lexical equivalence: service identifiers are compared using case-insensitive string equality 🔤
Conformance with URN syntax: the BNF in the 'Declaration of syntactic structure' above constrains the syntax for this URN scheme 📐
Validation mechanism: validation checks whether a given string is currently a validly-assigned URN [RFC3406]. Because the mapping mechanism is distributed, and because not every service is available everywhere, and not every mapping server may be configured with all current service registrations, validation in that sense isn't possible. The discovery mechanism for the mapping mechanism may also not be configured with all current top-level services 🥺
Scope: the scope for this URN is public and global 🌏
4. IANA Considerations 💅
This section registers a new URN scheme using the registration template from Section 3 🎀
Here's the map: Section 4.1 explains how to register new service-identifying labels 🗺️ Section 4.2 and Section 4.3 describe the sub-services for the first two services to be registered, sos and counseling. Section 4.4 has the initial registration table 💌
4.1. New Service-Identifying Labels
Services and sub-services are identified by labels that IANA manages, following the processes outlined in [RFC2434], in a new registry called "Service URN Labels". So creating a new service needs 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 and MUST be defined by the document that describes that top-level service 🧾
Entries in the registration table look like this:
Service Reference Description
--------------------------------------------------------------------
foo RFCxyz Brief description of the 'foo' top-level service
foo.bar RFCabc Description of the 'foo.bar' serviceTo keep things working 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 in the IANA registry from Section 4.1, using the top-level service label 'sos' 🚨
The 'sos' service type covers emergency services that need an immediate response, usually run by various branches of government or other public institutions 🚑 More sub-services can be added after expert review, but they must be of general public interest and have a similar emergency nature. The expert is designated by the ECRIT working group, its successor, or, if neither exists, the IESG. The expert review should only approve emergency services that are offered widely and in different countries, with roughly the same caller expectations about the 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 then dispatches help suited to the emergency. It covers all of the services listed below 🚨✨
urn:service:sos.ambulance: this service identifier reaches an ambulance service that provides emergency medical help and transportation 🚑💖
urn:service:sos.animal-control: animal control usually enforces laws and ordinances about animal control and management. It investigates animal abuse cases, teaches the community about responsible pet ownership and wildlife care, and provides housing and care for homeless animals, among other animal-related services 🐾
urn:service:sos.fire: the 'fire' service identifier summons the fire service, also called the fire brigade or fire department 🔥
urn:service:sos.gas: the 'gas' service lets people report natural gas (and other flammable gas) leaks or other natural gas emergencies 💨
urn:service:sos.marine: the 'marine' service refers to maritime search and rescue services, like the ones run by the coast guard, lifeboats, or surf lifesavers 🌊
urn:service:sos.mountain: the 'mountain' service refers to mountain rescue services (search and rescue activities in a mountainous environment). The term is sometimes also used for search and rescue in other wilderness environments 🏔️
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 tell citizens how to respond to potential poisoning. These poison control centers keep a database of poisons and appropriate emergency treatments 🧪
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 covers services where callers can get advice and support, often anonymously, but which don't need an emergency response. (Obviously, these services may transfer callers to an emergency service, or summon one, if the situation calls for it 🫶) More sub-services can be added after expert review, and they should be of general public interest. The expert is chosen the same way as described for the 'sos' service. The expert review should take into account whether these services are offered widely and in different countries, with roughly the same caller expectations about the services rendered 💜
urn:service:counseling: the generic 'counseling' service reaches a call center that transfers the caller based on their specific needs 📞🌸
urn:service:counseling.children: the 'children' service refers to counseling and support services tailored specifically to the needs of children. These services may, for example, give 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 🫂 We're taking this part seriously, bestie 💜
4.4. Initial IANA Registration ✨
okay so here's the starting lineup for IANA 🎀 the table below is the first batch of emergency and counseling services, and every single one of them points to RFC 5031 💖
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 enforcement5. Internationalization Considerations 🌸
bestie, these service labels are protocol elements (see [RFC3536]) 🧚 which means regular humans basically never see them. so the character set is locked down on purpose, the same way I described back in Section 3 💅
6. Security Considerations 🔥
okay this section is SERIOUS but also kind of fascinating 🙈
so the service URN, as an identifier on its own, doesn't seem to raise any special security issues ✨ the services it names are meant to be well-known, even when the actual service instance is access-controlled. which means privacy considerations don't apply to the URN itself 🦋
putting a service URN on a web page? likely no specific privacy issues there either 🌈
BUT (and this is the big plot twist 😭) ferrying the URN inside a signaling protocol can tell an attacker what kind of service the caller wants. for example, it becomes way easier for an attacker to automatically find every call going to emergency services or directory assistance 💀 so protocols that carry service URNs need their own appropriate, protocol-specific security mechanisms. no shortcuts, periodt 👑
the mapping protocol has a whole list of threats it needs to handle, which are laid out in [RFC5069]. that doc also covers the security stuff specific to using the service URN for emergency services 🚨
7. References 📚
7.1. Normative References 💜
these are the must-read sources the spec leans on heavily, so here they are, exactly as written:
[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,
October 1998.
[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.
[RFC4234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005.7.2. Informative References 🫶
these are the extra-credit reads 🍓 same deal, every entry kept exactly as written:
[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,
April 2001.
[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,
October 2001.
[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.
[RFC5069] Taylor, T., Ed., Tschofenig, H., Schulzrinne, H., and M.
Shanmugam, "Security Threats and Requirements for
Emergency Call Marking and Mapping", RFC 5069,
January 2008.Appendix A. Alternative Approaches Considered 🦋
okay this is my favourite bit, the "we tried these and nope'd out" list 💅 people keep bringing these ideas up, so this appendix quickly explains why this document didn't go with any of them 🧠
tel:NNN;context=+C uses tel URIs [RFC3966] 📞 here NNN is the national emergency number, and the country is picked out by the context C. it's easy for user agents to build, but really hard for proxies and other SIP elements to recognise. they'd have to know every number-context combo in the world and keep up with the occasional changes 😩 plus lots of these numbers already do other jobs. like, the emergency number in Paraguay (00) is also how you reach the international operator in the United States 🙈 and countries like Italy use 118 for emergencies, but that same number connects you to directory assistance in Finland 💀
tel:sos dodges name conflicts 🎀 but it means extending the "tel" URI "tel" [RFC3966], which is a whole thing. it also only works if every outbound proxy knows how to send requests to a proxy that can reach emergency services, because tel URIs don't identify the destination server 🚫
sip:sos@domain was earlier work that set aside a special user identifier, sos, inside the caller's home domain in a SIP URI, such as sip:sos@example.com 📮 this follows the convention from RFC 2142 [RFC2142] and the "postmaster" convention in RFC 2822 [RFC2822]. the upside is that dial plans in existing user agents could probably be converted to produce this URI, and only the home proxy for the domain has to understand the naming convention 🌟 the downside is that it overloads the user part of the URI with specific meaning instead of keeping it opaque. it also makes routing by the outbound proxy a special case that doesn't follow normal SIP request-URI handling rules, and it's SIP-specific. it doesn't stretch easily to other services either 😬
SIP URI user parameter is where you'd make a special URI like "aor-domain;user=sos" 🧁 this avoids the name conflict problem, but it needs mechanism-aware user agents that can actually emit this special URI. also, the 'user' parameter is meant to describe the format of the user part of the SIP URI, and this usage doesn't do that. adding other parameters still leaves it unclear which conventions should apply to the user and domain parts of the URL. and neither option is likely to be backward-compatible with existing clients 🥲
Special domain uses a special domain, like "sip:fire@sos.int", to identify emergency calls 🌍 it has similar properties to the "tel:sos" URI, except this one is a valid URI, which is cute. to make it usable, the special domain would have to be operational and point at an appropriate emergency services proxy. and 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 it got better thanks to comments from Leslie Daigle, Keith Drage, Benja Fallenstein, Paul Kyzivat, Andrew Newton, Brian Rosen, Jonathan Rosenberg (yes, listed twice 😭), Martin Thomson, and Hannes Tschofenig. thank you all, you're literally the best 💖
Author's Address 🎀
Henning Schulzrinne
Columbia University
Department of Computer Science
450 Computer Science Building
New York, NY 10027
US
Phone: +1 212 939 7004
EMail: hgs+ecrit@cs.columbia.edu
URI: http://www.cs.columbia.eduFull Copyright Statement ⚖️
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