This is a purely informative rendering of an RFC that includes verified errata. This rendering may not be used as a reference.

The following 'Verified' errata have been incorporated in this document: EID 1889
Network Working Group                                          A. Farrel
Request for Comments: 5513                            Old Dog Consulting
Category: Informational                                     1 April 2009

             IANA Considerations for Three Letter Acronyms

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

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   Three Letter Acronyms (TLAs) are commonly used to identify components
   of networks or protocols as designed or specified within the IETF.  A
   common concern is that one acronym may have multiple expansions.
   While this may not have been an issue in the past, network
   convergence means that protocols that did not previously operate
   together are now found in close proximity.  This results in
   contention for acronyms, and confusion in interpretation.  Such
   confusion has the potential to degrade the performance of the
   Internet as misunderstandings lead to misconfiguration or other
   operating errors.

   Given the growing use of TLAs and the relatively small number
   available, this document specifies a Badly Construed Proposal (BCP)
   for the management of a registry of TLAs within the IETF, and the
   procedures for the allocation of new TLAs from the registry.

1.  Introduction

   A Three-Letter Acronym (TLA) is a popular form of abbreviation
   usually based on the initial letters of a three-word term.  A formal
   definition of a TLA is provided in Section 2.

   TLAs are particularly popular within the Internet community where
   they serve as abbreviations in the spoken and written word.  As their
   popularity has grown, the measure of the value of an RFC (q.v.) is
   not only its successful implementation, interoperability, and
   deployment, but also the number of TLAs included in the text.

   For example, the Transmission Control Protocol (itself a TLA - TCP)
   [RFC0793] is extremely successful.  The specification contains no
   fewer than 20 distinct TLAs (although it should be noted that some
   are simple abbreviations rather than proper acronyms).  On the other
   hand, the Internet Stream Protocol Version 2 [RFC1819] is ambiguously
   referred to using the TLA ST2, and also as STII which is clearly not
   a TLA.  Further, the STII specification contains only 12 distinct
   TLAs, and it should be no surprise that STII has been far less
   successful than TCP.

   A common concern amongst diligent protocol implementers is that one
   acronym may have multiple expansions.  While this may not have been
   an issue in the past, network convergence means that protocols that
   did not previously operate together are now found in close proximity.
   Not only does this result in contention for acronyms, and confusion
   in interpretation of specification, it also leads to many wasted
   hours trying to select appropriate and suitably-unique names for
   variables within source code implementations.  Such confusion has the
   potential to degrade the performance of the Internet as
   misunderstandings lead to coding errors, compilation failures,
   misconfiguration, and other operating errors.

   Furthermore, it should be noted that we are rapidly approaching World
   Acronym Depletion (WAD).  It has been estimated that, at the current
   rate of TLA allocation, we will run out by the end of September this
   year.  This timescale could be worsened if there is the expected
   growth in demand for mobile acronyms, IP-TLAs, and TLA-on-demand.
   According to the definition provided in Section 2, there are 36**3 -
   10**3 = 45656 TLAs in total.  This number will so easily be depleted
   that we must institute some policy for conservation.

   The Internet Assigned Numbers Authority (IANA, helpfully, a four-
   letter acronym - although note that a four-letter acronym is an FLA
   and hence is, in its own way, a TLA) maintains registries of names
   and numbers for use within the Internet in order to avoid duplicate
   allocation of one of those names or numbers and the consequent
   confusion and failed interoperability that would arise.  It is,
   therefore, wholly appropriate that the IANA should manage the
   assignment and use of TLAs within the Internet.

   This document specifies a Badly Construed Proposal for the management
   of a registry of TLAs within the IETF, and the procedures for the
   allocation of new TLAs from the registry.

1.1.  RFC Editor Terminology List

   It is worth observing that the RFC Editor currently maintains a list
   of common terms, abbreviations, and acronyms.  While this list is
   highly useful for the construction of documents, it does not provide
   unambiguous interpretation of acronyms.

2.  Formal Definition of TLA

   Acronym - a word made up of the initial letters of the words in a

      For example, IETF is an acronym formed from the first letters of
      the phrase International Essential Tremor Foundation [URL-IETF].

   Three Letter Acronym (TLA) - an acronym comprising exactly three

      For example, RFC is a TLA formed of the first letters of the
      phrase Rugby Football Club [URL-CARDIFF].

   For our usage, we also allow digits within a TLA.  Thus, P2P is an
   acronym meaning Purchase to Pay [URL-P2P].  The digits 2 and 4 are
   specially used by clever people who have noticed that, when spoken,
   they sound like the words 'to' and 'for'.  Whether this is helpful
   may be left as an exercise for the user considering the brief
   conversation, below.

   A - Do you use the Internet Streams Protocol?
   B - Yes.  Do you use ST, too?
   A - No, I use ST2.
   B - That's interesting.  C uses ST2, too.
   A - I have a car horn application called Toot-toot.
   B - Really? Do you use ST2 to Toot-toot, too?

   Note, however, that an acronym made up entirely of digits might be
   frowned upon.

   Lastly, we must consider case-sensitivity.  Although acronyms often
   include upper or lowercase letters, no assumptions should be made
   about the interpretation of the acronym based on the case of its
   letters, so that both QOS and QoS clearly refer to the Queen of the
   South football club [URL-QOS] and [URL-QoS].

2.1.  A Note on Vocalization

   Acronyms are often articulated as words in spoken text.  This can be
   helpful in generating a cosy feel or a marketing buzz around a
   concept that offers a less-favorable reality.  For example, Claws and
   Teeth (CAT) can be pronounced "cat" making it seem quite cuddly.

   Other acronyms are always spelled out in order to avoid accidental
   misinterpretation or litigation.  For example, do not refer to your
   neighbor's Daughter or Granddaughter as anything other than their

   But care should be taken with vocalization, as well.  It will be
   noted that some letters have more syllables than the words they are
   used to represent.  In these cases, acronyms are to be avoided.
   Thus, the world wide web must never be assigned the acronym WWW.

   Finally, a word of caution about attempting to pronounce acronyms as
   words.  This can lead to serious injury for the inexperienced unless
   they happen to be native speakers of Czech.  Do not try to say XML in
   front of your mother-in-law, and don't attempt to talk about Open
   Office dot Org in polite company.

3.  Backward and Forward Compatibility

   It should be obvious to most RFC readers (MRRs) that TLAs are already
   widely used in Internet specifications.  This work is not intended to
   unnecessarily invalidate existing RFCs, although where such
   invalidation is necessary or desirable, this work can be used for
   that purpose.

   In order to support existing documents, IANA is required to search
   all existing RFCs for every existing acronym usage (EAU), but may
   filter that search to exclude non-TLAs.

   It will be noted that, as a result of that search, many duplicate
   meanings will be discovered.  For example, "OAM" will be found in a
   large number of RFCs, yet its meaning may be as diverse as "on a
   mission", "order of Australia medal", and "orbital angular momentum".

   This contention is best resolved by the judgement of Solomon -- each
   acronym usage will be allocated its share of the letters currently in
   use.  If there are three uses of an acronym, they will get one letter
   each; two existing uses would get one-and-a-half letters each; etc.

4.  IANA Considerations

4.1.  New Registry

   The Internet TLA Registry (ITR) should track the following

      - TLA
      - Unique interpretation
      - Defining RFC

4.2.  Reserved Values

   Certain key values are reserved.  That is, they are allocated in the
   registry by this document and may not be used for any other purpose.

      Acronym   Expansion                             Reference
      TLA       Two Letter Acronym                    [RFC5513]
      TBD       Two Be Deleted                        [RFC5513]
      RFC       Ready for Compost                     [RFC5513]
      PoS       Not particularly good                 [RFC5513]
      VPN       Very possibly no use                  [RFC5513]
      TCP       Totally bad proposal                  [RFC5513]
      USA       Universal Source of Acronyms          [RFC5513]
      NBG       This document                         [RFC5513]
      BCP       Badly construed proposal              [RFC5513]

4.3. Allocation Policy

   IANA shall apply the following allocation policies according to

   Experimental Use
      All TLAs of the form XX* where * is any letter or digit.

   First Come First Served
      All TLAs of the form X**, Y**, or Z** where * is any letter or
      digit.  Excepted from this are the TLAs of the form XX* as above.

   IETF Review
      All other TLAs.

5.  Security Considerations

   Many security algorithms are identified by TLAs.  It is a clear
   requirement that someone implementing, for example, MD5 should be
   understood to have encoded the well-known Maybe-Decrypted-
   Deciphered-Decoded-Disambiguated-and-Degraded algorithm, and not any
   other security algorithm with the same acronym.

6.  Acknowledgements

   I would like to thank the MPLS-TP design team for holding seemingly
   endless meetings during which the need for this document became

   Thanks to Daniel King for noticing that this document is a BCP.

7.  References

7.1.  Normative References

   [RFC5226]     Narten, T. and H. Alvestrand, "Guidelines for Writing
                 an IANA Considerations Section in RFCs", BCP 26, RFC
                 5226, May 2008.

7.2.  Informative References

   [RFC0793]     Postel, J., "Transmission Control Protocol", STD 7, RFC
                 793, September 1981.

   [RFC1819]     Delgrossi, L., Ed., and L. Berger, Ed., "Internet
                 Stream Protocol Version 2 (ST2) Protocol Specification
                 - Version ST2+", RFC 1819, August 1995.

   [URL-IETF]    International Essential Tremor Foundation,

   [URL-CARDIFF] Cardiff Rugby Football Club,

   [URL-P2P]     eProcumentStotl@nd,

   [URL-QOS]     Queen of the South Football Club,

   [URL-QoS]     Queen of the South Football Club,
EID 1889 (Verified) is as follows:

Section: 7.2.

Original Text:


Corrected Text:
This appears at the “[URL-QoS]” reference, the second reference to the Queen of the South Football Club.

According to the URI schemes registry[1] maintained by IANA, “ahttp” is not a valid URI scheme. It should probably be “http” instead.

The URI in its current form is inaccessible, because its meaning is not well-defined for users.

Author's Address Adrian Farrel Old Dog Consulting EMail: