Editing Telnet (section)

== Description ==
{{expand section|with=more details about the protocol itself|talk=Additional description|date=April 2025}}

The telnet protocol is a  [[client-server protocol]] that runs on a [[Reliability (computer networking)|reliable]] [[connection-oriented]] transport.{{citation needed|reason=This is basically true, but not stated in the source previously cited here.|date=April 2025}} Most often, a telnet client connects over [[Transmission Control Protocol|TCP]] to [[Port (computer networking)|port]] 23 or 2323, where a Telnet server application is listening.<ref name="rfc854">{{Cite IETF|last1=Postel |first1=J. |last2=Reynolds |first2=J. K. |date=1983 |title=Telnet Protocol Specification |rfc=854 |journal=Network Working Group |issn=2070-1721 }}</ref><ref>{{Cite web |title=Service Name and Transport Protocol Port Number Registry |url=https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml |access-date=2023-01-12 |website=www.iana.org}}</ref><ref name="srinivasa2021">{{Cite book |last1=Srinivasa |first1=Shreyas |last2=Pedersen |first2=Jens Myrup |last3=Vasilomanolakis |first3=Emmanouil |title=Proceedings of the 21st ACM Internet Measurement Conference |chapter=Open for hire |date=2021-11-02 |chapter-url=https://doi.org/10.1145/3487552.3487833 |series=IMC '21 |location=New York, NY, USA |publisher=Association for Computing Machinery |pages=195–215 |doi=10.1145/3487552.3487833 |isbn=978-1-4503-9129-0|s2cid=240357287 }}</ref> The Telnet protocol abstracts any terminal as a Network Virtual Terminal (NVT). The client must simulate a NVT using the [[#Technical details|NVT codes]] when messaging the server.


Telnet predated UDP/IP and originally ran over [[Network Control Protocol (ARPANET)|Network Control Protocol]] (NCP).<ref>{{Cite IETF|last=Postel |first=J. |date=1981 |title=NCP/TCP transition plan |rfc=801 |journal=Network Working Group |issn=2070-1721}}</ref> The telnet service is best understood in the context of a user with a simple terminal using the local Telnet program (known as the client program) to run a logon session on a remote computer where the user's communications needs are handled by a Telnet server program.

=== Telnet service ===
A Telnet service is an application providing services over the Telnet protocol. Most operating systems provide a service that can be installed or enabled to provide Telnet services to clients.<ref>{{Cite web |date=2025-04-11 |title=Telnet {{!}} Definition & Facts {{!}} Britannica |url=https://www.britannica.com/technology/Telnet |access-date=2025-05-10 |website=www.britannica.com |language=en}}</ref>

=== Name ===
While the official specification stylizes the name as TELNET, it is not defined therein as an acronym or abbreviation.<ref name="rfc854" />

In a 1972 paper, when discussing one of the early forms of the protocol, [[Stephen Crocker]] et al. used "TELNET" explicitly as an abbreviation of "telecommunications network."<ref name="crocker1971">{{cite book |last1=Crocker|first1=Stephen D.|last2=Heafner|first2=John F.|last3=Metcalfe|first3=Robert M.|last4=Postel|first4=Jonathan B.|chapter=Function-oriented protocols for the ARPA computer network |title = Proceedings of the November 16-18, 1971, fall joint computer conference on - AFIPS '71 (Fall)|year = 1971 |publisher = Association for Computing Machinery|doi = 10.1145/1478873.1478908 |isbn = 9781450379090 |pages = 271–279}}</ref>

In his 2015 book ''WHOIS Running the Internet: Protocol, Policy, and Privacy'', Internet researcher Garth O. Bruen claims that Telnet was originally short for "Teletype Over Network Protocol."<ref name="gruen2015">{{cite book |last=Bruen |first=Garth O. |title=WHOIS Running the Internet: Protocol, Policy, and Privacy |publisher=Wiley |year=2015 |isbn=9781118679555 |edition=1st |page=25}}</ref>