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Network Working Group                                          J. PostelRequest for Comments: 818                                            ISI                                                           November 1982The Remote User Telnet ServiceThis RFC is the specification of an application protocol.  Any host thatimplements this application level service must follow this protocol.This RFC was suggested by Mike Mulligan some months ago when he was atBBN.In the ARPANET Host-to-Host Network Control Protocol (NCP) and in theInternet Transmission Control Protocol (TCP) well known sockets or portsare used to identify services.  The general notion is that there are afew types of services that are distinct and useful enough to use the NCPor TCP demultiplexing mechanism directly.The most common of these is the Server Telnet which generally speakingdefines the network terminal access procedure for a system executive.That is, making a connection to the server Telnet port actually puts thecaller in contact with the system executive, for example, the TOPS20EXEC or the Unix Shell.On some small hosts there may be very limited functionality and noexecutive.  In such cases it may be useful to designate specific wellknown ports for specific applications.This memo specifies that the specific service of User Telnet may beaccessed (on hosts that choose to provide it) by opening a connection toport 107 (153 octal).  The Telnet Protocol is to be used on theconnection from the originating user to the server.EXAMPLE: REMOTE TELNET SERVICE ON THE BBN TC68KThe TC68K is a Terminal Concentrator based on the Motorola MC68000microprocessor.  It is used at Bolt Beranek & Newman to provide accessby terminals to the FiberNet, a local area network.The custom hardware provides one network connection, sixteen RS232terminal connections, and a programmable timer.The software is based on the Micro-Operating System (MOS) using the IP,ICMP, TCP, and Telnet protocols.  A user TC-Telnet application providesan interface to allow the user to use the network to connect to a host,Postel                                                          [Page 1]

RFC 818                                                    November 1982                                              Remote User Telnet Serviceproviding a network virtual terminal.  A server Telnet also exists onthe TC68K to serve as a front end for devices that have no awareness ofthe net.  This is used for remote printer/plotters and computers with nonetwork software.The TC68Ks at BBN are distributed about several buildings.  To providean operational tool to test remote TC68Ks, the TC68K software wasconfigured to put a user Telnet back to back with a server Telnet.  Anoperator can open a connection to a remote TC68K and appear to be aterminal local to that unit.  This verifies that the network pathbetween the two units is operational and provides the operator withaccess to statistics that are kept as part of the standard userTC-Telnet application.   Operator's         Local                  Remote         Remote   Terminal   <=TTY=> user      <=FiberNet=> server <=PTY=> user                      TC-Telnet              Telnet         TC-TelnetThis solution was attractive as the only extra piece of softwarenecessary for this was the "Pseudo Teletype" (PTY) device driver forMOS.  This "device" appears as a terminal to its application, but whatit is really doing is providing a character stream between twoprocesses.Postel                                                          [Page 2]