Remote User Telnet service

　　Network Working Group J. Postel

　　Request for Comments: 818 ISI

　　November 1982

　　The Remote User TelnetService

　　This RFCis the specification of an application protocol. Any host that　implements this application level service must follow this protocol.

　　This RFCwas suggested by Mike Mulligan some months ago when he was at　BBN.

　　In the ARPANET Host-to-Host Network Control Protocol (NCP) and in the　Internet Transmission Control Protocol (TCP) well known sockets or ports　are used to identify services. The general notion is that there are a　few types of services that are distinct and useful enough to use the NCP　or TCP demultiplexing mechanism directly.

　　The most common of these is the Server Telnet which generally speaking　defines the network terminal accessprocedure for a system executive.

　　That is, making a connection to the server Telnet port actually puts the　caller in contact with the system executive, for example, the TOPS20

　　EXEC or the UnixShell.

　　On some small hosts there may be very limited functionality and no　executive. In such cases it may be useful to designate specific well　known ports for specific applications.

　　This memo specifies that the specific service of User Telnet may be　accessed (on hosts that choose to provide it) by opening a connection to　port 107 (153 octal). The Telnet Protocol is to be used on the　connection from the originating user to the server.

　　EXAMPLE: REMOTE TELNET SERVICE ON THE BBN TC68K

　　The TC68K is a Terminal Concentrator based on the Motorola MC68000　microprocessor. It is used at Bolt Beranek &Newman to provide access　by terminals to the FiberNet, a local area network.

　　The custom hardware provides one network connection, sixteen RS232　terminal 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 provides　an interface to allow the user to use the network to connect to a host,　Postel [Page 1]

　　RFC818November 1982

　　Remote User Telnet Service

　　providing a network virtual terminal. A server Telnet also exists on　the TC68K to serve as a front end for devices that have no awareness of　the net. This is used for remote printer/plotters and computers with no　network software.

　　The TC68Ks at BBN are distributed about several buildings. To provide　an operational tool to test remote TC68Ks, the TC68K software was　configured to put a user Telnet back to back with a server Telnet. An　operator can open a connection to a remote TC68K and appear to be a　terminal local to that unit. This verifies that the network path　between the two units is operational and provides the operator with　access to statistics that are kept as part of the standard user　TC-Telnet application.

　　Operator's Local Remote Remote

　　Terminal <=TTY=> user <=FiberNet=> server <=PTY=> user

　　TC-Telnet Telnet TC-Telnet

　　This solution was attractive as the only extra piece of software　necessary for this was the "Pseudo Teletype" (PTY) device driver for　MOS. This "device" appears as a terminal to its application, but what　it is really doing is providing a character stream between two　processes.