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Network Working Group                           A. McKenzieRFC # 241                                       BBNNIC # 7671                                      29 September 1971Categories: B.1, C.1, I.1Updates: noneObsoletes:  Our Previous Verbal CommentsCONNECTING COMPUTERS TO MLC PORTS---------------------------------        Several times we have been asked if computers can be con- nected   through serial communication lines to ports on the Terminal IMP's   Multi-Line Controller (MLC) [related questions about the level of   software support provided by the Terminal IMP to such a connection,   have also been raised].  In the past we have said, "Please don't!" We   now say, "Sure, but will that really help you the way you think it   will?"        (1) Connections between computers and IMPs (i.e., the Host   interfaces) have been assumed to be error-free.  This assumption is   justifiable on the basis that the IMP and Host computers were   expected to be either in the same room (up to 30 feet of cable) or,   via the Distant Host option, within 2000 feet on well- controlled,   shielded cables.  A connection through common carrier facilities is   not comparably free of errors.  Usage of common- carrier lines for   connecting a terminal to an IMP, including the assumption of a human   at the terminal, is a situation in which the typical errors which do   occur can be accommodated.  Usage of the same wire, with the same   typical errors, for a computer-to- computer connection is likely to   be a situation in which the errors are unacceptable.  The present   version of the Terminal IMP does not provide error control either   within its hardware or within its software on any ports of the   Multi-Line Controller.  Further, we feel that computer-to-computer   connections over common carrier circuits should employ strong error   control, such as that                                                                [Page 1]

RFC # 241   used on the IMP/IMP circuits, and that attempts to use minimal error   control (e.g., character parity) is an undesirable technical choice.   Strong error control, with its retransmission scheme, not only would   imply significant changes in the Terminal IMP, but a non-trivial   hardware/software implementation at the remote computer end of the   circuit.        (2) Because the Terminal IMP has many obligations, the share of   its bandwidth which can be given to a Host coming in over the MLC   will be small.        (3) The command language provided at a port of the Multi- Line   Controller was designed with terminals and people in mind.  It   provides very few of the capabilities which a computer requires in   order to effectively utilize the communication network.  For example,   only a single pair of connections can be made from a given Terminal   TMP port; Host computers generally desire a larger number of   simultaneous connections to other Hosts on the network.  Assuming the   present Host/Host protocols, such a Host could not conveniently act   as a server.        If, despite these potential difficulties, connection of a   computer to the network through an MLC port appears to be useful, BBN   has no objection.  In fact, we would be extremely interested in   hearing about actual experience with this type of network connection.   AMcK:jm         [ This RFC was put into machine readable form for entry ]         [ into the online RFC archives by BBN Corp. under the   ]         [ direction of Alex McKenzie.                   12/96   ]                                                                [Page 2]