RFC 916 (rfc916) - Page 2 of 54

Reliable Asynchronous Transfer Protocol (RATP)

RFC 916                                                     October 1984
Reliable Asynchronous Transfer Protocol


1. Philosopy of Design

   Many tradeoffs were made in designing this protocol.  Decisions were
   made by above all ensuring reliability and then by favoring
   simplicity of implementation.  It is hoped that this protocol is
   simple enough to be implemented not only by small computers but also
   by stand alone devices incorporating microcomputers which accept
   commands over RS-232 lines.  Sophisticated but unnecessary features
   such as dynamic window management [TCP 81] were left out for
   simplicity's sake.  Having several packets outstanding at a time was
   eliminated for the same reason, and data queued to send when a
   connection is closed remotely is discarded.  This eliminates two
   states from the protocol implementation.

   The reader may ask why define this protocol at all, there are after
   all already RS-232 transport protocols in use.  This is true but some
   lack one or more features vitally important or are too complex.  See
   Appendix II for a brief survey.

      - A protocol which can only transfer data in one direction is
        unable to use a single RS-232 link for a full-duplex connection.
        As such it cannot act as a bridge between most computer
        networks.  Also it is not capable of supporting any applications
        requiring the two-way exchange of data.  In particular it is not
        a platform suitable for the creation of most higher level
        applications.  Unidirectional flow of data is sufficient for a
        weak implementation of file transfer but insufficient for remote
        terminal service, transaction oriented processing, etc.

      - Some of the existing RS-232 transport protocols allow the use of
        only fixed size packets or do not allow the receiver to place a
        limit on the sender's packets.  Where that block size is too
        large for the receiving end concentrator, that concentrator is
        likely to immediately invoke flow control.  This results in many
        dropped and damaged packets.  The receiver must be able to
        inform the sender at connection initiation what is the maximum
        packet size it is prepared to receive.

      - Some protocols have a number of features which may or may not be
        implemented at each site.  Examples are, several checksumming
        algorithms, differing data transmission restrictions, sometimes
        8-bit data, sometimes restricted ASCII subsets, etc.  The
        resulting requirement that all sites implement all the various
        features is rarely met.

   Finally, the size of this document may be imposing.  The document
   attempts to fully specify the behavior of the protocol.  A careful


Finn