RFC 1379 (rfc1379) - Page 2 of 38

Extending TCP for Transactions -- Concepts

RFC 1379              Transaction TCP -- Concepts          November 1992


1. INTRODUCTION

   The TCP protocol [STD-007] implements a virtual-circuit transport
   service that provides reliable and ordered data delivery over a
   full-duplex connection.  Under the virtual circuit model, the life of
   a connection is divided into three distinct phases: (1) opening the
   connection to create a full-duplex byte stream; (2) transferring data
   in one or both directions over this stream; and (3) closing the
   connection.  Remote login and file transfer are examples of
   applications that are well suited to virtual-circuit service.

   Distributed applications, which are becoming increasingly numerous
   and sophisticated in the Internet, tend to use a transaction-oriented
   rather than a virtual circuit style of communication.  Currently, a
   transaction-oriented Internet application must choose to suffer the
   overhead of opening and closing TCP connections or else build an
   application-specific transport mechanism on top of the connectionless
   transport protocol UDP.  Greater convenience, uniformity, and
   efficiency would result from widely-available kernel implementations
   of a transport protocol supporting a transaction service model [RFC-
   955].

   The transaction service model has the following features:

   *    The fundamental interaction is a request followed by a response.

   *    An explicit open or close phase would impose excessive overhead.

   *    At-most-once semantics is required; that is, a transaction must
        not be "replayed" by a duplicate request packet.

   *    In favorable circumstances, a reliable request/response
        handshake can be performed with exactly one packet in each
        direction.

   *    The minimum transaction latency for a client is RTT + SPT, where
        RTT is the round-trip time and SPT is the server processing
        time.

   We use the term "transaction transport protocol" for a transport-
   layer protocol that follows this model [RFC-955].

   The Internet architecture allows an arbitrary collection of transport
   protocols to be defined on top of the minimal end-to-end datagram
   service provided by IP [Clark88].  In practice, however, production
   systems implement only TCP and UDP at the transport layer.  It has
   proven difficult to leverage a new transport protocol into place, to
   be widely enough available to be useful for application builders.



Braden