RFC 1240 (rfc1240) - Page 2 of 8

OSI connectionless transport services on top of UDP: Version 1

RFC 1240                   OSI on top of UDP                   June 1991


   to be identical to the services and interfaces defined in ISO 8072
   and its Addendum 1, but we will in fact implement the ISO T-UNIT-DATA
   protocol on top of UDP.  By this means, OSI TPDU's can be delivered
   across the Internet network, and OSI connectionless upper layers can
   operate fully without knowledge of the fact that they are running on
   top of UDP/IP.  In essence, the OSI T-UNIT-DATA service will use UDP
   as its connectionless network service provider.

2.  Motivation

   The primary motivation for the standard described in this memo is to
   facilitate the process of gaining experience with OSI connectionless
   upper layers protocols, i.e., S-UNIT-DATA [ISO9548], P-UNIT-DATA
   [ISO9576] and A-UNIT-DATA [ISO10035], and connectionless transport
   protocol T-UNIT-DATA [ISO8602].

   Though many OSI standard applications such as X.400 and FTAM are
   connection-oriented, it is recognized in the OSI reference model
   [ISO7498/AD1] as well as in practice that the connectionless-mode
   operations are appropriate for certain distributed application
   classes and environments.  The following connectionless application
   classes were identified by ISO SC21/WG6 [ISOSC21/WG6 N184]:

         -    Request-Response Applications
         -    Broadcast/Multicast
         -    Inward Data Collection
         -    Migratory/Unreliable Processes

   Among them, the "request/response" client-server application class is
   the most prominent one, which is gaining popularity and importance.
   It is observed that the connection setup and tear-down protocol
   exchanges and complex connection-oriented protocol machines become
   unnecessary overheads for a simple request/response exchange between
   a client application and a server application, especially in reliable
   communications environments such as LAN and ISDN.  The OSI
   connectionless upper layers are thought to be highly effective and
   efficient, both in time and space, for the distributed application
   classes mentioned above.

   The stability, maturity and wide availability of UDP/IP are ideal for
   providing solid connectionless transport services independent of
   actual implementations.

3.  The Model

   The [ISO 8072/AD1] standard describes the OSI connectionless
   transport services definition. The [ISO 8602] standard describes the
   OSI connectionless transport protocols.  A defining characteristic of



Shue, Haggerty & Dobbins