OSI Connectionless Transport Services on top of UDP Version: 1

Status of this Memo

This document describes a protocol for running OSI Connectionless service on UDP. This RFC specifies an IAB standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "IAB Official Protocol Standards" for the standardization state and status of this protocol. Distribution of this memo is unlimited.

1. Introduction and Philosophy

The Internet community has a well-developed, mature set of layered transport and network protocols, which are quite successful in offering both connection-oriented (TCP) and connectionless (UDP) transport services over connectionless network services (IP) to end- users. Many popular network applications have been built directly on top of the TCP and UDP over the past decade. These have helped the Internet services and protocols to become widely-spread de facto standards. In the past few years, the ISO and CCITT have defined a well-architected set of upper layer standards which include connection-oriented and connectionless session, presentation, and application layer services and protocols. These OSI upper layer standards offer valuable services to application developers (e.g., dialogue control, transfer syntax, peer authentication, directory services, etc.) which are not currently offered by the TCP/IP standards.

As indicated in RFC 1006, it is desirable to offer the OSI upper layer services directly in the Internet without disrupting existing facilities. This permits a more graceful convergence and transition strategy from IP-based networks to OSI-based networks in the future. Using the approach of RFC 1006, this memo specifies how to offer OSI connectionless transport service using the User Datagram Protocol (UDP) [RFC768] of the TCP/IP suite.

We will define a Transport Service Access Point (TSAP) which appears 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.