This paper describes the design and implementation decisions that have been made in developing software to support the DARPA TCP/IP protocols for the IBM OS/370 environment at the University of California Division of Library Automation. The implementation is designed to support over 100 concurrent TCP connections, all of which are managed by a single program, which acts as a specialized sub-operating system. The system is optimized for line-by-line or screen-by-screen terminal traffic rather than character-by-character traffic. In addition, this TCP is designed to exploit the availability of the large main storage and processor speed available on the IBM/370. TCP/IP is generally considered to be a mature protocol specification; however, in the course of our implementation we found several parts to be either ambiguous or problematic — in particular, error handling and notification, ICMP and its relationship to other protocols, and synchronization of data flow with TCP callers. We also discuss problems encountered in trying to replace hardwired terminals in a public access environment with TCP and TELNET, and some protocol changes that would make these protocols more hospitable to our environment.
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