The Xpress transfer protocol (XTP), a transport and network layer protocol suitable for use as a SAFENET transfer service in the US Navy's emerging survivable adaptable fiber optic embedded network (SAFENET) specification, is described. The background protocol, the implementation environment, the communications architecture, the user interface, some working XTP demonstration programs, and some measured performance results are described. The experience with XTP shows that the implementation is stable; operational in PC and VME bus environments; and capable of being transmitted reliably over Ethernet, token ring, and fiber distributed data interface (FDDI) networks.>

The authors have developed a real-time messaging system for token ring networks. The system is currently operational in a shipboard environment. The system conforms to the IEEE 802.2 LLC and 802.5 token-ring standards and is consistent with the Navy's emerging SAFENET specification. The authors provide a library of 'C' routines which establish and manage sockets, transmit and receive messages, and report network status. They show a sample user interface for a basic datagram service and another for a reliable virtual circuit service. They present performance data from an implementation on PCs and PC/ATs. Using the proposed software, a single transmitting station can generate up to 1.42 Mb/s, and 100-byte messages can be processed every 4 ms.>

Abstract The Computer Networks Laboratory at the University of Virginia has developed a real‐time messaging service that runs on IBM PCs and PC/ATs when interconnected with a Proteon ProNET‐10 token ring local area network. The system is a prototype for a real‐time communications network to be used aboard ships. The system conforms to the IEEE 802.2 logical link control standard for type I (connectionless, or datagram) service, with an option for acknowledged datagrams. The application environment required substantial network throughput and bounded message delay. Thus, the development philosophy was to emphasize performance initially and to offer only primitive user services. After providing and measuring the performance of a basic datagram service, the intent is to add additional user services one at a time and to retain only those which the user can ‘afford’ in terms of their impact on throughput, delay, and CPU utilization. The current system is programmed in C. The user interface is a set of C procedure calls that initialize tables, reserve buffer space, send and receive messages, and report network status. The system is now operational, and initial performance measurements are complete. Using this system, an individual PC can transmit or receive approximately 200 short (about 100 bytes) messages per second, and the PC/AT operates at nearly 500 short messages per second.

The IEEE 802.4 token bus defines both synchronous and asynchronous message access classes. Their performance is compared for networks implementing a single message class. Throughput bounds are derived from the access class timer. It is shown that for some configurations, the asynchronous class yields lower observable message delays. Mean observable delay is minimized by allowing each medium access controller unrestricted service.