A comparative survey is presented of techniques used at the transport layer in eight representative protocols, most of which were designed to improve the protocol processing rate. The protocols are the relevant portions of the APPN, Datakit, Delta-t, NETBLT, OSI/TP4, TCP, VMTP, and XTP architectures. The protocols are described, and the functions under consideration are defined. No distinction is made as to whether these functions are carried out in a LAN, MAN, or WAN environment. The objective is to provide reliable, end-to-end transmission of data. The mechanisms required to support connection management, acknowledgements, flow control, and error handling are examined. Suitable techniques for designing light-weight transport protocols are identified. A discussion is presented as to which technique seems the most promising.>

This is an expanded version of an earlier report, adding, new results. The first part introduces a simple analytic model showing that dynamic routing may increase network throughput or lower delay when trunks are moderately loaded, but will reduce throughput or increase delay at heavy trunk loads. The second part of the paper presents simulation results characterizing: 1) the operation of a network "protected" by end-to-end flow control, 2) the operation of an "unprotected" network, 3) the transition between these two modes, 4) the effect of changing the update interval for the routing algorithms, 5) the effect of slow local loops, and 6) the effect of increasing the number of alternate paths available for dynamic routing. Overall, the results show that dynamic routing improves network performance only over a small parameter range, and should dynamic routing be used at all, it must be implemented with great care.

Criteria recently developed by the authors for optimum capacity assignment in message-switching networks are applied to a network model which now contains nodal processors as well as interconnecting links. Linear and stepped cost functions are examined and various performance and cost-performance curves are presented. An efficient design procedure is described for the tedious case of stepped cost functions. For general continuous cost functions and the minimax design the distribution functions of all point-to-point delays can be easily calculated.

This paper discusses two aspects of the performance and design of certain queued or buffered information transmission systems. Examples are buffered multiplexers and message-switching systems. The first part of the paper examines the theoretical performance of such a system as its output channel capacity and the number of its speed-limited information sources are increased proportionately. The aspects of performance considered are time delay and probability of overflow of the system's finite buffer capacity. Under the assumptions made (described in the text), system performance almost always improves as the size of the system is increased. The second portion of the paper considers the design of a communication system that must serve two classes of users, the two classes differing in average message length. Here the question is that of superiority of integrated or segregated communication system design under a channel-capacity constraint. Using average delay as a performance criterion it is shown that the integrated system is not always superior but becomes superior if there is sufficient excess capacity.