The performance of different implementations of the ISO transport protocol class 4 on top of a connectionless link-layer protocol in the presence of transmission errors is studied by means of simulation. A main goal of the study is to find robust protocol versions yielding good performance for all possible combinations of implementations. The performance measure investigated is the throughput that can be achieved in transferring files between two stations over a local area or long-distance network. The results are compared to those obtained for the ISO transport protocol class 2 on top of a connection-oriented link-layer protocol. It is assumed that data and acknowledgement frames could be lost or corrupted by transmission errors. The results show that, at the sender side, retransmit all always yields higher performance than retransmit first, and, at the receiver side, store results in higher performance than discard.>

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.>

Mean waiting-time approximations are derived for a single-server multi-queue system with nonexhaustive cyclic service. Non-zero switch-over times of the server between consecutive queues are assumed. The main tool used in the derivation is a pseudo-conservation law recently found by Watson. The approximation is simpler and, as extensive simulations show, more accurate than existing approximations. Moreover, it gives very good insight into the qualitative behavior of cyclic-service queueing systems.

The impact of various implementations of an end-to-end transport service on the performance of high-volume data transfers in a local-area network is investigated. The impact of using a connection-oriented logical-link control (LLC) protocol below a connection-oriented transport protocol is of particular interest. The performance measure is the throughput which can be achieved between two stations either from memory to memory or from disk to disk. The throughput was determined by simulation for various combinations of differing LLC protocols, disk models and processor speeds. The parameters for the simulation model were determined partially by measurements of an implemented file server. The results show that the performance penalty of a connection-oriented LLC protocol can be substantial, but can be significantly lowered when an acknowledgment accumulation strategy is applied.

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.