Harry Rudin

A survey of light-weight transport protocols for high-speed networks

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. >

New Optimization Criteria for Message-Switching Networks

This paper presents a new class of criteria for the optimum Capacity assignment in store-and-forward communication networks under a total fixed-cost constraint. Compared with conventional average-delay optimization these criteria are more sensitive to the needs of the individual user. Closed-form results are attained.

Automated protocol validation: One chain of development

Abstract The progress of one research effort in computer-automated protocol validation is summarized in this paper. It brings together in one place the results of a number of studies, some published and some to be published but all widely scattered in the literature. Described are a formal representation, the “duologue”, “phase-diagram”, and “state-pertubation” methods. These are discussed on the basis of a common example. Sample results from the validation of the CCITT X.21 interface are explained as an indication of what these techniques can achieve.

Protocol Development Success Stories: Part 1

Abstract Formal Description Techniques (FDTs) and automatable tools have long promised to make substantial contributions to the development of communication protocols. Have they? The answer is “Yes”; but, success is more often based on the capability to automate a tool than it is on the use of FDTs, per se. Several notable success stories are given here. The two goals for writing this paper were 1) to encourage more researchers to accept the challenge of attacking a real protocol and 2) to attract more industrial support of a vital development area.

Performance of Simple Multiplexer--Concentrators for Data Communication

Multiplexer-concentrators (or asynchronous multiplexers) are devices used to increase the efficiency of telecommunication systems into which the flow of information is erratic. In the analysis of such systems, many assumptions about the statistical nature of the input traffic can be made. The assumptions made here are constant message length, constrained buffer size, and finite number of message sources. The numerical technique given copes with the case of multiple output trunks, and the complete statistical behavior of the system is revealed in transient as well as steady-state form. Results are given graphically which show the effect of various statistical assumptions, the transient response of the system, the behavior of the tail of the distribution of queue states, and the effect of message clustering.

Challenges to the network: Telecoms and the internet

Abstract Readers are likely to be interested in “Challenges to the Network”, published recently (September, 1997) by the ITU. As you know, the International Telecommunications Union is a United Nations agency specialized in telecommunications and successor to the C.C.I.T.T. We know it best as the publisher of telecommunications standards. The book is based on the notion, that although the Internet of today rides on top of the telephone network, it is conceivable that this relationship will reverse in the future. This would have a strong impact on common carriers. The book is a compendium of commentary and useful information including a wealth of statistical data. An executive summary of the reports contents can be found on the World Wide Web; the URL is http://www.itu. int/indicators.

On the Optimization of Message-Switching Networks

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.

Protocol Analysis and Synthesis using a State Transition Model

The growing trends both to increase the sophistication of functions implemented in information-handling systems and to distribute these functions in different processes has resulted in an enormous growth in complexity. This complexity is particularly acute in the interactions or protocols which specify how these processes are synchronized and communicate with one another. However, formal methods are gradually being introduced to describe these interactions; see chapters 20, 21, 23, and 25 as well as [l]–[5].

Packet and circuit switching: Cost/performance boundaries

Abstract In this paper we make a comparison of circuit- and packet-switching techniques (in the context of data networks) from two points of view: delay performance and usage cost. In these analyses we differentiate between two traffic patterns: continuous and intermittent messages (where message blocks are interspersed with no-data intervals). The study shows that for the delay performance, message length, traffic pattern and line utilization are the most telling parameters. The dynamic costs for using the network are additionally governed by parameters such as distance, intermessage interval, length of dialogue and kind of switching processor. The results presented here show how these parameters interact and determined the boundary between the areas of operation more attractive for circuit or packet switching.

Time in Formal Protocol Specifications

The need for formal, machine-readable specification of the protocols used in distributed computer systems is widely accepted. In these formal protocol specifications relatively little attention has been paid to the problem of including time — the time it takes to execute various portions of the protocol as well as explicit values for timeouts. In this tutorial, models for including time are reviewed. Techniques for analyzing these models are then discussed. A comprehensive bibliography is included.