Bernd Meister

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. >

Waiting Lines and Times in a System with Polling

A communication system consisting of a number of buffered input terminals connected to a computer by a single channel is analyzed. The terminals are polled in sequence and the data is removed from the terminals buffer. When the buffer has been emptied, the channel, for an interval of randomly determined length, is used for system overhead and/or to transmit data to the terminals. The system then continues with a poll of the next terminal. The stationary distributions of the length of the waiting line and the queueing delay are calculated for the case of identically distributed input processes.

Service in a Loop System

The s ta t i s t ica l behavior of a loop service sys tem is s tudied. The sys tem consists of a main s ta t ion , a server and N s ta t ions ar ranged on a loop. Customers arr ive at each s ta t ion according to a r andom process. The server makes successive tours along the loop br inging customers from the N s ta t ions to the main s ta t ion. Two related measures of the grade of service are considered: the average queue length and the average v i r tua l wai t ing t ime at each s ta t ion.

Waiting-time approximations for cyclic-service systems with switchover times

Mean waiting-time approximations are derived for a single-server multi-queue system with nonexhaustive cyclic service. Nonzero switchover 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 (1984). The approximation is simpler and, as extensive simulations show, more accurate than existing approximations. Moreover, it gives very good insight into the qualitative behaviour of cyclic-service queueing systems.

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.

Waiting-time approximations for cyclic-service systems with switch-over times

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.

On the capacity of a discrete, constant channel

This paper is concerned with an iterative method for calculation of the capacity of a discrete, constant channel. Unlike the standard reference (Muroga 1953), in which Lagrange multipliers are used in the conventional form, the method described is based on techniques of mathematical programming. In addition, input signals of different duration are admitted. The algorithm proposed is very simple and has the advantage that it yields converging lower and uppper bounds for the capacity.

Waiting-time approximations in multi-queue systems with cyclic service

This study is devoted to mean waiting-time approximations in a single-server multi-queue model with cyclic service and zero switching times of the server between consecutive queues. Two different service disciplines are considered: exhaustive service and (ordinary cyclic) nonexhaustive service. For both disciplines it is shown how estimates of the mean waiting times at the various queues can be obtained when no explicit information on arrival intensities and service-time distributions is available, while only the utilizations at the queues and the lengths of the busy periods of the system can be measured. In the exhaustive case, a known mean waiting-time approximation is shown to be suitable for our purposes; in the nonexhaustive case, a new approximation has been derived which is simple and yet more accurate than existing approximations. Extensive simulation validates the approximation methods.

Connection-oriented versus connectionless protocols: A performance study

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.

A performance study of the ISO transport protocol

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. >