Showing papers on "Throughput published in 1975"

Packet Switching in a Multiaccess Broadcast Channel: Performance Evaluation

Abstract: In this paper, the rationale and some advantages for multiaccess broadcast packet communication using satellite and ground radio channels are discussed. A mathematical model is formulated for a "slotted ALOHA" random access system. Using this model, a theory is put forth which gives a coherent qualitative interpretation of the system stability behavior which leads to the definition of a stability measure. Quantitative estimates for the relative instability of unstable channels are obtained. Numerical results are shown illustrating the trading relations among channel stability, throughput, and delay. These results provide tools for the performance evaluation and design of an uncontrolled slotted ALOHA system. Adaptive channel control schemes are studied in a companion paper.

Packet Switching in a Multiaccess Broadcast Channel: Dynamic Control Procedures

Abstract: In a companion paper [1], the rationale for multiaccess broadcast packet communication using satellite and ground radio channels has been discussed. Analytic tools for the performance evaluation and design of uncontrolled slotted ALOHA systems have been presented. In this paper, a Markovian decision model is formulated for the dynamic control of unstable slotted ALOHA systems and optimum decision rules are found. Numerical results on the performance of controlled channels are shown for three specific dynamic channel control procedures. Several practical control schemes are also proposed and their performance compared through simulation. These dynamic control procedures have been found to be not only capable of preventing channel saturation for unstable channels but also capable of achieving a throughput-delay channel performance close to the theoretical optimum.

Improving Automatic Repeat-Request (ARQ) Performance on Satellite Channels Under High Error Rate Conditions

Abstract: Large round trip delay associated with satellite channels reduces the throughput for automatic repeat-request (ARQ) system of error control rather drastically under high error rate conditians. Ground segments that usually accompany satellite circuits at both ends introduce bursts of errors, during which block error rates tend to be quite high, bringing down the throughput to very low values. In this paper, some schemes that modify the currently known variations of ARQ (Stop-and-Wait and continuous systems) are suggested with a view to obtaining higher throughput under high block error rate conditions. Specifically, the modified Go-Back- N system appears to be quite attractive, as it gives substantial improvement with little additional complexity in system implementation.

On the Capacity of Slotted ALOHA Networks and Some Design Problems

Abstract: Packet switching over broadcast channels with random access schemes is of current interest for local distribution system and for satellite channels. This mode of operation is useful when the communicating devices are mobile and when the ratio of the peak to average data rate requirement of each device is high. Such systems have been analyzed for the case in which all communicating devices are within an effective transmission range of each other; either directly or through the satellite. In this paper, we address broadcast networks in which originating devices cannot directly reach the destination receiver. Thus, devices are introduced which receive these packets and repeat them to the destination. The capacity (maximum throughput) of such systems is determined, and design problems related to the number of repeating devices and the usefulness of directional antennas are resolved.

Speech transmission in packet-switched store-and-forward networks

Abstract: The past few years have seen a widespread and growing application of packet-switched store-and-forward networks for data communication between geographically separated computer installations. Such networks can provide connections between facilities with the many desirable properties of dedicated communication lines but at reduced costs which result from the time-sharing of the actual lines among many customers. Barring the failure of local terminal equipment, such a network provides connections among its customers which implicitly exist regardless of the load being placed on the network. However, the network characteristics seen by an individual customer will vary with overall network traffic, since the network will tend to deliver messages less frequently and with increased delay (possibly beyond the point of usefulness) as load increases. This property of packet-switched networks---guaranteed connections with variable throughput and delay---is just the reverse of that exhibited by circuit-switched networks such as the telephone system. When circuit-switched systems are heavily loaded, delay may be experienced in making a connection, but once it is established, its throughput and delay will not vary with other system activity.

Performance of Hybrid Error Control Schemes of Satellite Channels

Abstract: The effectiveness of hybrid error control schemes involving forward error correction (FEC) and automatic repeat request (ARQ) is examined for satellite channels. The principal features of the channel are: large round-trip transmission delay due to the satellite link, and burst errors introduced by the terrestrial links that connect the users to the satellite link. The performance is estimated for two channels described by Fritchman's simple partitioned finite-state Markov model, and is compared to that obtainable if the channel is considered as a binary symmetric channel of the same bit error probability. Results show that the hybrid schemes offer substantial improvement over ARQ and FEC, and that an optimum exists for the number of errors corrected to obtain maximum throughput efficiency.

A High Throughput Packet-Switched Network Technique Without Message Reassembly

Abstract: A new packet-switching network technique is described which, while utilizing certain aspects of the ARPANET technology, introduces a substantially different technique for handling traffic which is longer than a single packet in length. The technique is keyed to a common-user network environment, where a wide variety of subscriber types, ranging from computers to simple terminals, are to be serviced. Subscribers in most cases would be remotely located from the network switching nodes. By splitting the buffering between the originating and destination nodes and by essentially eliminating the segment reassembly process, substantial reductions in on-line buffering can be achieved, while still maintaining short response times for interactive messages and large bandwidths for long data exchanges. In this paper we describe the network operational concepts and traffic flow for various subscriber types, show specific examples and timing diagrams for message flows, and present a comparative analysis of the buffer sizing, throughput, and delay for this new technique compared to the well-known ARPANET technique of packet switching.

Local, Regional and Large Scale Integrated Networks

Abstract: : Network Analysis Corporation's contract with the Advanced Research Projects Agency has the following objectives: (1) to study the properties of packet-switched computer communication networks for local, regional and large scale data communications, (2) to develop performance measures and analyses for integrated command, control, and communication networks, ((3) to determine the cost/throughput/reliability characteristics of large packet-switched networks for application to Defense Department computer communication requirements, and (4) to apply recent computer advances, such as interactive display devices and distributed computing to the analysis and design of large scale networks. This report summarizes principal technical accomplishments during the reporting period as well as the tasks in progress. The body of the report describes detailed results in the area of Packet Radio Network initialization, connectivity monitoring, and stability control are given. These issues are addressed at two levels: (1) Procedures proposed for implementation in the Experimental Packet Radio Local Area Demonstration System: and (2) Extensions and additions for application in second generation DOD systems. Keywords: Data transmission systems; Communication and radio systems; Wave packets.

ARPA Internetwork Protocols Project Status Report

Abstract: : An Internetwork Communication Protocol was implemented which permits reliable interprocess communication to be established between hosts in different networks. Estimates of program size are made for a single connection version of the program for use in a mobile packet radio terminal. Preliminary throughput measurements indicate serious problems with the Very Distant Host interface and its related software. A plan for detailed analysis of delays in the system has been made and the results will be reported during the next quarter.