Showing papers on "Throughput published in 1985"

Throughput Analysis for Persistent CSMA Systems

Abstract: The channel throughput for a finite number of packet broadcasting users is analyzed for random access protocols, including slotted persistent carrier sense multiple access (CSMA) with and without collision detection and unslotted persistent CSMA with and without collision detection. We consider both p - and 1-persistent CSMA. Our results can be extended to infinite population cases (by taking the proper limit), where they agree with the known throughput expressions when available.

The Optimality of Unbalancing Both Workloads and Machine Group Sizes in Closed Queueing Networks of Multiserver Queues

Abstract: Using a closed queueing network model, we explore the consequences of varying workloads among multiserver queues that may be of unequal size. In addition, we solve the problem of assigning servers of similar types to the queues in the network to maximize expected throughput. We show that 1 unbalanced configurations of assigned servers are superior to balanced ones, and 2 unbalanced workloads are better than balanced ones. We find that there can be significant differences in system throughput from balanced versus unbalanced configurations/workloads. Finally, we discuss applications to planning problems of flexible manufacturing systems.

Flow Control in Local-Area Networks of Interconnected Token Rings

Abstract: We investigate flow-control issues in local-area networks consisting of multiple token rings interconnected through bridges. To achieve high throughput, bridges perform only a very simple routing and store-and-forward function, but are not involved in error- or flowcontrol. In case of congestion, bridges discard arriving frames, which will be recovered through an appropriate end-to-end protocol between the communicating stations. The end-to-end protocol considered is the IEEE 802.2 type-2 logical-link-control (LLC) protocol. Extensive simulations show that performance can be severely degraded if, in such a network, the LLC protocol is employed as defined today. Therefore, we suggest an enhancement to this protocol in the form of a dynamic flow-control algorithm. As our results demonstrate, this enhancement guarantees close-to-optimal network performance under both normal traffic load and overload conditions.

Pattern Code Modulation and Optical Decoding - A Novel Code-Division Multiplexing Technique for Multifiber Networks

Abstract: We consider the use of multiple high-capacity fibers for communications networking. Each user transmits, asynchronously, patterns of optical pulses distributed over the fibers and throughout a time frame. Each receiver has a distinct alphabet of patterns, which are detected by optical correlators. Optical correlation by fiber tapped delay lines provides speedy and easy-to-implement decoders. Thus the individual user obtains a transparent low-speed channel by code multiplexing. The reliability of this low-speed channel can be enhanced by redundantly coding the patterns sent by the user, for which the encoding and decoding processes can be performed electronically. This two-step encoding process is simple to implement, highly reliable at reasonable throughput, and provides asynchronous access with simple protocol. Various components and configurations of this access scheme are described. The information theoretic capacity and the error probability for these configurations are derived. We also demonstrate that hardlimiting and filtering at the receiver reduce error probability significantly.

Reliable Loop Topologies for Large Local Computer Networks

Abstract: Single-loop networks tend to become unreliable when the number of nodes in the network becomes large. Reliability can be improved using double loops. In this paper a highly reliable and efficient double-loop network architecture is proposed and analyzed. This network is based on forward loop backward hop topology, with a loop in the forward direction connecting all the neighboring nodes, and a backward loop connecting nodes that are separated by a distance ⌊√N⌋where N is the number of nodes in the network. It is shown that this topology is optimal, among this class of double-loop networks, in terms of diameter, average hop distance, processing overhead, delay, throughput, and reliability. The paper includes derivation of closed form expressions for diameter and average hop distance, throughput, and number of distinct routes between two farthest nodes. For fault-tolerance study, the effect of node and link failures on the performance of the network is analyzed. A simple distributed routing algorithm for reliable loop network operation is also presented.

Multidestination Protocols for Satellite Broadcast Channels

Abstract: Two retransmission procedures, the go-back- N (GBN) scheme and the selective repeat (SR) scheme, have been analyzed for data transfer from one transmitter to many receivers. We consider transfer of error-controlled bulk data over a satellite broadcast channel. Two retransmission strategies, the dynamic retransmission group reduction (DRGR) technique and the fixed retransmission group (FRG) technique, are proposed. We study the GBN and SR schemes for both strategies. Analytic expressions are derived for the throughput performance of the GBN scheme and of the SR scheme with infinite resources, while discrete event simulation is used to estimate the throughput of the selective repeat scheme with finite resources. Only the SR scheme using the DRGR technique provides acceptable performance for high-speed bulk data transfer. For the DRGR technique, the throughput falls logarithmically with an increase in the number of receivers. In contrast, the throughput for the FRG technique falls exponentially with an increase in the number of receivers.

Communication controller using multiported random access memory

Abstract: A communication controller for facilitating bidirectional digital data transfers between a host processor and various types of networks. The controller architecture is characterized by multiple independent data transfer buses coupled to a central multiple port random acces memory (20). The architecture avoids microprocessor bus contention in favor of RAM contention and thus enhances aggregate system throughput. Moreover, the buses are capable of performing operations concurrently to thereby further enhance system throughtput.

Output Processes in Contention Packet Broadcasting Systems

Abstract: The processes consisting of the packet interdeparture times in contention-type packet broadcasting systems are studied under the heavy-traffic assumption. The channel access protocols considered include slotted and unslotted ALOHA and carrier-sense-multiple-access (CSMA) with and without collision detection. Through analysis of the Channel activity cycle, the distribution, mean, and coefficient of variation of the packet interdeparture times are explicitly derived. Taking the reciprocal of the mean interdeparture time, we obtain the channel throughput. Cases with dissimilar users are mainly considered, and systems of statistically identical users are treated as special cases.

An Analysis of a Point-to-Multipoint Channel Using a Go-Back-N Error Control Protocol

Abstract: This paper contains a performance analysis of an error control protocol operating in a point-to-multipoint environment. This protocol, called broadcast go-back- N [BGB( N )], is a generalization of the standard go-back- N point-to-point protocol. Expressions for the message throughput and expected message delay are obtained. Numerical results are provided for a satellite communications system.

Analysis of a hybrid token-CSMA/CD protocol for bus networks

Abstract: A hybrid control token-CSMA/CD (Carrier Sense Multiple Acess with Collision Detection) protocol for medium access in local-area bus networks is introduced. This protocol is expected to perform as well as the better of the two component protocols at all times. Analytic results for the throughput and mean packet delay of our hybrid protocol are obtained. Numerical results showing the delay-throughput characteristics and comparisons of this protocol with control token and CSMA/CD are presented.

Delay analysis of interval-searching contention resolution algorithms

Abstract: The intelligent design of a random multiple-access communication system involves analyzing the tradeoffs among throughput rate, transmission delay, and stability subject to additional restrictions imposed by distributed processing requirements. Interval-searching contention resolution algorithms have been found to achieve high throughput, and simulations have shown that they also possess short average delay. A general approach to the delay analysis of interval-searching contention resolution is proposed based on solving an integral equation for the distribution of a quantity called the transmission lag. For a certain multibit feedback algorithm, this analytical technique leads to exact determination of the throughput-delay characteristic. For the celebrated " 0.487 " algorithm, the method yields upper and lower bounds to the curve of expected delay versus throughput that are in close agreement with simulation results.

Throughput--Delay Characteristics of Some Slotted-ALOHA Multihop Packet Radio Networks

Abstract: A Markovian model is formulated to find the throughputdelay performance for slotted-ALOHA multihop packet radio networks with a fixed configuration of packet radio units (terminals and repeaters) and fixed source-to-link paths for packets. Improvements in performance which are obtained by the adjustment of transmission parameters (suppression/acceleration) according to the states of nearby units and/or by having repeaters equipped with multiple buffers are demonstrated.

Rude-CSMA: A Multihop Channel Access Protocol

Abstract: In this paper, we define a two-parameter family of protocols designed for multihop packet radio networks. We call these protocols rude-CSMA because under certain circumstances, maximum throughput is obtained when nodes, even after sensing a busy channel, transmit packets anyway with a nonzero rate. The performance of these protocols is analyzed for various special and random topologies.

Mixing traffic in a buffered banyan network

Abstract: A model of Banyan networks is developed to account for their operational as well as topological characteristics. The model incorporates a description of the states of individual switching nodes and explicitly captures the interconnection patterns between stages. Accordingly, the performance of a network can be evaluated via an iterative procedure. Using the model, we analyzed one class of nonuniform traffic pattern referred to as “point-to-point” traffic that has particular significance to mixed voice, data, and video applications. The results obtained indicate that even a single dedicated channel (with point-to-point traffic) can significantly limit the throughput of the background uniform traffic. The paper concludes with several switch design strategies for switching point-to-point traffic using a self-routing switching network.

The Effect of Capture on Collision-Resolution Algorithms

Abstract: In many communication systems, the stronger of two or more overlapping packets might capture the receiver and thus be received without error. The effect of capture on collision-resolution algorithms in a slotted ALOHA type broadcasting network is investigated here. Extensions to the algorithms are suggested for both the situations in which the receiver can or cannot distinguish between success slots and capture slots. In particular, we present a class of retransmission schemes for packets that have been transmitted during capture slots but have not been received correctly. The performance analysis is confined to a simplified model in which the nodes of the network are divided into two groups and only packets sent by the nodes of one of them might be captured. For this simplified model and for each extended algorithm, explicit recursive equations are given, from which the average conditional collision-resolution interval length, as well as the maximal throughput, can be determined. As expected, we show that in the presence of capture, the performance of the network is improved and the maximal attainable throughput is increased. Extensions of the simplified model such as dividing the nodes into K groups instead of two, or considering the situation that capture depends on relative distances and transmission powers, are also discussed. For the latter situation we give simulation results.

Distributed Switching for Data Transmission over Two-Way CATV

Abstract: Most of tile present approaches to two-way interactive CATV focus on the centralized approach, in which all traffic must travel to the CATV head end. In this paper, we present a distributed approach, in which intelligent store-and-forward packet switches are to be installed at various locations on the cable. The analysis emphasizes three main criteria: the maximum traffic flow on the cable, the throughput of each switch, and the average message delay. Two possible schemes are compared. In one, the switches appear on the main trunk only. In the second, switches are used at branch locations as well.

Connection-oriented versus connectionless protocols: A performance study

Abstract: 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.

Application of Code Combining to a Selective-Repeat ARQ Link

Abstract: Various attempts have been made to devise ARQ schemes which maintain throughput at high channel bit error rates. Of these selective-repeat schemes, particularly hybrid verisons which employ error-correction coding, have proven most effective. However, even these schemes fail to provide useful throughput at very high bit error rates, despite a non-zero channel capacity. In this paper we demonstrate that a selective-repeat ARQ link employing code combining can maintain useful throughput at very high error rates (error rates approaching 50%). Moreover, with minor modifications this technique incurs no loss relative to previous schemes at low channel bit error rates. We substantiate these claims by comparing the throughput performance of code combining using a rate-?, constraint length 7 convolutional code on a selective-repeat ARQ link with other selective-repeat ARQ schemes.

Limited feedback sensing algorithms for the packet broadcast channel

Abstract: A slotted packet broadcast channel with an infinite user population is considered. A limited feedback sensing algorithm is proposed and analyzed for collision versus noncollision binary feedback. The algorithm bas maximum throughput equal to 0.42 (packets/slot), has uniformly good delay characteristics within its stability region, and is robust in the presence of feedback errors. A variation of the algorithm, for ternary feedback, attains maximum throughput 0.425 and bas uniformly good delay characteristics within its stability region. In contrast, the highest throughput limited feedback sensing algorithm existing for ternary feedback attains maximum throughput 0.456 , but induces relatively high delays for Poisson intensities below 0.3 .

Performance characteristics of two Ethernets: an experimental study

Abstract: Local computer networks are increasing in popularity for the interconnection of computers for a variety of applications. One such network that has been implemented on a large scale is the Ethernet. This paper describes an experimental performance evaluation of a 3 and a 10 Mb/s Ethernet. The effects of varying packet length and transmission speed on throughput, mean delay and delay distribution are quantified. The protocols are seen to be fair and stable. These measurements span the range from the region of high performance of the CSMA/CD protocol to the upper limits of its utility where performance is degraded. The measurements are compared to the predictions of existing analytical models. The correlation is found to range from good to poor, with more sophisticated models yielding better results than a simple one.

Collision resolution on the CSMA/CD bus

Abstract: This paper describes a collision resolution mechanism which operates in a CSMA/CD environment such as ethernet. A protocol using this mechanism, Enet II, is presented as a candidate for the second generation of ethernet. The protocol requires that all stations have only a single common piece of information, an upper bound on the propagation delay, which is already part of the 802.3 standard. With this information, the protocol can resolve collisions that do occur in the CSMA environment due to multiple arrivals within a busy period or a propagation delay. Although the throughput is not as high as can be achieved with timestamps and clocks, this protocol will operate correctly on a bus with 802.3 standard interfaces.

A Multiaccess Protocol for Multihop Radio Networks

Abstract: We describe an adaptive multiaccess channel protocol for use in radio networks with an arbitrary distribution of stationary hidden nodes, which provides the nodes with controlled, collision-free access to the channel. The protocol can be considered to belong to the BRAM [5] protocol family, but differs in significant ways from BRAM. In this paper we describe the tenets of the protocol, then develop the protocol, and finally develop analytic expressions for its expected throughput and delay performance. Given these delay-throughput expressions, we show how protocol "delay" optimization can be achieved by dynamic adjustment of a protocol parameter as the network traffic load changes.

Applications Of Coherent Optical Communication In The Network Environment

Abstract: Network architectures that utilize coherent optical technology are, analyzed. Applications of this rapidly maturing technology are shown to increase network capabilities - throughput, variety of services, etc. - and alleviate some of the protocol and switching difficulties found in traditional network architectures. The designs presented and analyzed in this paper are concerned with multiple - access and broadcasting networks.

Throughput of a satellite channel communication

Abstract: The throughput of a satellite channel communication is depending upon the link protocol. It is well known that the “classical” HDLC protocol is inadequate when applied to satellite links instead of short terrestrial links. Several modifications have been proposed to overcome this problem. The present paper gives an analysis and evaluation of a new class of protocols called “Virtual Subchannel schemes” which splits the satellite link into several components; these subchannels are assigned for transmission in cyclic order and are controlled independently of each other by the classical HDLC procedure.

A hybrid FARA/CSMA-CD protocol for voice-data integration

Abstract: A new hybrid packet switching protocol for voice-data integration is proposed and analysed The protocol adapts to the changing traffic conditions of both voice and data Network control is distributed over all nodes, thus eliminating the need for central switching or multiplexing Voice users follow a modified version of FARA, whereas CSMA-CD is adopted by data users for their channel access policy The analysis is based on the solution of a 2-state Markovian chain, after which the voice blocking probability, data packets delay and network throughputs are determined

Two-Level Multiaccess Schemes for Packet Satellite Systems with Low Duty Factor Terminals

Abstract: A two-level packet satellite network architecture is proposed to provide efficient communications for a large number of low duty factor terminals. At the first level, disjoint subnets of prioritized users employ a minislotted alternating priorities (MSAP) protocol. At the second level, a time division multiple access (TDMA) or frequency division multiple access (FDMA) uplink, and a time division multiplexed (TDM) or frequency division multiplexed (FDM) downlink is assumed, with the satellite regenerating and reformatting the data appropriately. Examples with a large number of terminals show that the two-level schemes provide superior delay performance over single-level methods for wide ranges of throughput.

Performance of the Tristan Computer Control Network

Abstract: An N-to-N token ring network of twenty-four minicomputers controls the TRISTAN accelerator complex. The computers are linked by optical fiber cables with 10 Mbps transmission speed. The software system is based on the NODAL, a multi-computer interpreter language developed at CERN SPS. Typical messages exchanged between computers are NODAL programs and NODAL variables transmitted by the EXEC and the REMIT commands. These messages are exchanged as a cluster of packets whose maximum size is 512 bytes. At present, eleven minicomputers are connected to the network and the total length of the ring is 1.5 km. In this condition, the maximum attainable throughput is 980 kbytes/s. The response of a pair of an EXEC and a REMIT transactions which transmit a NODAL array A and one line of program `REMIT A' and immediately remit the A is measured to be 95+0.039x ms, where x is the array size in byte. In ordinary accelerator operations, the maximum channel utilization is 2%, the average packet length is 96 bytes and the transmission rate is 10 kbytes/s.

Highly efficient error recovery protocol for satellite link (MN-SREJ)

Abstract: Data communications over a satellite link makes possible high-speed data transmission and simultaneous transmission of information to multiple receiving stations. Unless a high-quality link is provided, the throughput efficiency with the existing HDLC error recovery methods tends to decrease. Therefore, we have developed a new error control scheme (named Multi-Numbered Selective Reject (MN-SREJ) method, an improved version of SREJ of HDLC, which would permit high speed and reliable communication even under long propagation delay and poor transmission quality. By the use of MN-SREJ, more than one solution retransmission request can be made within one round-trip delay and, furthermore, at the checkpointing, all the unreached frame numbers can be sent to the sending station. The MN-SREJ method can be expanded easily from point-to-point communication to multicast communication, and the degradation of the throughput efficiency as the number of receivers is increased, is small. Furthermore, an approximate formula of the point-to-point communication throughput efficiency is derived for an arbitrary maximum number of outstanding frames and round-trip delay, and the analytical result is shown to coincide well with the simulation result.

"Supernodes" in Packet Radio Networks Employing Code Division Multiple Access

Abstract: CDMA provides new ways of allocating network resources to network nodes so as to match nonuniform traffic requirements. The enhancement of a node's throughput as a result of equipping it with several receivers, several transmitters or both is studied for the slotted ALOHA access scheme. It is also shown that funneling all of a node's inbound traffic via two of its neighbors can increase that node's inbound throughput put by up to 36% without any additional hardware and with simple and robust protocol support.