Packet output processes of CSMA and CSMA/CD protocols

This paper considers a generic CSMA and CSMA/CD protocol that allows one to unify the nonpersistent and one-persistent protocols as special cases, and solve the characterization problem under the infinite population model. Explicit expressions of the interdeparture time moment generating function, as well as expressions for the channel throughput and the variance of output process, are obtained for both slotted and nonslotted cases. In addition to direct simulation results, we also provide a novel statistical analysis/simulation procedure for the purpose of validating the infinite population model and the analytical results. Both approaches indicate that the infinite population model is quite appropriate for analyzing this generic protocol     

A simulation study of delay in multichannel CSMA/CD protocols

Simulation is used to estimate the performance of media access control (MAC) protocols derived from carrier-sense multiple access with collision detection (CSMA/CD), and operating in local area networks comprising several parallel broadcast channels. The influence of possible protocol and system alternatives on the network performance is discussed, based on results of the packet delay average, variance, mean square, coefficient of variation, and histogram, as well as the packet rejection probability due to lack of buffer space. The delay incurred by multipacket messages is estimated, comparing the single channel to the multichannel option. Numerical results indicate that the multichannel option provides reductions in both the packet delay average and variance, even when stations are only able to simultaneously receive from a subset of channels     

Stability and Optimization of the CSMA and CSMA/CD Channels

A comprehensive study of the stability and optimization of the infinite population, slotted, nonpersistent CSMA and CSMA/ CD channels is presented. The approach to both stability and performance optimization differs significantly from previous work, and provides a number of new results including robustness in stability and performance in the presence of channel and control parameter variations. It is first shown that both channels are unstable under the usual assumption of random retransmission delay. Pake's lemma is then applied to study the properties of a type of distributed retransmission control which provides stable channels. Basic results are in the form of inequalities which define stability regions in the space of channel and control parameters, and further permit one to specify controls which maximize channel throughput as a function of packet length and CD time with stability guaranteed. The delay versus throughput characteristic for the stabilized channels is derived and used to demonstrate the performance achievable with these channels.     

CSMA/CD Network Problem Threshold

CSMA/CD network transmission errors such as collisions, CRC errors, misalignment, etc. are statistical in nature. Although errors can vary randomly, a high level of errors does indicate specific network problems (e.g. equipment failure). This paper examines the random nature of collisions theoretically as well as from actual statistics, and establishes a threshold above which a network problem is indicated with a high probability.     

Finite Population CSMA/CD Networks

A continuous time Markov chain model of a nonpersistent carrier sense multiple access with collision detection (CSMA/CD) protocol is developed to determine the performance of finite population systems. The model allows a wide range of distributions for the length of packets and the lengths of the transmission detection and collision detection times. A stability measure for finite population asynchronous systems-the instantaneous expected drift-is developed. Performance calculations for many sample systems show that the following behavior is characteristic of these systems: a wide range of retransmission rates provides almost optimal performance; the instantaneous drift is a sensitive indicator of the stability characteristics of CSMA/CD networks; if high fixed retransmission rates are used, performance decays very rapidly when other network parameters cross critical thresholds. In addition, adaptive retransmission policies and the maximum length of a CSMA/CD cable network are found to be very sensitive to the distribution of the transmission detection time.     

Optimal capacity of p-persistent CSMA protocols

We deal with the characterization and computation of the p value, say p/sub opt/, corresponding to the maximum protocol capacity in p-persistent carrier-sense multiaccess (CSMA) protocols. The contribution of this paper is twofold. First, we give an analytical justification, and a numerical validation of a heuristic formula widely used in the literature to characterize the p/sub opt/. Second, we provide closed formulas for the p/sub opt/, and we show that the optimal capacity state, given the message length distribution, is characterized by an invariant figure: the Mp/sub opt/ product.     

CSMA/CD with Deterministic Contention Resolution

This paper presents a novel media access protocol CSMA/CD with deterministic contention resolution (DCR) for a local area network. It usually operates as CSMA/CD, but once a collision occurs it resolves the collision using a kind of implicit token passing. An analysis was conducted on DCR performance characteristics based on simulation studies and in comparison to conventional CSMA/CD and implicit token passing. It was found that they were very satisfactory in terms of throughput, message delay, and delay standard deviation, these performance characteristics make DCR attractive as a media access protocol for combined voice and data traffic. It has also been shown that this protocol assures robustness against various kinds of transmission errors and station failures. A prototype of a local area network using this protocol has been developed. It consists of a pair of optical fiber buses to which each station is attached via a pair of directional couplers.     

带有网络分割的CSMA／CD技术

通过在ＣＳＭＡ／ＣＤ局域网中引入网络分割这一新概念，建立了以太网模拟模型，改善了ＣＳＭＡ／ＣＤ技术在重负载下的性能。     

The delay characteristics of CSMA/CD networks

A continuous-time Markov chain model of the CSMA/CD (carrier-sense multiple-access with collision detection) protocol is used to find its delay characteristics. For both random-service-order (RSO) and first-come-first-serve (FCFS) CSMA/CD networks, matrix-geometric methods are used to derive and/or compute the throughput-delay and caudal-characteristics curves, the distribution and variance of the delay, and the rate of decay of the tail of the delay distribution. These results can be used to determine the suitability of RSO and FCFS CSMA/CD networks in applications in which they must carry delay-sensitive data. This is illustrated by an example which shows the significant improvement obtained in the delay characteristics of a particular network when FCFS is used instead of RSO     

Performance Analysis of Buffered CSMA/CD Systems

This paper presents a new approximation approach, called tagged user approach (TUA), for the queueing analysis of slotted CSMA/CD systems with a finite user population having either finite or infinite user buffer capacity. By assuming a symmetric channel, the performance analysis of the overall system is determined by the performance of an arbitrarily selected user, called the tagged user. With the further assumption that each user always operates with its equilibrium probability, the packet service time distribution can be obtained using a state flow graph by studying the channel contention scheme. The obtained packet service time distribution is then applied to the queueing analysis of the tagged user using the standard queueing theory. That is, the analysis of the channel contention scheme and the analysis of the user queueing behavior are decoupled in this paper. Hence, TUA can be applied to complicated systems such as those where each user buffer may have bulk packet arrivals and random service discipline as long as the corresponding queueing theory is available. Since a state transition probability matrix is not required in TUA, the required amount of computation is quite small. Simulation results verify the high accuracy of the analysis.     

A Matrix Representation of CSMA/CD Networks

A continuous time Markov chain model of asynchronous, nonpersistent CSMA/CD networks is developed which allows their complete characterization by a matrix whose dimensions are independent of the number of users in the network. The model provides an efficient reeursive algorithm for computing the performance of finite population networks. It also allows many analytical results to be obtained when an infinite population and a constant load retransmission policy are considered. These analytic results include necessary and sufficient conditions for stability, the distribution of the number of busy users, an exact closed form expression for the expected delay, and the exact upper bound on the throughput-all obtained via the properties of the matrix mentioned above. The results on stability show that, for this CSMA/CD model, the definitions of stability in terms of expected drift, nonnull recurrence, and maximum possible throughput exceeding actual loading are all equivalent. The model can approximate as closely as desired any distribution for the packet length, transmission detection time, and collision truncation time. Taking advantage of this freedom, the performance of CSMA/CD networks is shown to be very sensitive to the distribution of the transmission detection time.     

On transient behaviours of slotted CSMA protocols

CSMA protocols have been extensively studied under the assumption of an equilibrium condition. The results obtained in this manner provided useful insight for the development of packet radio and local area networks for the transmission of bursty data. The integration of isochronous and bursty traffic in the same network may, however, make the equilibrium assumption unrealistic, for example when fixed-length frames are defined, only a portion of which is devoted to the transmission of bursty data according to a CSMA protocol. In such cases, it is necessary to study the protocol behaviours in fixed-length time segments. This paper presents a technique for the analysis of slotted CSMA protocols in such an environment. Definitions for the transient throughput and transient average packet delay are introduced, and closed form expressions are derived for non-persistent and 1-persistent CSMA and CSMA/CD protocols with arbitrary distribution of the packet length. Numerical results help in the visualization of some interesting phenomena, peculiar to the CSMA operations in finite-length intervals.     

一种与CSMA/CD兼容的话音传输协议

简单介绍实时话音协议（RT－V），并且对该协议的不足之处作了补充和改进，使之更加完善。这种改进了的话音协议（M－VP）不仅与CSMA／CD兼容，而且增加了负载控制机理和访问次序的动态可变性，从而保证了在话音重载下数据所需的最小带宽，进一步提高了通道的利用率，改善网络传输话音／数据综合业务的性能。     

CSMA with reservations by interruptions (CSMA/RI): a novel approachto reduce collisions in CSMA/CD

This paper proposes an enhancement for the carrier sense multiple access with collision detection (CSMA/CD) protocol, called CSMA with reservations by interruptions (CSMA/RI). This new protocol uses a novel approach to reserve capacity by interrupting an ongoing packet transmission. The performance of the protocol is studied by simulations under realistic (long range dependent) traffic conditions and compared to the CSMA/CD, token ring protocols, as well as with the work conserving G/D/1 queue. It is demonstrated that CSMA/RI always offers better performance than CSMA/CD, and under certain realistic assumptions regarding packet size, the performance of CSMA/RI can be very close to that of token-ring and G/D/1     

Performance evaluation of a buffer-based CSMA/CD protocol for single channel optical Ethernet LAN

Using CSMA/CD, Ethernet suffers capture effect that makes it unsuitable for supporting real-time multimedia traffic. It does not guarantee delay bound and behaves poorly under heavy load conditions, leading to excessive delay, throughput degradation and packet loss because of excessive collisions. Aim of this paper is to increase throughput and reduce average packet transfer delay of CSMA/CD-based LAN by reducing collisions and eliminating packet loss. Here, each user has a finite buffer capacity that helps to reduce collisions and Ethernet capture effect. At the same time, to eliminate packet loss, a new special-jamming signal is used. The network performance in terms of throughput, average packet transfer delay and percentage of collision based on the proposed protocol shows significant improvements. Throughput is increased more than 10% whereas average packet transfer delay and percentage of collision are reduced to less than 1.5 ms and 3%, respectively, compared to conventional protocol.     

互连的CSMA／CD局部网络的性能测量和分析

把两个具有碰撞深测载波检测多路存取协议的局部网络由桥接器和光纤链路互连起来，进行性能测量和研究。这种测量涉及内部网络和中间网络由桥接器和光纤链路互种配置上。对网络的吞吐量和延迟性能的分析表明，桥接网络的损失对负载的依赖关系很大。这种损失，在开始时最高的，然而，随着负载的增加却又减少，本文在提出问题以后，接着对桥接的ＣＳＭＡ／ＣＤ网络进行介绍。然后描述测量结果和进行性能分析；最后给出结论。     

Performance analysis of CSMA/CD‐PS systems

Recently, the interest in wireless LANs has been increasing. For wireless LANs, light and simple terminals are desirable, and random access protocols such as CSMA and CDMA are preferable. In order to improve the performance of these protocols, some variations have been proposed. Among them is the CSMA/CD‐PS (Carrier Sense Multiple Access with Collision Detection and Packet Segmentation) protocol, in which a message to be transmitted is divided into several packet segments separated by short intervals to enable sensing the channel state. In this paper we analyze the performance of CSMA/CD‐PS systems and derive the Laplace–Stieltjes transform (LST) of the probability distribution function (PDF) of the message interdeparture time and that of the PDF of the message response time. We note that the analysis of the LSTs of the PDFs of performance measures is important, because in communication systems, the output process of each sub‐system may form the input process to another one and that in order to evaluate the performance of communication systems more accurately, we need the stochastic characteristics of relevant output processes. Through LSTs, we can calculate not only averages but also higher moments of performance measures such as coefficients of variation. As for the analysis, we first define the state of the system and observe it at those epochs just after the end of successful/unsuccessful message transmissions. Then we derive the state transition probability matrix and obtain the state probability distribution. Secondly we analyze the interdeparture time and response time distribution of the system to obtain their LSTs. We also present some numerical results for the channel utilization, the average and the coefficient of variation of the interdeparture time, and the average and the coefficient of variation of the message response time. This revised version was published online in June 2006 with corrections to the Cover Date.     

An approximate analysis of a buffered CSMA/CD

A continuous-time carrier-sense multiple access with collision detection (CSMA/CD) system with a finite number of homogeneous stations, each possessing an infinite buffer, is analyzed. The system and each station is treated approximately as an independent M/G/1 queuing system. Since stations are mutually dependent, the interference from other stations is taken into account, in terms of the service-time distribution. With this analysis, the mean message delay can be numerically obtained. The stability of the system is also discussed. In addition, the upper-bound condition for the transmission interval is presented that keeps the system stable. It is concluded that the stability of the system becomes more sensitive to the retransmission interval as the number of stations increases     

Performance analysis of CSMA/CD‐DRC system

Multimedia communication systems must handle two types of messages, one is data type and the other is voice type. Data type messages can tolerate longer delay but voice type ones cannot. Though communication systems with huge capacity by optical fibers and ATM switches have little problem for multimedia communication, most of the present LANs cannot handle messages, especially voice type ones, satisfactorily because of their poor capacity. In this paper we propose a new protocol for LANs, CSMA/CD‐DRC (Carrier Sense Multiple Access with Collision Detection and Dynamic Retransmission Control). This protocol is for the multimedia communication systems which must handle those two types of messages but do not have enough channel capacity, and controls retransmission rates dynamically to achieve higher throughput and shorter delay for voice type message. Moreover, we analyze the protocol in order to confirm its performance. In analysis we derive Laplace–Stieltjes transform (LST) of the probability distribution function (PDF) of the performance measures. Through LSTs, we can calculate not only averages but also higher moments of performance measures as well as coefficients of variation. We also present some numerical results, from which we find the proposed protocol can improve the system performance. This revised version was published online in June 2006 with corrections to the Cover Date.