In ATM networks, each node has its own buffer to store some cells. The buffer size represents a trade-off between cell loss and transmission delay, and therefore, it is of significant concern to evaluate the performance with respect to the buffer size. In this paper, we investigate the sensitivity of the loss probability with respect to the buffer size by considering a gradual input queue with a finite buffer. Gradual inputs are considered as those representing a bursty cell traffic. Applying the perturbation analysis technique to this model, we derive the strongly consistent sensitivity estimates, and combining with the likelihood ratio method, we confirm that our estimates lead to reasonable simulation results.

This paper analyzes an ATM switching node with correlated cell arrivals. An ATM switching node is modeled as a discrete-time finite-buffer queue. Cells arrive according to a semi-Markovian process, where the number of cell arrivals in a given slot depends on the state of the underlying (M-state) Markov chain in both the given slot and the previous slot. This paper presents analysis for various cell loss characteristics such as cell loss probability, the consecutive loss probability, and the distribution of loss period lengths. It also obtains characteristics of the cell output process from an ATM switching node including the joint distribution of successive cell interdeparture times, and the distributions of busy and idle periods of the cell output process. It is shown through numerical examples that both the correlation and the variation of cell arrivals significantly affect the cell loss and the output process characteristics.>

One purpose of a traffic shaping mechanism (such as the leaky bucket) is to smooth out an input process into an output process. In so doing, a question of interest is the following: to what extent has the input process been modified, or, to what extent does the output process conform to the input process? To this end, the authors define and characterize a conformance measure. They apply this idea to a leaky bucket in a high-speed network in which this issue may arise naturally. They show how to find the conformance measure for a leaky bucket with the Markovian arrival process.>

In broadband ISDN, different classes of traffic expect to receive different quality of service. One way of providing service is to implement a priority structure among traffic classes. The authors analyze a single server queue in which video and voice traffic receive priority over data traffic. Corresponding to the fixed cell size of ATM, they assume that service times are deterministic. They further assume that the high priority traffic is correlated and the arrivals are governed by a Markov chain. With these assumptions, they characterize the queue length distributions and the waiting time distributions for this problem. They show by numerical examples that the delay distribution depends highly on the correlations and that a priority service discipline is capable of providing very good service for real time traffic.>

The performance of an asynchronous transfer mode (ATM) switching node is analyzed, taking cell arrival correlation into consideration. An ATM switching node is modeled as a discrete-time finite-buffer queue. Cell arrivals are assumed to follow a semi Markovian process. Various characteristics of the cell loss and the distribution function of the cell output process from an ATM switching node are analyzed. The cell loss probability, the consecutive loss probability, the distribution of loss period lengths, the joint distribution of successive cell interdeparture times, and the distributions of busy and idle periods are determined. It is shown that both the correlation and the variation of cell arrivals significantly affect the cell loss and the output process characteristics.>

The paper provides a performance analysis of automatic-repeat-request (ARQ) protocols in connection-oriented transmission. Each message arriving at a transmitter is divided into several packets, which are continuously transmitted to a receiver according to go-back-N ARQ or selective-repeat ARQ protocols. Because of connection-oriented transmission, messages are served on a first come first served basis, i.e., transmission of a message is commenced after all packets in the previous message are successfully transmitted. For the two ARQ protocols, the authors derive the probability generating functions of message waiting time and queue length at an arbitrary instant, from which the average performance measures are explicitly obtained.>

An exact analysis is presented of an asynchronous (unslotted) multipacket CSMA/CD-DFT (carrier-sense multiple-access/collision detection with delayed first transmission) model and used to derive (1) the Laplace-Stieltjes transform of the probability distribution function (PDF) of the packet interdeparture time, (2) the LST of the PDF of the message interdeparture time, (3) the moment generating function (MGF) of the message response time, and (4) the MGF of the message response time conditioned on the number of packets necessary for transmission of a message. Higher moments as well as averages of these performance measures are important for performance evaluation of interconnected networks or integrated networks of voice and data. As the performance model allows each message to consist of a geometrically distributed number of constant-length packets, the result is also useful in examining the performance of error-prone CSMA/CD systems as well as the impact of random message sizes on the system performance. Numerical examples include comparisons between the DFT model and the IFT (immediate-first-transmission) model.>

An unslotted model of the nonpersistent CSMA/CD protocol is considered, and the effect of different packet size distribution functions on the system performance is investigated. Under the assumption that packet sizes obey a general distribution function, an exact analysis of the packet output process on the CSMA/CD channel and the packet delay process at each homogeneous station is presented. Statistics analyzed are the following: (1) the Laplace-Stieltjes transform (LST) of the probability distribution function (PDF) of the packet interdeparture time, (2) the autocorrelation coefficient of the packet interdeparture time, (3) the LST of the PDF of the packet delay, and (4) the LST of the PDF of the waiting time. In addition, explicit expressions for the LSTs, averages and variances of the interdeparture time, packet delay, and waiting time distribution functions are given under the heavy-traffic assumption. In numerical results, typical packet size distribution functions are applied to the analytical result, and their effects on the autocorrelation coefficient of the interdeparture time as well as the averages and coefficients of variation of the interdeparture time, packet delay, and waiting time are examined.>

A single CSMA/CD (carrier sense multiple access with collision detection) local area network which is connected to other networks by a gateway with finite buffer capacity is described. Its performance is analyzed by using an embedded Markov chain. For the service discipline of packets queuing at the gateway, three cases are considered: G-limited service discipline, E-limited service discipline, and G-decrementing service discipline. The state transition of the system is analyzed, and the Laplace-Stieltjes transforms of the probability distribution functions of idle and busy periods are derived. Equations for average performance measures are formulated. Numerical examples are used to examine the effect of external traffic on the packet delay and throughput at terminals as well as at the gateway for each service discipline. The results show that as a service discipline at the gateway, the limited service disciplines are preferable to the decrementing service discipline in that they more fairly allocate the channel bandwidth to terminals and the gateway. The numerical results also show that the performance of the gateway is substantially improved by using a higher retransmission rate at the gateway.>

An analysis is made of the throughput and delay performance of two classes of free-access tree algorithms with minislots. In one class, binary feedback information is available in minislots, and in the other, ternary feedback information is available. It is shown that the highest maximum throughput 0.56714 is achieved in the limiting case where the number of minislots in a (large) slot is infinity and minislot overhead is zero. A lower bound of the average transmission delays in these algorithms is analytically derived. The obtained lower bound is also a lower bound of the average delay of the whole class of the free-access algorithms.>

The performance of a multiversion conservative timestamp algorithm is evaluated by analyzing the response time of operations in a distributed database system. The random communication delay in the transmission channels of a long-haul network supporting the distributed database system causes transmitted operations to be received out of order. According to rules that are dependent on the number of versions, the scheduler reorders the operations to preserve the consistency of the database. Operations encounter extra delay in the process of reordering. The system is modeled by a queuing network. Response-time distributions are obtained analytically. Numerical results are presented to show the effect of the number of versions on the performance.>

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.>

A unified approach to general asymmetric polling systems with a single buffer at each station is presented. Two variations of single-buffer polling system are considered: the conventional system and the buffer-relaxation system. In the conventional system, a new massage is not allowed to queue until the previous message has been completely transmitted, while in the buffer-relaxation system, a newly arriving message can be stored in the buffer once the previous message's transmission has started. For each system, the Laplace-Stieltjies transform (LST) of the joint probability-distribution function (PDF) of station times is derived, from which the LST of the PDF of message delay is straightforwardly obtained.>

The semijoin provides a means of reducing the amount of data transmission among sites in a distributed database system. Previously the semijoin has been studied mainly for reducing communication cost in an environment with global public communication networks. In a local area system, however, wide bandwidth is usually available and the communication cost is virtually negligible. In view of this, we adopt a simplified model of a local area network, imposing no constraint on the transmission line capacity and the communication processing capability at each site. For this model, an efficient algorithm for obtaining the shortest semijoin schedule, in the sense of minimizing the total number of semijoin transmissions, is developed. It is based on a schedule diagram newly introduced to represent the semijoin schedule.

We first consider the interdeparture process of a symmetric polling system with single buffer at each station, where distributions of transmission time and switchover time are assumed to be general. Under the assumption that consecutive interdeparture times are independent, the probability distribution is analyzed and the LaplaceStieltjes transform is given. Numerical examples show that the coefficient of variation of interdeparture time is not monotonic with respect to the arrival rate. Based upon the analysis, we can obtain the characteristics of outbound traffic if we are concerned with unidirectional traffic flow. In general, however, there is inbound traffic from external networks in the interconnected communication system and its effect on performance characteristics should be taken into account. We next propose the model of a polling system having the traffic from outside the system. The model consists of homogeneous stations with single buffers and a depot station with infinite buffer where inbound traffic is dealt with. We analyze the model and obtain throughput and mean waiting time for the case of constant transmission time and constant switchover times. Numerical examples show that the throughput of the system is not sensitive to inbound traffic if the total load of the system is moderate.

This paper treats the file redundancy issue in distributed database systems, asking what is the optimal number of file copies, given the ratio r of the frequency of update requests to the frequency of all file access requests (i.e., queries and updates). Formulations of this type of problem, including optimal file allocation, have been attempted by a number of authors, and some algorithms have been proposed. Although such algorithms can be used to solve particular problems, it seems difficult to draw general conclusions applicable to a wide variety of practical distributed database systems. To probe into this hard to formulate but interesting problem, our paper constructs simplified network models of distributed database systems, and computes the optimal number of file copies, as well as their locations, to minimize the communication cost. For several network types, we plot the optimal number of file copies as a function of the ratio r.

Introduction of the packet switching technique into digitized voice communication may afford great advantages in efficient use of the channel, compared to both circuit-switched and DSI systems. Detailed characteristics, however, have not been obtained because of difficulty in the exact analysis. Hence, simalation models are developed in this paper for the packetized voice transmission system, and various characteristics such as tranmission delays and loss probability of voice packets are obtained. We further evaluate three types of voice packet reassembly strategy at the receiving terminal, and obtain the optimal packet length, which keeps both overall packet transmission delay and packet loss probabilty less than a certain permissible value. Comparison among three strategies is also stated.

A method for realizing a circuit and packet integrated access scheme in a satellite communication channel is considered. Two kinds of terminals are assumed, namely, bursty terminals for handling bursty traffic and heavily loaded terminals for long-holdingtime message traffic. In this method, the channel frame is divided into two subframes: one is for bursty terminals, and the other is for heavily loaded terminals. The subframe for heavily loaded terminals is further divided into two subchannels, a reservation subchannel (consisting of small slots) and a message subchannel. The bursty terminals transmit their packets in their dedicated subframes on the slotted ALOHA protocol. The heavily loaded terminal having a message transmits, first of all, a reservation packet in a randomly selected small slot of the reservation subchannel to reserve slots in the coming message subchannels. One slot in the same position of each of the succeeding message subchannels is reserved for the terminal until the end-of-use flag, transmitted from the terminal, is received by the satellite. Mean transmission delays for both kinds of traffic in this method are analytically obtained. We show that there exists an optimal frame length which minimizes mean transmission delay for one kind of traffic while keeping mean transmission delay for the other kind under some permissible value.

This paper considers a satellite communication system with the slotted ALOHA access mode where the satellite is assumed to have on-board regeneration ability and the finite buffer capacity for storing noncollided packets from the uplink. The system is analyzed with the downlink bandwidth restricted to1/Lof the uplink bandwidth, and with the conventional slotted ALOHA system whereL = 1and the buffer size at the satellite is equal to zero. Maximum throughput and throughput-delay characteristics of this system are analytically obtained. The satellite is given an optimal buffer size to achieve maximum throughput and minimum packet transmission delay. It is shown that the constraints that lead to the downlink bandwidth being lower than the uplink bandwidth do not necessarily result in throughput penalties in a buffered satellite system. Furthermore, when the total bandwidth which can be divided between up- and downlinks is given, if two or three times that of the downlink is assigned to the uplink and if the satellite has buffer storage space only for a few packets, we show that maximum throughput of the system will be improved about 40 percent with little change in delay characteristics in comparison with that of the conventional slotted ALOHA system where the given total bandwidth is equally divided between up- and downlinks.

Message, packet and line switching in computer communication networks are analyzed by a queueing model. Message transmission delay time and network throughput between a source-destination node pair are obtained as a function of various parameters including message length, traffic arriving at the network, and the number of switching nodes existing between the nodes. A criterion to determine the most suitable switching method under the given conditions is offered. Also, the maximum length of a packet in packet switching is discussed.