Throughput-delay Tradeoff Research Articles

Overload Performance of Several Processor Queueing Disciplines for the M/M/1 Queue

In a Variety of overloaded queueing systems (e.g., an overloaded call processing system), long delays can result either in poor service given to the customer or in customers, unknown to the system, turning bad. For example, in switching systems, long dial tone delays can result in customers initiating dialing before receiving dial tone. In this case the system will not receive all the digits and an unsuccessful call results. This can lead to the system expending real time on unsuccessful services and, therefore, reduces the effective throughput. Thus, there is a need for control Schemes which reduce the load offered to the processor by selectively refusing service to some customers in such a way as to keep delays, for those customers which are selected for service, small. This fact has been recognized and has led to improved strategies for local switches. In this paper we analyze and compare the performance of various queueing and service disciplines for an M/M/1 queue. We consider LIFO and FIFO Schemes with customer rejection mechanisms corresponding to pushing out or timing out older customers in queue. Delay distributions for served customers are obtained and comparisons based upon throughput-delay tradeoffs are presented. For the situation where Customers can turn bad at a random time after their arrival, we compare the throughput of good customers. The results presented are a mixture of classical results, which are briefly stated, and new results which are developed in more detail. The numerical results show a dramatic effect of the queueing and Service disciplines on the overload performance and a strong dependence of the throughput of successful services on the mechanism for customers turning bad. Although results are obtained for a single server queue, they can be used to approximately analyze overload control schemes which control access to distributed systems.

Multiple-access protocols for satellite packet communication networks: A performance comparison

This paper considers satellite packet communication networks with a large population of bursty users and presents an analytic comparison of the throughput versus average message delay trade-off characteristics of multiple-access protocols. The following six multiple-access protocols are examined: 1) slotted ALOHA, 2) reservation-ALOHA, 3) a reservation protocol with a slotted ALOHA reservation channel, 4) a reservation protocol with a TDMA reservation channel, 5) SRUC (Split Reservation Upon Collision), and 6) fixed assigned TDMA. All the protocols are required to ensure that all packets of a message are correctly received in the proper order at the destination. Then, a unified presentation of the delay-throughput performance of the protocols is given by means of an analytical technique called equilibrium point analysis. The throughput versus average message delay tradeoff characteristics are compared taking into account the system stability.

Diversity ALOHA--A Random Access Scheme for Satellite Communications

A generalization of the slotted ALOHA random access scheme is considered in which a user transmits multiple copies of the same packet. The multiple copies can be either transmitted simultaneously on different frequency channels (frequency diversity) or they may be transmitted on a single high-speed channel but spaced apart by random time intervals (time diversity). In frequency diversity, two schemes employing channel selections with and without replacements have been considered. In time diversity, two schemes employing a fixed number of copies or a random number of copies for each packet have been considered. In frequency diversity, activity factor-throughput tradeoffs and in time diversity, delay-throughput tradeoffs for various diversity orders have been compared. It is found that under light traffic, multiple transmission gives better delay performance. If the probability that a packet fails a certain number or more times is specified not to exceed some time limit (realistic requirement for satellite systems having large round trip propagation delay), then usually multiple transmission gives higher throughput.

Window Random Access Protocols for Local Computer Networks

In this paper we consider a local computer network in which users communicate with each other over a single bus. We develop window search algorithms with which to implement random access protocols on the bus. Two protocols, one nonadaptive and the other adaptive are described. The maximum throughputs and throughput-delay tradeoffs are provided for both. These protocols show significant improvement over previous random access protocols used in local computer networks. We also consider the problem of allowing new users to join the system.

Bottleneck Flow Control

The problem of optimally choosing message rates for users of a store-and-forward network is analyzed. Multiple users sharing the links of the network each attempt to adjust their message rates to achieve an ideal network operating point or an "ideal tradeoff point between high throughput and low delay." Each user has a fixed path or virtual circuit. In this environment, a basic definition of "ideal delay-throughput tradeoff" is given and motivated. This definition concentrates on a fair allocation of network resources at network bottlenecks. This "ideal policy" is implemented via a decentralized algorithm that achieves the unique set of optimal throughputs. All sharers constrained by the same bottleneck are treated fairly by being assigned equal throughputs. A generalized definition of ideal tradeoff is then introduced to provide more flexibility in the choice of message rates. With this definition, the network may accommodate users with different types of message traffic. A transformation technique reduces the problem of optimizing this performance measure to the problem of optimizing the basic measure.

Satellite Packet Communication--Multiple Access Protocols and Performance

Satellite communication systems have traditionally been designed for voice traffic. Multiple access protocols for conflict resolution have typically been channel-oriented with either fixed or demand assignment. Data communications, however, have much more diverse traffic characteristics and transmission requirements than voice communications. We present in this paper an overview of two major categories of packet-oriented multiple access protocols: contention and reservation protocols. A traffic model suitable for the data communications environment is first introduced. A key element in this model is user-specified message delay constraints. Our primary performance measure of a protocol is the channel throughput versus average message delay tradeoff characteristic. The main attributes of the two categories of packet-oriented protocols are discussed. Four specific contention protocols are described and their performance characteristics are examined. Design considerations of the two important components of reservation protocols, reservation channel and distributed global queue, are discussed. Three reservation protocols with distributed control are described. Finally the performance of channel-oriented protocols and the two classes of packet-oriented protocols are compared using a variety of traffic models.

Some Limit Theorems for Large Deviations

Some Limit Theorems for Large Deviations