leaky_bucket - Performance Characteristics of a...

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Performance Characteristics of a Packet-Based Leaky-Bucket Algorithm for ATM Networks Toshihisa OZAWA Department of Business Administration, Komazawa University 1-23-1 Komazawa, Setagaya-ku, Tokyo 154-8525, Japan E-mail: [email protected] 1999.10.19 Abstract A packet-based leaky-bucket algorithm functions like the early packet discard (EPD), and accepts a newly arriving packet if the probability that all the cells of the packet are accepted is high. We derive some performance characteristics of the cell and packet arrival processes that are accepted by the leaky-bucket algorithm. From these analyses, a method to determine the values of the parameters of the leaky-bucket algorithm and certain relations between this leaky-bucket algorithm and the generic cell rate algorithm (GCRA) are obtained. Keywords: ATM network, packet communication network, leaky bucket, queueing model, per- formance evaluation 1 Introduction Asynchronous Transfer Mode (ATM) is one of the fundamental technologies used to construct computer communication networks. Almost all computer communications now use Internet Protocol (IP) as the network layer protocol, where user data is divided into some packets called IP datagrams. In computer communications achieved over ATM networks, such a packet is further divided into cells of 53 bytes in data length including the headers at a router or a host, which terminates ATM virtual circuits (VCs). The packet is transmitted by cell-by-cell transmission in the ATM networks. Some performance problems may arise here because of the disagreement between the transmission data unit of IP and that of ATM: the former is a packet and the latter is a cell. One solution to resolve these problems is to implement packet-based traffic control mechanisms into the ATM networks. A typical example of such a mechanism is the early packet discard (EPD) [1, 2]. When congestion occurs at an ATM switch, some cells may be dropped at the output buFer while other cells of the packets that contain the dropped cells will still be transmitted. These transmitted cells waste network resources because their packets cannot be assembled at the destination, and this may cause a decrease in packet throughput. In order to prevent this phenomenon from occurring, the EPD drops all the cells of a newly arriving packet when the queue length of the output buFer is greater than a given threshold. In this paper, we deal with a packet-based leaky-bucket algorithm, which functions like the EPD, and study its characteristics from the viewpoint of performance assuming it to be used as the mechanism of usage parameter control (UPC) in ATM networks. In the next section, we introduce a generalized packet- based leaky-bucket algorithm with cell and token buFers, and provide a certain equivalency between the cell buFer and the token buFer. This equivalency allows us to use a simple algorithm with only a cell buFer in the rest of the paper. The processes of accepted cells and packets are analyzed in Sections 3 and 4. These results give a method to determine the value of the parameters of the leaky-bucket algorithm
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This note was uploaded on 10/16/2011 for the course ELECTRICAL EE251202 taught by Professor Rejaei during the Spring '10 term at Sharif University of Technology.

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leaky_bucket - Performance Characteristics of a...

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