UBC Theses and Dissertations
Evaluating real-time scheduling techniques for multimedia services over ATM Lam, Raymond Siu-Lun
In an ATM network, a single link may carry traffic for thousands of connections with different parameters and quality-of-service requirements. High-speed links, coupled with small cell size, require efficient schedulers that can handle cell arrivals and departures quickly. The design goals for bandwidth schedulers in ATM switches are presented, one crucial goal is the ability to guarantee service bandwidth to individual queues. Basically, scheduling algorithms can be divided into rate-based and schedule-based. Rate-based methods use a predefined set of allowable rates to allocate bandwidth to a connection, while schedule-based methods analyze the potential interactions between packets of different connections, and determine if there is any possibility of a deadline being missed. This thesis investigates the performances of various types of scheduling algorithms. In addition, we implement and simulate a rate-based algorithm called Self-Clocked Fair Queuing. We also investigate the feasibility of implementing such an algorithm. To determine the performance, we mainly look at two parameters: delay bound and jitter-delay bound. Several cases of traffic patterns are used in the simulations. Through the simulations, a bandwidth-coupling problem of SCFQ is identified. This bandwidth-coupling problem in SCFQ occurs because low bandwidth connections suffer a long delay and jitter-delay. To solve this, we propose a SCFQ hybrid algorithm called JEDD-SCFQ. Not only does this algorithm handles low-bandwidth connection fairly, it also provides nominal delay guarantees to all other connections.
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