Performance by Design: Computer Capacity Planning by Example

Chapter 14. Queuing Models with Load Dependent Devices

Introduction

Load-dependent devices (LD) are used to model service centers where the service rate varies with the number of customers present in its queue. Examples of servers with variable service times, depending on the current load, abound in modern computer-based systems. For example, multimedia traffic uses variable grades of service to control congestion. In congestion control mechanisms for continuous bit rate (CBR) traffic in broadband networks, bit dropping methods are used to discard certain portion of the traffic, such as the least significant bits, in order to reduce the transmission time (i.e., the service time) [11]. Thus, when a system has a large number of requests queued, new ...