1.4 Understanding and Applying Waiting Line Analysis

What is the effect on transmission between LANs when dataflow must cross a pair of remote bridges or routers? The answer to this question can be quite complex and is based on the use of waiting line analysis, which is an alternative term to the more popular expression of "queuing theory."

Chapter 4 investigates the application of waiting line analysis to network traffic that must use remote bridges, switches, or routers to reach their destination. After reviewing some of the terms associated with queuing theory, we will apply its use to answer some key questions associated with the use of remote bridges, switches, and routers. Those questions include: What is an optimum line operating rate for those devices? What is the effect of using single or multiple port devices? And what is the effect of altering the memory capacity of a bridge, switch, or router on its servicing capacity.

Commencing in Chapter 4 we begin to use a series of programs developed using Microsoft Corporation's QuickBASIC compiler and its Excel electronic spreadsheet program to facilitate performing a series of repetitive and tedious computations . The selection of QuickBASIC was based on the fact that it is very similar to Qbasic, which was included in MS-DOS version 5.0 and later versions of that operating system. In addition, readers with earlier versions of DOS can easily modify the QuickBASIC programs presented in this book to operate with the commonly available BASICA or GW-BASIC interpreters. Similarly, Excel represents the most popular electronic spreadsheet program currently in use. Through the creation of Excel templates, it becomes a relatively simple process for readers to modify such templates to tailor them to one or more specific operational requirements. Thus, most readers should be able to use the programs and templates presented in this book without additional cost.

To facilitate the use of the programs contained in this book, you can access them from the following Web site: http://www.crcpress.com/e_products/downloads/default.asp. At that Web address you will find three series of files you can download. One series of files has the extension .BAS and contains the source version of the QuickBASIC programs. If you have a QuickBASIC or QBasic compiler, you can easily modify those programs to reflect your specific networking environment and then compile and execute the modified program. With a little additional effort you can also use a BASICA or GW-BASIC interpreter to execute the programs presented in this book. For those readers who desire to execute programs without modification, a directly executable version of each program can be downloaded. Those programs have the same filename as the source language versions of programs presented in this book but have the extension .EXE. While you cannot modify those programs that are directly executable, many of those programs operate based upon a variable input, which allows you to adjust the use of those programs to your particular networking environment. A third series of programs you can download consist of Excel templates. The filename of each template is the same as that used in this book to facilitate their use.