Data Communications Networking Devices: Operation, Utilization and Lan and Wan Internetworking, 4th Edition

APPENDIX A

SIZING DATA COMMUNICATIONS NETWORK DEVICES

A.1 DEVICE SIZING

Of many problems associated with the acquisition of data communications network devices, one item often requiring resolution is the configuration or sizing of the device. The process of ensuring that the configuration of the selected device will provide a desired level of service is the foundation upon which the availability level of a network is built.

The failure to provide a level of access acceptable to network users can result in a multitude of problems. First, a user encountering a busy signal might become discouraged, take a break or do something other than redial a telephone number of a network access port. Such action will obviously result in a loss of user productivity. If the network usage is in response to customer inquiries, a failure to certify a customer purchase, return, reservation or other action in a timely manner could result in the loss of that customer to a competitor. With a little imagination, it becomes easy to visualize that the lifeline of the modern organization is its data communications network. An unacceptable level of access to the network can be considered akin to a blockage in the human circulatory system-harm will result and additional analysis and testing may become necessary to alleviate the problem.

In this appendix we will examine the sizing process, including the application of Erlang and Poisson formulae. Readers are referred to the book Practical Network Design written ...