Data Communications Networking Devices - 4th Ed.pdf

Data Communications Networking Devices: Operation, Utilization and LAN and WAN Internetworking, Fourth EditionGilbert HeldCopyright # 2001 John Wiley & Sons LtdISBNs: 0-471-97515-X (Paper); 0-470-84182-6 (Electronic)APPENDIX ASIZING DATACOMMUNICATIONSNETWORK DEVICESA.1 DEVICE SIZINGOf many problems associated with the acquisition of data communications networkdevices, one item often requiring resolution is the con®guration or sizing of thedevice. The process of ensuring that the con®guration of the selected device willprovide a desired level of service is the foundation upon which the availability levelof a network is built.The failure to provide a level of access acceptable to network users can result in amultitude of problems. First, a user encountering a busy signal might becomediscouraged, take a break or do something other than redial a telephone number ofa network access port. Such action will obviously result in a loss of userproductivity. If the network usage is in response to customer inquiries, a failureto certify a customer purchase, return, reservation or other action in a timelymanner could result in the loss of that customer to a competitor. With a littleimagination, it becomes easy to visualize that the lifeline of the modern organizationis its data communications network. An unacceptable level of access to the networkcan be considered akin to a blockage in the human circulatory system-harm willresult and additional analysis and testing may become necessary to alleviate theproblem.In this appendix we will examine the sizing process, including the application ofErlang and Poisson formulae. Readers are referred to the book Practical NetworkDesign written by this author and published by John Wiley & Sons for detailedinformation concerning network design techniques, including the equipment sizingprocess. This book contains a large number of tables that can be used to simplify thenetwork sizing process, of which extracts of those tables are contained in thisappendix. Readers may also wish to consider the convenience diskette set whichsupplements the previously mentioned book. This diskette set contains a series ofprograms which can be used to automate various network design problems.