Chapter 5: Sizing Communications Equipment and Line Facilities


Overview

Of the many problems associated with the acquisition of data communications networking devices, including LAN access controllers, multiplexers, and concentrators , 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 and, in may instances, is directly related to the number of dial-in lines connected to the device.

The appropriate sizing of local area network (LAN) access controllers is an important consideration for a large number of organizations. Because LAN access controllers can be used by Internet service providers (ISPs) as a mechanism to provide dial access to the Internet, they represent one of the most commonly employed data communications devices used by ISPs. Because it also enables government agencies, academia, and private organizations to provide dial-in access to their LANs, the LAN access controller also represents a popular communications product used by non-service providers. Although the term "LAN access controller" is commonly used by hardware manufacturers to denote a specialized product for enabling dial network users to access a LAN, another equivalent device that requires sizing is a "remote access server." Concerning the latter, remote access server support is included in the popular Windows NT and Windows 2000 operating systems as "remote access services" (RAS). If you install RAS on a Windows NT or Windows 2000 server to enable employees or customers to access your server or LAN, you can use the information in this chapter to determine the number of dial-in modems and access lines to connect to your server.

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 obviously will result in a loss of user productivity. If 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 customers to a competitor. This is similar to the situation where a long queue in front of a bank teller can result in the loss of customer accounts if the unacceptable level of service persists.

This chapter focuses attention on the application of telephone traffic formulas to the sizing of data communications equipment and line facilities. Although most telephone traffic formulas were developed during the 1920s, many are applicable to such common problems as determining the number of dial-in business and WATS lines required to service remote PC users, as well as the number of ports or channels that should be installed in communications equipment connected to the dial-in lines. To obtain an appreciation for the sizing process, we first examine several methods that can be used to size equipment and line facilities. This is followed by a detailed examination of the application of telephone traffic sizing formulas to data communications. More formally referred to as traffic dimensioning formulas, in this chapter we examine the application of the erlang B, erlang C, and Poisson formulas to data communications equipment and facility sizing problems.




Enhancing LAN Performance
Enhancing LAN Performance
ISBN: 0849319420
EAN: 2147483647
Year: 2003
Pages: 111
Authors: Gilbert Held

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net