Data Communications Networking Devices - 4th Ed.pdf

842 _____________________________________________ MULTIDROP LINE ROUTING ANALYSISoutbound until the ®rst character is received, or a total of 4.1 s. Thus, the averageterminal response time would be 4.1 ‡ 4.875)/2 or approximately 4.5 s.Front-end processing limitationsA second limitation concerning the use of multidrop circuits is the capability of thefront-end processor. In a large network that contains numerous terminal locations,the polling addressing capability of the front-end processor will limit the number ofdrops that can be serviced. Even if the processor could handle an in®nite number ofdrops, polling delay times as well as the effect of a line segment impairmentbreaking access to many drops usually precludes most circuits to a maximum of 16or 32 drops.Large networkdesignWhen the number of drops in a network requires the use of multiple multidropcircuits, the network designer will normally consider the use of a more complexalgorithm, such as the well known Esau and Williams formula. While suchalgorithms are best applied to network design problems by the use of computerprograms, the reader can consider a practical alternative to these complexalgorithms. This alternative is the subdivision of the network's terminal locationsinto servicing areas, based upon de®ning a servicing area to include a number ofterminals that will permit an average response time that is acceptable to the enduser.Then each segment can be analyzed using the minimum-spanning-treealgorithm to develop a minimum cost multidrop line to service all terminals withinthe servicing area.