Question

Determine the number of crosspoints and the total memory bits required for tst swutch defined a follows. number of lines is 32, single stage space switch, number of channels per frame is 30 and the time expansion is 2.

Answer 1

Of the three basic elements in a communications network (terminals, transmisrion *l-dia, and switches), switches are the most invisible to the users yet represent the mostimpoftant elements in terms of available service offerings. As mentioned in Chapterl, a major r.nilestone was established in 1965 when stored-program control switchingwas first introduced into the U.S. public telephone network. Stored-program controlprovides the means for implementing many innovative user services and for greatlysimplifying switch adminishation and maintenance.The use of computers to control the switching functions of a central office led tothe designation "electronic" switching [e.g., electronic switching sy$tem (ESS) orelectronic automatic exchange (EAX)]. However, the switching matrices of thesefirst-generation electronic switches are actually electromechanical in nature. The firstuse of electronic switching matrices o.cqrned in France in 1971, when digital switch-ing was applied to an end office envfriinment. Ironically, these first digital switchesdid not use stored-program control. Digital electronic switching matrices were first in-troduced into the U.S. public network in 1976 with AT&T's No. a EsS-digital tollswitch.In the late 1970s digital class 5 switches began to be installed in the United States,mo$tly in smaller end,offices as replacements for step-by-step switches. At that timemost major_ mettoi_oJif4n switching offices already had stored-program control fromNo. I ESS or No. I EAX machines. Because the digital toll and end office switchingmachines were initially installed in predominantly analog transmission environments,their digital matrix provided no direct benefit to network customers. The motivationfor the digital machines wa$ reduced costs for the operating companies: lower main--tenance, reduced floor space, simplified expansion, and lower manufabturing coststu.By the mid-1980s the interoffice hansmission environment had changed to be al-most exclusively digital. Thus analog-to-digital conversion costs moved from beingassociated with digital transmission links to being associated with analog switches,thereby further sealing the fate of analog toll or tandem switching technology. At thistime frame, end office ffansmission environments also began tJqe swing to a digital en-vironment. Interoffice trunks were already digital, digital loop barrier systems .