In networks covering large geographic expanses and even in cases of certain local networks, there may be a variation of the time of day of the BH or in a certain direction of traffic flow. It should be pointed out that the busy hour is tied up with a country's culture. Countries have different working habits and standard business hours vary. In Mexico, for
11 SPC stands for stored program control. This simply means a switch that is computer-controlled. SPC switches started appearing in 1975.
12ISDN stands for Integrated Services Digital Network(s). This is discussed in Section 12.4.
Figure 1.10 The backbone of a hierarchical network. The backbone traces the final route.
instance, the BH is more skewed toward noon because Mexicans eat lunch later than do people in the United States.
In the United States, business traffic peaks during several hours before and several hours after the noon lunch period on weekdays, and social calls peak in early evening. Traffic flow tends to be from suburban living areas to an urban center in the morning, and the reverse occurs in the evening.
In national networks covering several time zones where the difference in local time may be appreciable, long-distance traffic tends to be concentrated in a few hours common to BH peaks at both ends. In such cases it is possible to direct traffic so that peaks of traffic in one area (time zone) fall into valleys of traffic of another area. This is called taking advantage of the noncoincident busy hour. The network design can be made more optimal if configured to take advantage of these phenomena, particularly in the design of direct routes and overflow routes.
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