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7.6 A Simple Model 2 Configuration Example

Round Trip Delay

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Since there are only two segments in the worst case path, our network model for round trip delay only has a left end and a right end segment. There are no middle segments to deal with. We'll assume for the purposes of this simple example that the fiber optic MAUs are connected directly to the DTEs and repeater, which eliminates the need to add extra bit times for AUI cable length. Both segments in the worst-case path are the maximum allowable length, which means we can simply use the Max values from the round-trip delay table.

According to Table 7.1, the Max left end segment delay value for a 2 km 10BASE-FL link is 212.25 bit times. For the 2 km right end segment the Max delay value is 356.5 bit times. Add them together, plus 5 bit times margin, and the total is: 573.75 bit times. This is less than the 575 maximum bit time budget that is allowed for a 10-Mbps network, which means that the worst-case path is OK. All shorter paths will have smaller delay values, so all paths in this Ethernet system meet the requirements of the standard as far as round trip timing is concerned. Next, let's look at the interframe gap shrinkage.

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Quick Reference Guide to 10-Mbps Multi-Segment Configuration - 09 SEP 95

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