You should have a complete and up-to-date map of your network on hand that you can use to find the worst-case path between two DTEs. However, if your system is not well documented then you will have to investigate and map the network yourself. You need to find out what kinds of segments are in use, how long they are, the location of all repeaters, and how the system is laid out. Once you have this information, then you can determine what the maximum path is and what kinds of segments are used in the maximum path.

Once you've found your worst-case path(s), then the next thing you do is make a model of your path using the network model in Figure 7.4. You do this by assigning the segment at one end of your worst-case path to be a left end segment, which leaves a right end segment and possibly one or more middle segments. To help do this, you can draw a sketch of your worst-case path, noting the segment types and lengths. Then simply assign one of the end segments to be the left end, which leaves you with a right end segment. All other segments in the path become middle segments.