It takes twice as much hardware and twice as many cables to
accomplish the network in Figure 15-6, as
compared to using Frame Relay. In the figure, R1 requires two serial interfaces
and two separate CSU/DSUs. Also, the telco has to install two cables between the
local CO and the office building in Atlanta where R1 resides. Likewise, R2 needs
two CSU/DSUs, and it needs two cables run to the telco; the same goes for R3.
With the three-site Frame Relay network in Figure 15-4, you only needed one cable
from each router to the telco, one serial interface, and one CSU/DSU at each
router. Even in this small network, you already need more hardware and more
cables.
Now think about what happens when the company grows to 10 sites
or 100 sites. For each point-to-point line, R1 will need a separate physical
serial interface and a separate CSU/DSU, and the telco will need to run another
4-wire cable from the Atlanta CO to Fredsco's Atlanta headquarters. That
requires a lot of extra money for router and CSU/DSU hardware on Fredsco's part,
and the telco has to run many more cables. Running those cables costs money,
and, of course, Fredsco gets to pay for that.
In short, using leased lines will end up requiring more
hardware and costing more cash up front than using Frame Relay.
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