Figure 5-2 illustrates a fully meshed design, which has the most redundancy. However, this design has a few problems. As the internetwork grows, each router that is added will add to the overall traffic of the existing routers. This is especially true if the traffic has a lot of broadcasts. Also, each router needs to support the performance level needed in this design, which means that the routers need to be comparable. This design is costly both in equipment and in cost for the WAN connections.
Figure 5-3 illustrates a partially meshed topology that would be used in a Frame Relay network. This is often called redundant star configuration. It provides a fair amount of redundancy with a limited amount of meshing and without the negatives associated with fully meshed topologies.
The cost of bandwidth can be minimized by choosing the proper WAN technology, such as ISDN. The customer only pays for the use of ISDN. If the service is not used, the customer does not have to pay for access. Analog modem and Frame Relay connections have similar features, but often the customer has to pay an additional monthly fee for having access to the network. In the case of Frame Relay, the customer needs to pay a reoccurring fee for T1 or partial T1 access to the carrier's Frame Relay network.
Multiplexing or combining multiple services over the same bandwidth is a method of improving the efficiency of the bandwidth. Voice technology is a perfect example of using bandwidth more effectively. Now a point-to-point T1 between two offices can carry not only data, but also voice packets as well, using new hardware and compression technology. However, a critical component of this type of sharing of bandwidth is using Quality of Service techniques.
Figure 5-2 Fully Meshed Topology
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