Frame Relay Topologies

One of the first items you need to consider when designing a Frame Relay network, or any type of regional WAN, is how the connectivity will be laid out. When you are considering your Frame Relay for your choice in WAN mediums, you can choose from three basic design approaches:

• Star topology A topology in which endpoints on a network are connected to a common central switch by point-to-point links. The star topology's advantages include simplified management and minimized tariff costs. Unfortunately, its disadvantages are considerable. For example, the core router represents a single point of failure and limits overall performance for access to your backbone resources, because each end device arrives through a single physical connection. Another disadvantage is that a star topology is not scalable.

• Full-mesh topology A topology in which devices are organized in a mesh, with each network node having either a physical circuit or a virtual circuit connecting it to every other network node. The full-mesh topology offers some advantages over the star topology, such as a high level of redundancy and support for all network protocols. One disadvantage is the large number of virtual circuits required (one for every connection between routers), resulting in higher costs. Other disadvantages are replication of a large number of packets/broadcasts and the problems associated with it, and the complexity of configuration resulting from multicast capabilities in nonbroadcast environments.

• Partial-mesh topology A topology in which devices are organized in a mesh. Some network nodes are organized in a full mesh, but others are connected to only one or two other nodes in a network. When you combine the full-mesh topology with the star topology, you can enjoy the advantages offered by both topologies for your network environment, including improved fault tolerance, without sacrificing performance and management problems. Several forms of partial-mesh topologies exist. They are considered to provide the best balance for regional topologies in terms of the number of virtual circuits, redundancy, and performance.

As you can see, each of these topologies has its advantages and disadvantages. You should consider these in your overall network design.