A Wide Area Network topology refers to the arrangement or configuration of the elements of the network relative to each other. There are many different WAN topologies, but some of the most widely used are the point-to-point topology, ring topology, star topology and multi-tiered topology. Despite the similarity of the names to those of LAN topologies, these topologies are specific to WAN networks because of the great distances that often exist between nodes in a WAN.
In the point-to-point WAN topology all the network nodes are directly linked to each other. This is the simplest and least expensive WAN topology to implement. However, if a single node fails, the entire network fails. The point-to-point WAN topology is not suitable for networks with large distances between nodes; it works best in networks with as few as three nodes due to inherent problems with communication over direct links over long distances. Due to the direct links, the point-to-point topology has scalability issues.
In the ring WAN topology the network nodes are directly linked to each other, with all nodes linked to other nodes in a circular or ring-like configuration. This topology is more robust than the point-to-point topology, and is only slightly more expensive to implement. However, the ring WAN topology is vulnerable to failure, and is unsuitable for WANs covering large distances or containing many nodes due to the direct links; it also does not scale easily as the network expands.
In the star WAN topology the network nodes are all connected to a central hub rather than directly to each other. This creates a configuration in which the hub, using a concentrator router, sits at the center of the topology and the nodes radiate from it in a star-like pattern, giving the topology its name. The star WAN topology can cover large distances as nodes communicate directly with the hub rather than with each other. However, the concentrator router introduces a single point of failure and makes this topology vulnerable.
In an ideal network topology there would be direct links between all the nodes and multiple connected concentrator routers. This configuration is known as a full-mesh topology; however, it presents too many failure and scalability problems to be of practical use. The multi-tiered WAN topology combats the failure and scalability problems of the other topologies by combining direct node links with linked concentrator routers, combining the features of the star and ring topologies. The multi-tiered WAN topology is more expensive to implement than the other topologies, but is suitable for large networks covering distant geographical locations.
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