The network topology is the arrangement or relationship of the network devices, including its nodes and connecting lines. The network really has two shapes or two types of topology; one is physical and the other is logical.
The physical topology
The physical topology of a network is the actual physical and geometric layout of the network that we can see such as devices like routers, switches, and wireless access points, nodes and cables. There are several common physical topologies like point-to-point, ring, bus, star and mesh topologies.
The logical topology
A logical topology is how devices appear connected to the user. This topology defines the way a network transfers frames from one node to the next. This topology consists of virtual links between the nodes of a network. These logical paths are defined by data link layer protocols. The data link layer deals the logical topology of a network when controlling data access to the media. It is the logical topology that influences the type of network framing and media access control used.
Common Physical WAN Topologies
WAN’s are generally interconnected using the following physical topologies:
Only two devices are involved in a point-to-point connection, with one wire (or air, in the case of wireless) sitting between them.This is the simplest topology in networking. For this reason, this is a very popular WAN topology. Figure 3.18 illustrated the physical point-to-point topology.
Hub and Spoke
A hub and spoke network is a traditional and widely used topology for all types of networks. It’s also called the star topology. In this topology, a central site interconnects branch sites using point-to-point links. The Central site is called a hub and branch site is called spokes. Communication between two spokes always travels through the hub. Figure 3.19 illustrated the physical hub and spoke topology.
A mesh network is a network topology in which each node relays data for the network so this topology provides high availability but requires that every end system is interconnected to every other system. Therefore the administrative and physical costs can be very high. Each link is essentially a point-to-point link to the other node. Variations of this topology include a partial mesh where some but not all of the end devices are interconnected. 3.20 illustrated the physical mesh topology.