The network topology is the schematic 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 network 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. So, there are several common physical topologies like point-to-point, ring, bus, star, and meshThe physical topology has two different categories WAN and LAN topologies.
Common Physical WAN Topologies
WAN’s generally interconnected using the following physical topologies:
Point-to-point (PTP) topology connects two nodes directly to one another. Only two devices 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. The figure below illustrates 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 also known as a star topology. In this topology, a central site interconnects branch sites using point-to-point links. The Central site is known as hub and branch site known as spokes. Communication between two spokes always travels through the hub. The figure below illustrates the physical hub and spoke topology.
A mesh network is a network topology where 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 inter-connected. The figure below illustrates the physical mesh topology.
Physical LAN Topologies
Physical LAN topologies define how the end systems physically connected. We can connect, devices in LAN using the following physical topologies as illustrates in the figure below:
In Star topology, all end devices have connected to the central device. Early star topologies interconnected end devices using Ethernet hubs. However, star topologies now use Ethernet switches. The star topology is easy to install, very scalable (easy to add and remove end devices), and easy to troubleshoot.
All the data on the star topology passes through the central device before reaching the intended destination. Hub/Switch acts as a junction to connect different nodes present in Star Network, and at the same time, it manages and controls the whole of the network. Depending on which central device, “hub” and “Switch” can act as repeater or signal booster. Central device can also communicate with other hubs and switch of a different network.
Extended Star Topology
In an extended star topology, additional Ethernet switches interconnect other star topologies.
Bus Topology is the simplest of network topologies. All end systems (computers as well as servers) are connected to each other and terminated in some form on each end. Infrastructure devices such as switches not required to interconnect the end devices. Bus topologies using coax cables in legacy Ethernet networks because it was inexpensive and easy to set up.
In the ring topology, end systems are connected to a single circle of cable. Unlike the bus topology, the ring does not need termination. The signals travel around the loop in one direction and pass through each computer, which acts as a repeater to boost the signal and send it to the next computer. Ring topologies use in legacy Fiber Distributed Data Interface (FDDI) and networks.
The logical network topology
The logical topology is the way that the signals proceed on the network media or the way that the data passes through the network from one device to the next device without regard to the physical interconnection of the devices. In other words, it defines the way a network transfers frames from one node to the next. This topology also 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 with 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.