The term topology refers to the layout of the connected devices used in a network. It may also refer to the shape or structure of the network through the physical arrangement of the devices that may not correspond to the name or functionality of a particular topology. Network topologies are categorized into the following basic types namely bus, ring, and star topologies (Todd L, 2003).
In a bus topology, devices are connected linearly in a single cable, which acts as the backbone. This single cable acts as the shared communication medium (backbone) for all the devices attached to this cable using an interface connector. In this topology, a device wanting to communicate with other devices in the same network sends a message to the backbone cable, which all the devices see, but it’s only the intended recipient that gets to accept and process the message (Todd L, 2003).
Bus topology often has problems when two devices want to transmit at the same time on the same bus hence. As a result, bus networks systems have some scheme of collision handling or avoidance for communication. This collision avoidance can be either carrier sense multiple access or a bus master which controls access to the shared bus resource (Starlings, W, 2000).
This topology has several advantages including low cost as less cabling is required and it is easy to implement or install. However, it also has some disadvantages namely it limits the cable length and workstation numbers, a cable fault affects all other stations and as the number of workstations increases, the speed of the network slows down. Moreover, if the backbone cable fails, the entire network breaks down (Melissa C, 2003).
In-ring topology, each device is connected with or paired with two adjacent neighbors for communication purposes. Any message sent travels through a ring in the same direction either in a clockwise or anticlockwise manner. A signal is passed through each network card of each device and passed on to the next device. All devices have a cable home running back to the multi-access units (MAU). A message is relayed from one device to another and only the intended device accepts and processes the message (Todd L, 2003).
The main advantages of ring topology are that any cable failure affects only limited users, all users have equal access and each workstation has full access speed to the ring. However, this topology has some demerits for example a failure in any cable or device breaks the loop and can break down the entire network. In addition, it has costly wiring, difficult connections, and expensive adapter cards (Starlings, W, 2000).
Star topology has a central connection point called “hub”. This “hub” may be a hub, switch, or router. All the devices in this network connect to the hub with unshielded twisted pair (UTP) Ethernet. The main advantage of his topology is that a failure in any star network cable will only affect only one computer using that cable and not the entire LAN (Starlings, W, 2000).
In addition, it is easy to add new workstations, has a centralized network/hub monitoring. Like all other topologies, star topology has its disadvantages including any failure in the hub automatically leads to the failure of the entire network. in addition, hubs are slightly more expensive than thin Ethernet.
References
Todd Lammle (2003). CCNA Cisco certified network associate study guide. 4th edition.
Melissa Craft (2003). Faster smarter network + certification. Microsoft press. Redmond Washington.
Starlings, William (2000). Data and computer communication. 6Th Edition. Upper saddle river: NJ Practice hall.