Handout 2 - Network Topologies

Network Topologies

In terms of network implementation, a network topology is the physical layout of the network – how its cabling is mapped out. There are three ways a network can be physically laid out: as a bus, a star or a ring.

Bus Topology

In this arrangement, there is a main transmission line (usually coaxial cable), to which each computing device is connected. Data that is to be sent from one computing device to another is broadcast on the line, and each device listens to see if the data was sent to them.

The advantages of this topology are that it is cheap, easy to set up, does not require any hubs, and uses a relatively small amount of cable. However, there is a maximum distance that the cable can run and a maximum number of drop offs. In addition, if there is a networking error, the entire length of cable has to be searched for errors.

Star Topology

In this arrangement, all the computing devices are connected to a central device called a hub, via category 5 UTP cable. This topology adopts a strategy similar to the bus topology - data that is to be sent from one computing device to another is broadcast – it is transmitted to the hub and from there it is broadcast to all other connected devices, and each device listens to see if the data was sent to them.

Because each device that is part of this arrangement is connected to a central hub, adding and removing devices is simple and does not affect the rest of the network. One potential disadvantage, however, is the hub: it is expensive, and if it fails, the entire network goes down.

Ring Topology

In this arrangement, the computing devices are connected in a physical circle or physically closed loop. In order for data to be sent across the network, the device wishing to send data must posses a token (a special data packet), and after it has completed sending data it passes the token to the next device in the loop so that it can then send data.

The main drawback with this type of network is that if one device fails the network will not function. In reality, this type of network is implemented physically as a star topology using a MAU – Multi-station Access Unit, but functions logically as a ring.

Further Reading

Chapter 1 (pp. 47 – 62) of the course text.