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Star and mesh network topologies

Introduction
Stand-alone computers can be connected up in different ways to create a network of computers. The way that you connect them up is known as the network 'topology'. The three most common topologies are known as the 'star network', the 'bus network' and the 'ring network'. The OCR GCSE Computing specification asks that you know only about the star and mesh topologies. 

Star network topology
In a star network, all the computers are connected directly to a switch, which is then attached to the file server. You would also connect other pieces of equipment to the switch. For example, if you wanted to use a printer, you would attach a print server to the switch and then a printer to the print server. If you wanted to connect the network to other networks such as the Internet, you would attach a router to the switch. The switch has lots of sockets which allow you to connect many different workstations (otherwise known as 'computers' or clients' or PCs'). It can make many communications links with the server at the same time.

Star

Advantages of a star network

    • Star networks are reliable. Because each client has its own cable to the file server via the switch, if the cable to any particular client has a problem, the rest of the network isn't affected. 
    • Security is very good on a star network. This is because all the security software is on the server, and each client must go via the server to get to any other client.
    • When a client sends a file or any data across the network, it is first split up into 'packets' of data. A packet is an equal-sized block of data. These packets are then put on the cable and sent to their destination. Because a lot of packets of data are moving around the network, they can collide with each other. This is called a 'data collision'. Because each client has its own cable to the server via the switch in a star network, very few data collisions occur.

Disadvantages of a star network

    • Every client needs its own cable. Cables cost money so this type of layout can be expensive.
    • At the centre of every star network is a switch and file server. If either of these key pieces of hardware fails, the entire network becomes unusable.
    • In addition to the central switch and file server, additional switches may be necessary in different places using a star network. This means more cost.
    • Star networks require technical expertise to set it up. This is an additional cost factor.

Mesh network topology
In a mesh network, each client is connected to many other clients and sometimes, all of the other clients. Each client sends and receives its own data, but in addition, forwards on the data from other clients.

Mesh

Advantages of a mesh network

    • A mesh network is very reliable. Packets of data can be sent using different routes if a cable or client on one route has malfunctioned.
    • If any particular client stops working for any reason, the network can still continue using the other clients.

Disadvantage of a mesh network

    • A lot of cable is used in a mesh network and not all of them will be needed at all times. Although this is a very robust and reliable network, that comes at a cost.
    • The cabling in this kind of network is complex and therefore the maintenance costs are high.

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