Computer networks and topologies - OCRStar and mesh networks

Any device connected to a network is referred to as a node. All nodes are connected to the network either by wire or wirelessly.

A network's topology is the arrangement, or pattern, in which all nodes on a network are connected together. There are several common topologies that are in use, but today the most common topologies are:

• star topologies
• mesh topologies

Star topologies are used in many networks, large and small.

In a star topology all nodes indirectly connect to each other through one or more switches. The switch acts as a central point through which all communications are passed.

Large networks using a star topology are usually controlled by one or more servers. Hence, the client-server model usually uses a star topology. However, peer-to-peer networks can also have a star topology. Even though no single computer controls the network, all communications still pass through the central switch.

Advantages and disadvantages of using a star topology

Having nodes arranged in a star topology brings some benefits:

• each node is separately connected, therefore a failure of one node or its link, (transmission media), does not affect any other nodes
• new nodes can be added to the network simply by connecting them to the switch
• star networks tend to have higher performance as a message is passed on to its intended recipient only

However, star topologies also have their disadvantages:

• the whole network fails if the switch fails as no node can communicate
• a wired star topology requires plenty of cable - in a large network this can be expensive

Star topologies in use

Star topologies tend to be found in large organisations, such as educational establishments and businesses, where high performance is a must.

They are also found in home networks, especially those that are wireless. In this case, a router with a wireless access point (WAP) provides the central connection for all nodes.

Mesh networks

In a mesh topology there is no central connection point. Instead, each node is connected to at least one other node and usually to more than one. Each node is capable of sending messages to and receiving messages from other nodes. The nodes act as relays, passing on a message towards its final destination.

There are two types of mesh topology:

• full mesh topology
• partial mesh topology

Mesh networks are becoming increasingly popular due to their efficiency.

With a full mesh, each node is directly connected to every other node. This enables a message to be sent along many individual routes.

With a partial mesh, not all nodes are connected directly to each other. A partial mesh therefore has fewer routes for a message to travel along than a full mesh but is simpler to implement.

Wired mesh networks tend to be uncommon, mainly because connecting all nodes to all other nodes is expensive and impractical. However, wireless mesh networks are increasingly being used since it is far simpler and cheaper to connect using radio signals.

Advantages and disadvantages of using a mesh topology

Having nodes arranged in a mesh topology brings some benefits:

• messages can be received more quickly if the route to the intended recipient is short
• messages should always get through as they have many possible routes on which to travel
• multiple connections mean (in theory) that no node should be isolated
• multiple connections mean each node can transmit to and receive from more than one node at the same time
• new nodes can be added without interruption or interfering with other nodes

However, mesh topologies also have their disadvantages:

• full mesh networks can be impractical to set up because of the high number of connections needed
• many connections require a lot of maintenance

Mesh topologies in use

Mesh topologies are used where the reliability of network communication is very important:

• military organisations often use mesh topologies to avoid breakdowns in communication
• cities are increasingly using wireless mesh networks to help monitor traffic flow, sewage treatment and to help control street lighting
• emergency services, such as police and fire services, also use wireless mesh networks to ensure that communication is reliable
• some utility companies who provide gas and electric use mesh networks to allow smart meters to send readings automatically