Star Topology

In a Star Topology each computer is directly connected to the centralized Hub or a Switch. In this way, when computer A sends a data packet for computer B, the data flows through the Hub or Switch to which both computer A and B are connected. Different types of cables can be used in this scenario like coaxial cable, fibre optic cable and twisted pair cable.

The star topology reduces the chance of network failure by connecting all of the systems to a central node. When applied to a bus-based network, this central hub rebroadcasts all transmissions received from any peripheral node to all peripheral nodes on the network, sometimes including the originating node. All peripheral nodes may thus communicate with all others by transmitting to, and receiving from, the central node only. The failure of a transmission line linking any peripheral node to the central node will result in the isolation of that peripheral node from all others, but the rest of the systems will be unaffected.

If the star central node is passive, the originating node must be able to tolerate the reception of an echo of its own transmission, delayed by the two-way transmission time (i.e. to and from the central node) plus any delay generated in the central node. An active star network has an active central node that usually has the means to prevent echo-related problems.

A tree topology can be viewed as a collection of star networks arranged in a hierarchy. This tree has individual peripheral nodes (i.e. leaves) which are required to transmit to and receive from one other node only and are not required to act as repeaters or regenerators. Unlike the star network, the function of the central node may be distributed. As in the conventional star network, individual nodes may thus still be isolated from the network by a single-point failure of a transmission path to the node. If a link connecting a leaf fails, that leaf is isolated; if a connection to a non-leaf node fails, an entire section of the network becomes isolated from the rest.

In order to alleviate the amount of network traffic that comes from broadcasting everything everywhere, more advanced central nodes were developed that would keep track of the identities of different systems connected to the network. These network switches will “learn” the layout of the network by first broadcasting data packets everywhere, then observing where response packets come from.

Comparing Star networks to other types of network

Advantages

1. Easy to implement and extend, even in large networks
2. Well suited for temporary networks (quick setup)
3. The failure of a non-central node will not have major effects on the functionality of the network

Disadvantages

1. Limited cable length and number of stations
2. Maintenance costs may be higher in the long run
3. Failure of the central node can disable the entire network