Star network

Star networks are one of the most common computer network topologies. In its simplest form, a star network consists of one central switch, hub or computer, which acts as a conduit to transmit messages. Thus, the hub and leaf nodes, and the transmission lines between them, form a graph with the topology of a star. If the 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.

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.

Advantages

* Better performance: Passing of Data Packet through unnecessary nodes is prevented by this topology. At most 3 devices and 2 links are involved in any communication between any two devices which are part of this topology. This topology induces a huge overhead on the central hub, however if the central hub has adequate capacity, then very high network utilization by one device in the network does not affect the other devices in the network.
* Isolation of devices: Each device is inherently isolated by the link that connects it to the hub. This makes the isolation of the individual devices fairly straightforward, and amounts to disconnecting the device from the hub. This isolated nature also prevents any non-centralized failure to affect the network.
* Benefits from centralization: As the central hub is the bottleneck, increasing capacity of the central hub or adding additional devices to the star, can help scale the network very easily. The central nature also allows the inspection traffic through the network. This can help analyze all the traffic in the network and determine suspicious behavior.
* Simplicity: The topology is easy to understand, establish, and navigate. The simple topology obviates the need for complex routing or message passing protocols. As noted earlier, the isolation and centralization simplifies fault detection, as each link or device can be probed individually.

Disadvantages

The primary disadvantage of a star topology is the high dependence of the system on the functioning of the central hub. While the failure of an individual link only results in the isolation of a single node, the failure of the central hub renders the network inoperable, immediately isolating all nodes. The performance and scalability of the network also depend on the capabilities of the hub. Network size is limited by the number of connections that can be made to the hub, and performance for the entire network is capped by its throughput. While in theory traffic between the hub and a node is isolated from other nodes on the network, other nodes may see a performance drop if traffic to another node occupies a significant portion of the central node's processing capability or throughput. Furthermore, wiring up of the system can be very complex.

See also

*Bus network
*Ring network
*Mesh networking
*Token ring
*Token bus
*Tree and hypertree networks