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A bus network topology is a network architecture in which a set of clients are connected via a shared communications line, called a bus. There are several common instances of the bus architecture, including one in the motherboard of most computers, and those in some versions of Ethernet networks. Bus networks are the simplest way to connect multiple clients, but often have problems when two clients want to transmit at the same time on the same bus

A true bus network is passive Ð'- the computers on the bus simply listen for a signal; they are not responsible for moving the signal along. However, many active architectures can also be described as a "bus", as they provide the same logical functions as a passive bus; for example, switched Ethernet can still be regarded as a logical bus network, if not a physical one. Indeed, the hardware may be abstracted away completely in the case of a software bus.

The bus topology makes the addition of new devices straightforward. The term used to describe clients is station or workstation in this type of network. Bus network topology uses a broadcast channel which means that all attached stations can hear every transmission and all stations have equal priority in using the network to transmit data.( http://en.wikipedia.org/wiki/Network) The advantages of bus topology are

* Easy to implement and extend

* Requires less cable length than a star topology

* Well suited for temporary or small networks not requiring high speeds(quick setup)

* Cheaper than other topologies

Some of the Disadvantages

* Limited cable length and number of stations.

* If there is a problem with the cable, the entire network goes down.

* Maintenance costs may be higher in the long run.

* Performance degrades as additional computers are added or on heavy traffic.

* Proper termination is required (loop must be in closed path).

* Significant Capacitive Load (each bus transaction must be able to stretch to most distant link).

* It works best with limited number of nodes.

* It is slower than the other topologies

Star networks are one of the most common computer network topologies. A star network consists of one central switch, hub or computer, which acts as a conduit to transmit messages. 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 plus any delay generated in the 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. The Advantages of these networks are

* Performance: Data packets do not travel through any unnecessary nodes. Communication between any two devices on the network involves at most three devices and two links. The isolation of traffic between nodes means that heavy utilization from one device is invisible to other devices on the network, provided that the central hub retains adequate capacity.

* Isolation: Each device is isolated on its own link. This makes it easy to isolate individual devices from the network by disconnecting them from the hub. Any non-centralized failure will have very little effect on the network.

* Centralization: The network can easily be scaled or expanded by adding to the capacity of the hub node, or by adding additional devices to the star. The fact that all traffic passes through the central hub means that the hub can easily be used to inspect or control traffic through the network.

* Simplicity: The topology is easy to understand, establish, and navigate. Complex routing or message

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