Few people think about a computer network until it is down. A communications network consists of computer stations and server stations, as well as the hardware and software necessary to allow communication to flow throughout the network. Topology refers to the patterns in which the devices are connected. Each with it's own benefits and drawbacks, these patterns include bus, ring and star configurations.
Linear Bus Topology
Consisting of a single cable, bus topography is the most simple and common method of networking computers. Sometimes called a linear bus, computers are each linked independently to the single cable, which is often referred to as a backbone or segment. Data from the network is sent to all computers on the network, but the information is only delivered to the computer that matches the address from the original message.
Getting Around the Ring
In ring topology, computers are connected with a continuous circle of cable. Information travels in one direction, passing through every computer, so that each computer is connected directly to the computers on either side. In token passing, the token, or packet of data, travels around the ring collecting data until it reaches a computer with no information to send. At this time, the sending computer adds an address and pushes the information back around the ring until it finds the computer with the correct address. When the receiving computer sends a message back saying the data was received, the sending computer sends a new token around and the process begins again.
Active vs. Passive
In ring topology, the signals travel around the loop in one direction. Unlike the passive bus topology, the signals pass through every computer in the network giving the signal a boost while sending the data along to the next message. Because the signal passes through each computer, all the computers need to be turned on, and the failure of one computer can impact the entire network. Since computers on a bus network are not responsible for sending network data to another computer in the network, if one computer fails, the other computers are still connected to the network backbone so the data still flows. In bus topology, the speed of the network is affected by the number of computers on the network, since at any given time, only one computer can send information. This can cause a backup as other computers are waiting their turn to send data.
Pros and Cons
While bus topology is relatively inexpensive, and easy to implement and extend, there are some drawbacks. Heavy traffic can significantly slow the network and performance is effected when more computers are added. There is a limited number of stations, and a break in the main cable, or backbone, can disable the entire network. Since every computer can "see" the data, there may be issues with security. In ring topology, every device has the opportunity to transmit signals to the other devices on the network. The connections between the computers does not require a network server. While adding nodes can cause disruption, as the whole network must be shut down and rebooted, adding additional nodes has very little impact on bandwidth.
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