Network Factors

The shape of a network can take many different forms and these topologies can be connected by a variety of means. The differing topologies are Mesh, Bus, Ring and Star and each one will be examined and the advantages and disadvantages explored. These networks can be connected via Ethernet, Token Ring, Fiber Distributed Data Interface (FDDI) or wireless. Each of the connection methods will also be analyzed and the differences will be explained.

The term network topology refers to the physical layout of computers, cables, and other components that make up a network. The choice of one topology over another is important for the network professional and will have an impact on the type of equipment the network needs, the capabilities of the equipment, the growth of the network and the way the network is managed. The different types of topologies each require different communication methods and these will also have an influence on the network.

The first topology to be discussed is the bus topology. It consists of devices that are connected to a common shared cable. The bus topology is the simplest and most common method of networking computers with the computers set up in a straight line. The single cable that feeds all of the computers is known as the trunk (also called backbone or segment) and connects all of the network computers in a single line. The computers communicate by addressing data to a certain computer and sending out the data onto the cable via electronic signals. The signal is sent out on the bus and only the computer whose address matches the address encoded in the original accepts the information. A disadvantage of the bus topology is that only one computer can send data at a time and this limits the number of computers that can be on the network. The more computers on the bus, the more computers will be waiting to put data on the bus and slow down network performance. Another disadvantage is that if the trunk breaks or is becomes un-terminated, the network will cease to function since the signal will bounce. The advantage to a bus network is that if one computer on the bus fails, it will not affect the others on the bus.

A star topology has cable pieces from each computer connected to a central hub. The signals are transmitted from the sending computer through the hub to call computers on the network. The advantage of the star topology is centralized resources and management. A disadvantage of this type of network is that since each computer is connected to a central point, a large amount of cable is needed and if the central point fails, the entire network goes down. An advantage is that if one computer or its cable on the network fails, the rest of the network continues to operate.

The ring topology connects the computers on a single circle of cable. The signals travel around the loop in one direction and pass through each computer. This has the advantage that each computer can act as a repeater and boost the signal strength before sending the signal on. One method of passing information on the ring is known as token passing. "A token is a special series of bits that travels around a token-ring network. Each network has only one token" http://distancelearning.ksi.edu/demo/370/ch01d.htm

The token is passed from computer to computer until it gets to a computer that wants to send data. The computer that needs to send data modifies the token, puts an electronic address on the data and sends it onto the ring. The data is passed from computer to computer until it finds the one with the matching address. The receiving computer sends a message back out informing the sender that the data has been received. Once the sender verifies the receipt, it develops a new token and sends it out onto the ring.

In a mesh topology, each computer is connected to every other computer by a separate cable. This provides the redundancy and reliability not seen in the others. If one cable fails, another one can take over and pass the traffic. This has the advantage of ease of troubleshooting and increased network availability. The disadvantage is they are expensive to install because of the amount