Network Configuration and Network Topologies

Network Configuration and Network TopologiesThere are a variety of Network Configurations. It could be single user versus multi-user; client-server; peer-to-peer; centralised; or distributed.

Single User Versus Multi-user

Single user systems are networks in which workstations designed for use by one individual. Thus another person is not free to just long on to another machine using their username and password. This might be preferable in networks where security is a primary consideration. However if a users machine goes down, it might be some time before that user is able to do any useful work. Multi-user systems may be networks where more that one users share a workstation or are able to share a workstation. They might have a shared username and password. It may also be that they all have their own username and password but are able to use them at almost any work station as the need arises. So even though each user might have their own workstation, this might be necessary when users tend to move around the organization.Client-Server

This could be used in a database server, serving multiple workstations. Using a client/server model reduces the amount of network traffic; provides faster response times; gives greater data security; and reduces costs because the workstation does not need to be as powerful. One or more computers act as server(s) to the other computers on the network.Peer-to-Peer

When a small number of computers need to be connected and security is not an issue, then peer-to-peer is an appropriate configuration to use. It simply attaches the computers to a LAN and makes the facilities of each computer available to any other computer on the LAN. This is a cheap and simple way to allow different computers to share resources such as printers and files. Each computer stores files on its own storage device. Each computer has both network operating system and application software.Centralised

Distributed

Distributed systems allow one to organize computer systems together, that hold data at various locations and combine them together to produce useful information. In this manner systems can use the combined power of several computers to produce the results. The most common protocol or distributed systems is a client/server protocol. Basically the client computer requests a service from a server. The server processes the results and returns the results. On one network there might be several servers.There are many network topologies to choose from; in fact a network may consist of a combination of different segments. It could use bus; star; ring; hybrid; Carrier Sense Multiple Access (CSMA) or Fiber Distributed Data Interface (FDDI).Bus

A bus network uses a common cable to connect all the computers. The advantages are that: it is a very cheap means of networking as it uses the minimum of cable; and it is easy to add or remove computers. It is cheaper to implement than a star network because there is often less cable required. These however can never be totally secure as data from one workstation must pass many others. This should not be a problem under normal circumstances; however it is quite possible for hackers to illegally interrogate the packets of data as they go by. It is much harder to hack a star network. Disadvantages are if the main cable fails, the network goes down; it can take time to isolate faults; and the network degrades dramatically when highly loaded. This is because everybody is sharing the same communication link unless the bandwidth is high. This may be further aided by compression techniques.Carrier Sense Multiple Access (CSMA)CSMA will normally use a bus architecture, the best known of which is Ethernet. With this type of network all computers must sense the carrier (bus) at all times. When a computer wishes to transmit it does so immediately as long as it does not detect any data on the bus. If there is data being transmitted then the computer has to try again later. Sometimes two or more computers will start transmitting at the same time. If this happens then a collision occurs. Collisions will be detected by the computers that are transmitting and they will have to stop transmitting and try again later. If the network is heavily loaded then there will be many collisions and performance will deteriorate.Star NetworksA star network will have a computer in the centre of the star running an operating system that controls the network. This computer will go to each workstation in turn to discover whether it has any data to be transmitted. This process is known as polling. All other computers connect to it. If you have a high speed computer controlling the central node then very fast communication with all machines is possible. Some advantages of using the star network are if one cable fails it affects only one computer; it is simple to isolate faults; it is easy to add or remove computers; different computers can transmit at different speeds; it is more secure as messages are sent directly to the central computer and is not seen by the other computers. One disadvantage is that it uses a lot of cable so is expensive to install.Token Ring

In a ring network messages are passed around the ring in one direction only. In a token ring one of the computers generate a token and sends it around the ring. This protocol states that computers cannot transmit unless they receive a free token (a token that does not have any data on it). When a free token is received the computer attaches the data and sends it around the ring. This protocol also require that the receiving computer return an acknowledgement to state that the data has been received. When the sender receives the acknowledgment then it must pass on a free token. This is less secure as data intended for one recipient must pass through other machines to get to its destination. Since there are no collisions this form of LAN allows high-speed transmission. Collisions do not occur and so it is possible to calculate the maximum time that a message will take to get through. Also very high transmission rates are possible. Two disadvantages are that if the cable fails then the whole network goes down. If any one computer fails it can bring down the entire network.Hybrid

Local area networks may consist of a combination of the above topologies. So it is possible to have a bus backbone with star networks attached to it. Fiber Distributed Data Interface (FDDI)

These types of network use fibre optic cables. There were limitations in their use as not many NIC were equipped to accept data at the high rate capable by a fibre optic cable. They are similar to the ring network described earlier, however the work on a more complex dual-ring system. Another type of network is a mesh network. It is common for long distance networks. The mesh network may be fully interconnected or partially. For links between cities, between military systems and other systems where high reliability is needed, fully connected networks are used because there is a great deal of redundancy built in.