type of computer network tropology

type of computer network tropology

What is a Network topology

A topology – is the characteristic of a communication network that is concern both with the physical configuration of the cabling that is used to inter connect communicating system and the logical way in which system view the structure of the network. Topology is the therefore physical or logical arrangement of computers

Factors to consider when selecting a topology

1. Cost – whatever transmission medium is chosen for a Local Area Network has to be physically installed in the building, this maybe a lengthy process including the installation cables and raceways. For a Network to be cost effective one would strive to minimize installation cost. This may be achieved by using the proper hardware linking the cables, good modems, cost effective computers to reduced cost
2. Flexibility – one of the main benefit of a local Area Network is it ability to have the data processing and peripheral nodes distributed around a given area. This means that the computing power and equipment can be located close to the ultimate users. Because the arrangements of furniture, internal walls etc in the offices is often subject to change. The topology should allow for easy reconstruction of the network which involves moving existing nodes and adding new nodes
3. Reliability – The topology chosen for the network can help by allowing the location of the fault to be detected and to provide some means of isolating the faults

 

Types of Network Topologies

Network star topology also known as Radial topology

This topology consist of a central nodes to which all other nodes are connected, star topology is used in most existing information network involving data processing and voice communication. In many cases when a building is wired with a star topology, faced cables radiate out from the centre to intermediate connection point to wiring cables. This allows sufficient connection point to be provided for one sub – area, while providing flexibility in their allocation within that area

star topology

 

Advantages of star topology

• Diagnostic and isolation of problem is easy
• Easy to add a new computer system to the network
• Failure of one workstation does not affect the entire network
• Uses a single access protocols
• Provide ease of service
• Is very fast

Disadvantages of star topology

• There is central node dependency
• Becomes expensive when purchasing the nodes
• Always requires very long cable length when connecting many nodes

 

Bus Topology also known as Linear Topology

bus topology

 

It is the simplest method of networking computers. It consists of a single cable known as a trunk, backbone or segment that connects all the computers in the network. Each system is directly attached to a common communication channel. Signal that is transmitted over the channel makes up the messages.  As each message passes along the channel each system receives it, after receiving the message each system examine the destination address contained in the message, if the destination address tells a particular system that the message is addressed to it, that system accepts and process the message, if the message address tells the computer that the message is intended for another system, that computer will ignore the message

On a bus topology signals are send to all the computers in the network to keep the signal from bouncing back and forth along the cable a terminator (British Naval Connector) is placed at the end of the cable. In a bus topology only one computer can send data at a time, therefore the more computers in a bus the slower data transmission in the network

Advantages of Bus topology

• Cheap because of its simplicity
• Requires a short cable length
• Easy to expand the network
• Simple to setup compared to Star and Ring topology
• There is no chances of data collision since one computer transmit at a time
• Locating cable fault in a bus topology is relatively easy
• Bus topology is ideal for one to many data transmission
• Signal on the cable are bidirectional hence reaches all the nodes

Disadvantages of Bus topology

·         Fault diagnosis is difficult in a bus topology – detection of fault may have to be performed from any point in the network

·         Fault isolation is difficult – if fault in the node is detected  the node can simply be removed but if the fault is in network medium itself and entire segment of the Bus must be disconnected to isolate the fault

·         Repeater configuration – When a Bus type  network has its backbone intended for using a repeater, configuration maybe necessary thus may involve tailoring cable length, adjusting terminator etc

·         Computer nodes must be intelligence – each node on the network is directly connected to the central Bus. This means that each node must have method of deciding and detecting its own data

   Ring Topology

 

In Ring topology each node is connected to form a single, closed data path. Data from one node is passed along to the next node from which it will be examined, and if that node is not the intended destination, then it is transmitted to the next node until the destination is reached. Token ( a special bit pattern) is circulated in the network to enable a node to capture the data. Ring topology might be structured so that there are a number of information frames or slot in construct circulation. Node wishing to transmit first detects the arrival of an empty slot then inserts the data it wishes to send, and mark the frame as full. The receiving node takes the data and then marks the frame as empty. In implementation one particular node has the responsibility for generating the token or slot when the network is first constituted

Advantages of ring Topology

• The ability to achieve transmission rates of the order of 10 million bits per second
• Provision of local communication via a single channel
• No central server which reduces the cost of establishing the ring topology

Disadvantages

·         Failure of one node result into entire network failure

·         Detection of fault is very difficult in ring topology

·         Isolation of fault is not easy in this topology