Network Topologies Shaista Malik Network Topologies • The physical layout or the way in which the network connection are made is called topology. • It refers to the location of computer and how the cable runs between them. • It is important to select the right topology for the proper use of the computer network. 1. 2. 3. 4. 5. Bus Topology Star Topology Ring Topology Tree Topology Mesh Topology Bus Topology Computer A Terminator Computer B Cable Computer C Computer D Bus Topology • It is the simplest type of the network • Supports small numbers of computers • All the computers in network are connected to central wire known as bus. • The terminators are used at the end of a bus to absorb signal. • Collision occur if two computer transmit data at the same time. • Mostly used in peer to peer networks Working of Bus Network • The sending computer sends the data and address through the bus • The data and address move from one computer to other in network. • Each computer checks the address. • If it matches with the address of the computer the computer keeps the data otherwise the data moves towards the next computer. Advantages of Bus topology • It is simple and easy to use • It requires small length of cable to connect computer. • It is less expensive. • It is easy to extend a bus. • If one node fails it does not effect the rest of the network. Disadvantages of bus topology • It is difficult to troubleshoot • It only supports small numbers of computers • The network speed slows down as the number of computer increases. Star Topology • A star topology is designed with each node are connected directly to a central network hub. • Data on a star network passes through the hub before continuing to its destination. • The hub manages and controls all functions of the network. It also acts as a repeater for the data flow. Advantages of a Star Topology • Easy to maintain and modify • No disturbance to the network when connecting or removing devices. • Easy to detect faults and to remove parts. • Single computer failure does not bring down the whole network. • More flexible than other topologies. Disadvantages of Star Topology • Requires more cable length than a linear topology. • If the hub fails, nodes attached are disabled. • More expensive than linear bus topologies. Ring Topology • In this topology each computer connected to the next computer with last one connected to the first. • Data flows around the circle from device to device in one direction only. • It also known as token ring topology. • Data transfer rate is 4Mbps to 16 Mbps. • Recent token ring topology provide speed up to 100 Mbps. Working of Ring Topology • Every computer connected to the next computer in ring. • On a token ring network, a token governing the right to transmit is passed from one station to the next in a physical circle. • Each computer receives message from the previous computer and transmit it to the next computer. • The message flows in one direction. • The message passed to the ring until it reach its destination. Advantages of Ring topology • It is less expensive than star topology • Every computer has equal access to the network Disadvantages • Failure of one computer can effect the whole network • It is difficult to troubleshoot • Adding removing computer effects the whole network. Tree Topology • A tree topology combines characteristics of linear bus and star topologies. • It consists of groups of star configured computer connected to a linear bus backbone cable. • Tree topologies allow for the expansion of an existing network. Advantages of Tree topology • Point-to-point wiring for individual segments. • Supported by several hardware and software venders. Disadvantages of tree topology • Overall length of each segment is limited by the type of cabling used. • If the backbone line breaks, the entire segment goes down. • More difficult to configure and wire than other topologies. Mesh Topology • In mesh topology every device is physically connected to other device in the network. • A message can be sent on different path from source to destination. • Provide improved performance and reliability. • Mostly used in wide area network. Advantages • The use of dedicated link ensures that each connection carry its own load. • It eliminates the traffic problem. • If one link is unusable it does not harm the entire network. • It is easy to troubleshoot. Disadvantages • A full mesh network is very expensive. • It is difficult to install and configure. How data is transmitted across networks? • Switching Techniques are used for transmitting data across networks. • Three types of switching techniques are there. 1. Circuit Switching 2. Message Switching 3. Packet Switching Circuit Switching • Physical connection between the two computers is established and then data is transmitted from source to destination computer. • When a computer places a telephone call , the switching equipment within the telephone system seeks out a physical copper path from sender’s to receiver’s telephone. • It sets up end-to-end connection between computers before any data can be sent. Message Switching • The source computer sends the data to the switching office first which stores the data in its buffer. • It then looks for a free link to another switching office and then sends the data to this office. • Process is continued till the data is delivered to the destination computer. • It is also known as store and forward technique. Packet Switching • There is a tight upper limit on the block size. In message switching there was no upper limit. • A fixed size of packet is specified. • All the packets are stored in main memory in switching office. In message switching packets are stored on disk. • This increases the performance as access time is reduced.
