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Network Topologies Contents What is topology? Types of topology? Working of topologies Flow of data with in topologies Advantages and disadvantages What is Topology? The way devices on the network are physically connected is known as topology. or The physical layout or the way in which network connections are made is called a topology. Types of Topologies Four Types of Topology 1. 2. 3. 4. Bus Topology Star Topology Ring Topology Mesh Topology Bus Topology In bus topology, all computers or network nodes are connected to a common communication medium. This medium is a central wire called a “bus”. Working of Bus Topology If one computer wants to send the data to another computer in the network, it sends the data & destination address via the “bus”. This data & address move from one end of the network to the other. Each computer checks this address & if it matches with this computer, the computer keeps the data. Otherwise……………. the data moves to the next computer. a network setup using bus topology Data Flow Communication on the bus topology occurs in the following manner Sending the signal Signal bounce back Terminators Sending Signal Data is sent to all of the computers on the network Transmission of data is bi-directional Information is accepted only by the computer whose address matches Only one computer can send data on the cable at a time While two computers are communicating, all other computers remain in wait. Signal Bounce If the signals were allowed to continue, it would keep bouncing back and forth along the cable and stop other computers from sending signals. Backing of the signals is called bounce back. Terminators To stop the signals from bouncing, terminator is placed at each end of the cable to absorb free signals. Absorbing the signal clears the cable, so that other computers can send data. Terminators are used to avoid collisions. Bus topology uses coaxial cable as a medium. Advantages It is very simple, easy to use & reliable for very small networks It is easy to install and configure Least amount of cable is required to connect the computers so it is less expensive It is easy to extend as two cables can be joined to make a larger cable Disadvantages It can support only a small number of computers. As the number of computers increases, the network get slower. It is difficult to troubleshoot a bus. A cable break, fault in any one computer or a loose connection can breakdown the whole network. Each connector reduces the strength of the electrical signal Star Topology In star topology all the cables run from the computers to a central location, where they all are connected to a device called “HUB” Working of Star Topology If two computers want to share data , the sender computer sends the data to the hub & hub sends it to the receiving computer. Each computer communicate with each other by a central HUB. So, hub provide a central connection point for all computers across a network. Star topology uses a separate cable for each computer, that cable connects a computer to a central device i.e hub. a network setup using star topology Data Flow Multiple computers can send and receive data at the same time Each computer sends and receives data using its own cable Connectivity A specific device is used as a central component called “hub”. Advantages It is easy to modify & new computers can be added to the central hub or any computer can be removed without affecting the network. It is usually easy to troubleshoot a star network. If any computer in the star topology breaks down, the network is not affected. It is more flexible among the remaining topology. It is much fast topology. Multiple cable types supported by hubs. Disadvantages If the central hub fails, the whole network breaks down. Star network requires more communication cable than any other network. It is more expensive. Ring Topology Ring topology looks like the bus topology with connected ends. But……………… In functionality it is different. Working of Star Topology Each computer is connected to the next computer in the form of ring. Each retransmit what it receives from the previous computer. The message flow in one direction. Ring topology connects computers on a single circle of cable. There is no terminated ends Signals travel around the loop in one direction and pass through each computer. Unlike bus topology, each computer acts like a repeater to boost the signal and send it to the next computer. It is called endless topology. In ring topology, data flows in ring and in clock-wise direction. Ring topology is based on “Token Ring Mechanism”. a network setup using ring topology Token Passing…….. A token is passed around the network. The computer that has token can transmit data. Token is passed from computer to computer until it reaches to its destination. The destination device returns an acknowledgement to the sender. The token is then given to another device, giving it ability to transmit. The sending computer modified the token, puts address with the data and sends it around the ring. Data passed by each computer until it finds the computer with an address that matches. Token is used as a carrier. It is called token grab. Advantages All computers on the ring have equal access to the network. It performs well under a heavy load. Disadvantages Failure of one computer can affect the whole network. It is difficult to troubleshoot the ring network. Adding or removing a computer affects the whole network. a network setup using mesh topology