Question

Explain topology method used in LAN technology in detail.

Answer 1

LAN Topologies: Network topology is a physical schematic which shows interconnection of the many users. There are four basic topologies as under:

(i) Direct Connection or one to all topology

(ii) Star topology

(iii) Bus Topology

 (iv) Ring topology

 (i) Direct connection or one to one topology: In the one to all topology, there is a path between every node and every other node. The number of paths required is defined by the equation P = (n2 -n)/2, where n is number of nodes and P, total number of paths. Thus number of paths increases considerably as the number of nodes increases. Each node must be physically able to connect to paths to every other node so a very large connector and associated interface support circuitry is needed at each node. Adding a new node requires major rewiring and affects the software that manages communications for the system. 

(ii) Star Topology: In Star topology, all user nodes are connected to central node point that interconnects all the individual users links and nodes. Data flows from one node, through the star centre to the desired receiving node. The Central node is like a large switch which routes the data from the input line to the output line. Advanced central nodes can have multiple switching paths, so several paths exist at the same time. This topology is used in a telephone system central office. Addition of a new user node requires running only a single link from the star centre to the user without disturbing any other node. 

(iii)Bus Topology: This topology shares a single link or path way among all users. This common single path way is known as bus. In this topology, the link serves as a high way for all data signals, and users connect on to the bus at their node location. In bus configurations, network control is not centralized to a particular node. Here control is distributed among all nodes connected to the LAN. Data transmission on a bus network is usually in the form of small packets containing user addresses and data. When one node/user desires to transmit data to another station, it monitors the bus to determine if it is currently being used. If no other nodes/users are communicating over the network, the monitoring node/user can start to transmit its data. Each node must monitor all transmission on the network and determine which are intended for them. 

(iv) Ring Topology: In ring topology, all user nodes are connected with the physical path acting as links of a chain and the last user node is connected back to the first node. A signal going on to the next node must be processed by the first node, which then passes it through to the next node. Adding a new user requires breaking the ring temporarily, inserting the new node and then reestablishing the complete ring path.