Explain the terms topology used in LANs.

(i) LAN topologies: This network topology is a physical schematic that shows interconnection of the several users. There are four fundamental topologies as follows:

(a) One to all topology or direct connection

(b) Star topology

(c) Bus Topology

(d) Ring topology

(ii) Access methods utilized in LAN:

i. Switched access

ii. Multiple accesses

iii. Token passing access

(iii) CSMA/CD: this is an access method used mainly with LANs configured in a bus topology. Along with CSMA/CD, any station (node) can send a message to another station (or stations) as long as the transmission medium is free of transmissions from another station. Stations monitor (listen to) the line to find out if the line is busy. If the station has a message to transmit but the line is busy, this waits for an idle condition before transmitting message of this. If two stations transmit at similar time, collisions arise. When this occurs, the station first sensing the collision sends a special jamming signal to all other stations on the network. All stations then cease transmitting (back off) and wait a random period of time before attempting a retransmission. The random delay times for all stations are different, and therefore, permit for prioritizing the stations on the network. If successive collisions happen, the back off period for every station is twice. Along with CSMA/CD stations should contend for the network. A station has not guaranteed access to the network. To notice the occurrence of a collision, a station must be capable of transmitting and receiving simultaneously. CSMA/CD is used with most LANs configured in a bus topology. Ethernet is an illustration of a LAN which uses CSMA/CD.