Explain about CSMA/CD
It is an access method used mainly with LANs configured in a bus topology. With CSMA/CD, any station (node) can transmit a message to any other station (or stations) as long as transmission medium is free of transmissions from other stations. Stations monitor (listen to) line to determine if line is busy. If the station has a message to send though the line is busy, it waits for an idle condition before sending its message. If two stations transmit at the same instance, a collision takes place. When this happens, 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. Random delay time for every station is different and thus, allows for prioritizing the stations on the network. If successive collisions take place, back off period for each station is doubled. With CSMA/CD stations should contend for the network. A station isn't guaranteed access to network. To detect the occurrence of a collision, a station should be capable of receiving and transmitting simultaneously. CSMA/CD is used by most LANs configured in a bus topology. Ethernet is an example of a LAN which uses CSMA/CD.