Discuss the CSMA/CD and CSMA/CA protocols.

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.

CSMA/CA: this belongs to a class of protocols termed as multiple access methods. CSMA/CA stands for: Carrier Sense Multiple Access with Collision Avoidance. In Carrier Sense Multiple Access, a station wishing to transmit has to primary listen to the channel for a predetermined amount of time therefore as to check for any activity on the channel. If the channel is sensed "idle" then the station is allowed to transmit. If the channel is sensed like "busy" the station has to defer its transmission. It is the essence of both CSMA/CA and CSMA/CD. In CSMA/CA (Local Talk), a station sends a signal telling all other stations not to transmit only one time the channel is clear then sends its packet. In Ethernet 802.3, the station carries on to wait for a time and checks to observe if the channel is even free. If this is free, the station transmits, and waits for an acknowledgment signal which the packet was received.