Data communication network

DATA LINK LAYER


      Data link layer is responsible for converting data stream to signals bit by bit and to send that over the underlying hardware . Data link layer picks up data from hardware which are in the form of electtical signals, assembles them in a recognizable frame format, and hands over to upoer layer.

ALOHA :-             

              The aloha protocol was designed as a part of a project at the universe of Hawaii.

It provided data transmission between computers on several of the Hawaiian Islands.

Involving packet radio networks. Aloha is a multiple access protocol at the data link layer and proposes how multiple terminals access the medium without interferences or collision. There are two different versions of aloha.

1)      pure aloha: In pure aloha, the stations simply transmit frames whenever they want data to send. It does not check whether channel is busy or not before transmitting. In case two or more station transmits a frame, it expects the ack from the receiver. If it is not received within specific time, the station assumes that the frame or ack has been destroyed. Then the station waits for a random amount of times and sends the frame again. This randomness helps in avoiding more collisions. This scheme works well in small networks where the load is not much. But in largely loaded networks, this scheme fails poorly.              

                                                      . All the frames should be in the same length.

. stations cannot generate frame while transmitting or trying to transmit                                    frame.

. the population of stations attempts to transmit according to a poisson distribution.