So it is clear that the efficiency of slotted aloha is double of pure aloha and hence the throughput is also double In this case, efficiency will be maximum if a SINGLE NODE ACCESSES THE CHANNEL PER TIME SLOT It is also called the channel load that is the total number of requests made per time slot. Where G= the number of the station who visited to access the channel within a one-time frame that is Tfr seconds Therefore, in this case, the efficiency is given as This figure clearly shows that only those frames will be colliding which are transmitted within the same time slot of Tfr seconds. Where Tfr represent one-time frame (or one-time slot)īy this strategy, the chances of collision will be less as explained under: This is the discrete-time – the system that is this case station are allowed to start their transmission only at the discrete instance of time that is

Let the bandwidth of the channel is bps then the overall throughput of the channel (average successful transmission rate ) = SB (bps) Slotted Aloha THAT IS 18.39% To find the overall throughput of the channel : It means half station should transmit in one-time frame Tfr For maximum efficiency that is practically one station should transmit its frame in 2 Tfr for maximum efficiency. Now let us drive the efficiency of the pure aloha channel G is the number of stations who wish to access the channel in one frame time that is 1 Tfr In general pure aloha, the channel is given as S= Ge-2G Efficiency means the probability of successful transmission without collision. Now let’s define the efficiency of this channel. It clearly shows that the time duration within which the collision can take place is 2Tfr. It is a continuous-time system that is all stations can start sending their frames at any instance of time.Īs shown in the figure let us assume station A starts its transmission exactly at instant t=0, Now it will surely collide with the frame of some other station, if that other station starts transmitting its frame in the time interval. If a station does not receive an ACK packet then it waits for the random amount of time which is also called backoff time and then resends its frame, and waits for ACK to come.

After a fixed amount if its frame is transmitted successfully. Each transmitting station receives an acknowledgment in the form of a packet. Aloha Protocol is an acknowledgment based Protocol.

Pure aloha and slotted aloha