In slotted ALOHA time is divided into equal time slots of length greater than the packet duration
- In slotted ALOHA, time is divided into equal time slots of length greater than the packet duration.
- The subscribers each have synchronized clocks and transmit a message only at the beginning of a new time slot, thus resulting in a discrete distribution of packets.
- This prevents partial collisions, where one packet collides with a portion of another.
- As the number of users increase, a greater delay will occur due to complete collisions and the resulting repeated transmissions of those packets originally lost
- The number of slots which a transmitter waits prior to retransmitting also determines the delay characteristics of the traffic.
- The vulnerable period for slotted ALOHA is only one packet duration, since partial collisions are prevented through synchronization.
- The probability that no other packets will be generated during the vulnerable period is e-R
The throughput for the case of slotted ALOHA is given by
Trade-off between throughput and Throughput delay for ALOHA and slotted ALOHA packet radio protocols.