some info about "contention slot"
Contention Protocols resolve a collision after it occurs.These Protocols execute a collision resolution protocol after each collision
eg. Pure/Slotted Aloha, CSMA/CA(wireless), CSMA/CD(ethernet)
CSMA/CD : -To detect a collision, in the worst case, it takes twice the maximum propagation delay of the medium
Ethernet requires a minimum packet size and restricts the maximum length of the medium