Computer Networks Set 6 MAC sublayer MAC Sublayer

Computer Networks Set 6: MAC sublayer

MAC Sublayer Ñ When several users contend to use same medium, the DLL is divided into a LLC and a MAC sublayer. Ñ LLC handles previously described tasks. Ñ MAC handles access to the medium -channel allocation. Ñ Two families of channel allocation stategies: Ñ Static channel allocation: FDM, TDM, . . . Ñ Dynamic channel allocation: Allocates channel on a need-to-use basis. Several strategies.

MAC sublayer - ALOHA Ñ Assumptions: Independent stations, single channel, collision detection, slotted time or random access, carrier sense or not. Ñ Pure Aloha: Random access, Random wait time

MAC Sublayer - ALOHA Ñ Slotted Aloha: Slotted time, Synchronization needed.

MAC sublayer - CSMA Ñ Carrier sense multiple access protocols. Ñ Persistent CSMA: Continuous Carrier sense, Random access Ñ Nonpersistent CSMA: Random Carrier sense, Random access Ñ p-persistant CSMA: Random Carrier sense, Slotted access with probability p.

MAC Sublayer - CSMA comparison

MAC Layer - CSMA/CD Ñ CSMA with Collision Detection Ñ CSMA/CD can be in one of three states: contention, transmission, or idle.

MAC Layer -Collision Free Ñ Bit map protocol: ry countdown protocol:

MAC Sublayer - Collision free protocols Ñ

Required Reading Ñ Web sites on Aloha, CSMA.