Media Access Control (MAC)
Media Access Control (MAC) performs most of the data link layer functions
MAC refers to the need of control when devices transmit
- asynchronous transmission has no MAC (transmission when key is pressed)
- MAC is important when several devices share the same circuit (e.g., point-to-point line with half duplex requires taking turns)
Two approaches to MAC:
- 1.Controlled access (mainframe or its front end processor controls the circuit and determines which device can access the media at what time)
- X-ON/X-OFF
- Polling (sending a signal to the terminal giving it a permission to transmit or asking it to receive)
- hub go-ahead polling
- roll call polling (with or without priority; time-out)
- 2. Contention (sending when ever)