media access control
Channel Division Media Access Control (MAC Multiple Access Control) protocol:
divides resources based on multiplexing technology.
Heavy network load: shared channels are highly efficient and fair.
Light network load: shared channel is inefficient.
Random Access MAC Protocol: Conflict
Users randomly send information according to their wishes, and can monopolize the channel bandwidth when sending information.
Heavy network load: Conflict overhead.
Light network load: shared channel is highly efficient, and a single node can utilize the full bandwidth of the channel.
Polling Access MAC Protocol/Rolling Protocol/Rolling Access MAC Protocol:
It must not cause conflicts, but also occupy the entire bandwidth when sending .
There are two more important protocols: polling protocol and token passing protocol.
polling protocol
The master node takes turns "inviting" the slave nodes to send data. 
Problems:
1. Polling overhead 2. Wait latency 3. Single point of failure
Token Passing Protocol
Token: A specially formatted MAC control frame that does not contain any information. The use of the control channel ensures that only one node monopolizes the channel at the same time.
Collision-free token ring network
Each node can obtain the right to send data within a certain period of time (token holding time), instead of holding tokens unlimitedly.
Problems:
1. Token overhead. 2. Wait for the delay. 3. Single point of failure.
Applies to token ring networks (physical star topology, logical ring topology).
Networks that use token passing are often used in networks with heavy loads and large communications .