Comparison of Three LAN Media Access Control Methods

Comparison of Three LAN Media Access Control Methods The working principle and advantages and disadvantages of the three LAN media access control methods are as follows: 1. multi-Channel Access Method for carrier listeners with Conflict Detection: Working principle: each node listens to whether the channel is idle before sending data. If it is idle, data is sent immediately. If the channel is busy, send data after a period of time to the end of the information transmission in the channel. If two or more nodes send requests after the last message transmission is complete, it is determined as a conflict. If a conflict occurs, stop sending data immediately. Wait for a random period of time and try again. The principle is summarized as follows: First listen, then send and listen, conflict and stop, random delay and then resend. Advantages: The principle is relatively simple, technically easy to implement, and the workstations in the network are in an equal position, which does not require centralized control and does not provide priority control. Disadvantage: as the network load increases, the sending time increases and the sending efficiency decreases sharply. 2. token Bus Method: Working principle: the "token" is used in the bus topology (the token is a binary number of bytes, it is implemented by the "idle" and "busy" encoding marks, neither the destination address nor the passive address) as the control node to access the public transmission media indeed finalized media access control method, if a node has a data frame to send, it must wait for the arrival of the idle "token. After the node obtains the free token, it changes the token from "idle" to "busy" and then transmits data. Advantage: Each workstation shares the same power to the media, and can set a priority or not. It has a good throughput capability and increases as the data transmission rate increases, the connection distance is larger than that in CSMA/CD mode. Disadvantages: the control circuit is complex and costly. When the load is light, the transmission efficiency of the line is low. 3. card ring method: Working principle: Use a control sign called a "token". When no information is transmitted on the ring, the token is in the "idle" state, it is continuously transmitted from one workstation to another along the ring. When a workstation prepares to send information, it must wait until it detects and captures the token passing through the station, then, the control mark of the token is changed from "idle" to "busy", and a frame of information is sent concurrently. Other workstation can detect frames passing through this site at any time. When the destination address of the sent frame matches the address of this site, it will receive the frame. After the frame is copied, it will be forwarded again, the sent frame information will not be cleared until the frame is returned to the sending station one week along the ring and the receiving station points to the sending station, and keep the token flag in the idle status. When another new workstation needs to send data, according to the above process, it detects the token, modifies the status, assembles the information into frames, and sends a new round. Advantage: it can provide priority services with strong real-time performance. In heavy load loop, "tokens" Work cyclically, which is more efficient. Disadvantages: The environment maintenance is complex and difficult to implement.