MAC Protocols and CSMA/CD Essentials | Generated by AI
Question: What three specific problems must the Medium Access Control (MAC) protocol in a shared-medium LAN solve, and how can the basic concept of the CSMA/CD medium access control be simply summarized?
Answer:
Three Problems Solved by MAC Protocols in Shared-Medium LANs
In a local area network (LAN) where multiple nodes share the same transmission medium, the Medium Access Control (MAC) protocol is essential to coordinate data transmission and prevent chaos. It specifically addresses the following three core problems:
- Channel Allocation (Who sends?): Determining which node is allowed to transmit data at any given moment. Since the medium is shared, only one node should ideally transmit at a time to ensure data integrity.
- Collision Detection (Will there be a conflict?): Identifying whether a collision (data interference) will occur or has occurred when two or more nodes attempt to transmit simultaneously.
- Collision Resolution (How to handle conflicts?): Defining the specific procedure to follow when a collision is detected, ensuring that the involved nodes can retry transmission without causing immediate repeated collisions.
Basic Concept of CSMA/CD
CSMA/CD stands for Carrier Sense Multiple Access with Collision Detection. Its basic operational philosophy can be summarized in two main phases:
- “Listen before talk” (Carrier Sense): Before a node attempts to send data, it first listens to the channel to check if it is idle. If the channel is busy, the node waits; if it is idle, the node proceeds to send.
- “Listen while talking” (Collision Detection): While transmitting data, the node continues to monitor the channel. If it detects a signal distortion indicating a collision (another node started transmitting simultaneously), it immediately stops transmission, sends a jamming signal, and waits for a random backoff period before attempting to retransmit.
In short, the core logic is: Listen first, then send; listen while sending.
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