Protocol 01

CSMA — Carrier Sense Multiple Access

CSMA is a Media Access Control (MAC) protocol in which a node verifies the absence of other traffic before transmitting on a shared transmission medium. A sender first listens to the channel; only if it finds the channel idle does it proceed to transmit.

The 1-persistent variant transmits with probability 1 once the channel is sensed idle — the simplest approach but prone to collisions when multiple stations wait for a busy channel to clear.

Sense before transmit

No collision detection

Retry on failure

Used in early Ethernet

Protocol 02

CSMA/CD — Collision Detection

CSMA/CD extends CSMA by adding the ability to detect collisions during transmission. When a collision is detected, a jamming signal is sent, transmission is aborted, and each station waits a random backoff time before retrying.

The binary exponential backoff algorithm doubles the contention window after each collision (K = 0..15), dramatically reducing repeat collisions. Maximum retries K_max = 15; beyond that, the frame is aborted.

Detect collision mid-transmission

Jam signal broadcast

Binary exponential backoff

IEEE 802.3 (Classic Ethernet)

Protocol 03

CSMA/CA — Collision Avoidance

CSMA/CA is designed for wireless networks where collision detection is impractical. Instead of detecting collisions, it actively avoids them by waiting an Inter-Frame Space (IFS) and a random backoff window before transmitting.

After transmission the sender awaits an ACK from the receiver. No ACK means the frame was lost (possibly via collision), triggering a retry with an incremented attempt counter K, up to K_max = 15.

IFS wait before transmit

Random backoff slots

ACK-based confirmation

IEEE 802.11 (Wi-Fi)

Live Simulation Tick: 0

Node A Controls

Destination

B C D

Simulation Controls

Speed

Rate

Shared Medium IDLE

Idle

Busy

Collision

Idle Sensing Transmitting Backoff Collision Receiving Waiting

Event Log

Protocol Flowchart