Many LAN protocols are based on either CSMA (Carrier Sense Multiple Access)
or CSMA/CD (CSMA with collision detection) for media access. This application
shows the difference between the two algorithms in a space-time-diagram.
The horizontal axis shows 4 nodes (A, B, C, D) attached to a linear broadcast
bus, the vertical axis represents time. At time t0, node A senses the channel
is idle and thus begins transmitting. The packet propagates in both directions
along the broadcast medium. Although A is transmitting at time t1, the
packet has not reached node D and thus D senses an idle channel and begins
transmitting as well. A short time later both signals interfere and cause
a collision. CSMA does not perform collision detection and thus both nodes
continue to transmit their entire packet. On the other hand, with CSMA/CD
the nodes abort transmission a short time after detecting the collision.
The application allows you to detect the differences between the CSMA and
CSMA/CD algorithms while transmitting small, medium or large packets. Just
press the Start button!
(Example from J. F. Kurose, K. W. Ross: Computer Networking - Ch.:
link layer and local area networks)