Why must host A continue to transmit after host b sends runt frame post collision on ethernet? (CSMA/CD) Trying to understand example from computer networks: a systems approach ... -Host A sends Host B a frame at time t; * Packet arrives at B at time t + d; (d = one link latency) * Instant before frame arrives at B, B sends out its own frame which collides with the original frame. * B detects collision and sends out runt frame which reaches A at t + 2d; * **A must continue until t + 2d in order to detect collision. A transmits for 2d to be sure it detects all possible collisions** ... My question: I thought since CSMA/CD this meant all hosts were listening for collision so why would A have to keep on transmitting? I'm thinking so far that maybe B sends out runt frame to all hosts and when they collide closer to transmitting hosts (eg.A) those hosts send out their own runt frames (ie backoff happens post runt frame sending)

You need to take into account that signals in the network move at finite speed.

When the colliding parties are spaced apart, the later sender will detect the collision earlier than the other (as the earlier sender's signal has propagated further). The transmission period needs to be long enough so that the earlier sender reliably detects the collision as well. The jamming signal's form on a shared wire is designed to enable easy collision detection.

Note that early CSMA/CD networks used coaxial cable with a shared wire that did not allow instantaneous collision detection, unlike twisted pair or fiber where transmit and receive use separate channels.

Of course, CSMA/CD is all but obsolete and modern networks are completely collision-free.