On wikipedia there is this paragraph:
Since a pulse's runtime will never exceed slot time (the maximum theoretical time for a frame to travel a network), the NIC waits a minimum of slot time before retransmitting after a collision happened, in order to allow any pulse that was initiated at the time that the waiting NIC was requested to send, to reach all other nodes. By allowing the pulse to reach the waiting NIC, a local collision occurs (ie. while still sending) rather than a late collision occurring (after sending may or may not has ended). By having the collision occur at the NIC (local) and not on the wire (late) CSMA/CD implementation recover the situation by retransmitting later.
What is the waiting NIC referring to? Is it the NIC mentioned in the previous sentence or another NIC which was involved in the collision?
The NIC is "requested to send" by the upper OSI layer (in other words, by the node that it is attached to) ?
Why is the exponential back-off algorithm using multiples of the slot time?
I understand that the slot time is computed such that a node is still transmitting when the signal announcing the collision (jamming signal) arrives at it. But what does this have to do with how much time nodes should wait after a collision occurs?
Another wikipedia article states:
The maximum jam-time is calculated as follows: The maximum allowed diameter of an Ethernet installation is limited to 232 bits. This makes a round-trip-time of 464 bits. As the slot time in Ethernet is 512 bits, the difference between slot time and round-trip-time is 48 bits (6 bytes), which is the maximum "jam-time".
Why should there be a maximum jamming time?
Best Answer
That refers to any NICs waiting to send a frame, especially those involved in a collision.
The NIC is at OSI layer-1. OSI layer-2 for ethernet is the MAC layer. Layer-3 would be IP. Layer-4 is the transport protocol, e.g. TCP or UDP. Above layer-4 are the application layers (off-topic here). An application will start sending data to the transport layer, that then sends through the network layer to the MAC layer that gives it to the NIC.
That makes sure that the back-off time is never less than the slot time, and it is quick and easy to calculate.
That makes sure that all stations have heard the jamming signal, and no station will transmit while the jamming signal is still traversing the link. A host immediately next to the host doing the jamming will hear the signal before other hosts on the link, and it will stop hearing the jamming signal while it is still traversing the link.
Jamming when it is no longer needed will slow collision recovery, and therefore, unnecessarily reduce throughput on the link.