Collision Domain/Broadcast Domain
collision domain
A collision domain is an area where traffic collisions and congestion are likely to occur.
Repeaters and hubs that operate on Layer 1 are devices that shape, amplify, and relay degraded signals, so they do not control the flow of incoming traffic.

Therefore, Layer 1 devices do not control traffic by looking at MAC addresses, IP addresses, etc., but unconditionally copy received traffic to all ports other than the receiving port. transfer.
For example, a hub forwards incoming traffic to all ports except the port on which it was received.

As a result, traffic will flow even to a port that does not have a communication partner. In other words, unnecessary traffic flows, and collisions and traffic jams are more likely to occur.
As the number of hosts in the network increas