Why is a switch port a collision domain?

[tamnasidhart]

I'm just starting my IT education and this is probably a very basic question but I'm having trouble with it.
As far as I understand a collision domain is a part of a network where collisions can occur.
Let's say we have two PCs connected to a switch and nothing else.
Why is each port considered a collision domain when there's no collisions that can occur?

[Leo Laohoo]

ANSWER.

[MichaelMcCoy]

Hey,

You have somewhat answered your own question.  If you have two PC's connected to a switch, you are 100% right.  Collisions can not occur.  Each port being considered its own collision domain means that collisions can not occur.  If you had a hub (older technology) on these devices, each port did not have its own collision domain meaning that if a device was on the network talking, all other devices had to listen and wait until the line was clear.   

If that doesn't help, I will try to explain it again.  I almost confused myself.  lol

[mlund]

Hi

A switchport that is connected to pc is, as you stated, a collision domain.

Can there be collisions on that connection? Yes it can, under certain conditions.

If the switchport and pc is configured for half duplex, there can be collisions, it's not so easy to force them to generate collisions, but the longer the cable between the switchport and the pc is, the higher probability to get collissions it is. For copper twisted pair, if the cable is +100 meters long, there will be collisons. 

Or, if one end is configured for full duplex while the other is configured for half duplex. Then the half duplex port will see collisions, and also late collisions

/Mikael

[Joseph W. Doherty]

Possibly to confuse you further, a switch port is not always a collision domain.  Whether it is, or not, depends whether the port is in full duplex mode or half duplex mode.  Collisions cannot happen in the former, but can happen in the latter.  (Actually, they don't physically happen in the latter either, but physically full duplex ports, in half duplex mode, "simulate" them.)

In the latter, collisions could only happen between the PC and the switch.  Between PCs, frames are queued on the switch, regardless of duplex mode, so collisions cannot happen between the PCs.

[shonamui]

Collision Domain and Switch Port

Each and every switch's port is in a different collision domain by default, such a switch is a collision domain separator. The packets that come from varies devices connected to different switch's port never experience a collision. Please note - the modern switch's ports are full duplex (you may change the duplex configuration, such half and auto).

The half duplex port is considered a collision domain.