collision domain

gurutobe

what does it mean by collision domain? and what does it mean when you create separate collision domain?

MAC_Addy

A collision domain means that network packets can collide with each other.

mella060

Check out google.

Let me google that for you

Plenty of info out there. Basically, a collision domain is a section of a network where data packets can collide with one another when being sent on a shared medium or through hubs/repeaters, particularly when using early versions of ethernet. The bigger the collision domain the more chance there are of collisions happening. That is why hubs are not used today. Switches separate collision domains. Each port on a switch is a separate collision domain which means that collisions are eliminated.

I like to think of it as...

Routers separate broadcast domains - Layer 3
Switches separate collision domains - Layer 2

SubnetZero

In physics we define collisions as events that occur when two or more objects hit each other.

In Ethernet, the concept is the same but the objects are frames. In this way when two or more hosts transmit data at the same time the frames will collide causing the transmissions to become damaged.

Carrier Sense Multiple Access with Collision Detection or CSMA/CD was created in order to prevent this from happening, however collisions can still occur. In the event a collision does occur the end-stations must wait a certain amount of time before retransmitting the traffic again. This occurs because CSMA/CD employs Back-off algorithms which are used to determine when the colliding stations are able to safely retransmit.

In today’s networks this isn't a big deal since the majority of the world uses switches as opposed to hubs. Some things you will need to remember is where collision domains exist in a hubbed network vs a switched network.

Collision Domains operate at Layer 1 of the OSI model
- a hub is an entire collision domain since it forwards every bit it receives from one interface out every other interface
- on a switch every interface is it's own collision domain

In other words:

a 16 port hub = 1 collision domain
a 48 port switch = 48 collision domains

Sorry if this was redundant since others have already answered this for you.


HTH

gurutobe

Thank you very much, your answers were helpful.