What is the Collision domain in a computer network?

A collision in the computer network is a scenario where two or more hosts send packets over a shared channel at the same moment and the packets get lost as the signal collides.

While setting or using a computer network you might never worry about the collision frequency.  But it needs attention when the number of hosts keeps increasing and the network performance degrades because of too many collisions.
In this tutorial, we will discuss what is collision domain, along with how various network topologies and devices affect the amount of collision in the network.

What is the collision domain?

The subnetwork in which there are chances of collisions while transmitting data. In another tutorial on CSMA, we have described the protocol for avoiding collisions. But in that, there will be a delay if the collision domain is big. So it’s better to understand what is collision domain is while setting up a network.

Network Using a HUB:

HUB is a very basic device for creating a local area network. It is cheap and works at the physical layer of the OSI model.  When a host sends a packet to another, the hub places an electrical signal on all other ports. This is a kind of broadcast at the physical level.  If more than one computer sends the data the chances of collision are high. All computers connected to the HUB come under the same collision domain. 

If you add more computers, to the same device or with another device. The domain will keep expanding.  This will worsen the data communication experience. Because of that hubs are best suited for very small local area networks.

Switch and collision domain:

Another improved option for networking is a switch. The switch works on the data link layer. There are managed switch those works at layer 3 too.  But here we will cover layer two reference only. 

When a port receives a frame, it sends out the packet to the port that connects to the destination computer (in a contrast to HUB which sends to all ports).  This enables one-to-one communication between two computers.

The collision may occur when two computers send a message to the same destination.  So here the collision domain includes all communicating hosts. 

Collision domain with the router:

The network router purely works on the IP layer.  It connects multiple subnetworks of LANs. Collision in one subnetwork does not have any impact on another subnetwork. With a router, the collision domain is the number of subnetworks connected to the ports.