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 exact moment, and the packets get lost as the signal collides.

While using a computer network, you might never worry about packet collision at all. But it needs attention when the number of hosts in the network keeps increasing, and the network performance degrades because of too many collision occurrences.
In this tutorial, we will discuss the collision domain and 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 there will be a delay if the collision domain is significant. So it’s better to understand the collision domain while setting up a network.

Network Using a HUB:

HUB is a fundamental 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. 

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

Switch and collision domain:

Another improved option for networking is a switch. The switch works on the data link layer. Although there are managed switches, those work at layer three too. But here, we will cover layer two references only. 

When a port receives a frame, it sends the packet to the port that connects to the destination computer (unlike HUB, which sends it 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 works purely 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.