The beginners in the computer network have very often the difficulties to understand the notions of collision domain and broadcast. The two terms are often confused. In this article, I will clearly differentiate between these two concepts.
So first of all, what is a domain?
A domain is a region of a network or a type of computer network in which all user computers, printer accounts and other devices are registered. It is a central database located on one or more clusters (clusters) of mainframes, called domain controllers.
What is a collision domain?
A collision domain is, as the name implies, the part of a network where packet collisions can occur. A collision occurs when two devices send a packet simultaneously on the shared network segment. The packets collide and the two devices have to resend the packets, which reduces the efficiency of the network. Collisions often occur in a hub environment because every port on a hub is in the same collision domain. In contrast, each port on a bridge, switch or router is in a separate collision domain.
Note that each port of a hub is in the same collision domain. Each port on a bridge, switch or router is in a separate collision domain.
The diagram below illustrates the collision domains in an architecture:
There are 7 collision areas in the illustration above.
What is a broadcasting domain?
A broadcast domain is the domain into which a broadcast is transferred. A broadcast domain contains all devices that can join at the data link layer (Layer 2 of the OSI model) using broadcast. All ports on a hub or switch are by default in the same broadcast domain. All ports on a router are in the different broadcast domains and routers do not forward broadcasts from one broadcast domain to another.
The diagram below illustrates the diffusion domains in an architecture:
There are 4 areas of distribution in the illustration above.
Difference between collision and diffusion domain
| Collision area | Area of distribution |
| The Collision domain is a section of network that allows traffic to flow forward and backward. | A broadcast domain is a type of domain in which traffic flows throughout the network. |
| The Collision domain refers to a set of devices in which a packet collision can occur. | The broadcast domain refers to a logical set of computer systems that can be accessed without using a router. |
| Devices can include devices from other IP subnets. | The broadcast domain is never limited to the specific IP subnet for all types of IP broadcast. |
| A packet collision occurs when multiple devices transmit data over a single wire link. | The broadcast domain primarily uses a switched environment to broadcast, so no collisions occur. |
| Switches will crash in the collision domain. | Switches will never be interrupted in the broadcast domain. |
| In the collision domain, each port on a router is in the separate broadcast domains. | All ports on a switch or hub are likely to be in the same broadcast domain. |
