Collision and diffusion domain

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:

Collision areas
Collision areas

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:

Areas of dissemination
Areas of dissemination

There are 4 areas of distribution in the illustration above.

Difference between collision and diffusion domain

Collision areaArea 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.
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Adam Guipelbé

Ingénieur Systèmes et Réseaux

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