Collision Domain

A Collision Domain is a specific segment of a computer network where data packets can collide with one another when being sent over the network. This usually occurs in older Ethernet networks that use hubs or repeaters. In these types of networks, if two or more devices try to send data at the same time inside the same segment, their data packets can interfere with each other. This interference is called a collision.

When a collision happens, the devices must resend their data, which slows down the overall network performance. The more devices you have in a single collision domain, the higher the chance of collisions, making the network less efficient and slower.

In more technical terms, a collision domain is defined by the network hardware used. For example, in a network using hubs, all devices connected to the hub are part of a single collision domain. This is because hubs operate at the physical layer (Layer 1) of the OSI model and simply extend the network signal to all ports, without any intelligent switching or routing. Each device connected to the hub essentially "shares" the same communication medium, leading to potential collisions.

In contrast, modern networks primarily use switches, which operate at the data link layer (Layer 2) of the OSI model. Switches are smarter devices compared to hubs because they can send data directly to the intended recipient. Each port on a switch represents a separate collision domain. This means if you have one switch, each connected device has its own collision domain, greatly reducing the chance of collisions and improving network performance.

Collisions are detected using a method called Carrier Sense Multiple Access with Collision Detection (CSMA/CD). When a device wants to send data, it first checks if the communication medium is free. If it is, the device sends its data. If a collision is detected, it stops sending data, waits for a random period, and then tries again.

In summary, a Collision Domain is an area of a network where data packets can collide because they share the same communication channel. Modern devices like switches help create multiple, smaller collision domains, making networks faster and more efficient.