A LAN is network segment (wired or wireless) connecting multiple devices which becomes a network domain. If two devices are transmitting data at the same time in a network domain, they will collide and cause transmission failure due to the collusion of data. This network segment where all devices connecting to it and when transmitting data at the same which will result in collision is known as Collision Domain.
Hub and Switches are two major network devices used in LAN for connecting devices. Hub is a LAN network device that provides basic connectivity for all devices connecting to it. A hub is a single collision domain and hence, if all devices transmit at same time, there will collision. For example, if 8 port hub has 8 desktops connected to it and if more than 2 devices transmit data at same time, collision will happen.
A switch is sophisticated network device which has built in Application Specific Integrated Circuit (ASIC) which makes it more efficient and smarter. Switch can do processing unlike hub. ASIC enables the switch to do switching. Switch is multi-collision domain network device. It prevents collision using CSMA. In a switch, each ports becomes a single collision domain.
CSMA/CD (Carrier Sense Multiple Access with Collision Detection) is used in Ethernet Switches to prevent collision. This is reactive collision avoidance technology which detects a collision and sends a jam single to all devices connected to wait for sometime and then allow to transmit.
CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) is used in Wireless to prevent collision. Collision Avoidance by pro-actively listening to the wireless network and allow the wireless devices to transmit when the wireless channel is free.
Collision Domain in Network Topologies
Each LAN technology use a Network Topology model. Based on the Network Topology, the characteristics of the collision domain differs.
Bus Topology connects all the computer nodes in a bus line becomes a single collision domain and whenever any two computers try to transmit data, collision happens. Hub uses Bus topology and there is no method to prevent collisions.
Ring Topology connects all the computer nodes in a ring. A computer should have a token to transmit data. The token is passed between nodes and node holding the token can transmit the data. This reduces collision but not completely.
Star Topology connects all the computer nodes in a star model through a central node. Switched network is an example of Start Topology. Switch is a multi-collision domain and prevents collision using CSMA/CD.