diffrence between broadcast & collesion domain in HUB & Switch

engineer_vinay

Hi all,
Kindly provide me details , how to we identify the no. of collesion domain and broadcast domain in a network which is using switch/hub.

friendster7

Collision Domain

A group of Ethernet or Fast Ethernet devices in a CSMA/CD LAN that are connected by repeaters and compete for access on the network. Only one device in the collision domain may transmit at any one time, and the other devices in the domain listen to the network in order to avoid data collisions.
A collision domain is sometimes referred to as an Ethernet segment.

Broadcast Domain

Broadcasting sends a message to everyone on the local network (subnet).
Example for Broadcasting would be DHCP Request from a Client PC. The Client is asking for a IP Address.
But the client does not know, how to reach the DHCP Server. So the client sends a DHCP Discover paket
to EVERY PC in the local subnet (Broadcast). But only the DHCP Server will answer to the Request.

How to count them?

Broadcast Domain:

No matter how many hosts or devices are connected together.
If they are connected with a repeater, hub, switch or bridge, all these devices are in ONE Broadcast domain.
A Router is used to seperate Broadcast-Domains (we could also call them Subnets - or call them VLANs

).
So, if a router stands between all these devices, we have TWO broadcast domains.

Collision Domain:

Each connection from a single PC to a Layer 2 device (switch, bridge) is ONE Collision domain.
But be carefull with Bridges. To ONE of the Bridgeports, you can connect MORE than one pc, over an
(oldfashioned) 10Base2 or 10Base5 Bus-based Cable.
If 2 PCs are connected to a Bridge, like in the picture, this is ONE Collision Domain!
But if 5 PCs are connected with seperate cables to a switch, we have 5 Collision domains.
If this switch is connected to another switch or a router, we have one collision domain more.

If 5 Devices are connected to a Hub, this is ONE Collision Domain!
Each devices, which are conected to a Layer 1 device (repeater, hub) build all togeter ONE collision domain.