Collision Domain and Broadcast Domain in Computer Network

Prerequisite - Network Devices, Transmission Modes 

The most common network devices used are routers and switches. But we still hear people talking about hubs, repeaters, and bridges. Do you ever wonder why these former devices are preferred over the latter ones? One reason could be: 'because they are more efficient and powerful'. But what actually is the reason behind their efficiency? This is when terms like "Collision Domains" and "Broadcast Domains" come into the picture. 

Before going further, let us recall that a hub is a multiple-port repeater. Similarly, a switch is a multiple-port bridge so that you can understand why repeaters and bridges are not typically used in production networks(because of less number of ports). 

Now, narrowing it down to Hubs, Switches and Routers, let us discuss them in reference to the below domains. 

1. Collision Domain - 
   A Collision Domain is a scenario in which when a device sends out a message to the network, all other devices which are included in its collision domain have to pay attention to it, no matter if it was destined for them or not. This causes a problem because, in a situation where two devices send out their messages simultaneously, a collision will occur leading them to wait and re-transmit their respective messages, one at a time. Remember, it happens only in the case of a half-duplex mode.
2. Broadcast Domain - 
   A Broadcast Domain is a scenario in which when a device sends out a broadcast message, all the devices present in its broadcast domain have to pay attention to it. This creates a lot of congestion in the network, commonly called LAN congestion, which affects the bandwidth of the users present in that network. 
   
   From this, we can realize that the more the number of collision domains and the more the number of broadcast domains, the more efficient is the network providing better bandwidth to all its users.

So, which of our network devices break collision domains, and which of them break broadcast domains? 

• HUB - 
  We start with a hub because we should get rid of it as soon as possible. The reason being, it neither breaks a collision domain nor a broadcast domain,i.e a hub is neither a collision domain separator nor a broadcast domain separator. All the devices connected to a hub are in a single collision and single broadcast domain. Remember, hubs do not segment a network, they just connect network segments.
• SWITCH - 
  Coming to switches, we have an advantage over the hub. Every port on a switch is in a different collision domain, i.e a switch is a collision domain separator. So messages that come from devices connected to different ports never experience a collision. This helps us during designing networks but there is still a problem with switches. They never break broadcast domains, which means it is not a broadcast domain separator. All the ports on the switch are still in a single broadcast domain. If a device sends a broadcast message, it will still cause congestion.
• ROUTER - 
  Last, but not least, we have our savior. A router not only breaks collision domains but also breaks broadcast domains, which means it is both collisions as well as broadcast domain separators. A router creates a connection between two networks. A broadcast message from one network will never reach the other one as the router will never let it pass. 

Also, as repeaters and bridges differ from hubs and switches only in terms of the number of ports, a repeater does not break collision and broadcast domains, while a bridge breaks only collision domains. 

The following are the advantages and disadvantages of Collision Domain and Broadcast Domain in Computer Network:

Advantages of Collision Domain:

High Network Performance: Collision Domain helps to improve network performance by reducing collisions on the network, which can improve data transmission and reduce packet loss.

Efficient Use of Network Resources: Collision Domain enables efficient use of network resources, such as bandwidth, by reducing the number of collisions and avoiding wastage of network resources.

Better Network Security: Collision Domain can help to improve network security by reducing the risk of unauthorized access and network attacks, which can occur due to network congestion.

Disadvantages of Collision Domain:

Limited Scalability: Collision Domain may not be scalable in larger networks, as the number of devices connected to the network increases, which can lead to network congestion and performance degradation.

Complex Network Management: Collision Domain can be complex to manage, requiring the use of protocols such as Carrier Sense Multiple Access with Collision Detection (CSMA/CD), which can be difficult to configure and maintain.

Advantages of Broadcast Domain:

Efficient Network Communication: Broadcast Domain enables efficient network communication by allowing multiple devices to receive the same message simultaneously.

Simplified Network Management: Broadcast Domain can simplify network management by allowing administrators to manage network devices and policies more easily.

Improved Collaboration: Broadcast Domain can improve collaboration by enabling real-time communication and collaboration among network users.

Disadvantages of Broadcast Domain:

Increased Network Congestion: Broadcast Domain can lead to increased network congestion, particularly in larger networks, which can impact network performance and lead to packet loss.

Reduced Network Security: Broadcast Domain can reduce network security by increasing the risk of unauthorized access and network attacks, particularly in environments with a large number of devices.

References - 
CCNA, Todd Lammle