What is Unicast, Broadcast and Multicast?

Unicast, multicast, and broadcast happen at layer-2 and layer-3. Remember layer-2 is the data-link layer where the switch device works using the MAC addresses for communication, and layer-3 is the network layer where the router device works using the IP addresses for communication.

Here, “cast” refers to how many people or devices we send the data to. It can be unicast, multicast, or broadcast. These 3 methods are the types of communication, used to transmit packets over a network.

  • Unicast means one-to-one, data send to only one device means sender sends data to only one device.
  • Multicast means one-to-many (or many-to-many), data sent to multiple devices means sender sends data to many devices (not all devices like the broadcast).
  • Broadcast means one-to-all, data sent to all devices means sender sends data to all devices.

unicast multicast broadcast



What is Unicast?

Unicast is a one to one data transmission.

In computer networking, Unicast is a term, that is used when data is transmitted from one point to another point.

It is a one-to-one communication; that is one sender and one receiver. when one device transmits the data to another device then it is called unicast transmission. Generally, we use one-to-one communication on our daily basis like- sending a message, browsing a website, downloading a file, etc.

Some Examples:

  • Ex-1: A device having an IP address in a network wants to transmit the data to the device with IP address in another network, then this transmission is called Unicast transmission.
  • Ex-2: There are 4 computers connected to the switch device, so if pc1 wants to communicate with pc2, then they can directly communicate with each other so this is unicast communication because it is one-to-one communication.
  • Ex-3: Browsing a website is also unicast communication, where the web server acts as a sender and our computer acts as a receiver.
  • Ex-4: Downloading a file from an FTP server is another example of unicast transmission, where the FTP server acts as a sender and our computer acts as a receiver.


What is Multicast?

Multicast is a term, that is used when data is transmitted to multiple devices. This type of multicast transmission is used, when data is sent to a group. This type of transmission recline between the boundaries of unicast (one-to-one) and broadcast (one-to-all).

It can be one-to-many or many-to-many transmission means data send efficiently from one source (or many sources) to many destinations simultaneously, generally within a local network. So if we use the multicast transmission in the local network, then a frame contains the unique multicast MAC addresses of an application, protocol, or data stream.

In multicast transmission, when a device sends one copy of data then it is delivered to many devices (not delivered to all devices like in broadcast).


What is Broadcast?

Broadcast is a term, that is used when data is transmitted to all the devices.

It is a one-to-all transmission means there is one sender, but the information is delivered to all the connected receivers.

In broadcast transmission, when a device sends one copy of data, then that data will be delivered to all the devices.

This term “broadcast“, mostly used in cable TV transmission. TV signals are sent from one source (one point) to all the possible destinations (all points).

We can classify broadcasting techniques into two types:

Limited Broadcasting:

  • Information sends to all the devices on the same network.
  • When a device transfers data to all devices on the same network, it is referred to as limited broadcasting.

Direct Broadcasting:

  • Information is directly sent to all the devices on another network.
  • When a device in one network transfers data packet stream to all the devices on the other network, it is referred to as direct broadcasting.


You should also read: Data Transmission Modes

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