Unicast is a term in computer networking that describes the transmission of data to a single receiving address. In contrast, there's broadcast, where data is sent to all addresses in a network, or multicast, where data is sent to a specific group of addresses.
Unicast communication is typical for many Internet applications where data needs to be sent to a specific recipient, such as retrieving web pages, sending emails, or downloading files. In a unicast communication model, a sender sends data to a specific IP address, and a specific receiver responds by receiving the data and reacting to it.
Broadcast refers to a method of data transmission in a network where data is sent from a single source to multiple or all participants in the network. In contrast to Unicast, where data is sent from one source to a single recipient, and Multicast, where data is sent to a predefined group of recipients, in Broadcast, data is sent to all participants in the network, regardless of whether they need the data or not.
Broadcast is commonly used in networks to disseminate information that is of interest to all participants, such as ARP (Address Resolution Protocol) requests, where a device wants to identify the MAC address of another device on the network, or DHCP (Dynamic Host Configuration Protocol) requests, where devices request IP addresses from a DHCP server.
Although Broadcast provides a simple way to distribute data in the network, it can lead to network congestion, especially in larger networks, since all participants must receive the transmitted data regardless of whether it is relevant or not. For this reason, Broadcast is often used with caution in larger networks and replaced by more efficient techniques like Multicast where appropriate.