Unicast is a computer networking term that describes a type of transmission. Specifically, it relates to one-to-one communication. This means that one sender and one recipient are on a network together. Usually, both devices communicating have a unique IP address, either two IPv4 addresses or two IPv6 addresses.
Devices using an IPv4 address cannot communicate directly with an IPv6 device and vice versa. They need to be using the same addressing scheme. Some translation solutions exist between the two addressing schemes. However, they are not widely used. This is because almost all devices can be assigned both an IPv4 and an IPv6 address. That ability is due to the prevalence of “dual stack networking.”
This network could be the Internet, a private Intranet, or another type of connection – the critical part is that the sender and recipient can communicate over a network. Unicast transmissions are only ever between two single entities on a network, in contrast to multicast and broadcast, both of which are one-to-many transmissions, where one sender sends to many recipients. The two involved parties can communicate back and forth despite Unicast being a one-to-one transmission.
In other words, whether it’s a one-off document transmission from the sender to the recipient or, for example, a chat where messages are sent back and forth between two parties. It’s still a Unicast transmission even if the parties involved communicate back and forth.
Unicast (as well as broad- and multicast) is a routing scheme. This is another name for how network traffic is sent from A to B. The routing is done on layer 3 of the network layer’s OSI or Open System Interconnection model. Layer 3 protocols direct data flow when two computers communicate from separate LANs.