Unicast vs Broadcast vs Multicast

Unicast: One Sender, One Receiver

Sender ------------------> Single Receiver

Unicast is a direct, one-to-one communication - a single sender transmitting to exactly one specific destination. This is by far the most common traffic pattern on the internet: loading a webpage, sending an email, or a video call between two people.

Broadcast: One Sender, Every Device on the Local Network

Sender ------------------> EVERY device on the local network

Broadcast sends a single message to every device on the local network segment at once, whether they actually need it or not. As covered earlier in this project, ARP requests use exactly this pattern, since the sender doesn't yet know which specific device holds the information it needs.

Multicast: One Sender, a Specific Interested Group

Sender ------------------> Only devices that specifically subscribed to this group

Multicast sends a single message that's received only by devices that have explicitly joined a particular multicast group - a middle ground between unicast's one-to-one and broadcast's one-to-everyone. Streaming the same live video to many subscribed viewers efficiently is a classic multicast use case.

Comparing All Three

Why This Distinction Genuinely Matters

Choosing the wrong pattern wastes resources: using unicast to deliver identical content to a thousand separate viewers means sending a thousand separate copies, while multicast (where properly supported) can deliver that same content far more efficiently to exactly the group that actually wants it.