Unicast
One-to-One Delivery
A single sender talking to a single recipient. It sounds unremarkable — and that is the point: unicast is the quiet default behind almost everything you do online, from loading a page to a video call.
Unicast is one-to-one network delivery: one sender transmits data to one specific recipient, identified by its IP address. It is so ordinary that it usually goes unnamed — loading a web page, streaming a film, sending a message, joining a video call are all unicast. Each is a private conversation between your device and exactly one other endpoint, with packets addressed precisely to that destination.
The four delivery methods
Unicast is best understood alongside its siblings — the difference is simply how many recipients receive the data and how they are chosen:
| Method | Pattern | Example |
|---|---|---|
| Unicast | One-to-one | Loading a web page, a video call |
| Multicast | One-to-many (subscribers) | IPTV, live feeds on a managed network |
| Broadcast | One-to-all (local network) | A device announcing itself on the LAN |
| Anycast | One-to-nearest | Public DNS resolvers, CDNs |
Why unicast dominates the internet
The public internet runs on unicast almost exclusively. Multicast and broadcast generally work only within a single managed network, not across the internet, because forwarding group traffic across countless independent networks is impractical. So when you connect to a service, you get your own dedicated unicast stream — your packets and nobody else's. This gives each connection independence and reliability, at the cost of efficiency when the same content goes to many people.
The scaling challenge — and the CDN answer
Unicast's one-to-one nature raises an obvious question: if a million people watch the same live event, does the source really send a million separate copies? Essentially, yes — over the internet each viewer gets their own unicast stream. The trick that makes this work is the CDN: providers cache copies of the content on edge servers close to users, so each unicast stream travels only a short hop from a nearby server rather than all the way from one distant origin. Unicast stays simple and reliable; the CDN handles the scale.
Where you will see the term
Most of the time you never think about unicast because it is the default. The word surfaces mainly when contrasting delivery methods — in router configuration, IPTV setups that use multicast, or when discussing how a CDN and anycast route a request. Knowing that "unicast" simply means "the normal one-to-one case" makes those discussions far easier to follow.