Bitcoin &
the OSI Model

The Application layer is the part of the internet you interact with directly — your web browser, your email app, your Bitcoin wallet. This is where human-readable software lives.

At this layer, software sends requests and receives responses. Two computers "talk" to each other using agreed-upon rules called protocols.

The Presentation layer is responsible for making sure data is in a format both computers can understand. It also handles encryption — scrambling data so that only the intended recipient can read it.

Think of it as a translator and a locksmith working together: they put the message in the right language and lock it with a key before sending.

The Session layer manages the "conversation" between two computers — it starts the connection, keeps it going, and ends it cleanly when finished. If the connection drops, the Session layer handles reconnection.

Imagine two people on a telephone call: someone dials, they talk, and someone hangs up. The Session layer handles all of that behind the scenes.

The Transport layer is responsible for reliable delivery. It breaks large chunks of data into smaller packets, sends them, and checks that every packet arrives at the destination without errors. If a packet goes missing, Layer 4 requests it again.

Think of it as a courier service that tracks every parcel and will resend anything that gets lost.

The Network layer handles addressing and routing — deciding how to get data from one place to another across potentially thousands of different computers and networks.

Every device connected to the internet has an IP address — a unique number like a postal code. The Network layer uses these addresses to figure out the best path for your data to travel.

The Data Link layer handles the transfer of data between two devices that are directly connected — for example, your computer and your home router, or two computers on the same local network.

Each device on a local network has a MAC address (a unique hardware identifier). The Data Link layer uses these addresses to deliver data within a local area, before Layer 3 takes over for the longer journey across the internet.

The Physical layer is the most fundamental of all — it is the actual hardware: the cables, fibre optic lines, Wi-Fi radio signals, routers, network cards, and data centres that make the internet physically possible.

Without Layer 1, none of the other layers can exist. All digital data — emails, web pages, video calls, and Bitcoin transactions — ultimately travels as electrical signals, light pulses, or radio waves through physical infrastructure.