<aside> 📖 Layers

1. Application
   • Bi-directional reliable byte stream between two applications, using application-specific semantics (e.g. http, bit-torrent).
2. Transport
   • Guarantees correct, in-order delivery of data end-to-end.
   • Controls congestion.
3. Network
   • Delivers datagrams end-to-end. Best-effort delivery
   • no guarantees. Must use the Internet Protocol (IP).
4. Link
   • Delivers data over a single link between an end host and router, or between routers </aside>

<aside> 📖 The network layer is "special"

We must use the Internet Protocol (IP)

• IP makes a best-effort attempt to deliver our datagrams to the other end. But it makes no promises.
• IP datagrams can get lost, can be delivered out of order, and can be corrupted. There are no guarantees.

IP is the “thin waist”

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<aside> 📖 TCP: Transmission Control Protocol

UDP: User Datagram Protocol (No delivery guarantee)

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<aside> 📖 The 7-layer OSI Model

• The top 3 layers are known as the application layers
• The remaining 4 layers are known as teh data flow layers

Layers

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