Application layer

Intro

• Exists ENTIRELY on end systems, like PCs or phones.

Responsibilities

• Writing data to the network in the correct format
• Reading data
• Providing an application to users
• Error handling and recovery

Network Application Architectures

Client-Server Architecture

Split into client-side and server-side processes, which communicate using messages.

Servers

1. Generally, the server should be available all the time.
2. They have at least one reliable IP address with which they can be reached.

Clients

Clients use the internet to use services and consume content. Clients always initiate connections to servers, and servers wait on clients.

The web is a client-server architecture.

Data Centres

These are buildings which store servers.

Peer-to-Peer Architecture

No dedicated server is involved, and all devices involved are peers that communicate with each other. This can scale rapidly, since every machine is capable of being both a client and a server. This is used a lot for torrenting.