Introduction to Computer Networks

Overview of the internet

There are several different types of devices that make up the internet.

Hosts - Devices/end systems that are at the edge of the network.
Packet switches - Routers/switches that forward packets to other devices.
Communication links - Fibre/copper/radio transmission links between devices.
Networks - A collection of devices, routers and links managed by an organisation. These can be:
- Mobile networks.
- Home networks.
- Enterprise networks.
- Local ISPs
- National ISPs
- Content provider networks
- Datacenter networks

The internet is a network of networks that are generally enabled by interconnected ISPs.

Control the sending and receiving of messages. There are many different types for different purposes.

There are certain organisations that maintain open protocols for the internet:

Infrastructure provides services to applications. These services provide a programming interface to distributed applications:

Hooks - Allow sending receiving app to use the internet as a transport service.
APIs provide service options analogous to the postal service.

Define the format, order of messages sent and recieved among network entities, and action taken on message transmission, and receipt.

To find the time the following sequence of actions might happen:

sequenceDiagram
me->>you: Hi
you->>me: Hello
me->>you: Got the time?
you->>me: 2:00 pm