# Computer Networks

Common distributed systems based on widely used computer networks

* The internet
* Intranets
* Wireless networks

## The internet

Consists of a large number of interconnected collection of computer networks of different types. Features include:

* Computers interacting using a common means of communicating.
* Many different services (applications) (WWW, FTP, SFTP)
* A number of Intranets linked by backbones
* Internet Service Providers (ISPs), that provide access to services on the Internet while providing local services such as email and web hosting.
* A backbone network link with high transmission capacity
* Communication via Satellite, fiber optic cables and other high bandwidth circuits.

![Internet](https://2148890063-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FJFoKjcvVbdvZ6n8QnPBM%2Fuploads%2Fgit-blob-8239de6f6dbba214cd32daf1af28695f6fab67bb%2Finternet%20\(1\)%20\(1\).png?alt=media)

## Intranets

Is a portion of the Internet that is seperately administrated by organisations. Features:

* A boundary that can be configured to enforce local security policies.
* Several local area connections (LANs) linked by backbone connections.
* A connection to the Internet via a router allowing users within the intranet to acces services on the Internet.
* Firewalls to protect an intranet by preventing unauthorized messages leaving or entering by filtering incoming and outgoing messages.

![Intranet](https://2148890063-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FJFoKjcvVbdvZ6n8QnPBM%2Fuploads%2Fgit-blob-a60a5daf1a72a43edfc45808af7d3ff46b236cdc%2Fintranet%20\(1\)%20\(1\).png?alt=media)

## Wireless networks

Wireless networks allow the intergration of small computing devices (laptops, mobile phones etc)

Three popular paradigms that use wireless networks are:

1. **Mobile computing :** The mobile computing paradigm allows users to perform computing tasks on the move, while being part of a distributed system.
2. **Ubiquitous computing :** Where cheap computing devices are embedded in devices that are used in parts of parts of a distributed system.
3. **Internet of Things :** Everyday objects are addressable and connected to the internet and may be part of a distributed system.