3.5 Networks

Two or more computers

Either wirelessly or through cables

To Exchange information and data between other devices and to share recources

A computer network is created when two or more computers are connected through a connection either physically or wirelessly

It is a connection of networks, no one person or organisation owns the internet - this is know as collective or distributed ownership.

A service which is offered on the internet

Data sharing, collaboration Security Communication Remote access Roaming (same computer no matter where you log in) Centralised management Files are saved to a network server

Data breaches Viruses Malware Expensive Network speed could slow down Hacking Reliant on hardware

Personal Area Network - connects electronic devices within a user’s immediate area, it only ranges a few meters (an example would be Bluetooth) A PAN is anywhere in the world as long as you are there.

Local Area Network - a computer network within a limited area A LAN operates across a small geographical area such as a school, hotel using their own cabling using their own cabling or wireless A LAN is owned and controlled/managed by a single person or organisation A WLAN includes a router that allows devices to connect wirelessly

Wide Area Network - the technology that connects your computers, data centres, cloud applications, and clouds storage together. Operate over a wide geographical location in which the computers communicate using resources supplied by a ‘third party carrier’ such as BT The largest WAN is the world

A computer that is not connected to any other computer via a network

• A small unit of information transmitted over a network, such as the internet, from one device to another • Each communication is split into smaller pieces called packets • Each packet will contain the same number of bytes In addition to holding the payload, each packet is marked with the packet number so that the packets can be put together by the receiver

• Internet Protocol - the unique identifying number assigned to every device connected to the internet • Like every front door in the world, every computer in the world has an IP • IP addresses are four 8-bit numbers (0-255) separated by dots - 32 bits in total • It is set in software and can therefore be changed • It is hierarchical* - this means that it includes network, subnet, and host components - similar to a house address • IP addresses are used by routers to determine the best path to the destination *contains lots of different bits of information

When you make a telephone call, a dedicated connection is set up between you and the person you are calling for the duration of the call • This is called ‘circuit switching’ It works fine for phone calls, but there could never be enough lines for all the billions of people sending data across the internet Packet switching solves this problem

Each packet is 512 bytes Each packet is given a header containing: - The IP address it is going to - The IP address it is coming from - The sequence number on the packet - The number of packets in the whole communication Error checking data

Routers are a piece of hardware capable of routing packets from one place to another based on the IP address. They make up the ‘backbone’ of the internet Your home router, routes packets to the different devices on your home network Internet routers route packets around the world like a mail sorting office

It may be wireless with an antenna or wired with a network cable socket It is built into networked device Most modern computers and phones incorporate the NIC into the motherboard

Media Access Control (MAC) is assigned to each Network Interface card by the manufacturer Your computer may have more than one MAC address if it has both ethernet and WiFi connection A smartphone will have two different MAC addresses, one for WiFi, one for Bluetooth

• Switches connect each node (computer) in a network • They know the MAC address of all connected computers and devices • When a packet of data arrives, they can send it directly to the correct computer

• Hubs also connect each node in a network but do not look at the MAC address. • They send the data to all connected computers

Computers and other devices (known as nodes) all connect to the central switch/hub

Computers and other devices (known as nodes) are all connected to a central backbone cable Terminators are at each end of the cable to absorb signals and prevent them reflecting back down the cable Packets are broadcast to all devices on the network

• Better performance – as traffic increases the network performance will not be effected. • If one cable fails the other computers are not affected • No collisions – if switch is used • Better security (if switched is used) as data is not broadcast to all machines