Computer Science - Networks

Why do we use networks?

Sharing files + hardware devices (printers), access the internet, communication, collaboration

LAN

Small geographical area, owned + maintained by companies/households

WAN

Wide geographical area, owned + maintained by 3rd parties, users pay a fee, made up of many LANs

Bandwidth

Measure of capacity - how many bits transferred per second

Latencey

Measure of time - how long it takes to reach the destination (miliseconds)

Copper cable uses…

Electrical signals

Fibre optic uses…

Rays of light bouncing off edges of glass tube

Copper cable disadvantages

short distances, low speed,high latency, interference

Copper cable advantages

Easier to install, cheaper

Fibre optic disadvantages

More expensive, difficult to install

Fibre optic advantages

long distances, high speed, low latency, no interference

FTTC

Runs from telephone interchange to green street cabinets which connect to homes and businesses via copper cable

FTTP

Go directly to buildings for high performance connections

Wired advantages

Faster, lower latency, secure, less interference

Wireless advantages

Easier to install, flexible

Wired disadvantages

Harder to install + add more devices

Wireless disadvantages

Encryption needed, walls and objects block connection

Bluetooth range

10m

Zigbee

Low power radio waves, connects thousands of IoT devices

RFID

Electromagnetic fields used to track/identify tags with embedded radio transmitters/recievers

NFC

Electromagnetic fields create a high speed connection between 2 devices next to each other

Internet Backbone

A main data route on the internet owned by a major telecommunications company made up of many FO cables

Point of Presence (pop)

Allows local networks to connect to the internet, has a modem, router and switch

ISP

Internet service provider

NAP

network access point - connect internet backbones to form a worldwide mesh network

Router

forwards data between networks form source to destination using routing tables and information about traffic

IPv4

32 bits - 4 billion devices (not enough)

IPv6

128 bits

Dynamic IP adress

Used by devices, returned to an adress pool when no longer needed

DNS

Domain name system - directory of domains and IP adresses to allow for easier look-up

Internet

System of interconnected networks linking billions of devices worldwide

World Wide Web

A service hosted on the machines that are connected to the internet to provide web pages

Peer-to-peer (P2P)

Communication where the data travels directly to the recipient and not through a central controlling device (mesh networks)

Packet switching

The process of breaking data into packets and sending them over the internet

What does a header contain?

Source + destination Ips, sequence nuber, total packets, checksum

Application layer

Defines how user services operate e.g. web browsers and email (HTTP(s), FTP, SMTP, POP3)

Transport layer

Establishes a channel between source and destination, splits data into packets (TCP)

Information layer

Adds s+d IPs and routes them to recipient (IP)

Link layer

Defines how the data is transferred (Ethernet, Wifi)

Order of TCP/IP layers

A,T,I,L

Embedded system

A small computer that performs a specific function, often within a bigger system

Bus topology pros

Cheap, little cable, if a node fails the rest will work, easy to add devices

Bus topology cons

Main cable damage stops whole system, more devices means a slower speed, security risk

Star topology pros

Damaged cable does not affect whole system, secure, easy to locate faults, add devices easily(ish)

Star topology cons

Central node faliure stops whole system, performance depends on central node + number of nodes, expensive due to cabling

Mesh topology pros

Fault tolerant (rerouting), scalable, high performance

Mesh topology cons

Difficult and expensive installation