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1.2 Communication and Internet Technologies - Coggle Diagram
1.2 Communication and Internet Technologies
L1 Data Transmission
What is data transmission?
Data can be transferred from one point to another using various methods
Wirelessly using radio frequency
Optical fibre using light
Copper cable using electrical pulses
Infrared
Serial transmission
Bits are sent one signal at a time over a single wire
Very high data transfer rates can be achieved
Using fibre-optic cable
Used with USB (Universal Serial Bus)
Parallel transmission
Signals (bits) are sent simultaneously over a number of parallel wires
Skew
Each wire in a parallel cable has slightly different properties
Signals travel down wire at different speeds
Transmission must be over very short distances to reduce the problem
Computer data ribbons
Known as Parallel ATA Cables
Used inside the computer to connect components and drives
Advantages of serial over parallel transmission
Smaller, simpler and cheaper connectors such as those used for smartphones
'Crosstalk' creates interference between parallel lines, and can result in corrupted words which then need to be retransmitted
Serial links are more reliable over much greater distances than parallel links
Bandwidth
The amount of data that can be carried at one time
L2 Error Checking and Correction
Parity bits
Parity bits are used for error detection
Error checking
Computers need methods to check for data transmission errors caused by interference
Methods
Automatic Repeat reQuests (ARQ)
Computers using ARQ's will automatically return an acknowledgement that the data was correct
The simplest Stop-and-wait ARQ will resend the data if an acknowledgement is not received within a specific time period; it will assume that there was a flaw in the data or transmission error
It is sometimes used with mobile phone network data
Check digits
Check sums
Parity Bits
Computers use either odd or even parity
When sending a byte of data, one bit is used as a parity bit
This bit is set to a 1 or 0 to make the total number of 1s or 0s in the byte (including the parity bit) odd or even depending on the machine
Parity Odd or Even
An Even parity has an even number of 1-bits
If the byte is using even parity, then the parity bit needs to be 0 since there is already an even number of 1-bits
An Odd parity has an odd number of 1-bits
If the byte is using an odd parity, then the parity needs to be 1 to make the number of 1-bits odd.
Using parity for error detection
When data is transmitted, the parity bit is set at the transmitting end and parity is checked at the receiving end
If the wrong number of bits are 'on', an error has occured.
The receiving computer notifies the transmitting end and the data is resent
Check digits
Printed books and other products have a unique barcode with an ISBN (International Standard Book Number) or EAN (European Article Number)
The first 12 digits of the barcode are the unique item number, the 13th is the check digit
A check digit is an additional digit at the end of a string of other numbers designed to check for mistakes in input or transmission
This can be calculated using the Modulo 10 system
You calculate by adding them up, dividing it by 10, subtract the remainder from 10
L3 Introduction to the Internet
Internet Service Provider (ISP)
Every computer that is connected to the Internet is part of a network. You connect to the ISP that you are contracted with. When you connect to your ISP, you become part of their network. The ISP may then connect to a larger network and become part of that network.
An ISP is a company supplying connectivity to the Internet
They offer
Web Hosting
VOIP Facilities
Email Services
L4 Internet Principles of Operation
IP addressing
Every computer and other device connected to the Internet has an IP address
Packets are labelled with the sender's and the destination IP addresses
Packets are sent across the Internet separately via different routes and reassembled at the end
ISP's are allocated blocks of IP addresses
A PC on a network has 2 IP addresses- public and private
The public IP belongs to the router on your LAN
The private address is accessible only within the LAN
Once a message arrives at the router of your LAN, it will use the private IP address to identify which machine requested information from Google
Large IP ranges are allocated by continent
MAC Addressing
Your computer may have more than one MAC address, e.g. one for the ethernet and one for wireless
And a mobile phone may have two different MAC addresses- one for wireless and one for bluetooth
A Media Access Control (MAC) address is assigned to each Network interface Card (NIC) by the manufacturer
A MAC address looks like : 3B:14:E6:39:0A:2C
Every networked device in the world has a unique MAC address
There are 2 to the power of 48 possible addresses
Uniform Resource Locator (URL)
A URL is a web address
All web addresses are unique
Hypertext Transfer Protocol
HTTP
Hypertext transfer protocol is used for accessing and receiving web pages in the form of HTML files on the Internet
The protocol requests the web server to upload the requested web pages to the user's browser for viewing
HTTPS
Secure Hypertext Transfer Protocol encrypts the information so that it cannot be hacked
Packet Switching
Suppose you want to send a file of 3Mb across the Internet
The file is broken up into data 'packets' of 512 bytes
Each packet is given a header containing
The sequence number of the packet
The number of packets in the whole communication
The IP address it has come from
The IP (Internet Protocol) address it is going to
Cookies
Next time the client accesses the same server, the cookie file will also be sent, identifying the client
This would explain why:
You get automatically logged in to a website
You see online adverts relevant to you and your recent searches
Website preferences saved
A cookie is a small data file that a server will put on a client computer
Browser
The role of a browser
The client (i.e. the web browser) forwards this request to the server to access the web page
The server acknowledges the request and sends the HTML source code for the web page to the client
The client receives the page source code and renders it into a viewable web page
The user types a web address (URL) into the browser's address bar
L5 Security aspects
Malware
Viruses
A virus attaches itself to another file which will activate when you run the other file
They can then self-replicate and spread to others connected to you by:
Local network connection
Swapping removable disks
Email
Internet use, particularly in peer-to-peer file sharing websites where you are likely to upload files as well as download them
Worms
A worm is a standalone file that does not need a host program to attach itself to
Adware
Adware is responsible for the irritating pop-up adverts that you may see whilst using a computer
Adware programs install themselves on your computer in the same way as spyware
They rarely do any other harm
Trojan
A Trojan is a non-self-replicating virus that masquerades as a harmless file that you might want to open
Spyware
It can collect usernames and passwords, email addresses or credit card details
It can also install more spyware on your machine to read your cookies and change your system preferences
Spyware is software that covertly gathers information from your computer
The information is all sent back to the spyware author who can use or sell the data for advertising or crime including identity theft
Virus harm
Viruses, worms and Trojans bury themselves in your computer and can cause a range of issues
Destroying or damaging files and data
Spamming your address book contacts
Limiting hard disk space and memory
Consuming Internet bandwidth
Not all viruses cause harm
Hacking
Breaking security, defined as : 'Unauthorised access to programs or data
Guessing default or common passwords
Tricking people into download malware in order to gain access to their computer
Exploiting weaknesses in websites or system security to access information
Logging in as someone else without permission
Logging in as someone else without permission
Why do hackers do it?
To steal money
To steal or modify information
Some do it for pure mischief, or for a challenge
For political reasons, to expose wrongdoing, or to get revenge on people with opposing views
Anti-virus software
Usually deletes or quarantines infected files
Commonly finds all other malware including adware, worms, Trojans and spyware
Detects viruses
How anti-virus software works
Scans new files, downloads and external drives on your computer
Looks for suspect malicious code by comparison
Holds a dictionary of code snippets used in viruses
Dictionary kept up-to-date
L6 HTML Structure and Presentation
HTML
HyperText Markup Language
Web page code
You can look at the HTML code behind a web page
HTML code
Stores the location of images that are to be displayed
Uses <tags> to govern how to present sections of content
Resides in a text file containing in the content of the website to be displayed by the browser
Stores the locations of other websites (and bookmarks within webpages) that are linked to using hyperlinks
HTML structure and presentation
HTML code controls the content and function of a web page
CSS
Cascading Style Sheets (CSS) control its style and appearance