Data Transmission and Security Flashcards
Methods of transmission
- Copper cables using electrical pulses
- Radio frequency (wireless)
- optical fibre (light)
- infrared
Use of fibre optic cables
Carry almost 100% of worldwide internet and phone traffic
Bandwidth
Amount of data that can be carried at one time
Serial Transmission
Method:
Advantages:
Bits are sent one signal at a time
Advantages over parallel:
- smaller and simpler connectors
- crosstalk creates interference between parallel lines and can result in corrupted bytes which would need to be retransmitted
- serial links are much more reliable over greater distances than parallel
Parallel Transmission
- Signals (bits) are sent simultaneously over a number of parallel wires
Crosstalk
Crosstalk occurs when a signal from one line gets transferred to another line
Skew
Each wire in a parallel cable has slightly different properties so the signals travel down the wires at slightly different speeds. This means the transmission must be over very short distances to avoid this problem
Simplex Transmission
Data travels in one direction only
Half duplex transmission
Data can travel in both directions along a single cable, but not simultaneously (not in both directions at the same time)
(Full) Duplex transmission
Data can travel in both directions simultaneously using two cables
Bit rate and Baud rate
The speed of data is measured in bits per second
The baud rate is the rate at which the signal changes
Baseband means one signal (bit) is sent at a time down a serial connection
In standard baseband, bit rate = baud rate
Why serial transmission can be faster than parallel
With higher bandwidths, more than one bit can be coded in a signal, increasing the bit rate
- Bit rate of channel = baud rate x number of bits per
signal
Transmission errors
When data is transmitted, it doesn’t always arrive in the same format that it was sent
- Electric interference
- Power surges
- Synchronisation
- Wear and tear on the cable or connectors
Error checking
Computers need methods to check for data transmission errors caused by interference
These methods include the use of:
- Parity bits, blocks
- Check digits
- Check sums
- Automatic Repeat reQuests (ARQ)
Parity bits
Computers use either odd or even parity
When sending a byte of data one bit is used as a parity bit
This is bit is set to a 1 or a 0 to make the total number of 1s and 0s in the byte (including the parity bit) odd or even depending on the machine
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 occurred
The receiving computer notifies the transmitting end and the data is resent
Check digits
A check digit is an additional digit at the end of a string of other numbers designated to check for mistakes in input or transmission
Printed books and other products have a unique barcode with an ISBN (International Standard book number) EAN (European Article Number)
The first 12 digits of the barcode are the unique item number, the 13th is the check digit
This can be calculated using the Modulo 10 system
Check sums
A check sum works similar to a check digit
The checksum of all bytes in a data transmission is calculated using an algorithm
The check sum is sent with the data
The receiving computer recalculates the checksum based on the data it received and compares it with the checksum received or a known, expected value
If it does not match, the data may have been altered or corrupted during transmission and the data is resent
Automatic Repeat reQuests
Computers using ARQs 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 period of time period, it will assume that there was a flaw in the data or transmission error
What is the internet
A collection of interconnected networks, not the world wide web as that is a part of the internet
ISP
what do they supply
what they allow you to do
storage in an ISP
ISPs are companies supplying connectivity to the internet, email services, web hosting and VOIPs.
You connect to the Internet service provider that you are contracted with, when you connect to the ISP you become a part of their network. This ISP may connect to a larger network and become a part of that.
Every ISP has its own data storage facility.
Browser softwares
Examples
How to access
Internet explorer, google chrome and firefox are all browser softwares. One way to access a particular page is by typing its address into an address bar.
Cloud based services
Mini def
Examples
Servers host software or services that you can access.
Online storage:
Dropbox
OneDrive
Google Drive
Connecting to the internet
PC > Router > Modem > ISP > Internet
router provides access to local area network
modem connects to your internet service provider (ISP)
- modem no longer used in modern technology
ISP connects you to the internet
Modem
stands for modulator/demodulator
converts digital signal from computer and converts to analogue signal for phone lines
a second modem at the receiving end converts the signal back to digital
Router
A router is a hardware device that allows you to connect several devices to a single internet connection (home setting)
Many routers have a WAP (Wireless access point) allowing you to create a wireless access point
TCP/IP protocol
TCP (transmission control protocol)
- breaks up messages sent over the internet into packets
- reassembles packets at the other end
- detects errors
- resends lost messages
IP protocol
- routes the individual packets between sender and recipient
HTTP and HTTPS Protocol
HTTP (hyper text transfer protocol) 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 page to the users browser for viewing
HTTPS (secure protocol) encrypts the information so that it can not be hacked
Packet switching
files and packets micro def
packet header
Each file is broken up into packets
Each packet is given a header containing:
- IP address its going too (Internet protocol)
- IP address it came from
- Sequence number of the packet
- Number of packets in the whole communication
IP Addressing
Every device connected to the internet has an IP address
eg. 81. 101. 137. 12
Packets are labelled with the senders and the destinations IP address
Packets are sent across the internet along separate routes and reassembled at the end
Public vs Private IP addresses
A PC network has a public and private IP address
Public IP belongs to the router on your LAN
Private IP is accessible only through the LAN
ISPs are allocated blocks of IP addresses
Once a message arrives at the router of your LAN it will use the private IP address to identify which device requested information
MAC Addressing
in full and assigned by who
how many addresses and for what
what it looks like
similarity of and combinations
role
A media access control address is assigned to each Network interface card by the manufacturer.
Computers may have 2, one for ethernet and one for wireless or for a phone wireless and bluetooth
Hex value eg.
3B:14:E6:39:0A:2C
Every network device in the world has a unique MAC address
There are 2^48 possible MAC addresses
Role of a MAC address:
When you request a web page each router along the way uses the MAC address of the next router to send the data packet to the next leg of its journey.
URL
Uniform resource locator is a web page and all are unique
WWW.
Domains names (TDLs) .uk , .nz etc
DNS
Domain Name system
DNs technology allows you to type a URL into your web browser and it translates the web address into an IP address.
There are 13 DNS “root” servers worldwide that keep complete database of all names and IP addresses
Lower level DNS servers are owned by ISPs and hold parts of the database
When a DNS server receives a request not in its database it will pass it on until reaches one with the matching name and IP address
Cookies
A cookie is a small data file that a web server puts onto your computer when you visit a website
Cookies save any data entered such as registration details, passwords and relevant adverts for you as well as web preferences.
Role of a browser
how browser gets webpage/website on your computer
- User types web address (URL) into browser
- Browser forwards request to web server to access page
- Web server acknowledges request and sends HTML source code for the web page to the computer
- Source code is rendered (translated) into viewable web page
Malicious software
what it does
what it can/typically does
types x6
Malware is any software written with malicious intent.
- Disrupt computers from their work
- Corrupt files
- Record key presses and gather information
- Gain unauthorised access to a computer or files
Not all viruses cause harm, but the ones (most) that do:
- limiting hard disk space and memory
- destroying or damaging files and data
- spamming your address book with contacts
- consuming your internet bandwidth
Types of Malware:
Spyware,
gathers information, installs more spyware, sends information back to spyware author, sells to advertising companies or help with identity theft
Adware,
irritating pop ups, instals itself on a computer, rarely harms
Viruses,
small program that replicates by inserting itself in other computer programs
- attach them self to existing software programs and infect when you run that program
- self replicate
Worms,
a standalone file that does not need a host program to attach itself to
Trojans,
a non-self-replicating virus that masquerades as a harmless file that you might want to open
Ransomware,
malware used to lock your computer or access to your flies for which you are then asked to pay a fee to regain access
Botnets
A virus can compromise a computer and use the host’s storage and processing power to perform jobs
This computer can then become a part of a Botnet network ( a group of computers secretly cooperating to send spam or cause disruption on a much larger scale)
Computers in a botnet can:
- send email spam to other users
- store and distribute illegal material
- perpetrate a Denial of Service attack
DOS attacks
Denial of service attack
Frequently aimed at company or web servers to overload them or make them crash by:
- flooding servers with millions of requests
- absorbing 100% of its processor time or memory
- using all available bandwidth
Attempts to make a network or website unavailable to legit users and the motive is often revenge, blackmail or terrorism
Reducing the risk of any cyber security issues
- personal vigilance
- scan external devices and drives
- anti-virus softwares
- firewall software
Anti-virus softwares
what they do
how they do
- detects viruses
- deletes or quarantines infected files
- commonly finds all malware including adware, spyware,
worms and Trojans
Works by:
- holding a dictionary of snippets used in viruses
- scans new files, downloads, external drives on your computer
- looks for suspicious codes by comparison
- keeps a dictionary of know viruses up to date
Firewall
- acts as a filter or barrier between your own trusted
network and others - only allows certain data packets across that meets set
filtering rules
Hacking
Breaking security defined as unauthorised access to files or data
- Exploiting weaknesses in websites or security systems
to access data - Guessing default or common passwords
- Tricking people into downloading malware to gain
access to their computer - Logging in as someone else without their permission
In order too:
- pure mischief or a challenge
- steal money
- steal or modify information
- for political reasons, expose wrongdoing or revenge on opposing views
Black and white hats
Black hat hackers are illegally hacking with criminal intent
White hat hackers ethical hackers employed by companies to deliberately find holes in their own security
Grey hat hackers look for wholes in other systems and ask for a payment from those systems
Cracking
Not hacking
Illegally accessing program source code to change it or fool it to:
- Bypass security or licensing control
- prevent software from expiring
- unlock features that otherwise would require a subscription
Hyper Text Markup Language
International standard language that all pages can read and all pages are written in.
Webpages, webpage code
HTML Code
In a text file containing the content of the website to be displayed by the browser
Uses to govern how to present sections of content
Stores locations of images that are to be displayed
Stores the location of other websites that are linked to using hyperlinks
HTML vs CSS
HTML controls content and function of a web page
Cascading Style Sheets control its style and appearance
Writing HTML code
open <> and close >
Websites are made of a head and body
<h1> , <h2>, <h3>, <h4> - different headings (main , sub)
<img></img>
<em> </em>:
emphasis
<a>
Click here for more info
</a>:
link placed in middle line, click to access</h4></h3></h2></h1>
Adding CSS to a webpage
Define the style at the top between tags
h1 {colour:blue; text-align: centre}
Everything that falls inside the style tag, that html will adopt that style
Sector ==> h1 or other
Declaration ==> property and value
Property ==> colour or other
Value ==> blue or other
h1 {colour: blue;}
To add a CSS style:
Define a style for a particular tag eg. h1
or
Define a general style and attribute it to a new name eg. #page
Attribute style to a <div> block:
Image file on desktop
</div>
