Notes-for-CAIE

1.2 Communication and Internet Technologies

1.2.1 Networks

• explain the client-server model of networked computers
• give examples of applications which use the client-server model
• describe what is meant by the World Wide Web (WWW) and the Internet
• explain how hardware is used to support the Internet: networks, routers, gateways, servers
• explain how communication systems are used to support the Internet: The Public Switched Telephone Network (PSTN), dedicated lines, cell phone network
• explain the benefits and drawbacks of using copper cable, fibre-optic cabling, radio waves, microwaves, satellites
• show understanding of bit streaming (both real-time and on-demand)
• show understanding of the importance of bit rates/broadband speed on bit streaming

Client-server model [3]

For a bank, it features:

• The server holds the customers’ account data
• … and performs the requested tasks
• The clients send requests to the server,
• … server returns the result of the request

Examples of applications: [2]

• Sending and receiving email
• Using a print server
• Using a file server

World Wide Web (WWW) [3]

• is a collection of web pages stored on websites
• http protocol used to transmit data
• web pages are written in HTML

Internet [3]

• is the infrastructure of networks
• Internet stands for Interconnected Networks
• uses TCP/IP protocol

Public Switched Telephone Network(PSTN) [2]:

• Structure: All networks are connected together by switching centers
• Effect: Allows any telephone to communicate with another
• Via what: Data is transferred using existing telephone lines
• By how: When data is being transmitted, the computer dials the network to set up a connection
• Transmission: Data is transmitted in both directions at the same time

Routers & Gateways[3]:

• Both:
  • Connects 2 or more networks;
  • Receive and forward towards the destination[1] using IP address[1]
  • Assigns private IP addresses;
• Routers operate between similar networks
• Gateways operate between dissimilar networks

How a URL is converted into its IP address[3]

• URL is parsed to obtain its domain name
• Domain name is sent to DNS
• DNS holds a list of domain names and matching IP addresses
• DNS searched its data base for the domain name
• If DNS doesn’t find the domain name, the request is forwarded to a higher level DNS
• If the domain name is found, the IP address returns

Transmission media

	Twisted pair	Coaxial	Fibre-optic
Cost	Lowest	Higher	Highest
Bandwidth or data rate	Lowest	Higher	Much higher
Attenuation at high frequency	Affected	Most affected	Least affected
Interference	Worst affected	Less affected	Least affected
Need for repeaters	More often	More often	Less often

When talking about cables, consider SECURITY and BANDWIDTH ONLY

Using Fibre-optic cable than copper cable

Benefits [3]	Drawbacks [2]
Less interference in signal	Higher installing cost
More secure	Specialist needed to install
Greater bandwidth	Only transmits data in one direction

Using dedicated line[2]:

• Benefits: Faster connection[1]; higher security[1]
• Drawbacks: Expensive to maintain[1]

Benefits of Using wireless network

w18 13 Q7 [3]

• Devices can be more portable as they don’t have to connect with cables
• Easier to setup
• Add additional devices easier
• Many different types of devices can be connected at the same time

Hardware

Solid-state memory [3]

• no moving parts
• non-volatile
• make use of blocks of semiconductors
• Memory cells store voltages that can represent a 0 or a 1

Benefits of SSD than HDD[2]

• No moving parts so silent
• Robust
• Low latency

Purposes of RAM and ROM

• RAM: stores currently running parts of files
• ROM: stores boot up instructions

DRAM & SRAM [4]:

w16 11 Q2 [2]

• DRAM has to be refreshed
• DRAM has slower access time
• DRAM is less expensive
• DRAM can have higher data density
• DRAM is used in main memory, SRAM is used in cache memory

Input Devices

• Touch screen
• Microphone
• Games pad

Internal tech of Keyboard

w16 11 Q4 [2]

• Uses switches and circuits to translate keystrokes into signals the computer can understand
• When key pressed, a circuit is completed and a signal is sent

Internal tech of Tracker-ball mouse [3]

• The ball touches horizontal and vertical rollers
• When the ball rotates,
• one or both of the rollers rotate as well

Internal tech of Optical Disc | Scanner | Optical mouse

w16 11 Q4 [2] for each

• Laser shines onto the <disc

  mouse

  document>

• Sensor detects reflected light

For Optical Disc | Scanner:

• Light intensity is converted to a digital value

For Optical mouse :

• … and translate the change in surface detail
• … into movement

Internal tech of Touch screen

Capacitive:

• is made from materials that store electric charge
• when touched, charge transferred to the finger
• sensors at the corners detect the charge
• coordinates used to calculate the position

Internal tech of Microphone[3]

• has a diaphragm
• The incoming sound wave causes vibration of the diaphragm
• An electrical signal is produced

Output Devices

Internal Tech of Laser Printer[3]:

• The revolving drum is initially given an electrical charge
• A laser beam scans back to forth across the drum and discharges certain points
• The drum is coated with oppositely charged toners
• The pattern on the drum is transferred to the paper
• The electrical charge is removed from the drum

Internal tech of Inkjet Printer[7]:

• Print Head[5]:
  • contains a large number of very small nozzles
  • ink is fed to each nozzle from a reservoir
  • fires droplets of ink onto the paper
  • The print head moves horizontally across the paper
  • ink is drawn from the reservoir ready for printing the next dot
• Stepper motor[2]:
  • Connected to the print head by a belt
  • Moves the print head across the paper

Components of Speaker:

w17 13 Q5 [3]

• diaphragm
• permanent magnet
• coil of wire

Internal tech of Speaker[4]:

w17 13 Q5 [4]

• An electric current in the coil creates an electromagnetic field;
• Changes in the audio signal causes the direction of the electric current to change,
• which changes the polarity of the electromagnet,
• and causes the coil to vibrate;
• The movement of the coil causes the diaphragm to vibrate and create sound waves.