2.1 Types and methods of data transmission

Types of data and transmission

Analogue Data

• Continuous, non-discrete data. Example: Sound wave

Digital Data

• Discrete data with only two values (binary)

Analogue Transmission

• Continuous electrical signal in the form of a wave
• Many communication media uses analog (landlines)

Digital Transmission

• Sends data as distinct pulses (either on or off)
• Works similarly to how data travels through computer

ADC: Analogue to Digital converter
DAC: Digital to Analogue converter
ADC and DAC are required when computers use analogue transmission

Packets:

Data is broken down into packets to be transmitted
A packet of data contains

• Packet Header

  • Destination address
  • Packet serial number
  • Originator’s address
  • Packet Size

• Payload

  • The Actual data

• Trailer

  • A Method of identifying that it’s the end of packet
  • An error-checking method

Packet Switching

• Data is broken down into packets
• Each packet could take a different route
• A router controls the route a packet takes
• Packets may arrive out of order
• Once the last packet has arrived, packets are reordered

Methods of Data Transmission (Classified by size)

Serial

• One bit sent at a time over a single wire
• Benefits:
  • More accurate over long distance
  • Data less likely to be out of sync
  • Cheaper
  • Less chance of data corruption
• Drawbacks:
  • Slower
  • Suitable for smaller data size
• Applications: Telephone lines, Modem and computer connection

Parallel

• Data of several bits (usually 1 byte) is sent down several wires at the same time.
• Benefits:
  • Faster
• Drawbacks:
  • Many wires may lead to interference/crosstalk¹
  • More expensive
  • Cannot be used in long distance
  • Difference in voltage between wires may cause jitter
• Applications: Internal circuits (buses), data from computer to printer

Methods of Data Transmission (Classified by direction)

Simplex

• Data sent in one direction only
• Examples: Television broadcasting, Sensor to computer, Input device to computer, computer to output device, Sending data to or from a device

Half-Duplex

• Transmission in both directions but not at the same time
• Example: Walkie-talkie

Full-Duplex

• Transmission in both directions simultaneously
• Example: Telephone call, Voice over IP, Instant messaging, Broadband connection, Video conferencing

Universal Serial Bus (USB)

• A serial data transmission method used for external data transfer
• USB consists of:
  • Four-wire shielded cable
  • Two wires are used for power and earth
  • Two wires are used in data transmission
• Advantages:
  • Device detected automatically
  • Fits only one way
  • Backward Compatible
  • Industry Standard
  • Supports multiple data transmission speeds
  • Can be used to power device
• Disadvantages
  • Maximum cable length is 5 meters
  • Might have overheating issues
  • There is a limit in transmission rate