Chapter 2 (Data Transmission)

• Hexadecimal representation is a way of representing data using 16 symbols, typically the digits 0-9 and the letters A-F.
• What does a packet contain?

  Packet Header

  Payload

  Trailer
• Definition of Packet Header

  Contains information about contents of packet and destination
• Definition of Payload

  Actual data that user sends to receiver
• Definition of Trailer


  Contains information about any error checking methods that may be used
• Define Packet Switching

  Method of transmitting data packets across a network. Each data packet is able to take an individual pathway across the network.
• Definition of Network


  Computers and devices are joined using cables or wireless technology
• Define Router

  Network component that examines a data packet
• Methods of Data Transmission

  Serial

  Parallel

  Simplex

  Half - duplex

  Full - duplex
• What is serial and parallel data transmission


  Serial - Data is sent one bit at a time down a single wire

  
  

  Parallel - Data is sent multiple bits at a time down multiple wires
• List down some advantages and disadvantages of Serial Data Transmission

  Advantages:

  Less chance of data being skewed (Wrong order)

  Less chance of interference

  Cheaper to manufacture and buy

  
  

  Disadvantages:

  Slow to transmit data
• List down some advantages and disadvantages of Parallel Data Transmission

  Advantages:

  Fast to transmit data

  
  

  Disadvantages:

  Increases risk of data being skewed

  More chance of interference, meaning higher chance of error in data

  Expensive to manufacture and buy
• Define

  Simplex Half-duplex Full-duplex

  Simplex - Data is transmitted in a single direction only

  
  

  Half-duplex - Data is transmitted in both directions but only one at a time

  
  

  Full-duplex - Data is transmitted in both directions at same time
• What does USB stand for

  Universal Serial Bus
• Advantages and Disadvantages of USB

  Advantages

  Less errors in connecting devices are likely to be made

  Data can be transferred quickly

  USB can be used to power a device, so no need for another power source

  
  

  Disadvantages

  Length of USB is limited

  Transmission speed isn't as fast as ethernet
• What are the three error detection methods

  Parity check

  Checksum

  Echo Check
• Define Parity Check

  Parity Check - Error detection method that adds an additional bit to each byte to create an odd or even sum
• Define Checksum

  Checksum - Performs calculation on data to create a checksum value. The value will be compared after transmission to see if they match
• Define Echo Check

  Echo Check - Sends copy of transmitted data back to sender to compare with the original data sent
• Automatic Repeat Request (ARQ)

  
  

  What are two main ways that an ARQ can operate

  Acknowledgement - Message sent from one device to another to indicate whether data is received correctly

  
  

  Timeout - Period of time set and used to wait for an acknowledgement to be received
• Process of negative acknowledgement method


  Send device transmits first data packet

  Receive device gets data and check for errors

  If receive device detects errors, sends a - acknowledgement to sender

  Sender receives - acknowledgement, knows data was received incorrectly, resends data packet.

  Timeout is set by send device.

  If send device doesn't receive - acknowledgement within set time period.

  Sends next data packet.