Types and Methods of Data Transmission

2026 What You Need to Know (Syllabus Objectives)

By the end of these notes, you should be able to:

  1. Packets and Packet Switching

    • Understand that data is broken down into packets to be transmitted
    • Describe the structure of a packet (header, payload, trailer)
    • Describe the process of packet switching

  2. Methods of Data Transmission

    • Describe how data is transmitted using serial, parallel, simplex, half-duplex, and full-duplex methods
    • Explain the advantages and disadvantages of each method
    • Explain which method is most suitable for different scenarios

  3. Universal Serial Bus (USB)

    • Understand the USB interface and how it transmits data
    • Explain the benefits and drawbacks of USB

1. Data Packets

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What Are Data Packets?

When you send data over the internet (like an email, photo, or video), it doesn't travel as one big chunk. Instead, it gets broken down into small pieces called packets.

Think of it like sending a long letter: instead of mailing one giant envelope, you tear the letter into smaller pieces, put each piece in a separate envelope, and send them all. At the other end, someone puts all the pieces back together to read your full letter.

Why use packets?

  • Small pieces of data are faster and easier to send through networks
  • If one packet gets lost or damaged, you only need to resend that small piece, not the whole file
  • Different packets can take different routes through the network, making the overall transmission more efficient

Structure of a Packet

Every packet has three main parts:

1. Packet Header

This is like the address label on an envelope. It contains important information needed to deliver the packet:

  • Source address (originator's address) - where the packet came from (the sender's IP address)
  • Destination address - where the packet needs to go (the receiver's IP address)
  • Packet number - which piece this is (e.g., packet 1 of 5, packet 2 of 5, etc.)

2. Payload

This is the actual data being sent - the real content you want to transmit. It could be part of a text message, a piece of an image, a chunk of a video, or any other type of data.

3. Trailer

This comes at the end of the packet and contains:

  • Error-checking information - helps detect if the data got corrupted (damaged or changed) during transmission
  • End of packet notification - signals that the packet is complete

Example of How Data Is Packeted

Let's say you want to send the message "THIS IS A MESSAGE :)" over the internet.

The message would be broken down into 4 packets:

Packet 1:

  • Header: Source IP: 197.34.213.4, Destination IP: 185.124.20.1, Packet number: 1
  • Payload: "THIS"
  • Trailer: Error check, end notification

Packet 2:

  • Header: Source IP: 197.34.213.4, Destination IP: 185.124.20.1, Packet number: 2
  • Payload: "IS A"
  • Trailer: Error check, end notification

Packet 3:

  • Header: Source IP: 197.34.213.4, Destination IP: 185.124.20.1, Packet number: 3
  • Payload: "MESSAGE"
  • Trailer: Error check, end notification

Packet 4:

  • Header: Source IP: 197.34.213.4, Destination IP: 185.124.20.1, Packet number: 4
  • Payload: ":)"
  • Trailer: Error check, end notification

Error Checking

Error checking helps make sure that packets arrive correctly without corruption.

Corruption means the data in a packet has been changed, lost, or gained extra information that wasn't originally there. This can happen due to interference or problems during transmission.

The trailer contains information that allows the receiving device to check if the data arrived correctly. If corruption is detected, the receiver can request that packet to be sent again.

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