Types and Methods of Data Transmission (Copy)

When large data is transmitted over a network, it is divided into smaller, manageable units called packets.
Reasons for using packets:
- Efficient use of network bandwidth.
- Easier error detection and correction.
- Prevents single transmission errors from corrupting entire files.
- Allows packets to take different routes, optimising network traffic.

Packet Header – Contains control information:
- Destination address – IP address of the recipient device.
- Originator’s address – IP address of the sender.
- Packet number – Sequence number so packets can be reassembled in correct order.
- Protocol information – Communication protocol details (e.g., TCP, UDP).
Payload – The actual data being transmitted (e.g., part of a file, image, or message).
Trailer – Contains error detection data:
- Checksum or Cyclic Redundancy Check (CRC) to ensure data integrity.
- May also signal the end of the packet.

Step-by-step:
1. Sender breaks the message/file into packets.
2. Each packet is given a header and trailer.
3. Packets are sent independently across the network.
4. Routers examine destination addresses and choose the best available route for each packet (routes may differ).
5. Packets may arrive out of order due to different routes taken.
6. Receiving device buffers packets until all arrive.
7. Packets are reordered based on their sequence numbers.
8. Error checks are performed using checksums.
9. Missing or corrupted packets are re-requested.
Advantages of packet switching:
- Efficient network usage.
- Fault tolerance (packets can be rerouted).
- Reduces transmission delay in congested networks.
Disadvantages:
- Packets can arrive out of order or be delayed.
- Requires more processing at the destination.

Serial Transmission
- Sends bits one after another over a single channel or wire.
- Advantages:
  - Reliable over long distances.
  - Requires fewer wires.
  - Less risk of data skew (misalignment).
- Disadvantages:
  - Slower than parallel for short distances.
- Uses: USB, network cables.
Parallel Transmission
- Sends multiple bits simultaneously over multiple wires.
- Advantages:
  - Higher speed for short distances.
- Disadvantages:
  - Data skew over long distances due to signal timing differences.
  - Requires more wiring (bulkier cables).
- Uses: Internal computer data buses, older printer connections.

Simplex
- Data flows in one direction only.
- Example: Keyboard to computer.
- Advantage: Simple design.
- Disadvantage: No feedback possible.
Half-Duplex
- Data flows in both directions, but only one direction at a time.
- Example: Walkie-talkies.
- Advantage: More efficient than simplex for two-way communication.
- Disadvantage: Can’t send and receive simultaneously.
Full-Duplex
- Data flows in both directions simultaneously.
- Example: Telephone calls, modern Ethernet.
- Advantage: Fastest method for two-way communication.
- Disadvantage: More complex hardware needed.

Uses serial transmission to send data bit by bit over a pair of data lines.
Supports plug-and-play – devices are recognised automatically when connected.
Provides power supply to devices (e.g., charging a phone).
Uses differential signalling for error reduction.

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