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Explain packet fragmentation with example.

Understanding Packet Fragmentation in Computer Networks

What is Packet Fragmentation?

  • Dividing a large data packet into smaller fragments.
  • Necessary when a packet exceeds the Maximum Transmission Unit (MTU) of a network link.
  • Ensures successful transmission across networks with varying MTUs.

The MTU's Role

  • Maximum Transmission Unit (MTU) defines the largest packet size a network can handle.
  • Different networks (e.g., Ethernet, Wi-Fi) have different MTUs.
  • Exceeding the MTU leads to packet loss or transmission errors.

Fragmentation Process

  • The source host divides the large packet into smaller fragments.
  • Each fragment contains a header indicating its sequence number and fragment offset.
  • Fragments are transmitted individually across the network.

Reassembly Process

  • The destination host receives all fragments.
  • The destination host reassembles the fragments based on their sequence numbers and offsets.
  • The original large packet is reconstructed.

Example Scenario

  • A host sends a 2000-byte packet over a network with a 1500-byte MTU.
  • The packet is fragmented into two fragments: a 1500-byte fragment and a 500-byte fragment.
  • Each fragment has its own header information.
  • Both fragments are transmitted separately.
  • The receiving host reassembles the fragments to reconstruct the original 2000-byte packet.

Potential Issues

  • Fragmentation increases network overhead due to multiple headers.
  • Packet loss of a single fragment results in the need for retransmission.
  • Incorrect reassembly due to lost or misordered fragments causes errors.
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