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Network Data Units#

Datagram vs Segment vs Packet vs Frame vs Fragment

Datagram#

Datagram is only used in two places.

Usages:

  • UDP Datagram (Transport Layer)
  • IP Datagram (Network Layer)

Segment#

Usages:

  • TCP Segment (Transport Layer)

Packet#

Packet is the most general term to describe a unit of data in a network. Usually a packet is the actual data (payload) needs to be sent wrapped in some protocol-defined headers. Mostly use in Transport Layer and Network Layer.

Usages:

  • TCP Packet (same as TCP Segment) (Transport Layer)
  • UDP Packet (same as UDP Datagram) (Transport Layer)
  • IP Packet (same as IP Datagram) (Network Layer)

Frame#

Frame is only used in Link Layer or Physical Layer.

Fragment#

Fragment is used when data needs to be chopped/split into smaller pieces or fragments due to MTU (Maximum Transmission Unit) limitation.

References#