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Multiplexing & Demultiplexing

COMP211 Lectures

These notes are low-effort, due to catching up in this module. See the videos and slides for more detail.

Demultiplexing

Each IP datagram carries the source and destination IP address and a transport-layer segment. This segment includes:

  • Source Port
  • Destination Port
  • Other Header Fields
  • Application Data

Connection-less Demultiplexing

This is used by UDP. To create a socket you can use the following Java code:

DatagramSocket socketName = new DatagramSocket(12345);

IP/UDP datagrams with same destination port #, but different source IP addresses and/or source port numbers will be directed to same socket at receiving host.

Connection-Oriented Demultiplexing

TCP socket is identified by a 4-tuple:

  • Source IP Address
  • Source Port Number
  • Destination IP Address
  • Destination Port Number

The receiver uses all four values (4-tuple) to direct the segment to the appropriate socket.

Server may support many simultaneous TCP sockets:

  • Each socket is identified by its own 4-tuple.
  • Each socket is associated with a different connecting client.

Differences

  • UDP - Demultiplexing using destination port number (only).
  • TCP - Demultiplexing using 4-tuple: source and destination IP addresses, and port numbers.