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Transport Services and Protocols

• Provide logical communication between application processes running on different hosts
  • Logical communication: The two connecting sides; the sender and the receiver are logically connected to each other by a direct link
  • In real life hosts may be hundreds of kilometers apart but in a logical view they are directly connected
• Transport protocols provides communication services directly to applications running on end systems
• Role of Transport Protocols:
  • Send side:
    • Breaks application-layer messages into smaller chunks called segments
    • Passes these segments to the network layer
  • Receive side:
    • Reassembles received segments into the original message
    • Delivers the reassembled message to the application layer
• Transport protocol available to apps: TCP, UDP

Transport layer vs. Network layer

• Network Layer → Provides logical communication between hosts
• Transport Layer → Provides logical communication between processes

Multiplexing and Demultiplexing

Multiplexing

• When a process sends data to transport layer through sockets, transport layer is going to:
  • multiplex the data and put it in segments
  • add information into the transport layer header that is going to be used later for demultiplexing

Demultiplexing