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The Transport Layer

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Computer Networks Tutorial


Transport Layer : OSI Model

  • The Transport Layer is the middle layer(4th Layer) of the OSI Model. The Transport-Layer acts as the transition point between the functions performed by Upper layers(Application Layer, Presentation Layer, Session Layer) & Lower layers(Network Layer, Data Link Layer, Physical Layer).
  • This layer is responsible for end to end data transmission service using connection oriented or either through connection-less protocols.
  • Data received from Upper layers application are combined into data streams and are transmitted to the receivers end in exact format as it was in original.
  • Hiding of sensitive details of data from networks and providing data transmission in a transparent mode is also done by the transport layer itself.


Transport Layer : Functions & Features

  • Segmentation : Large data is divided into smaller segments at the senders end and then these smaller segments are recombined in exact format before it is received at receivers end.
  • Error Control : Distortion, Un-delivery of data packets and noise in data packets results in error and this is prevented using Transport Layer too and this feature is called Error Control.
  • Flow Control : Transport-Layer ensures that faster data transmission and slow data absorption or slow data transmission and faster data absorption must not occur.
  • Transport-Layer performs Multiplexing & De-multiplexing functions too.
  • Connection oriented service using TCP(Transmission Control Protocol) Protocol & Connection less service using UDP(User Data-gram Protocol) Protocol are performed by transport layer.


This image describes the architecture and working of transport layer in computer networks.

Transport Layer : Architecture


Transport Layer : Devices

  • Network Devices.
  • Network Gateways.