Transport Layer
The Transport layer is the 4th layer from the top, it provides communication services directly to the application processes running on the different hosts.
Several services provided by the transport layer are as follows:
- End-to-end delivery
- Addressing
- Reliable delivery
- Flow control
- Multiplexing
End-to-end delivery
The transport layer ensures end-to-end delivery directly from the source to the destination.
Addressing
The transport layer provides the user address which is explicitly mentioned as a station or port, the port variable represents a particular TS-user of a specified station known as a Transport Service access point (TSAP).
Reliable delivery
The transport layer retransmits the lost and damaged packets.
It has four aspects:
- Error control
- Sequence control
- Loss control
- Duplication control
Flow control
It is used to stop the sender from overloading the receiver with too much data. When overloaded with data, the receiver discards the packets and asks to retransmit them.
Multiplexing
Multiplexing is done to improve transmission efficiency. It can be done in the following two ways:
- Upward multiplexing
- Downward multiplexing
References