The function of Transport Layer

Computer Networks:

Physical Layers

Data link Layer(DLL)

Network Layer

Transport Layer:

Session and Presentation Layer:

Application Layer:

Function Of Transport Layer

Transport Layer

Transport Layer is the fourth Layer from the top of the OSI model.
Transport Layer is to provide the communication service directly to the application process running on different host.
Transport Layer is responsible for ensuring the data packets arrived at the destination and.
transport layer mostly often used TCP or UDP.

Working of transport layer

1) At the Sender Side:

Transport layer receive the data from application layer and perform segmentation (divide the message into segments, adds the source and destination port number into the header of the segment) and transfer the message to the network layer.

2) At receiver site:

At receiver side the transport layer receives data from the network layer, then identify the port number and forward the message to the appropriate port in the application layer.

Responsibilities / function of transport layer:

End to End delivery.
Addressing.
Reliable delivery
Flow control
Multiplexing

End To End delivery:

The transport layer transmit the entire message to the destination therefore it ensures the end to end delivery of the entire message from source to the destination.

Reliable delivery:

It is ability to correct error that can happen during data transmission over the network if data is accidentally change in the transmit, error correction and checksum would perform.

Reliable delivery has four aspect:

Error control
Sequence control
Lost control
Duplication control.

Error control:

The primary role of Reliability is error control, transport layer protocols are designed to provide error free transmission. The data link layer also provide the error handling mechanism but it ensures only node to node error free delivery, where is the transport layer ensures error free at the end to end.

Sequence control:

At the sender side the transport layer divide the data into segments with header files, at the receiver side the transport layer ensures that the segments of the transmission can be correctly assemble.

Lost control:

The transport layer insurance that all the fragments/ segments arrive at the destination not some of them. It insurance that all the segments received at the receiver side.

Duplicate control :

The transport layer guarantees that no duplication data arrive at the destination. Sequence number are used to identify the loss packet it also discarded the same sequence number at receiver site.

Follow control:

The transport layer provides a flow control mechanism between the systems. TCP also provide data loss due to the fast sender and slow receiver by imposing some flow control technique. It use the method of sliding window protocol which is accomplished by the receiver by sending a window back to the sender informing the size of the data it can receive.

Multiplexing and Demultiplexing

Multiplexing is when data is acquired from several processes from the centre and merge into one packets along with header and send a single packet. Multiplexing allows the simultaneous use of different processes over and network that is run on a host the processes are different differentiate it by their port number.

De multiplexing 12 many is required at the receiver site when the message is distributed into different processes transport received the segment of data from the network layer distributed and deliver it to it to the appropriate processor running on the receiver machine.

Addressing:

Addressing is ability to communicate with the correct application on the computer addressing typically uses network ports to assign each centre and receiver application specific port number on the machine. But combining the IP addresses used in the network layer and the port of the transport dear each application can have a unique address