The transport layer is the fourth layer of the Open System Interconnection (OSI) model. In this layer, all the modules and processes for transporting/transmission of the data have been put under this layer.
The transport layer establishes a connection with a distant network host. The transport layer establishes an end-to-end or peer-to-peer secure connection between processes on two distant network hosts.
It takes data from the upper network layers (such as from the application layer), breaks those data into smaller-sized segments, calculates all the bytes, and delivers them to its lower layer (network layer). gives off.
So in this way you can understand the transport layer that its main function comes under these functions:
- Taking data from the upper network layer,
- than breaking those data into smaller chunks,
- giving these data units to the network layer, and
- Making sure all the pieces reach the other end properly.
Functions of transport layer
- Service point addressing
- Connection control
- Flow control
- Segmentation and reassembly
- Error control
Service point addressing:-
In this layer the header holds a service point network address which is the port address.
This layer receives the message of the computer system being the correct process, which is helpful in delivering each data packet to the correct computer. This does not happen at the network layer.
These are of two types:
- Connectionless Transport Layer – In this, all the small segments are assigned the status of a separate independent data packet and then delivered to the transport layer of the destination machine.
- Connection-Oriented Transport Layer – In this, the connection or connection with the destination machine is established even before the data packet reaches the right place.
Flow control helps the network receiving data packets in the data link layer to capture the congestion inside the data. Then he warns all the neighbors above or below the surface in advance of this.
These devices then pass this congestion information to the upper layer protocols so that the transmission of data can be restored.
Segmentation and reassembly:-
Before sending any message, it is divided into smaller segments, each segment has a sequence number which helps in reassembling any message back together in its order.
As soon as the message reaches it is reassembled and the packets lost in transmission are also replaced.
In this layer, error control is performed over the end-to-end network to ensure that the transport layer that receives the message, receives the complete message. Error correction is done by retransmitting.
Transport layer protocols
transport layer protocols two types:-
- TCP:- Transmission Control Protocol
- UDP:- User Datagram Protocol
TCP is a reliable protocol which means that the destination receiving the message always sends positive or negative messages about the data packet so that the sender knows that the data packet has reached properly or no.
If a positive message is received, the sender is assured and if a negative message is received by the receiver, the data packets are re-sent.
Some of the features of TCP are:-
- It takes into account the activity that the receiver receives the data in the order in which the data is sent to it.
- It is a connection-oriented protocol. This means that it is necessary to establish a connection between the source and the destination before transferring the data, otherwise, it will not work.
- It also provides mechanisms to check errors and recover data.
- It establishes an end-to-end communication system and provides quality of service as well as flow control.
- It operates in client-server point-to-point mode.
- Most importantly, it provides a full-duplex server which means it fits the role of both sender and receiver.
It is a simple transport layer communication protocol that requires very little communication mechanism. It uses a network IP service for delivery. In this, the sender does not expect any kind of message from the receiver, due to which its processing becomes very easy.
Some of its other features are as follows:-
- UDP is used when the sender does not require any kind of acknowledgment from the receiver.
- UDP is the best protocol for data packets flowing in the same direction.
- It is simple and prefers query-based communication. It is stateless.
- It does not guarantee the delivery of the data i.e. it does not tell whether the data has reached the receiver or not.
- It is a suitable protocol for VoIP or multimedia streaming.