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So now we're in the fourth layer of the OSI reference model, the transport layer.

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Welcome to the layer of TCP.

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The transport layer is the level at which system reliability and quality are ensured.

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The basic function of the transport layer is to accept data from the layer above.

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Split it up into smaller units.

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Pass these data units to the network layer.

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And ensure that all the pieces arrive correctly at the other end.

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Okay, so now let's look at the functions of the transport layer in detail.

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Service point addressing.

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Transport layer header includes service point address, which is the port address.

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This layer gets the message to the correct process on the computer, unlike network layer, which gets

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each packet to the correct computer.

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Segmentation and reassembling.

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A message is divided into segments.

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Now, each segment contains a sequence number which enables this layer to reassemble the message.

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The message is reassembled correctly upon arrival at the destination and replaces packets which were

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lost in transmission.

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Connection.

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Control.

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It includes two types connectionless transport layer.

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Each segment is considered as an independent packet and delivered to the transport layer at the destination

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machine.

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Connection oriented transport layer.

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Before delivering packets.

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Connection is made with the transport layer at the destination machine.

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Flow control.

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In this layer, flow control is performed end to end.

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The rate of data transmission between two nodes must sometimes be managed to prevent a fast sender from

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transmitting more data than can be supported by the receiving data buffer, causing a buffer overrun.

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And we don't want that.

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Error control.

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Error control is performed end to end in this layer to ensure that the complete message arrives at the

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receiving transport layer without any error.

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Error correction is done through retransmission.

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On the Internet, TCP and UDP provide the services for most applications.

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Coming up next, we'll look at all the other details of the transport layer under TCP and UDP topics.