NETWORK LAYER&

TRANSPORT LAYER

NETWORK LAYER

IT IS RESPONSIBLE FOR THE SOURCE-TO-DESTINATION DELIVERY OF A PACKET

ACROSS MULTIPLE NETWORKS.

WHEREAS THE DATA LINK OVERSEES THE DELIVERY OF THE FRAME BETWEEN

TWO SYSTEMS ON THE SAME NETWORK.

. . . .

IF TWO SYSTEMS ARE CONNECTED TO THE SAME NETWORK, THERE IS NO NEED

OF THE NETWORK LAYER.

HOWEVER IF THE TWO SYSTEMS ARE CONNECTED TO TWO DIFFERENT

NETWORKS, THERE IS A NEED OF NETWORK LAYER TO ACCOMPLISH SOURCE TO

DESTINATION DELIVERY.

Relationship b/w network ,transport and data link layers.

Other

Responsibilities

LOGICAL ADDRESSING

PHYSICAL ADDRESSING IMPLEMENTED BY THE DATA LINK LAYER HANDLES THE

ADDRESSING PROBLEM LOCALLY.

BUT IF A PACKET PASSES THE NETWORK BOUNDARY, WE NEED ANOTHER

ADDRESSING SYSTEM TO HELP DISTINGUISH THE SOURCE AND DESTINATION

SYSTEMS.

NETWORK LAYER ADDS A HEADER TO THE PACKET COMING FROM THE UPPER LAYER

THAT INCLUDES THE LOGICAL ADDRESSES OF THE SENDER AND RECEIVER.

ROUTING

WHEN INDEPENDENT NETWORKS OR LINKS ARE CONNECTED TO CREATE A

LARGE NETWORK, THE CONNECTING DEVICES (ROUTERS) ROUTE THE PACKETS

TO THEIR FINAL DESTINATION.

NETWORK LAYER PROVIDES THIS MECHANISM.

Source-to-destination delivery

TRANSPORT LAYERTRANSPORT LAYER IS RESPONSIBLE FOR SOURCE-TO DESTINATION (END-TO-

END) DELIVERY OF THE ENTIRE MESSAGE..

WHEREAS THE NETWORK LAYER OVERSEES END-TO-END DELIVERY OF

INDIVIDUAL PACKET AND IT DOESN’T RECOGNIZE ANY RELATIONSHIP BETWEEN

THE PACKETS.IT TREATS THEM INDEPENDENTLY (EVEN IF THEY ARE NOT).

THE TRANSPORT LAYER ENSURES THAT THE WHOLE MESSAGE ARRIVES INTACT

AND IN ORDER.

Relationship b/w session, transport and network layer.

Other

Responsibilities

SERVICE-POINT ADDRESSINGCOMPUTERS RUN SEVERAL PROGRAMS AT SAME TIME. THIS MEANS DELIVERY

NO ONLY FROM ONE COMPUTER TO OTHER BUT ALSO FROM SPECIFIC PROCESS

ON ONE COMPUTER TO SPECIFIC PROCESS ON OTHER.

THE TRANSPORT LAYER THEREFORE INCLUDE A TYPE OF ADDRESS CALLED

SERVICE-POINT ADDRESS(PORT ADDRESS) .NETWORK LAYER GETS EACH

PACKET TO THE CORRECT COMPUTER AND THE TRANSPORT LAYER GETS THE

ENTIRE MESSAGE TO THE CORRECT PROCESS ON THE COMPUTER.

SEGMENTATION AND REASSEMBLY

A MESSAGE IS DIVIDED INTO TRANSMITTABLE SEGMENTS WITH EACH SEGMENT

CONTAINING A SEQUENCE NUMBER.

THESE NUMBERS ENABLE THE TRANSPORT LAYER TO REASSEMBLE THE

MESSAGE CORRECTLY AND IDENTIFY AN REPLACE PACKETS THAT WERE LOST IN

TRANSMISSION.

CONNECTION CONTROL

THE TRANSPORT LAYER CAN BE CONNECTIONLESS OR CONNECTION ORIENTED.

A CONNECTIONLESS TRANSPORT LAYER TREATS EACH SEGMENTS AS

INDEPENDENT PACKETS AND DELIVER IT TO TRANSPORT LAYER AT THE

DESTINATION MACHINE.

A CONNECTION-ORIENTED TRANSPORT LAYER MAKES A CONNECTION WITH

TRANSPORT LAYER AT THE DESTINATION MACHINE FIRST BEFORE DELIVERING

THE PACKETS. AFTER ALL DATA IS DELIVERED THE CONNECTION IS TERMINATED.

ERROR CONTROL

TRANSPORT LAYER CONTROLS ERROR BY PROVIDING A MECHANISM TO DETECT

DAMAGED, LOST AND DUPLICATE SEGMENTS.

ERROR CORRECTION IS ACHIEVED BY RETRANSMISSION OF THE SEGMENTS.

ERROR CONTROL IS PERFORMED PROCESS-TO-PROCESS RATHER THAN OVER A

LINK.

FLOW CONTROL

IF THE RATE AT WHICH THE DATA ABSORBED BY THE RECEIVER IS LESS THAN

THAT PRODUCED BY THE SENDER, THAN THE TRANSPORT LAYER IMPOSES A

MECHANISM TO AVOID OVERWHELMING THE RECEIVER.

THIS IS PERFORMED END-TO-END RATHER THAN ACROSS THE LINK.

Thank You !