Internetworking and network layer

Jun 16 • Notes • 3808 Views • 2 Comments on Internetworking and network layer


The physical layer and the data link layer of the particular network locally.These two layers are used for the delivery of the data on the network from one node to the other node.

The internetwork is made of five networks-4 LANs and 1 WAN.




Need for Network Layer-

  • To solve the problem of the delivery through different links the network or the internetwork layer was designed.The network layer is responsible for host to host delivery and for the routing of the packets through switches.
  • When the packet arrives the switch consults its routing table and then finds the interface.e from which the packet must be sent.Then the packet after some changes in the header with the routing informations are passed to the data link layer.The network layer at the destination is responsible for some address verification.

Internet as a Datagram Network

The internet at the network layer is the packet switched network.The internet has been chosen as the datagram approach to the switching in the network layer.It uses the universal addresses defined in the network layer to route packets from the source to the destination.The switching at the network layer in the internet uses the datagram approach to the packet switching.Packets in the IPv4 layer are called as datagrams.



 datagram map

datagram map

Internet as a Connectionless Network-

The delivery of the packet can be accomplished by connection oriented or connection less network.In the connection oriented the source first makes the connection with the destination before sending the packet.after the connection is established a sequence of the packets from same source to the destination are sent one after the other in the sequential manner.when all the packet data are sent the connection is terminated.


A datagram can flow through different networks.Each router decodes the Ipv4 datagram from the frame it receives then processes it further encaptulates it in the other frame.The size of the frame  received depends on the protocol used by the physical layer through which the frame travelled.


The implementation of the checksum in the IPv4 packet follows the same principles.

  • The value of the checksum field is set to 0.
  • The header is divided into 16 bit sections and then added together.The result is complemented then inserted into the chechsum field.
  • The checksum in the IPv4 covers only the packets not data.


The header of the Ipv4 datagram is made up of the two parts

  • fixed part
  • variable part.

The fixed part is 20 bytes long and the variable part is around 40 bytes long.

Option as the signifies that are not required by the datagram.They can be used for the network testing and debugging.The options are not required for the Ipv4 header option processing is required for the Ipv4 software.



1.Larger address space

2.Better header format

3.New options to allow functionality

4.Allowance for extension for more security

Packet Format

Each packet is compised of the base header followed by the payload.The payload consists of the two parts-

1.optional extention header from the upper header

Extension Headers

The length of the base header is fixed at 40 bytes.To give greater functionality to the IP datagram the base headers can be followed by upto six extension headers.May be these headers are the options in the IPv6.


Due to the huge number of the systems on the internet the transition from IPv4 to IPv6 can’t happen suddenly.It takes considerable amount of the time before every system in the internet can move from IPv4 toIPv6,The transition must be smooth to prevent any losses in the system.


1.What is the need for network layer??

Ans-To solve the delivery through the different layers the network layer or the inter network layer was designed.It is responsible for the host to host delivery and the routing of the packet through switches.

2.Explain internet as the datagram network.

Ans-The internet has been chosen as the datagram approach to the switching in the network layer.It makes the use of the universal addresses defined in the network layer to route packets from souce to destination.

3.Give the advantages  of using Ipv6.

Ans-The advantages are-

  • Larger address space
  • Better header format
  • New optios to allow functionalities
  • Allowance for extention
  • support for more security

IES Syllabus-

1. IES Syllabus for Electronics and Telecommunication

2.IES Syllabus for General ability

GATE Syllabus-

1.Gate Syllabus for Electronics and Telecomm.

2. GATE syllabus for Computer Science and Information Technology 2014

3.GATE syllabus for Engineering Science

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2 Responses to Internetworking and network layer

  1. sunny says:

    After reading this article my knowledge about internetworking and network layer has increased through

  2. Dinesh says:

    In Interview the first question about the networking is abut the layers…

    this article gives the superb and quick overview about the network layers so this is a weightaged article

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