A research paper on the concept of network layer explaining its terminologies, uses, and functionalities. This paper was presented by me as an NTCC report in 2nd Year of B.Tech Computer Science.

1. A Project Report
On
Network layer
Submitted to
Amity University, Uttar Pradesh
In partial fulfillment of the requirements for the award of the degree
Of
Bachelor of Technology
In
Computer Science and Engineering
SUBMITTED BY: UNDER SUPERVISION OF:
Mr. Rishabh Shukla Ms. Nidhi Chandra
A2305216665 Dept. Of computer science
3CSE-3(Y) ASET, Noida

2. Declaration by the student
I, Rishabh Shukla student of B. Tech. (CSE) hereby declare that the project titled
“Network layer” which is submitted by me to Department of ASET, Amity University,
Uttar Pradesh, Noida, in partial fulfilment of requirements for the award of the degree of
Bachelor of Technology in Computer science, has not been previously formed the basis
for the award of any degree, diploma or other similar title or recognition. The Author
attests that permission has been obtained for the use of any copy righted material
appearing in the Dissertation / Project report other than brief excerpts requiring only
proper acknowledgment in scholarly writing and all such use is acknowledged.
Signature
Noida
Date
Name and Signature of Student

3. CERTIFICATE
This is to certify that Mr. Rishabh Shukla student of B.Tech. in Amity School of
Engineering and Technology has carried out the work presented in the project of the
term paper entitle ‘NETWORK LAYER’ as a part of the first year program of
Bachelor of Technology in Computer science & Engineering from Amity School of
Engineering and Technology, Amity University, Noida, Uttar Pradesh under my
supervision.
Ms. Nidhi Chandra
Dept. Of computer science
ASET, Noida.

4. ACKNOWLEDGEMENT
I would like to take this opportunity to express my gratitude towards all the people who
have in various ways helped in the successful completion of the project. I must convey
my gratitude to my project and faculty guide Ms. Nidhi Chandra for giving me the
constant source of inspiration and help in preparing the project, personally correcting
my work and providing encouragement throughout the project.
I also thank all my faculty members for steering me through the tough as
well as easy phases of the project in a result-oriented manner with concern attention.
Finally, I would like to thank my friends, family because it was their support,
encouragement and sources of knowledge are responsible for the success of this term
paper. If the support shown by the above members was not available then I doubt the
project would not be so easily completed by me.

5. CONTENTS
1. Abstract
2. Introduction
3. Network layer
4. Internetworking
5. IP prefix
6. IP forwarding
7. IP helper(DHCP AND ARP)
8. Packet fragmentation
9. Routing
10. Dijkstra’s algorithm
11. Conclusion
12. References

6. ABSTRACT
The layer, which controls the operation of the subnet is known as Network Layer. It is
the third layer in OSI model. It supervises host-to-host packet delivery – several
physical networks could separate hosts.
This layer helps in controlling the traffic in subnet network. It helps in identifying each
device uniquely to allow global communication. While the UDP and DHCP are the IP
helpers.
It decapsulates packets from one and encapsulates them for another network. Through
internetworking, we can connect different types of networks to send the packet where
packet fragmentation takes place.
The network layer provides the functional and procedural means of transferring data.
It determines the optimal route for sending a packet from one host to another and
encapsulate packets received from upper-layer protocols. The network layer responds
to issues service request to the data link layer and service requests from the transport
layer.

7. INTRODUCTION
The Open Systems Interconnection model (OSI) is created by International Standards
Organization as a framework, reference model to explain how different networking
technologies work together and interact.
It is categorized into seven logical layers. Each layer has specific functions. All layers
work together in the correct order to move data around a network.

8. NETWORK LAYER
Out of seven OSI layers, network layer serves at third place. We need network layer as
it sends frames between the hosts and it networks with links and switches. There are
various shortcomings as it fails at large networks as routing table blows off. Moreover,
it does not work across one link layer technology. The main functionality of network
layer is scaling, heterogeneity and bandwidth control.
SERVICES PROVIDED BY NETWORK LAYER TO TRANSPORT LAYER
The network-service model defines the characteristics of end-to-end transport of data
between one end of the network to the other, i.e. between sending and receiving end
systems.
1. DATAGRAMS ‘OR’ CONNECTIONLESS SERVICE
2. VIRTUAL CIRCUITS; CONNECTION ORIENTED SERVICE
Both models implement store and forward packet switching. When routers receive the
complete packet, they temporarily store it until forwarding.
DATAGRAM MODEL
The general name for packets containing a destination address.
Each router contains a forwarding table. Packets may take different paths between the
same source and destination.

9. VIRTUAL CIRCUIT MODEL
These packets contain a short label. (no global meaning and is unique for a link)
Phases:
The connection should set up and the path should be chosen.
Data transfer
Circuit is deleted

10. INTERNETWORKING
Internetworking is a method to connect a network to other networks through gateways
that provide a common route to information packets between networks.
Internetworking makes it possible for networks to make a data connection between
them, operated by different entities using a common data communication.
Pioneered by Vint Cerf and Robert E. Kahn, also known as “father of the internet".
WHY WE NEED INTERNETWORKING?
1. Difference in service models (datagram model or virtual circuit model)
2. Addressing
3. Quality of service
4. Packet size (Different link layer technology can handle different size packets)
5. Security (whether encrypted)
IPv4 (INTERNET PROTOCOL)

11. 1. Header
2. Version
Protocol version
3. IHL
32-bit bytes-header length
4. Type of service
It gives the combination of reliability and speed.
5. Total length
It tells the total length of the entire datagram.
6. Identification
All fragments have the same identity.
7. DF
Don't Fragment and destination cannot reassemble.
8. More Fragments
It means it is the last segment.
9. Fragment offset
Fragment number within a datagram, minimum of 8-byte fragments.
10. Time to live
11. Header checksum
Its function is to verify the headers.
12. Source and Destination Address
It is the 32-bit IP address of the source and the destination.

12. IP ADDRESSES AND IP PREFIXES
IPv4 uses 32-bit address and the IPv6 uses the 128-bit address. Regional Internet
Registries (RIRs) allocate chunks of address space as contiguous ranges of addresses,
each of which constitutes a "prefix". IP prefix is a contiguous range of addresses
containing a number of addresses that is a power of two and with the smallest address
being a multiple of that same power of two. The value of static IP address will not
change in the network while dynamic is always temporarily assigned when an internet
connection is made.
I.e. for example:128.12.0.0/16 is 128.12.0.0
 More specific prefix has a longer prefix and smaller number of IP addresses.
 Less specific prefix has a shorter prefix and a large number of IP addresses.
PUBLIC IP ADDRESSES
 Has a valid destination on the global internet
 They must be allocated to you before
 IPv4 mostly exhausted time for Ipv6.
PUBLIC IP ADDRESSES
 Can be freely within private networks (company, home)
 for example:15.0.0.0/19
To connect private network to public network we need to connect public IP address and
NAT (Network address translation) to connect to the worldwide internet.

13. ALLOCATION OF PUBLIC IP ADDRESSES
IANA (Internet Assigned Network authority) delegates IP addresses to regional bodies
such as APNIC (Asia Pacific), RIPE (Europe), LACNIC (Latin America) etc.
Regional bodies delegate the IP addresses to companies in their region. Companies
Further provide it to their customers.
IP FORWARDING
It is a process used to determine the path used to send a packet or a datagram. In IP
forwarding one prefix contains all the IP addresses of the network. We can put the entire
entry for one prefix. To list the next hop for IP prefixes the Node uses a table.
LONGEST MATCHING PREFIX:
Prefixes in the table might overlap to overcome this longest matching forwarding rule is
followed. For each packet, find the longest prefix containing the destination address i.e.
the most specific entry.
Forward the packet to the next hop router for that prefix.
Distinction between hosts and router-
The router does the routing followed by forwarding while Hosts send the data traffic to
the nearest router.
Host forwarding table uses 0.0.0.0/0 as a default route that catches all IP addresses.
FLEXIBILITY OF THE LONGEST MATCHING PREFIX
 To provide default behavior we can add a less specific prefix to the forwarding table.
It is used to send the traffic going outside an organization to a border router.
 We can add the more specific prefix to provide a special behavior in case of security
where you want to send the packet to the longer path.

14. IP HELPERS
We did manual configurations to get the IP address in old days but now protocols are
used for automatically configuring addresses. This shifts the burden from the user to the
IT folks.
 DHCP (Dynamic host configuration protocol) -
It is been around since 1993 and is now widely used to lease the IP address to the nodes
and provide other parameters like network prefix, the address of a local router, DNS
server etc.
It runs over UDP ports 67, 68 and is a client server application.
If a node lost its connection it will send a broadcast message to all hosts and it would be
received by the DHCP server to get it configured in ipv4 this message is in form of
255.255.255.255.
DHCP MESSAGES:
The client and the DHCP server must be in one IP hop. First, the client sends the
message call to discover to the server. The server responds it which is referred as offer
.then the host sends the request to the server that it likes to take that address. After that,
the server sends an acknowledgment to the host.
Once the lease is over, need to repeat the process.

15.  ARP (Address resolution protocol) :
Sending an IP packet arises a problem because a node needs a link layer address to send
the frame over the local link and how to get the destination link address from the
destination IP address. This is provided by ARP.
Source
ethernet
Dest.
Ethernet
Source IP Dest. IP Payload
From ARP: From DHCP
ARP sits right on top of the link layer.it asks node with the target IP to identify itself
and uses the broadcast message.
ARP
ETHERNET
The node sends the request, which is broadcast. The target sends the reply.
There is discovery protocol that helps to find nodes each other like zero-conf, bonjour.

16. PACKET FRAGMENTATION
We use packet fragmentation to connect networks with different maximum packet sizes.
We either need to split the packets or discover the largest size to use.
Different networks have different maximum packet sizes called MTU (Maximum
Transmission Unit) . For example:
Ethernet 1.5K
WiFi 2.3K
We prefer large packets for efficiency. We will send few bits sending those headers and
routers have to process few packets to process same information.
There are two types to solve packet size solution. One is the fragmentation method
where we split large packets in the network if they are too big to send. The other is the
discovery method where the largest packet that fits on the network path and uses it.
IPv4 routers perform fragmentation while the IPv6 do not fragment and drop the packet
larger than MTU.
IPv4 Fragmentation
Routers fragment packet that is too large to forward. While
the receiving host reassembles to reduce a load on the router.

17. IPV4 FRAGMENTATION PROCEDURE:
*Routers split a packet that is too large. Typically break into large pieces.
*Copy IP header to pieces
*Adjust length on pieces
* Set offset to indicate position
*Set more fragments on all pieces except last.
Host receive if that means the packet has been fragmented and reassembles them.
Identification field link pieces together, MF tells receiver when it has all pieces.

18. ROUTING
ROUTING FORWARDING
Process of deciding in which process of sending
The direction the traffic should be sent. Packet on its way.
Spanning trees provides basic connectivity while routing uses all the links to find the
best path.
ALGORITHM PROPERTIES:
1. Correctness
2. Simplicity
3. Stability
4. Optimality
5. Scalability
6. Fairness

19. Further routing can be classified as :
*Adaptive Routing
It is centralized, adaptive and distributive.
*Nonadaptive routing
It uses the shortest routing using algorithms.
SHORTEST PATH ROUTING
It minimizes the number of hops along the path. Minimizes the mean packet delay and
maximizes the network throughput.

20. DIJKSTRA’S SHORTEST PATH ALGORITHM
In this process mark all the nodes with infinite distance except source.
Sink node=destination node
Working node=source node
1. Mark the working node permanent
2. Examine the adjacent nodes in turn
3. Examine the tentative nodes and mark the node with the node with the smallest
labelled value as permanent,
4. This node becomes the new working node.
Working node is not equal to sink.
5.Reconstruct the path backward from sink to source.

21. Conclusion
The Network layer is highly focused on getting the packet from source to destination.
Sometimes it does it through different networks where internetworking comes into play.
It has also been helpful for transport layer by providing datagram and virtual circuit
model.
The packets are fragmented when sending through different networks. While the IP
helpers ARP and DHCP shifts the burden of manual configuration from user to IT folks.
Routers help in sending packets over the network as it contains routing table. The
network layer must know the topology of the subnet and choose appropriate paths
through it.

22. References
1. Network Layer - https://en.wikipedia.org/wiki/Network_layerwww.cs.bgu.ac.il
2. Osi Model - https://en.wikipedia.org/wiki/OSI_model
3. https://web.cs.wpi.edu/~cs4514/b98/week4-nl/week4-nl.html
4. https://www.techopedia.com/definition/24204/network-layer
5. Yemini, Yechiam. "The OSI network management model." IEEE
Communications Magazine 31.5 (1993): 20-29.
6. Ge, Jian Xia, and Wen Ya Xiao. "Network layer network topology discovery
algorithm research." Applied Mechanics and Materials. Vol. 380. Trans Tech
Publications, 2013.