Name: Mayuri Pawar

Regno: 201071026
Branch: Comps
Date: 16/11/22
COMPUTER NETWORKS
EXPERIMENT 9

Aim: To Study of Network simulator (NS) and Simulation of Congestion Control

Objective:
In this experiment, we will be learning about Network simulator (NS).and
Simulation of Congestion Control Algorithms using NS.

Theory:
NET WORK SIMULATOR (NS2)
Ns overview
 Ns programming: A Quick start
 Case study I: A simple Wireless network
 Case study II: Create a new agent in Ns
Ns overview
 Ns Status
 Periodical release (ns-2.26, Feb 2003)
 Platform support
 FreeBSD, Linux, Solaris, Windows and Mac
Ns functionalities
 Routing, Transportation, Traffic sources
 Queuing disciplines, QoS
Wireless
 Ad hoc routing, mobile IP, sensor-MAC
 Tracing, visualization and various utilitie
 NS(Network Simulators)

Most of the commercial simulators are GUI driven, while some network
simulators are CLI driven. The network model / configuration describes the
state of the network (nodes,routers, switches, links) and the events (data
transmissions, packet error etc.). An important output of simulations are the
trace files. Trace files log every packet, every event that occurred in the
simulation and are used for analysis. Network simulators can also provide
other tools to facilitate visual analysis of trends and potential trouble spots.
Most network simulators use discrete event simulation, in which a list of
pending "events" is stored, and those events are processed in order, with
some events triggering future events— such as the event of the arrival of a
packet at one node triggering the event of the arrival of that packet at a
downstream node.
Simulation of networks is a very complex task. For example, if congestion is
high, then estimation of the average occupancy is challenging because of high
variance. To estimate the likelihood of a buffer overflow in a network, the time
required for an accurate answer can be extremely large. Specialized techniques
such as "control variates" and "importance sampling" have been developed to
speed simulation.
Examples of network simulators
There are many both free/open-source and proprietary network simulators.
Examples of notable network simulation software are, ordered after how often
they are mentioned in research papers:
1. ns (open source)
2. OPNET (proprietary software)
3. NetSim (proprietary software)
Uses of network simulators
Network simulators serve a variety of needs. Compared to the cost and time
involved in setting up an entire test bed containing multiple networked
computers, routers and data links, network simulators are relatively fast and
inexpensive. They allow engineers, researchers to test scenarios that might be
particularly difficult or expensive to emulate using real hardware - for instance,
simulating a scenario with several nodes or experimenting with a new protocol
in the network. Network simulators are particularly useful in allowing
researchers to test new networking protocols or changes to existing protocols
in a controlled and reproducible environment. A typical network simulator
encompasses a wide range of networking technologies and can help the users
to build complex networks from basic building blocks such as a variety of nodes
and links. With the help of simulators, one can design hierarchical networks
using various types of nodes like computers, hubs, bridges, routers, switches,
links, mobile units etc.
Various types of Wide Area Network (WAN) technologies like TCP, ATM, IP etc.
and Local Area Network (LAN) technologies like Ethernet, token rings etc., can
all be simulated with a typical simulator and the user can test, analyze various
standard results apart from devising some novel protocol or strategy for
routing etc. Network simulators are also widely used to simulate battlefield
networks in Network-centric warfare
There are a wide variety of network simulators, ranging from the very simple
to the very complex. Minimally, a network simulator must enable a user to
represent a network topology, specifying the nodes on the network, the links
between those nodes and the traffic between the nodes. More complicated
systems may allow the user to specify everything about the protocols used to
handle traffic in a network. Graphical applications allow users to easily visualize
the workings of their simulated environment. Text-based applications may
provide a less intuitive interface, but may permit more advanced forms of
customization.
Packet loss
occurs when one or more packets of data traveling across a computer network
fail to reach their destination. Packet loss is distinguished as one of the three
main error types encountered in digital communications; the other two being
bit error and spurious packets caused due to noise. Packets can be lost in a
network because they may be dropped when a queue in the network node
overflows. The amount of packet loss during the steady state is another
important property of a congestion control scheme. The larger the value of
packet loss, the more difficult it is for transport layer protocols to maintain
high bandwidths, the sensitivity to loss of individual packets, as well as to
frequency and patterns of loss among longer packet sequences is strongly
dependent on the application itself.
Throughput
This is the main performance measure characteristic, and most widely used. In
communication networks, such asEthernetorpacket radio throughput or
network throughput is the average rate of successful message delivery over a
communication channel. The throughput is usually measured in bits per second
(bit/s or bps), and sometimes in data packets per second or data packets per
time slot this measures how soon the receiver is able to get a certain amount
of data sent by the sender. It is determined as the ratio of the total data
received to the end-to-end delay. Throughput is an important factor that
directly impacts the network performance
Delay
Delay is the time elapsed while a packet travels from one point e.g., source
premise or network ingress to destination premise or network degrees. The
larger the value of delay, the more difficult it is for transport layer protocols to
maintain high bandwidths. We will calculate the end to end delay
Queue Length
A queuing system in networks can be described as packets arriving for service,
waiting for service if it is not immediate, and if having waited for service,
leaving the system after being served. Thus queue length is a very important
characteristic to determine how well the active queue management of the
congestion control algorithm has been working.

Conclusion:
We have successfully studied about Network simulator (NS) its types and uses
along with the Simulation of Congestion Control Algorithms using NS