Aim:
To Study of Network
simulator (NS).and Simulation of Congestion Control Algorithms using
NS
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 unctionalities
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.
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:
- ns (open source)
- OPNET (proprietary software)
- 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
morepacketsof data travelling across a computer networkfail to
reachtheir destination. Packet loss is distinguished as one of the
three main error types encountered in digital communications; the
other two being bit errorand 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 transportlayer
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.
This is the main
performance measure characteristic, and most widely used.
Incommunicationnetworks, such asEthernetorpacket radio, throughputor
network throughputis the average rate of successfulmessage delivery
over a communication channel. The throughput is usually measured
inbitsper second (bit/s orbps), andsometimes indata packetsper second
or data packets pertime slotThis measure how soon the receiver is
able to get a certain amount of data send 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 which 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 valueof delay, the more difficult it is for transport layer
protocols to maintain highbandwidths. We will calculate 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 thesystem after being served. Thus queue length is very
important characteristic to determine that how well the active queue
management of the congestion control
algorithm has been
working.
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