The document describes two experiments conducted using the OPNET simulation tool. Experiment 1 involves simulating a TCP network using different congestion control mechanisms and analyzing OSPF routing. Experiment 2 compares the bus and star network topologies by creating networks with each in OPNET and collecting statistics on traffic and delay. The objectives are to get familiar with OPNET, study TCP algorithms, simulate OSPF routing, and understand the pros and cons of different topologies. Tasks for each experiment are described in detail, including how to set up the simulations, configure nodes and links, select statistics, and run the simulations.

1. St a g e : P h a s e 1
E XPE RI M E N T N O 0 1: A N A L Y SI S O F T C P C O N G E ST I O N C O N T RO L
M E C H A N I SM A N D O SPF RO U T I N G PRO T O C O L U SI N G O PN E T
SI M U L A T O R.
Release date:April 8, 2015
Submitted By:
Name: Nusrat Jahan Sadia Islam Shachi
Roll: IT -12013 IT-12030
Y ear:3rd Semester:2nd
Objectives:
 Get familiar with simulation tool-OPNET.
 T o study the behaviour and implementation ofslow start and congestion avoidance
algorithms.
 T o simulate the OSPF routing scheme in an IPnetwork.
 T o know the effect ofdividing the network into various areas.
Therefore the analysis covers the new features introduced by TCP and OSPF.
Task 1:
Overview:
Previous versions ofTransport Control Protocol (TCP) start a connection with the senderinjecting
multiple segments into the network, up to the window size advertised by the receiver. This is fine when
the hosts are placed on the same LAN. But if there are routers and slower links between the sender and
the receiver differentproblems can arise. Some intermediateroutermust queuethe packets and it is
possible for the router to run outofspace in the queue. The algorithm to avoid this is called slow start.
Beginning transmission into a network with unknown conditions requires TCP to slowly probe the
network to determine the available capacity, in order to avoid congesting the network with an
inappropriately largeburstof data. Slow start adds another window to the sender's TCP, i.e., the
congestion window, called cwnd. Although congestion avoidanceand slow start are independent
algorithms with different objectives, in practice they areimplemented together. When congestion occurs
TCP must slow down its transmission rate ofpackets into the network, and then invokes slow start to get
things going again.

2. Creating Network:
1. Create a new project. (File New).
2. Name the project acronym TCP and the scenario NoDrop. Here, acronym must be substituted
with the student's own acronym!
3. Create an empty scenario with Europe as a map and no technologies included.
4. Open the internet toolbox object paletteifit's not already open and add an Application Configure
object to the workspace. Rename this object to Applications.
5. Edit the Application Definitions ofthe objectand set the Application name to FTP Application.
Choose the FTP application and set the following values (Application Definitions Row 0 
Description  FTP).
6. Add a Profile Configure object to the workspace and renameit to Profiles.
7. Edit the Profile Configuration ofthis object by adding a new profile and naming it FTP Profile.
8. Applications should be named FTP Application. Set Start Time Offset to constant (5) and
Duration to End of Profile. Set Repeatability to Once at Start Time.
After the configuration ofthe application and profileobjects, we will now create the network for analysing
the behaviour ofthe TCP protocol.Place a subnet over Paris in the workspaceand name the subnet Paris.
Enter now the Paris subnet.
9. Place an ethernet server in the workspaceand rename it to Server Paris.Place an ether-
net4 slip8 gtwy router in the workspacenext to the server and renameit to Router
Connect the server and the router with a 100BaseT cable
10. Open the server's attributes and add FTP Application as a SupportedService in the
Application list item. Set the Server Address to Server Paris.
10. Expand TCP Parameters and disable both Fast Retransmit and Fast Recovery.
Save your changes and exit the Paris subnet. Now place a subnet over Stockholm and set its name to
Sthlm. Enter now the Stockholm subnet.
12. Place an ethernet wkstn in the workspace. Renameit to Client Sthlm. Furthe rmore,

3. place an ethernet4 slip8 gtwy router in the workspace next to the client and rename it to
Router Sthlm. Connect the client and the router with a 100BaseT cable.
13. Edit the attributes of the client such that it uses the FTP Profile created earlier and set the client
Address attributes to Client Sthlm.
14. Set the symbolic name of Application:Destination Preferences to FTP Serverand set
The actual Name to the name ofthe serverin Paris.
Save your changes and exit the Stockholm subnet. We will model now the networks between Paris and
Stockholm as an Internet Protocol (IP) cloud.Place an ip32 cloud on the workspace.
15. Connect the routerin the Paris subnet to the Europa Internet IP Cloud with a PPP DS3
cable.
16. Connect the router in the Sthlm subnet to the Europa Internet IP Cloud with a PPP DS3
Cable.

4. Before running the congestion avoidance simulation you will need to select the statistics that we want to
analyze later. Thus, for the server in Paris you will need to select the Congestion Windows Size (bytes)
statistic (Node Statistics  TCP Connection  Congestion Windows Size (bytes)).
17 . Right click on the Congestion Window Size (bytes) and select Change Collection mode.
Check the advancecheckbox in the pop-up dialog.
Run the simulation 10 minutes. Visualize now the results ofthe simulation.
18. View the results by choosing: Object statistics Choose From Maps Network Paris 
Server Paris  TCP Connection Congestion Window Size (bytes).

6. Task2 :
Overview:
The Open Shortest Path First (OSPF) protocol is an Interior Gateway Protocol (IGP) used for ro uting in IP
networks. It is a link state protocol employing Dijkstra’s algorithm to calculate the leastcost path. The
algorithm calculates the shortest path to each destination based on the cumulative cost required to reach
that destination. The cumulativecost is a function ofthe cost o fthe various interfaces needed to be
traversedin order to reach thatdestination. The cost(or the metric) ofan interfacein OSPF is an
indication ofthe overhead required to send packets across that interface.The cost ofan interface is
calculated based on the bandwidth.
Creating a Network:
1. Create a new project (File  New).
2. Name the project acronym OSPF and the scenario to NoAreas. Here, acronym must b e
substitutedwith the student's own acronym.

7. 3. Select an empty scenario.
4. Select Office and set both the x span and y span to 200. Do not include any technologies.
Review the values and click OK. Open the object paletteand change the paletteto routers. (See Figure 17)
5. Place 10 slip8 gtwy's in the workspace.
6. Change the object palette to internet toolbox.
7. Connect all the routers using PPP DS3 links and rename the nodes.
8. Assign OSPF as the routing protocol for yournetwork. You should select the All interfaces.
9. Auto-assign IP addresses for yournetwork.
10. Configure the cost ofdifferent interfaces.
Now is time to configure the traffic demands between several routers in your network. (Traffic  Create
Traffic Flows IP Unicast)
11. What is the Create a traffic demand between router Band router D with traffic originating from
router B.
12. Create a traffic demand between router Cand router Hwith traffic originating from router C.
The paths ofthe traffic demands should be now visible. To hide the traffic demands select View 
Demand Objects  Hide All. Save the project.
Configure OPNET to run the simulation for 30 minutes for each scenario. Display the simulation results for
each scenario (Protocols  IP  Demands  Display Routes for Configured Demands).

8. Conclusion:
With the help ofthis lab, we have learnt how data packetis transferred in any network system. From the
second task ofOSPF, we have accomplished the work ofpassing ofdata packet through any path in the
minimum cost.

9. St a g e : P h a s e 2
E XPE RI M E N T N O 0 1: SI M U L A T I O N O F N E T WO RK U SI N G B U S A N D
ST A R T O PO L O G Y .
Release date:April 8, 2015
Submitted By:
Name: Nusrat Jahan Sadia Islam Shachi
Roll: IT -12013 IT-12030
Y ear:3rd Semester:2nd
Objectives:
 Get familiar with simulation tool-OPNET.
 To simulate a network usinga simple star and bus topology.
 To know the comparison betweenbusand star topology.
Task 1:
Overview:
Networks are being upgraded or deployed from scuffall over the world. The area ofnetwork planning is
thus fetching all the more noteworthy. Networks have grown swiftly over the past few decades, with
confront of connecting the relevant networks together,so that the users can sharethe network’s wealth.
Topology refers to the way in which the network ofcomputers is connected. Each topology is suited to
specific tasks and has its own advantages and disadvantages. The choiceoftopo logy is dependent upon
type and number ofequipment being used, planned applications and rate ofdata transfers, required
response timesand finally the cost. Thereare FOUR major challenging topologies BUS, RING, STAR, and
FDDI. Most networking software supports all topologies. In bus topology, a common cable connects all
the nodes and provides for the backboneofa network essentially.In star topology,each node is connected
to a central hub.
Creating network using Bus topology:

10. 1. Start Riverbed Modeler Academic Edition ⇒Choose New from the File menu.
2. Select Project ⇒Click OK ⇒ Name the project <yourinitials>_Ethernet, and the scenario Coax_2
⇒ Make sure that the Use Startup Wizard is checked ⇒Click OK.
3. In the Startup Wizard: Initial Topology dialog box,make sure that Create Empty.Scenario is
selected⇒Click Next ⇒ Choose Office from the Network Scale list ⇒ Click Next ⇒ Assign 200 to
X Span and keep Y Span as 100 ⇒Click Next twice ⇒Click Finish.
4. Close the Object Tree dialog box.
5. Select Topology Rapid Configuration.From the drop-down menu choosebus and click OK.
6. Click the Select Models button in the Rapid Configuration dialog box.From the Model List drop-
down menu chooseethcoax and click OK.
7. In the Rapid Configuration dialog box, set the following eightvalues and click OK.
To choosethe statistics to be collected during the simulation.

11. 8. Right-click anywhere in the project workspace and select Choose Individual Statistics DES from
the pop-up menu.
9. In the Choose Results dialog box, choosethe following 2 statistics:
A. Traffic Received(in packets/Sec) by the traffic sinks across all nodes.

12. B. Traffic Sent (in packets/sec) by the traffic sources across all nodes

13. .
Here we need to configure the duration ofthe simulation:
1. Click on the Configure / Run Simulation button.
2. Set the duration to be 2.0 minutes.
Task 2:
Creating network using Star topology:
1. Start Riverbed Modeler Academic Edition ⇒Choose New from the File menu.

14. 2. Select Project ⇒Click OK ⇒ Name the project <yourinitials>_Ethernet, and the scenario Coax_2
⇒ Make sure that the Use Startup Wizard is checked ⇒Click OK.
3. In the Rapid Configuration dialog box, set the following six values:Center Node Mod=
ethernet16_hub, Periphery Node Model = Ethernet station, Link Model = 10BaseT, Number =16,
Y =50, and Radius = 42 Click OK.
The 10BaseTlink represents an Ethernet connection operating at 10Mbps
To choosethe statistics to be collected during the simulation:
10. Right-click anywhere in the project workspace and select Choose Individual Statistics DES from
the pop-up menu.
11. In the Choose Results dialog box, choosethe following 3 statistics:
A. Ethernet Delay –this represents the end-to-end delay ofall packets received by all the
station.

15. B. Traffic Received (in packets/Sec) by the traffic sinks across all nodes.

16. C. Traffic Sent (in packets/sec) by the traffic sources across all nodes

17. Here we need to configure the duration ofthe simulation:
1. Click on the Configure / Run Simulation button.
2. Set the duration to be 2.0 minutes.
Conclusion:
As we have learnt how to createnetworks using differenttopology, we can use the idea to create
improved and better network system. This lab also provides us clearconceptabout the comparison of
the topologies.