Netsim experiment manual

NetSim Experiment Manual - 1 -
NetSimTM
Experiment Manual

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List of Experiments
Simulation Experiments
Introduction
1. Introduce students to network simulation through the NetSim simulation package,
Create a simple network model with multiple scenarios, collect statistics on
network performance through the use of NetSim tools, analyze statistics and draw
conclusions on network performance …..Page (7)
Internetworks
2. To understand IP forwarding within a LAN and across a router (Note: NetSim
Standard Version is required to run this experiment) …..Page (12)
3. Study the working of the spanning tree algorithm by varying the priority among
the switches …..Page (18)
TCP
4. To understand the working of “Connection Establishment“ in TCP using NetSim
(Note: NetSim Standard Version is required to run this experiment)
…..Page (23)
5. During client-server TCP downloads study the throughputs of Slow start +
Congestion avoidance (also known as Old Tahoe) and Fast Retransmit (also
known as Tahoe), Congestion Control Algorithms …..Page (28)
WLAN
6. To study how the Bit Error Rate (loss) and data of a Wireless LAN (IEEE
802.11b) network varies as the distance between the Access Point and the wireless
nodes is varied …..Page (36)
Routing
7. Study the working and routing table formation of Interior Routing Protocols, i.e.
Routing Information protocol (RIP) and Open Shortest Path First (OSPF)
…..Page (41)

Queuing Theory
8. M/D/1 Queue:
I. To create an M/D/1 queue: a source to generate packets, a queue to act as
the buffer and server, a sink to dispose of serviced packets
II. To study how the delay of such a queuing system varies …..Page (51)
Legacy Networks
9. Study the throughput characteristics of a slotted aloha network …..Page (57)
10. Understand the impact of bit error rate on packet error and investigate the impact
of error of a simple hub based CSMA / CD network …..Page (62)
11. To determine the optimum persistence of a p-persistent CSMA / CD network for a
heavily loaded bus capacity …..Page (66)
ATM
12. Study the effect of Peak Cell Rate (per Sec) and Cell Delay Variation Tolerance
on the performance of an ATM Networks …..Page (70)
13. Study the performance of FIFO, round Robin and Priority queuing techniques in
an ATM network …..Page (75)
BGP Networks
14. Study the working of BGP and formation of BGP Routing table …..Page (86)
MPLS Networks
15. Study how the LSP varies for different traffic in MPLS -TE (Traffic Engineering)
…..Page (92)

Cellular Networks
GSM
16. Study how call blocking probability varies as the load on a GSM network is
continuously increased …..Page (98)
CDMA
17. Study how the number of channels increases and the Call blocking probability
decreases as the Voice activity factor of a CDMA network is decreased
.....Page (102)
Wireless Sensor Networks
18. Study the Super Frame Structure and analyze the effect of SuperFrame order on
throughput …..Page (107)
Personal Area Networks
ZigBee
19. Analyze the scenario shown, where Node 1 transmits data to Node 2, with no path
loss and obtain the theoretical throughput based on IEEE 802.15.4 standard.
Compare this with the simulation result …..Page (112)
Programming Exercises:
Write a C program for the following exercises and link your code to NetSim
How to De-bug your code linked to NetSim’s Programming Exercise …..Page (117)
Framing Sequence
20. Bit Stuffing and character stuffing …..Page (119)
Error Detecting Code
21. Cyclic Redundancy Check …..Page (128)

Cryptography
22. Encryption and Decryption using substitution ciphers …..Page (134)
Switching
23. Minimum Spanning Tree algorithm …..Page (138)
Address Resolution protocol
24. Working of ARP …..Page (142)
Routing Information protocol (RIP)
25. Verification of distance vector routing algorithm …..Page (147)
Open Shortest Path First Protocol (OSPF)
26. Verification of Link state routing Algorithm …..Page (150)
Transmission Flow Control Protocols
27. Verification of Stop and Wait protocol …..Page (153)
28. Verification of Go Back N protocol …..Page (156)
29. Verification of Selective Repeat Protocol …..Page (160)

Experiment 1
Objective: Introduce students to network simulation through the NetSim simulation
package. Create a simple network model with multiple scenarios, collect statistics on
network performance through the use of NetSim tools and analyze statistics and draw
conclusions on network performance.
Part A:
Introduce students to network simulation through the NetSim simulation package.
Theory:
• What is NetSim?
NetSim is a network simulation tool that allows you to create network scenarios, model
traffic, and study performance metrics.
• What is a network?
A network is a set of hardware devices connected together, either physically or logically.
This allows them to exchange information.
A network is a system that provides its users with unique capabilities, above and beyond
what the individual machines and their software applications can provide.
• What is simulation?
A simulation is the imitation of the operation of a real-world process or system over
time.
Network simulation is a technique where a program models the behavior of a network
either by calculating the interaction between the different network entities
(hosts/routers, data links, packets, etc) using mathematical formulae, or actually capturing
and playing back observations from a production network. The behavior of the network
and the various applications and services it supports can then be observed in a test lab;
various attributes of the environment can also be modified in a controlled manner to
assess how the network would behave under different conditions.

• What does NetSim provide?
Simulation: NetSim provides simulation of various protocols working in various
networks as follows: Internetworks, Legacy Networks, BGP Networks, MPLS
Networks, Advanced Wireless Networks, Cellular Networks, Wireless Sensor
Networks, Personal Area Networks and Cognitive Radio Networks. Users can open,
save, and delete experiments as desired. The different experiments can also be analyzed
using the analytics option in the simulation menu.
Programming: NetSim covers various programming exercises along with concepts,
algorithms, pseudo code and flowcharts. Users can also write their own source codes in
C/C++ and can link them to NetSim.
Some of the programming concepts are Address resolution protocol (ARP), Classless
inter domain routing (CIDR), Cryptography, Distance vector routing, shortest path,
Subnetting etc.
Real time: Frame capture is covered in this section. It is used to capture packets when
there is an active data transfer taking place and also provides performance metrics. Note:
This menu is available only in Academic Version.
Basics: NetSim basics, gives a brief introduction and theoretical knowledge on different
Internetworks, Legacy Networks, Advanced wireless Networks, MPLS Networks,
Cellular Networks, VLAN and Devices. Basics also provide more than 200 animations
for better understandability of networking concepts.
Utilities: This section handles the user management section used for adding/deleting
users, setting passwords etc.

Part B:
Create a Simple network model with multiple scenarios. Collect statistics on network
performance through the use of NetSim. Analyze statistics and draw conclusion on
network performance.
Theory:
• Network model: A Network model is a flexible way of representing devices and their
relationships. Networking devices like hubs, switches, routers, nodes, connecting
wires etc. are used to create a network model.
• Scenario: A Scenario is a narrative describing foreseeable interactions of types of
input data and its respective output data in the system.
• Network performance: The fundamental parameters that measure the performance
of a network are:-
• Utilization and Delay:
Utilization is the fraction of the available bandwidth used for transmission of data
expressed as a percentage (%).
Delay is the amount of time taken for a packet to travel from one end of the network
to the other.
Click and
drop the
hub
Click and
drop the
node
Right click
on node to
set
properties
Click here
to simulate
Click here
to enable
the trace

Delay= queuing delay (ms) + transmission time (ms) + medium access time (ms).
Where queuing delay is the time the packet/frame waits in the queue prior to
transmission, transmission time is the time taken by a packet/frame to travel across
one hop, and medium access time is the time the data waits in the head of the queue to
access the medium.
• What are network statistics?
Network statistics are network performance related metrics collected at the end of a
simulation run. The report at the end of the completion of an simulation experiment
include metrics like throughput, simulation time, frames generated, frames dropped,
frames errored, collision counts etc, and their respective values.
• What is NetSim analytics used for?
It is used to compare and analyze various protocols scenarios under Internetworks,
Legacy Networks, BGP Networks, MPLS Networks, Advanced Wireless
Networks - MANET, Advanced Wireless Networks – WiMAX, Cellular
Networks, Wireless Sensor Networks, Personal Area Networks and Cognitive
Radio Networks. Parameters like utilization, loss, queuing delay, transmission time
etc of different sample experiments are compared with help of graphs.
Metrics
Click to export
the values to
excel sheet
Click to view
the network
Click to edit
and re-run

Plot the chart
here
Click on
protocols to
select the
experiments
Click to
select the
metrics

Experiment 2
Objective:
To understand IP forwarding within a LAN and across a router
Note: NetSim Standard Version is required to run this experiment
Introduction:
Nodes in network need MAC Addresses in addition to IP address for communicating with
other nodes. In this experiment we will see how IP-forwarding is done when a node wants
to send data within a subnet and also when the destination node is outside the subnet.
PART 1: - GUI MODE
Simulation:
How to Create Scenario & Generate Traffic:
Step1:
Simulation New Internetworks
Step2:
Click drop Wired Nodes, Switches and Router onto the Simulation Environment as
shown below.

Step3:
Create the Samples as follows,
Sample Inputs:
Sample 1:
Set the Wired Node Properties as follows,
Node Properties Wired Node 1
Transmission
Type
Point to Point
Destination Wired Node 2
Traffic Type Custom
Packet Size Distribution Constant
Packet Size (bytes) 1460
Packet Inter
Arrival Time
Distribution Constant
Packet Inter
Arrival Time (µs)
20000
TCP Properties
TCP Disable

Enabling the packet trace:
• Click Packet Trace icon in the tool bar. This is used to log the packet details.
• Give a file name and select file type as .csv. Then, Check “All the Attributes”
button for Common Attributes, TCP and WLAN.
• And Click on Ok button. Once the simulation is completed, the file gets stored in the
location specified.
Simulation Time- 10 Seconds
(Note: The Simulation Time can be selected only after doing the following two tasks,
• Set the properties of Nodes
• Then click on the Simulate button).
Analysis:-
Intra-LAN-IP-forwarding:
• ARP PROTOCOL- WORKING
• PACKET TRACE Analysis
A Brief Explanation:
NODE-1 broadcasts ARP_Request which is then broadcasted by SWITCH-4. NODE -2
sends the ARP_Reply to NODE-1 via SWITCH-4. After this step, data is transmitted
from NODE-1 to NODE-2. Notice the DESTINATION_ID column for ARP_Request
type packets.
Source Switch
ARP REQUEST
Destination
ARP Response
ARP REQUEST
ARP Response

Sample 2:
Set the Wired Node Properties as follows,
Transmission Type Point to Point
Destination Wired Node3
Traffic Type Custom
Packet Inter
Arrival Time
Packet Inter
Arrival Time (µs)
20000
TCP Properties
TCP Disable
• Give a file name and select file type as .csv. Then, Check “All the Attributes”
button for Common Attributes, TCP and WLAN.
• And Click on Ok button. Once the simulation is completed, the file gets stored in the
specified location.
Simulation Time - 10 Seconds

Analysis:-
Across-Router-IP-forwarding:
• PACKET TRACE Analysis
A Brief Explanation:
NODE-1 transmits ARP_Request which is further broadcasted by SWITCH-4. ROUTER-
6 sends ARP_Reply to NODE-1 which goes through SWITCH-4. Then NODE-1 starts to
send data to NODE-3.
Data
Packet
ARP request for
Destination’s MAC
address
ARP
Response
Source
Default Gateway
ARP request for
Default Gateway’s
MAC address
ARP response for
Default Gateway’s
MAC address
Source
Default Gateway
Source
STEP-1
STEP-2
Data Packet

If the router has the address of NODE-3 in its routing table, ARP protocol ends here and
data transfer starts that is PACKET_ID 1 being sent from NODE-1 to NODE-3. In other
case, Router sends ARP_Request to appropriate subnet and after getting the MAC
ADDRESS of the NODE-3, it forwards the packet which it has received from NODE-1.
PART 2: - Changing default Gateway
Do Sample 2 in PART 1 with the difference that in the properties of NODE-1, change
the default gateway to some other value, for ex. “192.168.2.76” and click on Simulate
button.
You will get error. Because NODE-1 will check the IP address of NODE-3 and then
realize that it isn’t in the same subnet. So it will forward it to default gateway. Since the
default gateway’s address doesn’t exist in the network, error occurs.
Inference:
When a node has to send data to a node with known IP address but unknown MAC
address, it sends an ARP request. If destination is in same subnet as the source (found
through subnet mask) then it sends the ARP (broadcast ARP message) request. Otherwise it
forwards it to default gateway. Former case happens in case of intra-LAN
communication. The destination node sends an ARP response which is then forwarded by
the switch to the initial node. Then data transmission starts.
In latter case, a totally different approach is followed. Source sends the ARP request to
the default gateway and gets back the MAC address of default gateway. (If it knows
which router to send then it sends ARP request to the corresponding router and not to
Default gateway) When source sends data to default gateway (a router in this case), the
router broadcasts ARP request for the destined IP address in the appropriate subnet. On
getting the ARP response from destination, router then sends the data packet to
destination node.

Experiment 3
Objective:
Study the working of the spanning tree algorithm by varying the priority among the
switches.
Theory:
Refer NetSim Basics on Spanning Tree.
Procedure:
How to Create Scenario Generate Traffic:
Please navigate through the below given path to,
• Create Scenario: “Help NetSim Help F1 Running Simulation via GUI
Internetworks Create Scenario”.
Create the scenario as shown below,
(Note: Minimum three switches are needed in the simulation to study about spanning tree
formation.)

Sample Inputs:
Inputs for the Sample experiments are given below,
Sample 1:
Node
Properties
Wired Node 1 Wired Node 2
Transmission
Type
Point to Point Point to Point
Destination Wired Node2 Wired Node1
Traffic Type Custom Custom
Packet Size Distribution Constant Distribution Constant
Packet Size
(bytes)
1460 Packet Size
(bytes)
1460
Packet Inter
Arrival Time
Distribution Constant Distribution Constant
Packet Inter
Arrival Time
(µs)
20000 Packet Inter
Arrival Time
(µs)
20000
(Note: Wired Node 3 is not generating Traffic to any other Wired Nodes)
Switch
Properties
FE_LAN_8_
Port Switch 1
FE_LAN_8_
Port Switch 2
FE_LAN_8_
Port Switch 3
Switch
Priority
2 1 3
(Note: Switch Priority for all the ports of Switch has to be same and all other properties of
Switch is default)
• Set the properties of Nodes and Switches

Sample 2:
Node
Properties
Wired Node 1 Wired Node 2
Transmission
Type
Point to Point Point to Point
Destination Wired Node2 Wired Node1
Packet Size Distribution Constant Distribution Constant
Packet Size
(bytes)
1460 Packet Size
(bytes)
1460
Packet Inter
Arrival Time
Distribution Constant Distribution Constant
Packet Inter
Arrival
Time (µs)
20000 Packet Inter
Arrival
Time (µs)
20000
(Note: Wired Node 3 is not generating Traffic to any other Wired Nodes)
Switch
Properties
FE_LAN_8_
Port Switch 1
FE_LAN_8_
Port Switch 2
FE_LAN_8_
Port Switch 3
Switch
Priority
1 2 3
(Note: Switch Priority for all the ports of Switch has to be same and all other properties of
Switch is default)
• Set the properties of Nodes and Switches

Output:
• To view the output, click the View Spanning Tree Link available on the Performance
Metrics screen under Resources.
Sample 1:
Sample 2:

Inference:
In the Sample 1, FE_ LAN _8 Port_Switch 2 was assigned least priority and was selected
as a Root switch. The Green line indicates the forward path and the Black line indicates
the blocked path. The frame from Wired Node1 should take the path through the FE_
LAN _8 Port_Switch 2 to reach the Wired Node2.
In the Sample 2, FE_ LAN _8 Port_Switch 1 was assigned least priority and selected as a
Root switch. In this case, the frame from Wired Node1 can directly reach the destination
Wired Node2.

Experiment 4
Objective:
To understand the working of “Connection Establishment” in TCP using NetSim.
Note: NetSim Standard Version is required to run this Experiment.
Introduction:
When two processes wish to communicate, their TCP’s must first establish a connection
i.e. initialize the status information on each side. Since connections must be established
between unreliable hosts and over the unreliable internet communication system, a “three-
way handshake” with clock based sequence numbers is the procedure used to establish a
Connection. This procedure normally is initiated by one TCP and responded by another
TCP. The procedure also works if two TCPs simultaneously initiate the procedure. When
simultaneous attempt occurs, each TCP receives a “SYN” segment which carries no
acknowledgement after it has sent a “SYN”.
The simplest three-way handshake is shown in the following figure.
TCP A TCP B
1. CLOSED LISTEN
2. SYN-SENT A: SEQ=100CTL=SYN SYN-RECEIVED
3. ESTABLISHED  B: SEQ=300ACK=101CTL=SYN, ACK  SYN-RECEIVED
4. ESTABLISHED A: SEQ=101ACK=301CTL=ACK ESTABLISHED
5. ESTABLISHED A: SEQ=101ACK=301CTL=ACKDATA ESTABLISHED
Fig: Basic 3-Way Handshake for Connection Synchronization
Explanation:
The above figure should be interpreted in the following way. Each line is numbered for
reference purposes. Right arrows () indicates the departure of a TCP Segment from
TCP A to TCP B, or arrival of a segment at B from A. Left arrows ( ) indicates the
reverse.TCP states represent the state AFTER the departure or arrival of the segment (whose
contents are shown in the center of each line).Segment contents are shown in abbreviated form,
with sequence number, control flags, and ACK field. In line2 of the above figure, TCP A begins

by sending a SYN segment indicating that it will use sequence numbers starting with sequence
number 100. In line 3, TCP B sends a SYN and acknowledges the SYN it received from TCP A.
Note that the acknowledgment field indicates TCP B is now expecting to hear sequence 101,
acknowledging the SYN which occupied sequence 100. At line 4, TCP A responds with an empty
segment containing an ACK for TCP B's SYN; and in line 5, TCP A sends some data.
Simulation:
Step1:
Step2:
Click drop Wired Nodes and Router onto the Simulation Environment as shown below.

Step3:
Set the properties of the WiredNode1 as follows:
Generally Wired Node properties will be as follows:
Wired Node Properties Values
Transmission Type Point to point
Destination Wired Node X (X will vary)
Traffic Type FTP
Router Properties: Accept default properties for Router.
• Select the required attributes and click OK. Once the simulation is completed, the file
gets stored in the location specified.
Note: make sure that after enabling the packet trace you select the TCP option in the
Internetworks and then select the required attributes.
Simulation Time - 10 sec
By clicking on “simulate” we will get the following results:

Fig: The Network Metrics
Explanation of “Connection Establishment” using packet trace
• Go to the specified directory where the packet trace file has been saved.
• Open the file in excel.
Note: Please refer,
• Help NetSim Help F1 Generating Packet TraceHow to import Packet Trace
to Excel?
Fig: 3-way Handshake using packet trace.
In EXCEL go to DATA and select FILTER option to view only the desired rows and
columns as shown in the figure
Line 1, 2, 4 and 5 of the above table are ARP related packets and not of interest to us in
this experiment.
In line 3 of the above figure we can see that NODE-1 is sending a control packet of type
TCP_SYN requesting the connection with the NODE-2, and this control packet is first
sent to the ROUTER-3 (receiver ID). In line 6, the ROUTER-3 is sending the TCP_SYN

packet that has been received from NODE-1 to the NODE-2. In line 7, NODE-2 is
sending the control packet of type TCP_SYN_ACK to NODE-1, and this control packet
is first sent to the ROUTER-3. This TCP_SYN_ACK is the ACK packet for the
TCP_SYN packet. In line 8, ROUTER-3 is sending the TCP_SYN_ACK, (received from
NODE-2) to the NODE-1. In line 9, NODE-1 is sending the TCP_ACK to NODE-2 via
ROUTER-3 making the CONNECTION_STATE as TCP_ESTABLISHED.
Once the connection is established, we see that a packet type of type “DATA” is sent
from the NODE-1 to the NODE-2 in line 10.
Example Assessment Question:
• Explain the working of “Closing a connection” in TCP using the NetSim’s packet
trace.

Experiment 5
Objective:
During client-server TCP downloads study the throughputs of Slow start + Congestion
avoidance (also known as Old Tahoe) and Fast Retransmit (also known as Tahoe),
Congestion Control Algorithms.
Theory:
One of the important functions of a TCP Protocol is congestion control in the network.
Given below is a description of how Old Tahoe and Tahoe variants (of TCP) control
congestion.
Old Tahoe:
Congestion can occur when data arrives on a big pipe (i.e. a fast LAN) and gets sent out
through a smaller pipe (i.e. a slower WAN). Congestion can also occur when multiple
input streams arrive at a router whose output capacity is less than the sum of the inputs.
Congestion avoidance is a way to deal with lost packets.
The assumption of the algorithm is that the packet loss caused by damaged is very small
(much less than 1%), therefore the loss of a packet signals congestion somewhere in the
network between the source and destination. There are two indications of packets loss: a
timeout occurring and the receipt of duplicate ACKs
Congestion avoidance and slow start are independent algorithms with different objectives.
But when congestion occurs TCP must slow down its transmission rate and then invoke
slow start to get things going again. In practice they are implemented together.
Congestion avoidance and slow start requires two variables to be maintained for each
connection: a Congestion Window (i.e. cwnd) and a Slow Start Threshold Size (i.e.
ssthresh). Old Tahoe algorithm is the combination of slow start and congestion avoidance.
The combined algorithm operates as follows,
1. Initialization for a given connection sets cwnd to one segment and ssthresh to 65535
bytes.

2. When congestion occurs (indicated by a timeout or the reception of duplicate ACKs),
one-half of the current window size (the minimum of cwnd and the receiver’s
advertised window, but at least two segments) is saved in ssthresh. Additionally, if the
congestion is indicated by a timeout, cwnd is set to one segment (i.e. slow start).
3. When new data is acknowledged by the other end, increase cwnd, but the way it
increases depends on whether TCP is performing slow start or congestion avoidance.
If cwnd is less than or equal to ssthresh, TCP is in slow start. Else TCP is performing
congestion avoidance. Slow start continues until TCP is halfway to where it was when
congestion occurred (since it recorded half of the window size that caused the problem in
step 2). Then congestion avoidance takes over.
Slow start has cwnd begins at one segment and be incremented by one segment every
time an ACK is received. As mentioned earlier, this opens the window exponentially:
send one segment, then two, then four, and so on. Congestion avoidance dictates that
cwnd be incremented by 1/cwnd, compared to slow start’s exponential growth. The
increase in cwnd should be at most one segment in each round trip time (regardless of
how many ACKs are received in that RTT), whereas slow start increments cwnd by the
number of ACKs received in a round-trip time.
Tahoe (Fast Retransmit):
The Fast retransmit algorithms operating with Old Tahoe is known as the Tahoe variant.
TCP may generate an immediate acknowledgement (a duplicate ACK) when an out-of-
order segment is received out-of-order, and to tell it what sequence number is expected.
Since TCP does not know whether a duplicate ACK is caused by a lost segment or just a
re-ordering of segments, it waits for a small number of duplicate ACKs to be received. It
is assumed that if there is just a reordering of the segments, there will be only one or two
duplicate ACKs before the re-ordered segment is processed, which will then generate a
new ACK. If three or more duplicate ACKs are received in a row, it is a strong indication
that a segment has been lost. TCP then performs a retransmission of what appears to be
the missing segment, without waiting for a re-transmission timer to expire.

Procedure:
How to Create Scenario
• Help NetSim Help F1 Running Simulation via GUI Internetworks Create
Scenario”.
Sample Inputs:
Follow the steps given in the different samples to arrive at the objective.
Sample 1.a: Old Tahoe (1 client and 1 server)
In this Sample,
• Total no of Node used: 2
• Total no of Routers used: 2
The devices are inter connected as given below,
• Node 1 is connected with Router 1 by Link 1.
• Router 1 and Router 2 are connected by Link 2.
• Node 2 is connected with Router 2 by Link 3.
Set the properties for each device by following the tables,
Traffic Type Custom
Packet Size
Packet Inter Arrival Time
Packet Inter Arrival Time (µs) 1300
TCP Properties
MSS(bytes) 1460
Congestion Control Algorithm Old Tahoe
Window size (bytes) 8

Link Properties Link 1 Link 2 Link 3
Medium Type E2 CAT5 E2
Uplink Speed (Mbps) 8.448 10 8.448
Downlink Speed(Mbps) 8.448 10 8.448
Uplink BER 10-6
10-6
10-6
Downlink BER 10-6
10-6
10-6
Simulation Time - 10 Sec
• Set the properties of Node , Router, Link
Sample 1.b: Tahoe (1 client and 1 server)
Do the experiment as sample 1.a, and change the TCP congestion control algorithm to
Tahoe.
Sample 2.a: Old Tahoe (2 clients and 2 servers)
In this Sample,
• Total no of Wired Node’s used: 4
• Wired Node 1 and Wired Node 2 are connected with Router 1 by Link 1 and Link 2.
• Wired Node 3 and Wired Node 4 are connected with Router 2 by Link 4 and Link 5.
• Wired Node 1 and Wired Node 2 are not transmitting data in this sample.

Node Properties Wired Node 3 Wired Node 4
Destination Wired Node 1 Wired Node 2
Packet Size
Distribution Constant Constant
Packet Size (bytes) 1460 1460
Packet Inter Arrival Time (µs) 1300 1300
TCP Properties
MSS(bytes) 1460 1460
Congestion Control Algorithm Old Tahoe Old Tahoe
Window size (bytes) 8 8
Link Properties Link 1 Link 2 Link 3 Link 4 Link 5
Medium Type E2 E2 CAT5 E2 E2
Uplink Speed (Mbps) 8.448 8.448 10 8.448 8.448
Downlink Speed(Mbps) 8.448 8.448 10 8.448 8.448
Uplink BER 10-6
10-6
10-6
10-6
10-6
Downlink BER 10-6
10-6
10-6
10-6
10-6

Sample 2.b: Tahoe (2 clients and 2 servers)
Do the experiment as sample 2.a, and change the congestion control algorithm to Tahoe.
Sample 3.a: Old Tahoe (3 clients and 3 servers)
In this Sample,
• Total no of Node’s used: 6
• Nodes 1, Node 2 Node 3 are connected with Router 1 by Link 1, Link 2 Link 3.
• Nodes 4, Node 5 Node 6 are connected with Router 2 by Link 5, Link 6 Link 7.
• Node 1, Node 2 and Node 3 are not transmitting data in this sample.
Node Properties Wired Node 4 Wired Node 5 Wired Node 6
Destination Wired Node 1 Wired Node 2 Wired Node 3
Traffic Type Custom Custom Custom
Packet Size
Distribution Constant Constant Constant
Packet Size (bytes) 1460 1460 1460
Distribution Constant Constant Constant
Packet Inter
Arrival Time (µs)
1300 1300 1300
TCP Properties
MSS(bytes) 1460 1460 1460
Congestion Control
Algorithm
Old Tahoe Old Tahoe Old Tahoe
Window size
(bytes)
8 8 8

Link
Properties
Link 1 Link 2 Link 3 Link 4 Link 5 Link 6 Link 7
Medium Type E2 E2 E2 CAT5 E2 E2 E2
Uplink Speed
(Mbps)
8.448 8.448 8.448 10 8.448 8.448 8.448
Downlink
Speed(Mbps)
8.448 8.448 8.448 10 8.448 8.448 8.448
Uplink BER 10-6
10-6
10-6
10-6
10-6
10-6
10-6
Downlink BER 10-6
10-6
10-6
10-6
10-6
10-6
10-6
Sample 3.b: Tahoe (3 clients and 3 servers)
Do the experiment as sample 3.a, and change the TCP congestion algorithm to Tahoe.

Comparison Table:
TCP
Downloads
Metrics
Slow start +
Congestion
avoidance
Fast
Retransmit
1 client and 1 server
Throughput(Mbps) 6.46 7.04
Segments Retransmitted +
Seg Fast Retransmitted
191 229
2 clients and 2 servers Throughput(Mbps) 8.86 9.43
266 253
3 clients and 3 servers
Throughput(Mbps) 9.24 9.41
295 315
Note: To calculate the “Throughput(Mbps)” for more than one client, add the individual
client throughput which is available in Application Metrics (or Metrics.txt) of
Performance Metrics screen. In the same way calculate the metrics for “Segments
Retransmitted + Seg Fast Retransmitted”.
Inference:
User lever throughput: User lever throughput of Fast Retransmit is higher when
compared then the Old Tahoe (SS + CA). This is because, if a segment is lost due to error,
Old Tahoe waits until the RTO Timer expires to retransmit the lost segment, whereas
Tahoe (FR) retransmits the lost segment immediately after getting three continuous
duplicate ACK’s. This results in the increased segment transmissions, and therefore
throughput is higher in the case of Tahoe.

Experiment 6
Objective:
To study how the Bit Error Rate (loss) and data of a Wireless LAN (IEEE 802.11b)
network varies as the distance between the Access Point and the wireless nodes is varied.
Theory:
Basics Internetworks Wireless LAN IEEE 802.11 PHY.
In most of the WLAN products on the market based on the IEEE 802.11b technology the
transmitter is designed as a Direct Sequence Spread Spectrum Phase Shift Keying (DSSS
PSK) modulator, which is capable of handling data rates of up to 11 Mbps. The system
implements various modulation modes for every transmission rate, which are Different
Binary Phase Shift Keying (DPSK) for 1 Mbps, Different Quaternary Phase Shift Keying
(DQPSK) for 2 Mbps and Complementary Code Keying (CCK) for 5.5 Mbps and 11
Mbps.
Large Scale Fading represents Receiver Signal Strength or path loss over a large area as a
function of distance. The statistics of large scale fading provides a way of computing
estimated signal power or path loss as a function of distance and modulation modes vary
depends on the Receiver Signal Strength.
Procedure:
• Create Scenario: “Help NetSim Help F1 Running Simulation via GUI
Internetworks Create Scenario”.
Sample Inputs:
In this Sample experiment, 1 Wireless AP and 2 Wireless Nodes (WirelessNode1 and
WirelessNode2) need to be click dropped onto the Simulation environment. Connect
the AP and the Nodes. Set the below properties for AP, Wireless Nodes and Wireless
Link. Run the simulation. Upon completion of the experiment “Save” them for
comparisons that can be carried out in the “Analytics” section by using export to Excel

Then follow these steps, Wireless Node 1 transmits data to Wireless Node 2
• Experiment 1: Distance between Node1 and Node2 to Access Point is 5m.
• ……. And so on till all 65 meter distance.
Inputs for the Sample experiment are given below:
Access Point Properties AP 1
Protocol IEEE802.11b
Buffer Size(MB) 5
RTS Threshold(bytes) 2347
Retry Limit 7
Transmission Type DSSS
Standard Channel 1_2412
Transmitter power (Milli Watts) 100
SIFS 10
Slot Time 20
CW Minimum 31
Wireless Node Properties Node 1
Transmission Point to Point
Destination Node2
Traffic Type Custom
Application Data size Distribution Constant
Data Size (bytes) 1375
Inter Arrival Time Distribution Constant
Packet Inter Arrival 1000

Time (µs)
ARP Retry Interval 10
ARP Retry Limit 3
Protocol IEEE802.11b
RTS Threshold(bytes) 2347
Retry Limit 7
Transmission DSSS
Standard Channel 1_2412
Transmitter power (Milli Watts) 100
SIFS 10
Slot Time 20
CW Minimum 31
Link Properties Link 1
Medium Type WIRELESS
Uplink Speed (Mbps) 11
Downlink Speed (Mbps) 11
Frequency 2412
Path Loss Exponent 3.5
Fading Figure 1.0
Log Normal
Shadowing-Standard
Deviation(dB)
0
(Note: The Simulation Time can be selected only after the following two tasks,
• Set the properties for the Wireless Nodes, AP and Wireless Link.
• Click on the Simulate button).

Output:
To view the output by using NetSim the Sample experiments need to be added onto the
Analytics interface. The navigation for analytics is -“Simulation

Analytics”
Select the experiments by selecting
• Internetworks
• Click the Browse button to select the Metrics.txt files
• Click on “Export to .csv”
Comparison Chart:
To draw these graphs by using Excel “Insert Chart” option and then select chart type as
“Line chart”.
Graph I
Graph II
11 Mbps
5.5 Mbps
2 Mbps
1 Mbps

Graph I
Sl.
No
Approx
Range (m)
Data Rate
(Mbps)
Modulation Loss (%)
1. 1 – 17* 11 CCK11 Exponential Increases.
2. 17 – 24* 5.5 CCK5.5 The BER first falls as the data
rate drops. Then it starts to
exponential increase.
3. 24 - 40* 2 DQPSK The BER falls as the data rate
drops. Then it starts to
4. 40 – 70* 1 DBPSK The BER first falls as the data
rate drops. Then it starts to
* denotes the modulation ranges affected by fading effect.
*** All the above plots highly depend upon the placement of Node in the simulation
environment. So, note that even if the placement is slightly different the same set of
values will not be got but one would notice a similar trend.
Graph II
The data rate between the Access Point and the wireless nodes decreases. This is because
data rate dependents on the received power at the receiver. Received power is directly
proportional to (1 / distance).

Experiment 7
Objective: Study the working and routing table formation of Interior routing protocols,
i.e. Routing Information Protocol (RIP) and Open Shortest Path First (OSPF).
Theory:
RIP
RIP is intended to allow hosts and gateways to exchange information for computing
routes through an IP-based network. RIP is a distance vector protocol which is based on
Bellman-Ford algorithm. This algorithm has been used for routing computation in the
network.
Distance vector algorithms are based on the exchange of only a small amount of
information using RIP messages.
Each entity (router or host) that participates in the routing protocol is assumed to keep
information about all of the destinations within the system. Generally, information about
all entities connected to one network is summarized by a single entry, which describes the
route to all destinations on that network. This summarization is possible because as far as
IP is concerned, routing within a network is invisible. Each entry in this routing database
includes the next router to which datagrams destined for the entity should be sent. In
addition, it includes a metric measuring the total distance to the entity.
Distance is a somewhat generalized concept, which may cover the time delay in getting
messages to the entity, the dollar cost of sending messages to it, etc. Distance vector
algorithms get their name from the fact that it is possible to compute optimal routes when
the only information exchanged is the list of these distances. Furthermore, information is
only exchanged among entities that are adjacent, that is, entities that share a common
network.
OSPF
In OSPF, the Packets are transmitted through the shortest path between the source and
destination.

Shortest path:
OSPF allows administrator to assign a cost for passing through a link. The total cost of a
particular route is equal to the sum of the costs of all links that comprise the route. A
router chooses the route with the shortest (smallest) cost.
In OSPF, each router has a link state database which is tabular representation of the
topology of the network (including cost). Using dijkstra algorithm each router finds the
shortest path between source and destination.
Formation of OSPF Routing Table
1. OSPF-speaking routers send Hello packets out all OSPF-enabled interfaces. If two
routers sharing a common data link agree on certain parameters specified in their
respective Hello packets, they will become neighbors.
2. Adjacencies, which can be thought of as virtual point-to-point links, are formed
between some neighbors. OSPF defines several network types and several router
types. The establishment of an adjacency is determined by the types of routers
exchanging Hellos and the type of network over which the Hellos are exchanged.
3. Each router sends link-state advertisements (LSAs) over all adjacencies. The LSAs
describe all of the router's links, or interfaces, the router's neighbors, and the state of
the links. These links might be to stub networks (networks with no other router
attached), to other OSPF routers, or to external networks (networks learned from
another routing process). Because of the varying types of link-state information,
OSPF defines multiple LSA types.
4. Each router receiving an LSA from a neighbor records the LSA in its link-state
database and sends a copy of the LSA to all of its other neighbors.
5. By flooding LSAs throughout an area, all routers will build identical link-state
databases.
6. When the databases are complete, each router uses the SPF algorithm to calculate a
loop-free graph describing the shortest (lowest cost) path to every known destination,
with itself as the root. This graph is the SPF tree.
7. Each router builds its route table from its SPF tree

Simulation:
Sample 1:
Step1:
Step2:
Click drop Routers, Switches and Nodes onto the Simulation Environment as shown

Step3:
Set the properties of the WiredNode1 as follows:
Set the properties of the 8Port_Router1 as follows:
Switch Properties: Accept default properties for Switch.
Link Properties: Accept default properties for Link.
• Set the properties of Node, Switch Router

Sample 2:
To model a scenario follows the same steps given in Sample1 and
Set the Router properties as given below
Link Properties:
Medium Type CAT - 5 CAT – 5 CAT - 5 CAT - 5 CAT - 5
Uplink Speed 100 100 100 10 10
Downlink Speed 100 100 100 10 10
Switch Properties: Accept default properties for Switch.
• Set the properties of Node, Switch Router

Inference:
RIP
In Distance vector routing, each router periodically shares its knowledge about the entire
network with its neighbors. The three keys to understanding the algorithm,
1. Knowledge about the whole network
Router sends all of its collected knowledge about the network to its neighbors
2. Routing only to neighbors
Each router periodically sends its knowledge about the network only to those routers
to which it has direct links. It sends whatever knowledge it has about the whole
network through all of its ports. This information is received and kept by each
neighboring router and used to update that router’s own information about the
network.
3. Information sharing at regular intervals
For example, every 30 seconds, each router sends its information about the whole
network to its neighbors. This sharing occurs whether or not the network has changed
since the last time information was exchanged
In NetSim the Routing table Formation has 3 stages
Initial Table: This table will show the direct connections made by each Router.
Intermediate Table: The Intermediate table will have the updates of the Network in every
30 seconds
Final Table: This table is formed when there is no update in the Network.
The data should be forwarded using Routing Table with the shortest distance
The RIP table in NetSim
• After running sample1, click RIP table in Performance Metrics screen. Then click the
router to view the Routing table.
• We have shown the routing table for Router 1,

Shortest Path from Wired_Node1 to Wired_Node2 in RIP
Wired_Node1Switch1Router1Router4Router5Switch2Wired_Node2

OSPF
The main operation of the OSPF protocol occurs in the following consecutive stages and
leads to the convergence of the internetworks:
1. Compiling the LSDB.
2. Calculating the Shortest Path First (SPF) Tree.
3. Creating the routing table entries.
Compiling the LSDB
The LSDB is a database of all OSPF router LSAs. The LSDB is compiled by an ongoing
exchange of LSAs between neighboring routers so that each router is synchronized with
its neighbor. When the Network converged, all routers have the appropriate entries in
their LSDB.
Calculating the SPF Tree Using Dijkstra's Algorithm
Once the LSDB is compiled, each OSPF router performs a least cost path calculation
called the Dijkstra algorithm on the information in the LSDB and creates a tree of shortest
paths to each other router and network with themselves as the root. This tree is known as
the SPF Tree and contains a single, least cost path to each router and in the Network. The
least cost path calculation is performed by each router with itself as the root of the tree
Calculating the Routing Table Entries from the SPF Tree
The OSPF routing table entries are created from the SPF tree and a single entry for each
network in the AS is produced. The metric for the routing table entry is the OSPF-
calculated cost, not a hop count.
The OSPF table in NetSim
• After running sample2, click OSPF Metrics in Performance Metrics screen. Then
click the router to view the Routing table
• We have shown the routing table for Router 1

Shortest Path from Wired_Node1 to Wired_Node2 in OSPF
Wired_Node1Switch1Router1Router2Router3Router5Switch2Wired_N
ode2
Note: The Cost is calculated by using the following formula
Reference Bandwidth = 100 Mbps
For Example,
Let us take,
Link Speed UP = 100 Mbps

Experiment 8
Objective:
M/D/1 Queue:
I. To create an M/D/1 queue: a source to generate packets, a queue to act as the
buffer and server, a sink to dispose of serviced packets.
II. To study how the queuing delay of such a system varies.
Theory:
In systems where the service time is a constant, the M/D/1, single-server queue model,
can be used. Following Kendall's notation it indicates a system where:
• Arrivals are a Poisson process with parameter λ
• Service time(s) is deterministic or constant
• There is one server
For an M/D/1 model, the total expected queuing time is
Where µ = Service Rate = 1/Service time and ρ is the utilization given as follows,
To model an M/D/1 system in NetSim, we use the following model
Traffic flow from Node 1 to Node 2 (Node 1: Source, Node 2: Sink)
Inter-arrival time: Exponential Distribution with mean 2000 µs
Packet size: Constant Distribution with mean of 1250 bytes

Note:
1. Exponentially distributed inter-arrivals times give us a Poisson arrival process.
Different mean values are chosen as explained in the section Sample Inputs.
2. To get constant service times, we use constant distribution for packet sizes. Since, the
service (which in our case is link transmission) times are directly proportional to
packet size (greater the packet size, greater the time for transmission through a link), a
constant packet size leads to a constant service time.
Procedure:
Create Scenario: “Simulation New Internetworks”.
Nodes 1 and Node 2 are connected with Router 1 by Link 1 and Link 2 respectively. Set
the properties for each device as given below,
Sample 1
Disable TCP in the Transport Layer in Node Properties.
Traffic Type Custom
Packet Inter Arrival Time (µs) 2000
Packet Inter Arrival Time Distribution Exponential

Router Properties: Accept the default properties for Router.
Simulation Time: 100 Sec
Observation:
Even though the packet size at the application layer is 1250 bytes, as the packet moves
down the layers, some overhead is added which results in a greater packet size. This is the
actual payload that is transmitted by the physical layer. The overheads added in different
layers are shown in the table:
Therefore, the payload size = Packet Size + Overhead
= 1250 + 54
= 1304 bytes
Link Properties Link 1 Link 2
Medium Type CAT-5 CAT-5
Uplink Speed (Mbps) 10 10
Downlink Speed (Mbps) 10 10
Uplink BER No Error No Error
Downlink BER No Error No Error
Uplink Propagation Delay (ms) 0 0
Downlink Propagation Delay
(ms)
0 0
Layer Overhead
(Bytes)
Transport Layer 8
Network Layer 20
MAC layer 26
Physical Layer 0
Total 54

Theoretical Calculation:
By formula,
µ = Service Rate
Service rate is nothing but the time taken to service each packet and is given by
Service rate µ = Link capacity (bps) / (Payload Size (Bytes) * 8)
= (10×106
) / (1304*8)
= 958.59 packets / sec
λ = Arrival rate
Arrival rate the rate at which packets arrive (Packets per second)
Inter-arrival time = 2,000 micro sec
Arrival rate λ = 1,000,000 / Inter Arrival time
= 1,000,000/2000
= 500 packets / sec
ρ = Utilization
ρ = λ/µ
= 500/958.59
= 0.522
By formula, Queuing Time =
= 569.61 micro sec

Output:
After running the simulation, check the “Mean Delay” in the Application Metrics.
Mean Delay = 2671.333 micro sec
This “Mean Delay” is the sum of Queuing Delay, Total Transmission time and Routing
Delay.
Total Transmission Time is the sum of transmission time through Link 1 and Link 2.
Transmission time through each link is the same and is given by:
Transmission time through each link =
=
= 1043.2 micro sec
Routing Delay is approximately 1 micro sec and can be found from the Event Trace. It is
the difference between “Physical In” and “Physical Out” time for the Router.
Therefore, for simulation
Queuing Delay = 2671.333 – (2 × 1043.2) – 1
= 583.933 micro sec
Note: Obtained value is slightly higher than the theoretical value because of initial delays
in forming ARP table, Switch table and Routing table etc.
Sample 2
Keeping all the other parameters same as in previous example, if Packet Inter Arrival
Time is taken as 1500 micro sec, then
λ = 666.67 packets per sec
Utilization ρ = λ/µ = 666.67/958.59 = 0.695

And Queuing Time T = 1188.56 micro sec
From NetSim,
Mean Delay = 3324.278 micro sec
Therefore, Queuing Time = 3324.278 - (2×1043.2) – 1
= 1236.878 micro sec
Note: Obtained value is slightly higher than the theoretical value because of initial delays
in forming ARP table, Switch table and Routing table etc.
A Note on M/M/1 queuing in NetSim
M/M/1 queue can be generated similarly by setting the “Packet Size Distribution” as
“Exponential” instead of “Constant”. However, the results obtained from simulation
deviate from the theoretical value because of the effect of packet fragmentation.
Whenever a packet with size greater than Transport Layer MSS and / or MAC Layer
MTU (which is 1500 bytes in NetSim) is generated, it gets fragmented in the application
layer. Then the packet is sent as multiple frames, and makes it impossible to calculate the
exact queuing time.

Experiment 9
Objective: Plot the characteristic curve throughput versus offered traffic for a Slotted
ALOHA system.
(Reference: Computer Networks, 3rd Edition. Andrew S. Tanenbaum)
Theory:
ALOHA provides a wireless data network. It is a multiple access protocol (this protocol is
for allocating a multiple access channel). There are two main versions of ALOHA: pure
and slotted. They differ with respect to whether or not time is divided up into discrete
slots into which all frames must fit.
Slotted ALOHA:
In slotted Aloha, time is divided up into discrete intervals, each interval corresponding to
one frame. In Slotted ALOHA, a computer is required to wait for the beginning of the
next slot in order to send the next packet. The probability of no other traffic being
initiated during the entire vulnerable period is given by which leads to
Where, S (frames per frame time) is the mean of the Poisson distribution with which
frames are being generated. For reasonable throughput S should lie between 0 and 1.
G is the mean of the Poisson distribution followed by the transmission attempts per frame
time, old and new combined. Old frames mean those frames that have previously suffered
collisions.
It is easy to note that Slotted ALOHA peaks at G=1, with a throughput of or
about 0.368. It means that if the system is operating at G=1, the probability of an empty
an slot is 0.368
Calculations used in NetSim to obtain the plot between S and G:
Using NetSim, the attempts per packet time (G) can be calculated as follows;
Where, G = Attempts per packet time
TA = Total Attempt
PT = Packet time (in milli seconds)
ST = Simulation time (in seconds)

The throughput (mbps) per frame time can be obtained as follows:
Where, S = Throughput per frame time
PT = Packet time (in milli seconds)
PS = Packet size (in bytes)
Calculations for the packet time:
In the following experiment we have taken packet size=1498 bytes (1472 + 26
Overheads)
Bandwidth is 10 Mbps and hence, packet time comes as 1.198 ms.
Procedure:
How to Create Scenario:
• Create Scenario: “Help NetSim Help Running Simulation via GUI Legacy
Networks Create Scenario”.
Obtain the values of Throughput and Total Attempts from the statistics of NetSim
simulation for various numbers of traffic generators.
Sample Inputs:
Input for Sample 1: Node 1 transmits data to Node 2.
Node Properties NODE 1
Transmission Point-to-Point
Destination Node-2
Traffic Type Data
Application Data Size
Application Data Size (bytes) 1472
Inter Arrival Time
Inter Arrival Time 20000

Input for Sample 2: Node 1 transmits data to Node 2, Node 2 transmits data to Node 1.
Experiment 1: Node 1 transmits data to Node 2.
Experiment 2: Node 1 transmits data to Node 2, and Node 2 transmits data to Node 1.
Experiment 3: Node 1 transmits data to Node 2, and Node 2 transmits data to Node 3,
and Node 3 transmits data to Node 1.
And so on do the experiment by increasing the number of nodes generating traffic as 4, 5,
7, 9, 10, 15, 20 22 and 24 nodes.
Node Properties NODE 1 NODE 2
Transmission Point-to-Point Point-to-Point
Destination Node-2 Node-1
Traffic Type Data Data
Application Data Size (bytes) 1472 1472
Inter Arrival Time
Inter Arrival Time 20000 20000

Comparison Table:
Number of
nodes
generating
traffic
Throughput
(mbps)
Total
attempts
Throughput
per packet time
Attempts per
packet time
1 0.59 499 0.06 0.06
2 1.2 3308 0.12 0.39
3 1.8 4953 0.18 0.59
4 2.4 6691 0.24 0.80
5 2.9 9180 0.29 1.09
7 2.8 14012 0.28 1.67
9 2.7 14868 0.27 1.78
10 2.7 15078 0.27 1.80
15 2.6 16037 0.26 1.92
20 2.5 16437 0.25 1.96
22 2.4 16496 0.24 1.97
24 2.4 16755 0.24 2.00
We have obtained the following characteristic plot for the Slotted ALOHA, which
matches the theoretical result.

Note: The optimum value is slightly less than the theoretical maximum of 0.368 because
NetSim’s simulation is per real-world and includes overheads, inter-frame gaps etc.

Experiment 10
Objective:
Understand the impact of bit error rate on packet error and investigate the impact of error
of a simple hub based CSMA / CD network
Theory:
Bit error rate (BER): The bit error rate or bit error ratio is the number of bit errors
divided by the total number of transferred bits during a studied time interval i.e.
For example, a transmission might have a BER of 10-5
, meaning that on average, 1 out of
every of 100,000 bits transmitted exhibits an error. The BER is an indication of how
often a packet or other data unit has to be retransmitted because of an error.
Unlike many other forms of assessment, bit error rate, BER assesses the full end to end
performance of a system including the transmitter, receiver and the medium between the
two. In this way, bit error rate, BER enables the actual performance of a system in
operation to be tested.
Bit error probability (pe): The bit error probability is the expectation value of the BER.
The BER can be considered as an approximate estimate of the bit error probability. This
estimate is accurate for a long time interval and a high number of bit errors.
Packet Error Rate (PER):
The PER is the number of incorrectly received data packets divided by the total number
of received packets. A packet is declared incorrect if at least one bit is erroneous. The
expectation of the PER is denoted as packet error probability pp , which for a data packet
length of N bits can be expressed as,
It is based on the assumption that the bit errors are independent of each other.
Derivation of the packet error probability:
Suppose packet size is N bits.
is the bit error probability then probability of no bit error=1-
As packet size is N bits and it is the assumption that the bit errors are independent. Hence,
Probability of a packet with no errors =
A packet is erroneous if at least there is one bit error, hence

Probability of packet error=1-
Procedure:
How to create a scenario and generate traffic:
• Create Scenario: “Help NetSim Help Running Simulation via GUI Non-
Internetworks Legacy Networks Create Scenario”.
Example 1:
Create samples by varying the bit error rate (10-6
, 10-7
, 10-8
, 10-9
, No error) and check
whether packet error output matches the PER formula.
Sample Inputs:
In this sample experiment, two nodes and one hub are clicked and dropped on the
environment builder. And following experiments are performed.
Inputs for the sample experiments are given below,
• Click and drop Hub on the environment builder.
• Click and drop Node1 over the hub.
Node Properties Node1
Destination Node 2
Inter Arrival Time (µs) 2500
MTU Size(bytes) 1500
Hub Properties Sample 1 Sample 2 Sample 3 Sample 4 Sample 5
Data rate (Mbps) 10 10 10 10 10
Error Rate (BER) No Error 10-9
10-8
10-7
10-6
Physical Medium Twisted
Pair
Twisted
Pair
Twisted
Pair
Twisted
Pair
Twisted Pair

Example 2:
Sample Inputs:
In this sample experiment, four nodes and one hub are clicked and dropped on the
environment builder. And following experiments are performed.
Inputs for the sample experiments are given below,
• Click and drop Hub on the environment builder.
• Click and drop Node3 over the hub
• Click and drop Node4 over the hub
Node Properties Node1 Node3
Transmission Type Point to Point Point to Point
Destination Node 2 Node4
Inter Arrival Time (µs) 2500 2500
MTU Size(bytes) 1500 1500
Hub Properties Sample 1 Sample 2 Sample 3 Sample 4 Sample 5
Data rate (Mbps) 10 10 10 10 10
Error Rate (BER) No Error 10-9
10-8
10-7
10-6
Physical Medium Twisted
Pair
Twisted
Pair
Twisted
Pair
Twisted
Pair
Twisted
Pair
• Set the properties for the Nodes The Hub

NetSim simulation output:
Example 1: One node transmission
BER Packets
Errored
Total
packets
0
1E-09
1E-08
1E-07
1E-06
0
1
2
49
472
40000
40000
40000
40000
40000
Example 2: Two nodes transmission
BER Packets
Errored
Total
packets
0
1E-09
1E-08
1E-07
1E-06
0
1
9
96
921
80000
80000
80000
80000
80000
Packet size for the calculation of the output table=1500 bytes or 12000 bits
Comparing Packets errored with Bit error rate:
Inference:
From the Graph, we see that as the error rate is increased the number of errored packets
increase. The increase is exponential since the error rate is increased in powers of 10.

Experiment 11
Objective:
To determine the optimum persistence of a p-persistent CSMA / CD network for a
heavily loaded bus capacity.
Theory:
Carrier Sense Multiple Access Collision Detection (CSMA / CD)
This protocol includes the improvements for stations to abort their transmissions as soon
as they detect a collision. Quickly terminating damaged frames saves time and bandwidth.
This protocol is widely used on LANs in the MAC sub layer. If two or more stations
decide to transmit simultaneously, there will be a collision. Collisions can be detected by
looking at the power or pulse width of the received signal and comparing it to the
transmitted signal. After a station detects a collision, it aborts its transmission, waits a
random period of time and then tries again, assuming that no other station has started
transmitting in the meantime.
There are mainly three theoretical versions of the CSMA /CD protocol:
1-persistent CSMA / CD: When a station has data to send, it first listens to the channel
to see if anyone else is transmitting at that moment. If the channel is busy, the station
waits until it becomes idle. When station detects an idle channel, it transmits a frame. If a
collision occurs, the station waits a random amount of time and starts all over again. The
protocol is called 1-persistent because the station transmits with a probability of 1
whenever it finds the channel idle.
Ethernet, which is used in real-life, uses 1-persistence. A consequence of 1-persistence is
that, if more than one station is waiting for the channel to get idle, and when the channel
gets idle, a collision is certain. Ethernet then handles the resulting collision via the usual
exponential back off. If N stations are waiting to transmit, the time required for one
station to win the back off is linear in N.
Non-persistent CSMA /CD: In this protocol, before sending, a station senses the
channel. If no one else is sending, the station begins doing so itself. However, if the
channel is already in use, the channel does not continually sense it for the purpose of
seizing it immediately upon detecting the end of the previous transmission. Instead, it
waits a random period of time and then repeats the algorithm. Intuitively this algorithm
should lead to better channel utilization and longer delays than 1-persistent CSMA

p-persistent CSMA / CD: This protocol applies to slotted channels. When a station
becomes ready to send, it senses the channel. If it is idle, it transmits with a probability of
p. With a probability q=1-p it defers until the next slot. If that slot is also idle, it either
transmits or defers again, with probabilities p and q respectively. This process is repeated
until either the frame has been transmitted or another station has begun transmitting. In
the latter case, it acts as if there had been a collision (i.e., it waits a random time and starts
again). If the station initially senses the channel busy, it waits until the next slot and
applies the above algorithm.
How does the performance of LAN (throughput) that uses CSMA/CD protocol gets
affected as the numbers of logged in user varies:
Performance studies indicate that CSMA/CD performs better at light network loads. With
the increase in the number of stations sending data, it is expected that heavier traffic have
to be carried on CSMA/CD LANs (IEEE 802.3). Different studies have shown that
CSMA/CD performance tends to degrade rapidly as the load exceeds about 40% of the
bus capacity. Above this load value, the number of packet collision raise rapidly due to
the interaction among repeated transmissions and new packet arrivals. Collided packets
will back off based on the truncated binary back off algorithm as defined in IEEE 802.3
standards. These retransmitted packets also collided with the newly arriving packets.
Procedure:
How to create a scenario and generate traffic:
Scenario:

Sample Input:
In this Sample experiment 12 Nodes and 2 Hubs need to be clicked and dropped onto the
Environment Builder.
Input for the Sample experiments (i.e. Totally 11 Samples) are given below,
Sample Input 1:
In the first sample for each Node the following properties have to be set,
Node Properties Values to be Selected
Transmission Type Broadcast
Traffic Type Data
No. of Nodes Transmitting 12
Persistence 1
MTU Size(bytes) 1500
Vary persistence from 1/2, 1/3, 1/4, 1/5… 1/12, to generate other experiments.
Data Input Configuration: (This window is obtained when Data is selected in Traffic
Type):
Inter Arrival Time Distribution Exponential
Mean Inter Arrival Time(µs) 1000
Hub Properties common for Hub1 and Hub2:
Hub Properties Values to be
Selected
Data Rate(Mbps) 10
Error Rate (bit error rate) No error
Physical Medium Twisted Pair

• Set the properties for the Nodes The Hub
Output:
After simulation of each experiment, click on the network statistics and note down the
user level throughput values. Open an excel sheet and plot a graph for these noted values
against their respective persistence values.
Comparison Chart:
Inference:
As the number of logged in users is quite large in this experiment, the performance of a
p-persistent CSMA/CD network with large p, is not optimal because of a large number of
collisions. Therefore, we have minimum throughput when the persistence was 1/2. But as
persistence is decreased (lower and lower probabilities), the likelihood of collisions
reduce and hence throughput starts to increase. However, beyond a certain limit, in this
case 1/11 the probability of transmitting packets becomes very low and hence there aren’t
many transmissions. Therefore, throughput starts to decline. In this experiment with 12
nodes generating traffic, we notice that the maximum throughput is at a persistence value
lying between 1/9 and 1/11.
Optimum

Experiment 12
Objective
Study the effect of Peak Cell Rate (per Sec) and Cell Delay Variation Tolerance on the
performance of an ATM Networks
Procedure:
Inputs
In this Sample,
• Total no of CPEs used: 2
• Total no of Switches used: 2
• CPE 1, CPE 2 is connected with Switch 1 and Switch 2 by Link 1 and Link 3
respectively.
• Switch 1 is connected with Switch 2 by Link 2.
Set the properties of Switch and CPE by following the tables for each sample,
Switch Properties Switch 1 Switch 2
Scheduling Technique Priority Priority
Buffer Size (KB) 8 8
Link Properties Link 1 Link 2 Link 3
Bit Error Rate No Error No Error No Error
Physical Medium E0 E0 E0
Distance (km) 1 1 1

Inputs for Sample 1
CPE Properties CPE 1
Destination CPE 2
Traffic Type Data
Distribution Exponential
Mean Application Data Size (bytes) 1500
Inter Arrival Time
Mean Inter Arrival Time (µs) 20000
Peak Cell Rate (cells/second) 1000
Cell Delay Variation Tolerance
(µs)
1000
Inputs for Sample 2
Destination CPE 2
Traffic Type Data
Inter Arrival Time
(µs)
2000

Inputs for Sample 3
Destination CPE 2
Traffic Type Data
Inter Arrival Time
(µs)
3000
Inputs for Sample 4
Destination CPE 2
Traffic Type Data
Inter Arrival Time
(µs)
4000

Inputs for Sample 5
Destination CPE 2
Traffic Type Data
Inter Arrival Time
(µs)
5000
Simulation Time – 10 sec
Output
To view the output by using NetSim Sample experiments need to be added onto the
Analytics interface. Given below is the navigation for analytics -
“Simulation

Analytics”
• Legacy Networks
• Select the Experiments (Note: Click one experiment after another to compare the
experiments in the Analytics interface).
• Select the Metric: Queuing Delay (ms)

Comparison Charts:
Inference
To see Peak Cell Rate and Cell Delay Variation Tolerance definitions go to NetSim
Basics Menu.
When the Peak Cell Rate and Cell Delay Variation Tolerance are changed from 1000 to
5000, the Number of Cells transmitted increases. This is because the conformance of the
traffic depends on the Peak Cell Rate and the Cell Delay Variation Tolerance. As the
number of cells transmitted increases, queuing delay also increases.

Experiment 13
Objective
Network performance analysis with an ATM switch implementing different scheduling
techniques like First in First out (FIFO), Priority, and Round Robin
Theory
In an ATM network, scheduling of cells is the major task of any ATM switch. Scheduling
is the process by which the ATM switch determines the sequence of flow of the cells in
network. The scheduling is done on various properties like service type, cell category,
queue length, arrival time etc.
First In First out (FIFO): FIFO is the simplest way of scheduling. As the name
suggests, in this technique, the preference is given to that cell which comes first in the
queue irrespective of its priority value. The one which comes next waits until the first
finishes. The drawback of this technique is that some cells of very high priority like audio
service encounter extra delay that is not ignorable.
Priority: In this technique, each cell is assigned a certain priority value based on its
traffic parameters. The scheduler checks the availability of highest priority cells and
schedules them before going for the lower priority cells. The drawback of this algorithm
is that cells of lowest priority starve for the resources when there are a large number of
higher priority cells.
Round Robin: In this technique, the scheduler gives equal preference for all priority
types. Therefore, scheduler processes one cell of each priority type (If available) before
going for the next cell and cycles through them. Here starvation never occurs because no
priority is given. Round robin scheduling may not be desirable if QoS of the different
priority type are highly variable.
Procedure:
In this experiment, we are going to analyze the link Utilization (%) of the outgoing link
from an ATM switch

First In First Out (FIFO):
In NetSim, Select SimulationNewLegacy Networks ATM
Please navigate through the below given path,
Inputs
In all Samples,
• Total no of CPE used: 4
• Total no of ATM switch used: 2
The device are interconnected as given below
• CPE 1 is connected with switch 1 by link 1.
• Switch 1 and switch 2 are connected with link 3.
Scheduling technique FIFO FIFO
Buffer size 4096 KB 4096 KB
Destination CPE 3
Traffic Type Data

Inter arrival time
Mean Inter-arrival time (µs) 10000
Generation rate (Mbps) 8
Scheduling FIFO
Peak cell rate (cells/sec) 99999
Cell delay Variation tolerance (µs) 99999
GCRA type VSA
Destination CPE 4
Traffic Type Voice
Codec Constant
Inter-arrival time (µs) 20000
Service Type CBR
Scheduling FIFO
Cell delay Variation tolerance (µs) 99999
GCRA type VSA
Bit Error Rate
(BER)
No Error No Error No Error No Error No Error
Physical medium E2 E2 E0 T1 T1
Data Rate (Mbps) 8.448 8.448 0.064 1.54 1.54
Distance 1 1 1 1 1
Simulation Time –10 sec

• Set the properties of CPE and Switch,
“Save” it, upon completion of the experiment.
Output:
Select the metrics Utilization and Delay report (Link). Note down the link utilization of
link 4 and link 5.
Priority:
In the simulation environment window create the following scenario
How to Create Scenario generate traffic:
Inputs:
In all Samples,

Scheduling technique Priority FIFO
Destination CPE 3
Traffic Type Data
Inter arrival time
Mean Inter-arrival time (Micro-sec) 10000
Scheduling FIFO
Cell delay Variation tolerance (Micro-sec) 99999
GCRA type VSA
Destination CPE 4

Traffic Type Voice
Codec Constant
Inter-arrival time (Micro-sec) 20000
Service Type CBR
Scheduling FIFO
GCRA type VSA
Bit Error Rate
(BER)
Data Rate (Mbps) 8.448 8.448 0.064 1.54 1.54
Distance 1 1 1 1 1
Simulation Time –10 sec
Output:
link 4 and link 5.

Round Robin:
In the simulation environment window create the following scenario
How to Create Scenario generate traffic:
Inputs:
In all Samples,

Scheduling technique Round Robin FIFO
Bit Error Rate
(BER)
Data Rate (Mbps) 8.448 8.448 0.064 1.54 1.54
Distance 1 1 1 1 1
Destination CPE 3
Traffic Type Data
Inter arrival time
Mean Inter-arrival time (Micro-sec) 10000
Scheduling FIFO
GCRA type VSA
Destination CPE 4
Traffic Type Voice
Codec Constant
Inter-arrival time (Micro-sec) 20000

Service Type CBR
Scheduling FIFO
GCRA type VSA
Simulation Time –10 Sec.
Output:
link 4 and link 5.

Comparison:
Traffic analysis:

CPE 1 is transmitting Data traffic (being generated at 8 Mbps) to CPE 3 through links 1,
3, and 4. CPE2 transmitting voice traffic (being generated at 4 Mbps) to CPE4 through
link 2, 3, and 5. Here, voice traffic has priority over data traffic.
Link speed of link 1 and 2 is high (8.448 mbps) as compared to data rate and also the
PCR and CDVT of CPE1 and CPE 2 are high. So there is a low probability that these
cells will be dropped. Therefore, all the cells reach switch1 where scheduling will
happens.
Link speed of link 3 is very low (0.064 mbps) which means it does not have enough
resources to handle the cells. Hence, it will only pass those cells that have high priority
(based on Scheduling technique). Link speed of 4 and 5 is high compared to link 3 and so
there is no queue is buildup on switch 2. Based on what type of cells pass through link 3,
determines the utilization of the link 4 and link 5.
Inference:
As we see in chart 1 and table 1, the utilization of link 4 is double of link 5 in case of
FIFO. Because, in case of FIFO, scheduler gives preference to which come cells first.
Note that the data rate of CPE1 id double than CPE2 data rate and link speed is same
hence switch 1 gets two cells from CPE 1 and one cell from CPE2. Hence, switch 1
schedules two packets of CPE1 and one packet of CPE2. Therefore, the number of packet
transmitted through link 4 is double than link 5 and hence utilization is also double.
In case of priority, the utilization of the link 4 is 0.006 % and link 5 is 4.138%. This is
because the ATM scheduler gives priority to the voice traffic (generated by CPE2 to CPE
4 via link 2, 3, and 5) over data traffic (generated by CPE 1 to CPE 3 via link 1, 3 and 4).
The generation rate of voice traffic is 4 mbps which is much greater than the link speed of
link 3 (0.064mbps). Hence, scheduler only schedules voice traffic and data traffic keeps
waiting in the queue.
In case of round robin the utilization of both the links is the same. Because, in case of
Round robin, scheduler schedules the packet in circular fashion means one packet from
CPE1 and one packet from CPE2. Note that the data rate of CPE1 and CPE2 is
sufficiently high to ensure presence of a packet in the buffer from both the CPEs.
Therefore, the number of packets transmitted through link four is same as link five and
hence utilization is also same.

Experiment 14
Objective:
Study the working of BGP and formation of BGP Routing table.
Theory:
In BGP, the Packets are transmitted between the Autonomous system using Path vector
Routing.
Path Vector Routing:
Path vector routing is used for inter-domain routing. It is similar to distance vector
routing. In path vector routing we assume that there is one Router (there can be many) in
each autonomous system which acts on behalf of the entire autonomous system. This
Router is called the Border Router. The Border Router in one Autonomous System
creates a routing table and advertises it to neighboring Border Router which belongs to
neighboring autonomous systems. The idea is same as distance vector routing except that
only Border Routers in each autonomous system can communicate with each other. The
Border Routers advertises the path, not the metric, in its autonomous system or other
autonomous systems.
Procedure:
• Create Scenario: “Help NetSim Help Running Simulation via GUI BGP
Sample Inputs:
• Total no of CPE s used: 4
• Total no of Internal Routers used: 2
• Total number of Border Routers used: 2
• CPE 1 and CPE 2 are connected with Internal Router 3 by Link 1 and Link 2.
• Internal Router 3 and Border Router 1 are connected by Link 3.
• Border Router 1 and Border Router 2 are connected by Link 4.

• Border Router 2 and Internal Router 4 are connected by Link 5.
• Internal Router 4 is connected with CPE 3 and CPE 4 by Link 6 and Link 7
respectively.
If you want to select your internal gateway protocol as RIP then here is the information
you need to fill in for Router properties
CPE Properties CPE 1 CPE 2
Destination CPE 3 CPE 4
Priority Low Low
Application Data size
Application Data size (bytes) 1472 1472
Inter Arrival Time
Mean Inter Arrival Time (µs) 20000 20000
Router
Properties
BGP Router1 BGP Router2 Internal Router3
Port 1 Port 2 Port 1 Port 2 Port 1 Port 2 Port 3
Buffer Size
(KB)
8 8 8 8 8 8 8
Scheduling
Type
Priority Priority Priority Priority Priority Priority Priority
Protocol Type RIP BGP BGP RIP RIP RIP RIP
Periodic Time 30 - - 30 30 30 30
Expiration
Time
180 - - 180 180 180 180
Garbage
Collection
Time
120 - - 120 120 120 120
Local
Preference
- 100 100 - - - -
MED - 0 0 - - - -

If you want to select your internal gateway protocol as OSPF then here is the information
you need to fill in for Router properties
Router Properties Internal Router4
Port 1 Port 2 Port 3
Buffer Size (KB) 8 8 8
Scheduling Type Priority Priority Priority
Protocol Type RIP RIP RIP
Periodic Time 30 30 30
Expiration Time 180 180 180
Garbage Collection Time 120 120 120
Local Preference - - -
MED - - -
Router
Properties
BGP Router1 BGP Router2 Internal Router3
Port 1 Port 2 Port 1 Port 2 Port 1 Port 2 Port 3
Buffer Size
(KB)
8 8 8 8 8 8 8
Scheduling
Type
Priority Priority Priority Priority Priority Priority Priority
Protocol
Type
OSPF BGP BGP OSPF OSPF OSPF OSPF
Priority 255 - - 255 255 255 255
Local
Preference
- 100 100 - - - -
MED - 0 0 - - - -

• Set the properties of CPE Routers
Upon completion of the experiment “Save” it for comparison that can be carried out in
the “Analytics” section.
Router Properties Internal Router4
Port 1 Port 2 Port 3
Buffer Size (KB) 8 8 8
Scheduling Type Priority Priority Priority
Protocol Type OSPF OSPF OSPF
Priority 255 255 255
Local Preference - - -
MED - -
Link
Properties
Link 1 Link 2 Link 3 Link 4 Link 5 Link 6 Link 7
Distance (km) 1 1 1 1 1 1 1
Bit Error Rate
(BER)
No
Error
No
Error
No
Error
No
Error
No
Error
No
Error
No
Error
Physical
Medium
E2 E2 CAT5(
10Mb
ps)
1000
Mbps
CAT5(
10Mb
ps)
E2 E2
Link Weight 1 1 1 1 1 1 1

Output:
After running this scenario, in Network performance screen, click View Routing table
link. Then the following screen would appear
If you click over the internal routers, you will get the RIP/OSPF routing table for internal
routers. If you click over the Border router 1 or 2, you will get the routing table for
Border routers. We have shown the routing tables for Border Router 1 and 2.

The Border Routers store the CPE’s Network address in its Routing Table as shown in the
above Tables under “Destination” column.
Inference:
First the internal Routing tables (RIP/OSPF table) are formed among all the Routers
belonging to each of the Autonomous systems. The Border Routers containing the
network address of all the CPEs in it’s AS represents the routing table of it’s AS. Border
Routers in each AS, having ability to communicate with another AS, pass their Routing
tables resulting in the formation of external Routing tables (BGP table). Then actual
packet transmission takes place from Source to Destination between Autonomous
systems.

Experiment 15
Objective:
Study how the LSP varies for different traffic in MPLS -TE (Traffic Engineering)
Theory:
Traffic Engineering is the process of controlling how traffic flows through one’s network
so as to optimize resource utilization and network performance. Traffic Engineering is
needed in the Internet mainly because current IGPs (Interior Gateway Protocols – RIP,
OSPF) always use the shortest paths to forward all traffics. But MPLS with traffic
engineering use different paths to forward different traffics.
Procedure:
• Create Scenario: “Help NetSim Help Running Simulation via GUI MPLS
Sample Inputs:
Sample 1:
In this Sample,
• Total no of CPE’s used: 4
• CPE 1, 2 and Router 2, 3 are connected with Router 1 by Link 1, 2, 3, 4 respectively.
• Router 2,3 and CPE 3,4 are connected with Router 4 by Link 5,6 7, 8 respectively
CPE Properties CPE 1 CPE2
Priority Low Low
Reserved Bandwidth (Mbps) 6 6

Simulation Time –10 Sec.
• Set the properties of CPE Router,
Upon completion of the experiment “Save” it for comparison
Output:
After running this scenario, in Network performance screen, click View LSP link. Then
the following screen would appear.
Click 10.1.7.2(CPE-1) to view the LSP for CPE 1’s traffic.
Router Properties Router1 Router2 Router3 Router4
Buffer Size (KB) 8 8 8 8
Scheduling Type Priority Priority Priority Priority
Routing Properties
Protocol Type OSPF OSPF OSPF OSPF
Router Priority 255 255 255 255
MPLS Properties
Traffic Engineering Enable Enable Enable Enable
Link Properties Link 5 Link 6 Link 7 Link 8
Distance (km) 1 1 1 1
Bit Error Rate (BER) No Error No Error No Error No Error
Physical Medium CAT5 (10 Mbps) CAT5 (10 Mbps) E2 E2
Physical Medium E2 E2 CAT5 (10 Mbps) CAT5 (10 Mbps)

Reserved Bandwidth of CPE1’s traffic is 6 Mbps. CPE 1’s traffic is sent through 4 and 6
links. So Remaining Bandwidth of 4 and 6 links are 4 Mbps (10-6).
Reserved Bandwidth of CPE 2’s traffic is also 6 Mbps. Since Link 4 and 6’s remaining
bandwidth is less than the Reserved Bandwidth of CPE 2’s traffic, CPE 2’s traffic is sent
through the another path through 3 and 5 links.

Sample 2:
In this Sample,
• Total no of CPE’s used: 4
• CPE 1, 2 and Router 2, 3 are connected with Router 1 by Link 1, 2, 3, 4 respectively.
• Router 2,3 and CPE 3,4 are connected with Router 4 by Link 5,6 7, 8 respectively
CPE Properties CPE 1 CPE2
Priority Low Low
Reserved Bandwidth (Mbps) 6 6
Physical Medium E2 E2 CAT5 (10 Mbps) CAT5 (10 Mbps)
Physical Medium CAT5 (10 Mbps) CAT5 (10 Mbps) E2 E2

Simulation Time –10 Sec
• Set the properties of CPE Router,
Upon completion of the experiment “Save” it for comparison
Output:
After running this scenario, in Network performance screen, click View LSP link. Then
the following screen would appear.
CPE 1’s traffic is sent through 4 and 6 links
Router Properties Router1 Router2 Router3 Router4
Buffer Size (KB) 8 8 8 8
Scheduling Type Priority Priority Priority Priority
Routing Properties
Protocol Type OSPF OSPF OSPF OSPF
Router Priority 255 255 255 255
MPLS Properties
Traffic Engineering Disable Disable Disable Disable

Click 10.1.8.2(CPE-2) to view the LSP for CPE 2’s traffic
CPE 2’s traffic is also sent through 4 and 6 links
In Without traffic engineering all the traffics will be sent through the same shortest path.
Inference:
In Traffic Engineered MPLS network, according to the traffic constraint different traffics
will be sent through different paths. But in without traffic engineering, all traffics will be
sent through same shortest path.

Experiment 16
Objective
Study how call blocking probability varies as the load on a GSM network is continuously
increased.
Procedure:
• Create Scenario: “Help NetSim Help Running Simulation via GUI Cellular
Inputs
In this Sample,
• Total no of BTS used: 7
• Total no of MS used: Vary from 4 to 22 in steps of 2.
• All the MS is placed in the range of BTS1

Set the properties of BTS and MS by following the tables for each sample,
BTS Properties BTS1
Maximum Uplink bandwidth 891.0 MHz
Minimum Uplink bandwidth 890.0 MHz
Maximum Downlink bandwidth 936.0 MHz
Minimum Downlink bandwidth 935.0 MHz
Channel bandwidth 200 kHz
Number of time slot 8
Inputs for Sample 1
Number of MS = 4
MS Properties MS 1 MS 3
Destination MS 2 MS 4
Transmission Type Point to Point Point to Point
Traffic Type Voice Voice
Call Details
Distribution Exponential Exponential
Mean Call Interval Time (sec) 300 300
Distribution Exponential Exponential
Call Duration 60 60
Codec
Codec GSM-FR GSM-FR
Packet Size 33 33
Service Type CBR CBR
Generation rate 0.0132 0.0132
Mobility Model No Mobility No Mobility

Inputs for Sample 2
Number of MS = 6
MS Properties MS 1 MS 3 MS 5
Destination MS 2 MS 4 MS 6
Transmission Type Point to Point Point to Point Point to Point
Traffic Type Voice Voice Voice
Call Details
Distribution Exponential Exponential Exponential
Mean Call Interval Time
(sec)
300 300 300
Distribution Exponential Exponential Exponential
Call Duration 60 60 60
Codec
Codec GSM-FR GSM-FR GSM-FR
Packet Size 33 33 33
Inter Arrival Time (µs) 20000 20000 20000
Service Type CBR CBR CBR
Generation rate 0.0132 0.0132 0.0132
Mobility Model No Mobility No Mobility No Mobility
Likewise, increase the number of MS by 2 and set properties up to 22 MS.
Output
“Simulation

Analytics”
• Cellular Networks
• Select the Metric: Call Blocking probability

Comparison Charts:
*** All the above plots highly depend upon the placement of Mobile station in the
simulation environment. So, note that even if the placement is slightly different the same
set of values will not be got but one would notice a similar trend.
Inference
When the number of MS is increased from 4 to 22 the call blocking probability increases
from 0 to 0.48. This is because; as we increase the number of mobile stations more calls
are generated. This increases the traffic load on the system more calls generated
implies more channel requests arrive at the base station but the number of channels in
each base station is fixed (In this experiment it is 40).
Total number of channels in system = 40
Number of channels per BTS = 40/7 = 5
Number of traffic channels in each BTS = 4 (Here 1 channel is RACH)
So when the base station does not find any free channel the call is blocked.
An additional observation is that the call blocking is zero until 8 MS. This is because the
number of channels is sufficient to handle all call that 8 MS may generate. Only after this
does the base station not finds free channels and block calls.

Experiment 17
Objective
Study how the number of channels increases and the Call blocking probability decreases
as the Voice activity factor of a CDMA network is decreased
Procedure:
• Create Scenario: “Help NetSim Help Running Simulation via GUI Cellular
Inputs
In all Samples,
• Total no of BTS used: 1
• Total no of MS used: 22
• All the MS is placed in the range of BTS1
Set the properties of BTS and MS by following the tables for each sample,

MS Properties MS 1 MS 3 MS 5 MS 7 MS 9
Destination MS 2 MS 4 MS 6 MS 8 MS 10
Transmission
Type
Point to Point Point to
Point
Point to
Point
Point to
Point
Point to
Point
Traffic Type Voice Voice Voice Voice Voice
Call Details
Distribution Exponential Exponential Exponential Exponential Exponential
Mean Call
Interval Time
(sec)
300 300 300 300 300
Distribution Exponential Exponential Exponential Exponential Exponential
Call Duration 60 60 60 60 60
Codec
Codec GSM-FR GSM-FR GSM-FR GSM-FR GSM-FR
Packet Size 33 33 33 33 33
Inter Arrival
Time (µs)
20000 20000 20000 20000 20000
Service Type CBR CBR CBR CBR CBR
Generation rate 0.0132 0.0132 0.0132 0.0132 0.0132
Mobility
Model
No Mobility No Mobility No Mobility No Mobility No Mobility
Likewise, MS 11 to MS 12, MS 13 to MS 14, …, and MS 21 to MS 22.
Inputs for Sample 1
BTS Properties BTS
Standards IS95A/B
Total bandwidth 1.25 MHz
Chip rate 1.2288 McPS
Voice Activity factor 1.0
Transmitter power 20 W
Path loss exponent 3
Fading figure 0.5
Standard deviation 11
Change the voice activity factor from 1.0, 0.9, 0.8, 0.7…. to 0.1.

Output
“Simulation

Analytics”
• Cellular Networks
• Select the Metric: Call Blocking probability Number of channel
Comparison Charts and Inference:
Chart 1
When the system Voice activity factor decreases from 1.0 to 0.1, the number of channels
increases from 3 to 37. (Note: All other parameters like Bandwidth 1.25 MHz, chip rate
1.2288McPS, target SNR 6, Path loss exponent 3, Fading figure 0, and standard deviation
11, are constant in all the samples taken.)
In CDMA network, the number of channels is inversely proportional to the voice activity
factor.
Chart 1 is a mirrored form of
x
y
1
= graph. (This is because VAF is decreasing along
+ve X)

Chart 2
*** All the above plots highly depend upon the placement of Mobile station in the
simulation environment. So, note that even if the placement is slightly different the same
set of values will not be got but one would notice a similar trend.
When voice activity factor is decreased the number of channels available increases. Thus
the system has more number of channels to handle the same number of calls (Note -
Number of MS is constant and their properties are same across all experiments. So, they
generate approximately same number of calls throughout).
Let us also understand why the call blocking probability of Sample1, Sample2, and
Sample3 is equal and again is equal for Sample4, sample5. In this experiment, all the
mobile stations are placed on only BS: base station1. One call requires 2 channel (One is
for caller party and another is for called party). So, even if base station 1 has one free
channel, the also the call is blocked.

So, here also in this particular scenario where caller and called party are in BTS1, BTS1
can handle only 1 call at a time. The one extra channel that is not available in sample1 is
wasted throughout. So, number of blocked calls or call blocking probability is same as
sample1.
Sample1 Sample2
Total number of channel = 3.
Number of traffic channel = 3-1 = 2.
Means BTS can handle only 1 call at a time.
Total number of channel = 4
Number of traffic channel = 4-1 = 3.

Experiment 18
Objective:
Study the SuperFrame Structure and the analyze the effect of SuperFrame order on
throughput
Introduction:
Coordinator in a PAN can optionally bound its channel time using a SuperFrame structure
which is bound by beacon frames and can have an active portion and an inactive portion.
The coordinator may enter a low-power (sleep) mode during the inactive portion.
The structure of this SuperFrame is described by the values of macBeaconOrder and
macSuperframeOrder. The MAC PIB attribute macBeaconOrder, describes the interval at
which the coordinator shall transmit its beacon frames. The value of macBeaconOrder,
BO, and the beacon interval, BI, are related as follows:
for 0 ≤ BO ≤ 14, BI = aBaseSuperframeDuration * 2BO
symbols.
If BO = 15, the coordinator shall not transmit beacon frames except when requested to do
so, such as on receipt of a beacon request command. The value of macSuperframeOrder
shall be ignored if BO = 15.
An example of a SuperFrame structure is shown in following Figure.
Fig: An example of the Super Frame structure

Theoretical Analysis:
From the above SuperFrame structure,
If SuperFrame Order (SO) is same as Beacon Order (BO) then there will be no inactive
period and the entire SuperFrame can be used for packet transmissions.
If BO=10, SO=9 half of the SuperFrame is inactive and so only half of SuperFrame
duration is available for packet transmission. If BO=10, SO=8 then (3/4)th of the
SuperFrame is inactive and so nodes have only (1/4)th of the SuperFrame time for
transmitting packets and so we expect throughput to approximately drop by half of the
throughput obtained when SO=9.
Percentage of inactive and active periods in SuperFrame for different SuperFrame Orders
is given below
Beacon
Order
(BO)
SuperFrame
Order (SO)
Active part of
SuperFrame (%)
Inactive part of
SuperFrame (%)
Throughput
estimated (%)
10 10 100 0 200% of T
10 9 50 50 Say T = 19.166
(Got from simulation)
10 8 25 75 50 % T
10 7 12.5 87.5 25 % T
10 6 6.25 93.75 12.5 % of T
10 5 3.125 96.875 6.25 % of T
10 4 1.5625 98.4375 3.12% of T
10 3 0.78125 99.21875 1.56 % of T
We expect throughput to vary in the same as the active part of the SuperFrame as sensors
can transmit a packet only in the active portion.

Simulation:
Please refer,
• Create Scenario: “Help NetSim Help Running Simulation via GUI Wireless
Sensor Networks Create Scenario”.
Click drop one Node onto the Simulation Environment as shown.
Agent Properties: Accept default properties for Agent.
Sensor Properties: Change the following property for Sensor.
Sensor Properties Values
Sensing Interval (ms) 3
Sink Node Properties: Change the following properties for PAN Coordinator.
Sink Node Properties Values
Beacon Order 10
Super frame Order 10, 9, 8 …. 3 (Vary per experiment)
Run the simulation for different Super Frame Order (change from 10 to 3).

Environment Properties: Accept default properties for Environment.
Simulation Time -30 Sec.
Note: The Simulation Time can be selected only after doing the following two tasks,
• Set the properties of Node, PAN Coordinator Environment.
• Click on the Simulate button and save the experiment.
The following are the throughputs obtained from simulation for different SuperFrame
Orders.
SF
Order
Throughput
(Kbps)
10 10.05
9 5.09
8 2.540
7 1.286
6 0.6144
5 0.3008
4 0.1408
3 0.0576
Comparison Chart:

Note: To obtain throughput from simulation,
*** All the above plots highly depend upon the placement of Sensor in the simulation
environment. So, note that even if the placement is slightly different the same set of
values will not be got but one would notice a similar trend.
Inference:
From the comparison chart both the simulation and theoretical throughputs match except
for the case with no inactive period because a sensor will be idle if the last packet in its
queue is transmitted and if a packet is generated in inactive period then the packet has to
wait in the queue till the next SuperFrame and so sensor has packets waiting in its queue
and so it cannot be idle in the next SuperFrame, but if there is no inactive period then
there might be no packets waiting in the queue and so sensor can be idle resulting in
lesser throughput.

Experiment 19
Objective:
Analyze the scenario shown, where Node 1 transmits data to Node 2, with no path loss
and obtain the theoretical throughput based on IEEE 802.15.4 standard. Compare this
with the simulation result.
Introduction:
IEEE Standard 802.15.4 defines the protocol and compatible interconnections for data
communication devices using low-data-rate, low-power, and low-complexity short-range
radio frequency (RF) transmissions in a wireless personal area network (WPAN). In
Wireless sensor network IEEE 802.15.4 standard is used in MAC and PHY layers.
IEEE 802.15.4 PHYs provide the capability to perform CCA in its CSMA-CA
mechanism. The PHYs require at least one of the following three CCA methods: Energy
Detection over a certain threshold, detection of a signal with IEEE 802.15.4
characteristics, or a combination of these methods.
Theory:
• A packet transmission begins with a random backoff (in number of slots, each slot of
20 duration) which is sampled uniformly from 0 to followed by a
CCA.
• A CCA failure starts a new backoff process with the backoff exponent raised by one,
i.e., to macminBE+1, provided it is lesser than the maximum backoff value given by
macmaxBE.
• Maximum number of successive CCA failures for the same packet is governed by
macMaxCSMABackoffs, exceeding which the packet is discarded at the MAC layer.
• A successful CCA is followed by the radio turnaround time and packet transmission.

• If the receiver successfully receives the packet i.e., without any collision or corruption
due to PHY layer noise, the receiver sends an ACK after the radio turnaround time.
• A failed packet reception causes no ACK generation.
• The transmitter infers that the packet has failed after waiting for
macAckWaitDuration and retransmits the packet for a maximum of
aMaxFrameRetries times before discarding it at the MAC layer.
Note: In NetSim the radio turnaround time after a CCA success is not considered.
Simulation:
Please navigate through the below given path for Create Scenario Help
• Create Scenario: “Help NetSim Help Running Simulation via GUI Personal
Area Networks Create Scenario”.
Create the scenario as shown above.
Node 1 Properties:
Node Properties Wireless Node 1
Transmission Type Point-to-Point
Destination Wireless Node 2
Traffic Type Custom
Packet Size

(Note: If the size of the packet size at the Physical layer is greater than 127 bytes, the
packet gets fragmented. Taking into account the various overheads added at different
layers (which are mentioned below), the packet size at the application layer should be less
than 80 bytes.)
PAN Coordinator Properties:
Sink Node Properties Values
Beacon Mode Disable
Environment Properties:
Environment Properties Values
Channel Characteristics No Path Loss
Simulation Time: 100 Sec
Throughput obtained from the simulation is 90.154 kbps
Note: Throughput may vary based on the distance between nodes.
Theoretical Analysis:
We have set the Application layer payload as 70 bytes in the Node1 properties and when
the packet reaches the physical layer various other headers gets added like
Packet Inter Arrival Time(µs) 4000
DSR Properties
Ack Type Link Layer Ack
Data Link Layer
ACK Request Enable
Max Frame Retries 7
Physical Layer
Transmitter power (mW) 1

App layer Payload 70 bytes
Transport Layer Header 8 bytes
Network Layer Header (IP + DSR) 28 bytes
MAC Header 5 bytes
PHY Header 6 bytes
Packet Size 117 bytes
In simulation, by default NetSim uses Unslotted CSMA/CA and so a packet transmission
happens after a random backoff, CCA and is followed by turn-around-time and ACK
packet and each of them occupies specific time set by the IEEE 802.15.4 standard as per
the timing diagram shown below.
From standard each slot has 20 Symbols in it and each symbol takes 16µs for
transmission
Symbol 16 µs
Slots 20 * 0.32 ms
Random Backoff Average 3.5 * 1.12 ms
CCA 0.4 * 0.l28 ms
Turn-around-Time 0.6 * 0.192 ms
Packet Transmission Time 11.7 * 3.744 ms
Turn-around-Time 0.6 * 0.192 ms
ACK Packet Time 0.6 * 0.192 ms
3.5
Slots
0.6
Slots
0.6
Slots
0.6
Slots
0.4
Slots
CCA
Turn
around
Time
Random
backoff
Avg [0,7]
117 bytes
11.7 Slots
Packet Turn
around
Time
Ack

Total Time 17.4 * 5.568 ms
Inference:
Throughput from theoretical analysis matches the results of NetSim’s discrete event
simulation.
(Note: The slight difference in throughput is due to fact that the average of random
numbers generated for backoff need not be exactly 3.5 as the simulation is run for short
time and also in Network layer DSR protocol is running so, route setup process will take
some time.)
As we go on increasing the simulation time, the throughput value obtained from
simulation approaches the theoretical value as can be seen from the table below:
Note: In NetSim Academic version to run the simulation with 200 sec simulation time we
can use CLI.
Throughput from simulation 100.470 kbps
Throughput from analysis 100.574 kbps
Simulation Time (sec) Throughput (kbps)
10 100.072
50 100.419
100 100.470
200 100.537

How to De-bug your code linked to NetSim’s Programming Exercise
In NetSim, programming exercise menu, users can write and link their code as
executables (*.exe). If the user’s *.exe file does not provide the correct output, NetSim UI
will display the message “Error in User Code”. To de-bug your code on getting this
message, follow the steps given below:
1. Run the scenario again in sample mode. On completion, minimize NetSim and
keep it running without closing the programming exercise.
2. Open your code in Visual studio 2005 (or in Eclipse development environment).
This is how your code should look when opened in Visual studio as a project
(Refer visual studio help on how to create a Win 32 based Exe project)
3. Right click on your project and select properties as shown below
4. Inside the properties window select Debugging and edit the Command Arguments
as shown

5. Inside command argument add the following two paths
a. Path in which NetSim is installed within double quotes “ “. This is usually
C:Program FilesNetSim Standard. This can be got by right clicking on
the NetSim icon and selecting Find target or open file location.
b. The windows temporary path which has the NetSim folder for temporary
data. This can be got by Start Run and typing %temp%/NetSim
c. On clicking this, you will get a path similar to C:Documents and
SettingsGeorgeLocal SettingsTempNetSim. As mentioned above, this
should also be in double quotes “ “, and there should be a single space
between the first path and the second path. For example: C:Program
FilesNetSim_Standard_SW_7.1 C:Documents and
SettingsGeorgeLocal SettingsTempNetSim
6. Now add a breakpoint to your code in your function or in the main ( ), and
proceed with de-bugging
7. At the end check if the output.txt present in the %temp%NetSim path and the
temp.txt present in the %temp%NetSim path are exactly similar. Exact similarity
would indicate that your code will work fine when you run it in use mode the next
time.

Experiment 20- Bit Stuffing and character stuffing
Objective: Write a C/C++ program to verify bit stuffing and character stuffing algorithm
Part A - Bit Stuffing
Theory:
When data is transmitted, the transmitter should distinguish between the start and the end
of the data. This is done to ensure that the receiving node reads the data completely. This
is accomplished by appending a unique pattern of bit stream before and after the data.
Care should be taken to ensure that this unique pattern does not occur in the data itself. If
the pattern appears in the data then the data is broken. The process of appending a unique
pattern and breaking the pattern is known as framing.
Bit Stuffing is one of the framing methods, in which each frame begins and ends with a
special bit pattern ‘0111110’, called a flag byte.
Whenever the sender’s data link layer encounters six consecutive 1’s in the data, it
automatically stuffs a 0 bit into the outgoing bit stream to break the pattern.
Algorithm:
1. Get the Value of Destination Address, Source Address, Data, CRC Polynomial
and Error Status by reading Input.txt.
2. Call the function fnASCII_to_Binary () to get the Binary Values for each
characters in the Data field.
3. Call the function fnBitStuffing () to do the bit stuffing process.
4. Calculate the checksum by calling the function fnCheckSum_Calculation.
5. Initialize nLoop1, nCount and nIndex to zero.
6. Combine the Destination Address, Source Address and Binary Values in single
character array.
7. Loop through all the bits
Check nLoop_Length = 0 nLoop_Length 8
Check pszBits [nLoop_Length] == 1
Increment nCount by 1

Stuffed Destination Address [nIndex] = ‘1’
Check nCount == 5
Increment nIndex by 1
nCount = 0
Else
nCount = 0
Check nLoop_Length == 7
nIndex = 0
8. Similarly repeat step6 for the Source Address and Binary Values for the
stuffing process.
9. Call the function fnDestuffing () to do the destuffing process.
10.Initialize nLoop1, nCount and nIndex to zero.
11. Loop through all the bits
Check pszBits [nLoop_Length] == 1
Increment nCount by 1
Check nCount == 5
Loop through all the bits
pszBits [nIndex] = pszBits [nIndex + 1]
nCount = 0
Else
nCount = 0
12.Call the function fnASCII_to_Binary () to get the ASCII values and the
message sent by the Transmitter.
13.Write those values into Output.txt.

Procedure:
To begin with the experiment, open NetSim
Click on Programming from the menu bar, select framing Sequence and then select Bit
Stuffing
Step 1:
Select the User mode to write your own program in C/C++, compile and link to NetSim
software for validation. Click on the F1 (help) for details on how to proceed with your
own code.
Continue with the steps as given for Sample mode.
Select Mode
Click here to view concept, algorithm,
pseudo Code flow chart

Step 2:
Here enter the source address, destination address and the data which you want to give as
an input. Now click Run button to execute the program.
Results (to be filled up by the students):
Enter the
input data
Enter the
Source address
Enter the
Destination address
Click Run to execute

Part B - Character Stuffing
Theory:
When data is transmitted, the transmitting node should distinguish between the start and
the end of the receiving node to read the data completely. This is accomplished by
appending a unique pattern of bit stream before and after the data.
Care is taken that this unique pattern does not occur in the data. If the pattern appears in
the data, it is broken. The process of appending a unique pattern and breaking the pattern
is known as framing.
Character stuffing is one of the framing methods, in which each frame starts with DLE
STX (Starting delimiter) character sequence and ends with DLE ETX (Ending delimiter)
character sequence.
Characters for DLE STX or DLE ETX may occur in the data. To solve this problem the
transmitting node inserts a DLE character just before each DLE character occurring in the
data.
Bit Stuffed output

Algorithm:
1. Get the Value of Starting Delimiter, Destination Address, Source Address, Data,
Checksum and Ending Delimiter by reading Input.txt.
2. Call the function fnCharacterStuffing () to do the character stuffing process.
3. Loop through all the bytes in Destination Address
Check szDestinationAddress [nLoop1] != ‘0’
sz_Stuffed_DestinationAddress [nIndex] = szDestinationAddress [nLoop1]
Check szDestinationAddress [nLoop1] == szStartingDelimiter [0]
sz_Stuffed_DestinationAddress [nIndex] = szStartingDelimiter [0]
Check szDestinationAddress [nLoop1] == szEndingDelimiter [0]
sz_Stuffed_DestinationAddress [nIndex] = szEndingDelimiter [0]
Increment nLoop1 by 1
sz_Stuffed_DestinationAddress [nIndex] = '0';
4. Similarly repeat step3 for Source Address, Data and Checksum.
5. Call the function fnDeStuffing () to do the destuffing process.
6. Copy all the bytes from Stuffed Destination Address to Destuffed Destination
Address
7. Loop through all the bytes in Destuffed Destination Address
Check sz_Destuffed_DestinationAddress [nLoop1] != ‘0’
Check sz_Destuffed_DestinationAddress [nLoop1] ==
szStartingDelimiter [0] sz_Destuffed_DestinationAddress [nLoop1]
== szEndingDelimiter [0]
Check nIndex strlen (sz_Destuffed_DestinationAddress)
sz_DeStuffed_DestinationAddress [nIndex] =
sz_DeStuffed_DestinationAddress [nIndex + 2];
nIndex = 0
Else if sz_Destuffed_DestinationAddress [nLoop1] ==
szStartingDelimiter [0] || sz_Destuffed_DestinationAddress [nLoop1] ==
szEndingDelimiter [0]
Check nIndex strlen (sz_Destuffed_DestinationAddress)
sz_DeStuffed_DestinationAddress [nIndex] =
sz_DeStuffed_DestinationAddress [nIndex + 1];
nIndex = 0

Increment nLoop1 by 1
8. Similarly repeat step7 for Source Address, Data and Checksum and write those
values into Output.txt.
Procedure:
Click on Programming from the menu bar, select framing Sequence and then select
Character Stuffing
Step 1:
software for validation. Click on the F1 (help) for details on how to proceed with your
own code.
Select Mode
pseudo Code Flow chart
Enter the starting
delimiter

Step 2:
Here enter the source address, destination address, check sum, starting ending delimiter
and the data which you want to give as an input. Now click Run button to execute the
program.
Enter the
Destination address
Enter the
Source address
Enter the input data
Enter the checksum
Enter the ending delimiter

Character stuffed output

Experiment 21 - Cyclic Redundancy Check
Objective: Write a C/C++ program to implement cyclic redundancy check.
Theory:
Cyclic redundancy check (CRC) is a type of function that takes as input a data stream of
any length, and produces an output. Bit strings are treated as representation of
polynomials with coefficients of ‘0’ and ‘1’.
The Sender and Receiver must agree upon the Generator Polynomial in advance. The size
of data must be greater than the size of the Generator polynomial to compute the
checksum.
The computed checksum is appended to the transmitting frame. If the receiver gets the
frame it tries dividing it by Generator polynomial, if there is a reminder there has been a
transmission error, else no error.
The Generator polynomial for CRC 12 is x12
+ x11
+ x3
+ x2
+ x1
+ 1
The Binary equivalent of CRC - 12 is 1100000001111
Algorithm:
No Error Case
Sender side
• Read the input from Input.txt. Parse the file content.
• Call the In-built function read File.
1. Convert the data string to be transmitted into binary representation.
2. Get ASCII value of the first character.
3. Divide the ASCII value by 2; append the remainder to a string. The quotient
is taken as the next number for the division.
• Repeat the above division processes until the quotient of the number is less than 2.
• Finally we get the remainder string having 1’s and 0’s, which is the binary
representation of that character.

• Continue above process for all the characters in the data string.
• Append 12 ‘0’s to the final binary string formed by the above step.
• Divide the binary converted data string using the Generator Polynomial (given
above CRC 12).
• Take the MSB 13 bits from the binary data string.
• If the leading bit of the binary data string is ‘0’, do an XOR operation with the 13
bits of ‘0’s and get the remainder which is also 13 bits.
• Else if the leading bit of the binary data string is ‘1’, do an XOR operation with
the 13 bits with binary converted CRC 12 polynomial and get the remainder which
is also 13 bits.
• The first bit of the remainder is left out and the remainder is made to 12 bits.
• If there are successive bits in the data, make the previous remainder bit to 13 bits
by bringing down the next bit in the data
• Convert the final remainder into HEXA equivalent character.
• Divide the final remainder into blocks of 4 bits.
• Convert each block into equivalent HEXA character.
• Thus the output of this whole process will be a 3 - nibble checksum that is
attached to the transmitting frame.
Receiver side
• Repeat the Steps 1 to 4 of the Sender side CRC coding and get the CRC value for
the data.
• Convert the HEXA equivalent string to its binary format. This is the Hexadecimal
to binary conversion process.
• Append the binary format of the above step to the CRC variable. Then append 12
‘0s’ to the CRC variable.
• Repeat the Steps 6 and 7 of the Sender Side CRC coding to calculate the CRC
value for the receiver side.

Error Case
Sender side
• Get the input from Input.txt. Parse the file content.
• Call the In - built function read File.
1. Convert the data string to be transmitted into binary representation.
2. Get ASCII value of the first character.
3. Divide the ASCII value by 2; append the remainder to a string. The quotient
is taken as the next number for the division.
• Repeat the above division processes until the quotient of the number is less than 2.
• Finally we get the remainder string having 1’s and 0’s, which is the binary
representation of that character.
• Continue above process for all the characters in the data string.
• Append 12 ‘0’s to the final binary string formed by the above step.
• Divide the binary converted data string using the Generator Polynomial (given
above CRC 12).
• Take the MSB 13 bits from the binary data string.
• If the leading bit of the binary data string is ‘0’, do an XOR operation with the 13
bits of ‘0’s and get the remainder which is also 13 bits.
• Else if the leading bit of the binary data string is ‘1’, do an XOR operation with
the 13 bits with binary converted CRC 12 polynomial and get the remainder which
is also 13 bits.
• The first bit of the remainder is left out and the remainder is made to 12 bits.
• If there are successive bits in the data, make the previous remainder bit to 13 bits
by bringing down the next bit in the data
• Convert the final remainder into HEXA equivalent character.
• Divide the final remainder into blocks of 4 bits.
• Convert each block into equivalent HEXA character.
• Thus the output of this whole process will be a 3-nibble checksum that is attached
to the transmitting frame.

Receiver side
• Repeat the Steps 1 to 4 of the Sender side CRC coding and get the CRC value for
the data.
• Make some errors in the string CRC by changing certain characters. The error
string is stored in the variable CRC.
• Write the Error string CRC into the file ‘Input.txt’. The file path for the file
‘Input.txt is the path where you have installed the NetSim application.
(Compulsory).
• Convert the HEXA equivalent string CRC to its binary format. This is the
Hexadecimal to binary conversion process.
• Append the binary format of the above step to the CRC variable. Then append 12
‘0s’ to the CRC variable.
• Repeat the Steps 6 and 7 of the Sender Side CRC coding to calculate the CRC
value for the receiver side.
Procedure:
Click on Programming in the menu bar, select Error Detecting Codes and then select
Cyclic Redundancy Check.
The scenario will be obtained as shown below. Follow the steps.
Step 1:
software for validation. Click on the F1 (Help) for details on how to proceed with your
own code.

When you
Results:
Error condition: No Error
Select Mode
Select any of
the
algorithms
Select Error
condition
Click here to add the
input text file
Click here to
view concept,
algorithm,
Pseudo Code
flow chart
Click Run to
execute
Click here to interface
source code

Error condition: Error

Experiment 22 - Encryption and Decryption using substitution ciphers
Objective: Write a C/C++ program to implement Encryption and Decryption using
substitution ciphers
Theory:
A substitution cipher is a method of encryption by which units of plaintext are substituted
with cipher text according to a regular system; the units may be single letters (the most
common), pairs of letters. The receiver deciphers the text by performing an inverse
substitution.
Each letter of the plain text is exchanged using another letter according to the key value
given by the user.
The user has to give the message and encrypt that message using the key value. The
encryption is done based on the ASCII value of the alphabetical letter and the key value.
ASCII value of each letter in the plain text is incremented by the key value. The
encrypted text is called as Cipher text.
Example - If the plain text first letter is A, ASCII value of A is 65 and the key value is 1
then the encrypted value is 65 + 1 = 66, which is B.
Plain text : tetcos Plain text the user wants to encrypt
Key value : 1 The key value by which the plain text is encrypted
Cipher text : ufudpt Cipher text which is encrypted according to the key value.
ASCII value of each letter in the plain text is incremented by 1 (key value) and get the
cipher text.
Algorithm:
• Read the plain text and key value from the input file.
• For i=1 to length (plain text)
1. Get the ascii value of ith
character.
2. Add the key text to that ascii value.

3. If the plain text is alphabet then the cipher text should also be alphabet and
vice versa.
4. The alphabet series for this case is, a, b, c, d...x, y, z, a, b, c, d…
A, B, C, D…X, Y, Z, A, B, C…
5. The user should add key value according to the process to be taken, in such a
way that the series should continue as explained in the previous point.
Procedure:
Click on Programming from the menu bar, select Cryptography and then select
Substitution.
Step 1:
When you select the User mode, you have to write your own program in C/C++, compile
and link to NetSim software for validation. Click on the F1 (Help) for details on how to
proceed with your own code

Now select Decryption option and then click Run button to get back the original text.
Enter the plain text
Enter the Key
text
Encryption
Select Mode
Click here to view
concept, algorithm,
pseudo Code
Flow chart
Click Run to
execute
Generated Cipher
text

Decrypted original text
Click Run
Select Decryption

Experiment 23 - Minimum Spanning Tree
Objective: Write a C/C++ program to implement minimum spanning tree using Krushal’s
algorithm
Theory:
The spanning tree algorithm is used to prevent loop formation in a Local Area Network,
while ensuring connectivity to all network segments.
To convert a network as a mathematical graph, nodes are viewed as vertices of the graph,
while connecting links are viewed as edges of the graph.
If the original graph has n vertices, then the tree formed has n-1 edges. The connecting
lines involved in the spanning tree can transfer data. Others are blocked for data transfer.
Kruskal algorithm calculates a spanning tree by sorting out the edges in the increasing
order of weights.
The working of Kruskal’s algorithm is as follows,
• Consider a graph with 6 Switches.
• The edges are sorted in the ascending order of the weights.
• The smallest edge from the list is selected and if the addition of the edge in the
spanning tree doesn’t form a cycle, then the edge is added in the spanning tree. If
it forms a cycle, then that edge is discarded.
Note: Initially the spanning tree is empty.
• The above step is repeated until there are no edges in the list, or there are n-1
edges in spanning tree where n is number of nodes.
• If there are n-1 edges in the spanning tree, the spanning tree for the graph is
formed.
• If there are no edges in the list and there are less than n-1 edges in the spanning
tree, then no spanning tree can be formed for the graph.

Edge Weight Status
Switch3-Switch 6 20 Selected
Switch3-Switch4 20 Selected
Switch2-Switch3 60 Not Selected
Switch4-switch5 80 Not selected
Sorted list showing selected/deselected edges
Algorithm:
• Read the number of nodes, input edges from the ‘Input.txt’.
• List all the edges of the graph in the ascending order of weight.
• Pick the smallest edge from the list and check if the addition of the edge in the
spanning tree doesn’t form a cycle. Then add the edge in the spanning tree. If it
forms a cycle, then discard that edge. Note: Initially the spanning tree is empty.
• Repeat the above step until there are no edges in the list, or there are n-1 edges in
spanning tree where n is number of nodes.
• If there are n-1 edges in the spanning tree, the spanning tree for the graph is
formed
• If there are no edges in the list and there are less than n-1 edges in the spanning
tree, then no spanning tree can be formed for the graph.
Procedure:
Click on Programming from the menu bar, select Spanning tree.

Step 1:
When you select the User mode, you have to write your own program in C/C++,
compile and link to NetSim software for validation. Click on the F1 (Help) for details on
how to proceed with your own code.
Step 2:
Click on the one switch followed by the other to have a connection between them
and then click Run button to execute the program.
Select Mode
Click here to view
concept, algorithm,
pseudo Code flow
Select Algorithm
Select No. of Switches

The lines in green color show the spanning tree path and the lines in red color shows the
blocked path.
Output Table

Experiment 24 - Address Resolution Protocol
Objective: Write a C/C++ program to verify Address Resolution Protocol
Theory:
ARP is a layer – 3, Internet Protocol (IP) that is used to identify a Node’s Medium Access
Control (MAC) Address for communication. ARP is used to identify the MAC Address of
a node based on the IP Address. For transmission to happen between two systems, the
source node should know both IP Address and MAC Address of the destination node.
Working of ARP is as follows:
1. The Source Node broadcasts an ARP Request to all the nodes available in the
network. The request is broadcasted in a format. The ARP Request Format
contains following details:
• The IP Address of the Source Node, i.e. Source IP.
• The IP Address of the Destination Node, i.e. Destination IP.
• The MAC Address of the Source Node, i.e. Source MAC.
• The MAC Address of the Destination Node, i.e. Destination MAC.
Initially this would not be known. Hence a Broadcast Address is filled in.
Once the Destination Node replies to the ARP Request sent by the Source,
then only the destination MAC Address is obtained. The reply sent by the
destination node to the source node will contain the MAC address of the
destination node.
2. The Destination Node replies to the Source with an ARP Reply. The reply is sent
to the source in the ARP Reply Format. The ARP Reply Format contains
following details:
• The IP Address of the Destination Node, i.e. Source IP. (Note: Here
Destination Node becomes the Source Node, since the ARP Reply is
transmitted by the Destination Node).
• The IP Address of the Source Node, i.e. Destination IP. (Note: Here
Source Node becomes the Destination Node, since the ARP Reply is
delivered to the Source Node).

• The MAC Address of the Source Node, i.e. Source MAC. In this case
Destination Node is the Source Node.
• The MAC Address of the Destination Node, i.e. Destination MAC. In this
case Source Node is the Destination Node as it is receiving the ARP reply.
Algorithm:
1. Receive the inputs from the input file input.txt as defined in the Programming
Guidelines.
2. After reading the address, get the Class value of the source node and the
destination node.
3. If the Network address of the source and the destination are not same, then,
• Write the result into the output file.
4. If the network address of the source and destination matches, but if the host id is
not present in the network list,
5. Else
Procedure:
Click on Programming from the menu bar and select Address Resolution Protocol.
Step 1:
proceed with your own code.

Step 2:
Step 3:
As soon as you select a particular number of nodes those many nodes will be created in
your environment which is shown below
Select the Mode
Select the Number of
Nodes

Results:
After you click RUN button you can see the ARP request message being broadcasted
from the source node to all other nodes and destination node reply with an ARP reply
message to the source node as shown in the following screen shots.
Shows the IP address of
the selected Nodes
Enter ARP request and ARQ
reply system
Click Run to
execute
Click here to view Concept, Algorithm,
Pseudo Code Flow chart

ARP request format
ARP reply format

Experiment 25 - Distance Vector Routing
Objective: Write a C/C++ program to verify the distance vector routing algorithm
Theory:
Distance Vector Routing is one of the routing algorithms used in a Wide Area Network
for computing shortest path between source and destination. The router is one of the
main devices used in a wide area network. The main task of the router is routing. It forms
the routing table and delivers the packets depending upon the routes in the table – either
directly or via an intermediate device (perhaps another router).
Each router initially has information about its all neighbors (i.e., it is directly connected).
After a period of time, each router exchanges its routing table among its neighbors. After
certain number of exchanges, all routers will have the full routing information about the
area of the network. After each table exchange, router re-computes the shortest path
between the routers. The algorithm used for this routing is called Distance Vector
Routing.
Algorithm:
Repeat the following steps until there is no change in the routing table for all routers.
• Take the Next Router routing table and its neighbor routing table.
• Add the router entry that is not in your own routing table, but exists in any one of the
other routing tables. If the new router entry exists in more than one neighbor, then
find the minimum cost among them. The minimum cost value details are taken as a
new entry: such as source router, intermediate router, destination router and cost
value, etc.
• Update the source router routing table cost value if both the destination router and the
intermediate router field value have the same value as any one of the neighbors’
routing entry.
• Update the source router’s routing table entry with the new advertised one if the
intermediate router value in the source table is not same, but the cost value is greater
than the its neighbor’s entry.
• Write the next stage of routing table into the file.
Repeat steps 1 to 5 for all routers.

Check whether any changes are made in any of the routers. If yes, then repeat the above
steps, otherwise, quit the process.
Procedure:
Click on Programming from the menu bar and select Distance Vector Routing
Select the Mode
Connect the Routers
Click Run to execute the Program

Output Table

Experiment 26 - Link State Routing
Objective: Write a C/C++ program to verify the Link state routing Algorithm.
Theory:
The router is one of the main devices used in a wide area network. The main task of the
router is routing. It forms the routing table and delivers the packets depending upon the
routes in the table – either directly or via an intermediate device (perhaps another router).
Link state algorithm is a method used to find the shortest path between a source router
and a destination router based on the distance and route the packets through that route.
Algorithm:
1. Start with the router: the root of the tree
2. Assign a cost of 0 to this router and make it the first permanent router.
3. Examine each neighbor router of the router that was the last permanent router.
4. Assign a cumulative cost to each router and make it temporary.
5. Among the list of temporary routers
5. a. Find the router with the smallest cumulative cost and make it permanent.
5. b. If a router can be reached from more than one direction
5. b. 1. Select the direction with the shortest cumulative cost.
6. Repeat steps 3 to 5 until every router becomes permanent.
Procedure:
Click on Programming from the menu bar and select Shortest Path. In shortest path select
Link State Routing algorithm.

and link to NetSim software for validation. Click on F1 (Help) link for details on how to
Select Mode
Select Link State
Connect the Routers
Click Run to execute the Program

Inference (to be filled up by the students):
Here, Router 1 is taken as the source and Router 3 as the destination. The paths are
connected with input as the distance. The figure indicated in green line shows the shortest
path.
Output
table

Experiment 27 - Stop Wait Protocol
Objective: Write a C/C++ program to implement stop wait protocol.
Theory:
Stop and Wait is a reliable transmission flow control protocol. This protocol works only
in Connection Oriented (Point to Point) Transmission. The Source node has window size
of ONE. After transmission of a frame the transmitting (Source) node waits for an
Acknowledgement from the destination node. If the transmitted frame reaches the
destination without error, the destination transmits a positive acknowledgement. If the
transmitted frame reaches the Destination with error, the receiver destination does not
transmit an acknowledgement. If the transmitter receives a positive acknowledgement it
transmits the next frame if any. Else if its acknowledgement receive timer expires, it
retransmits the same frame.
Algorithm:
Start with the window size of 1 from the transmitting (Source) node.After transmission of
a frame the transmitting (Source) node waits for a reply (Acknowledgement) from the
receiving (Destination) node.
If the transmitted frame reaches the receiver (Destination) without error, the receiver
(Destination) transmits a Positive Acknowledgement.
If the transmitted frame reaches the receiver (Destination) with error, the receiver
(Destination) do not transmit acknowledgement.
If the transmitter receives a positive acknowledgement it transmits the next frame if any.
Else if the transmission timer expires, it retransmits the same frame again.

If the transmitted acknowledgment reaches the Transmitter (Destination) without error,
the Transmitter (Destination) transmits the next frame if any.
If the transmitted frame reaches the Transmitter (Destination) with error, the Transmitter
(Destination) transmits the same frame.
This concept of the Transmitting (Source) node waiting after transmission for a reply
from the receiver is known as STOP and WAIT.
Procedure:
Click on Programming from the menu bar and select Transmission Flow Control. The
scenario is as shown in the following two figures.
Next the following window appears and its description is given.
and link to NetSim software for validation. Click on the F1 (help) icon for details on how
to proceed with your own code.
Select Mode
Enter input error rate
Click Run to execute program
pseudo Code flow chart
Stop Wait

Continue with the steps as given for sample mode. As soon as you begin to enter the input
data file the following window appears and you select the input data file from where you
have stored.
Result:
Click Run button to view the output.
Inference:
Due to increase in the error rate, no of errored packets also increase. If errored packets
increase no of retransmitted packets also increase.
Output table
Data file
that is added

Experiment 28 - Go Back N Protocol
Objective: Write a C/C++ program to implement Go Back N protocol.
Theory:
Go Back N is a connection oriented transmission. The sender transmits the frames
continuously. Each frame in the buffer has a sequence number starting from 1 and
increasing up to the window size. The sender has a window i.e. a buffer to store the
frames. This buffer size is the number of frames to be transmitted continuously. The size
of the window depends on the protocol designer.
Operations:
A station may send multiple frames as allowed by the window size.
Receiver sends an negative ACK if frame i has an error. After that, the receiver discards
all incoming frames until the frame with error is correctly retransmitted.
If sender receives a negative ACK it will retransmit frame i and all packets i+1, i+2, ...
which have been sent, but not been acknowledged.

Algorithm:
The source node transmits the frames continuously.
Each frame in the buffer has a sequence number starting from 1 and increasing up to the
window size.
The source node has a window i.e. a buffer to store the frames. This buffer size is the
number of frames to be transmitted continuously.
The size of the window depends on the protocol designer.
For the first frame, the receiving node forms a positive acknowledgement if the frame is
received without error.
If subsequent frames are received without error (up to window size) cumulative positive
acknowledgement is formed.
If the subsequent frame is received with error, the cumulative acknowledgment error-free
frames are transmitted. If in the same window two frames or more frames are received
with error, the second and the subsequent error frames are neglected. Similarly even the
frames received without error after the receipt of a frame with error are neglected.
The source node retransmits all frames of window from the first error frame.
If the frames are errorless in the next transmission and if the acknowledgment is error
free, the window slides by the number of error-free frames being transmitted.
If the acknowledgment is transmitted with error, all the frames of window at source are
retransmitted, and window doesn’t slide.
This concept of repeating the transmission from the first error frame in the window is
called as GOBACKN transmission flow control protocol.
Procedure:
To begin with the experiment, open NetSim.
Click on Programming from the menu bar and select Transmission Flow Control.
The scenario will be as shown in the following two figures.

and link to NetSim software for validation. Click on F1 (help) for details on how to
have stored.
Select Mode
Go Back N
Enter input bit error rate
Click Run to
execute program
Click here to view Concept, Algorithm, Pseudo
Code and Flow chart

Result: Click Run to view the output.
Data file that is added
Output table

Experiment 29 - Selective Repeat Protocol
Objective: Write a C/C++ program to implement Selective Repeat protocol.
Theory:
Selective repeat is Similar to Go Back N. However, the sender only retransmits that frame
for which a negative ACK is received
Advantage over Go Back N:
• Fewer retransmissions.
Disadvantages:
• More complexity at sender and receiver.
• Receiver may receive frames out of sequence.
Operations:
A station may send multiple frames as allowed by the window size.
Receiver sends a negative ACK if frame i has an error. After that, the receiver does not
discard all incoming frames as in Go Back N.
If sender receives a negative ACK it will retransmit only frame i which is the error frame.

Algorithm:
The source node transmits the frames continuously.
Each frame in the buffer has a sequence number starting from 1 and increasing up to the
window size.
The source node has a window i.e. a buffer to store the frames. This buffer size is the
number of frames to be transmitted continuously.
The receiver has a buffer to store the received frames. The size of the buffer depends
upon the window size defined by the protocol designer.
The size of the window depends according to the protocol designer.
The source node transmits frames continuously till the window size is exhausted. If any of
the frames are received with error only those frames are requested for retransmission
(with a negative acknowledgement)
If all the frames are received without error, a cumulative positive acknowledgement is
sent.
If there is an error in frame 3, an acknowledgement for the frame 2 is sent and then only
Frame 3 is retransmitted. Now the window slides to get the next frames to the window.
If acknowledgment is transmitted with error, all the frames of window are retransmitted.
Else ordinary window sliding takes place. (* In implementation part, Acknowledgment
error is not considered)
If all the frames transmitted are errorless the next transmission is carried out for the new
window.
This concept of repeating the transmission for the error frames only is called Selective
Repeat transmission flow control protocol.
Procedure:
To begin with the experiment, open NetSim.
Click on Programming from the menu bar and select Transmission Flow Control.

and link to NetSim software for validation. Click on the F1 (help) for details on how to
have stored.
Select mode
Selective Repeat
Enter input bit error rate
the program
Click here to view Concept, Algorithm, and
Pseudo Code Flow chart

Result: Click Run to view the output.
Data file that is added
Output table

Netsim experiment manual

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