Simulation
and testing of New Protocol
As the RelUDP Protocol was being developed,
it was continuously tested in the Network Simulator.
It is possible to insert print statements to
make the output more understandable but there
is a program that comes with NS which creates
a graphical interface that can be used to study
the protocols performance.
5.2 Network Animator (NAM)
NAM is a Tcl based animation tool for viewing
network simulation traces. It supports topology
layout and packet level animation
Figure 37 Users view of the Network simulator
When the Network Simulator finishes the simulation
it is capable of producing one or more text-based
output files that contain detailed simulation
data. The Tcl scripts that actually run the
simulation determine this. The data can be
used for simulation analysis or as an input
to a graphical simulation display tool called
Network Animator (NAM). NAM has a useful graphical
user interface that allows the user to play,
fast forward, rewind or pause the simulation.
It was vital to test the Protocol during development
to ensure that the functions work as expected.
It is also useful to compare the protocol against
other developed protocols to see the results.
The various simulations will be described in
the oncoming sections.
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Simulation
1 – A simple network |
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The first simulation consists of a simple
two-node topology as shown in figure 38. This
simulation is simple but illustrates some basic
functionality of the RelUDP protocol. It illustrates
the protocol sending a packet (figure 39) and
replying with an acknowledgement packet (figure
40).
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Simulation
2 – A simple network with Packet
loss |
|
The second simulation consists of a similar
topology used in Simulation 1. This topology
shown in figure 41 adds one aspect to simulation
1. This simulation introduces more functionality
of the RelUDP protocol. By introducing an error
model between the two nodes, random packets
are dropped. This will test the protocol dealing
with dropped packets in the network. The protocol
can be seen to retransmit the dropped packets
in this simulation illustrating its reliability.
Figure 42 shows a screenshot of the Protocol
running this simulation, notice the packet
being dropped.
Figure 42 Simulation 2 running
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Simulation
3 – A complex network with minimal
congestion |
|
Figure 43 Simulation 3 Network Topology
The third simulation consists of a more complex
network. Firstly it consists of four end point
nodes, two of which are using the regular UDP
protocol, and two of which are using the new
Protocol RelUDP. This topology is shown in
figure 43.
The RelUDP protocol will first start transmitting
data across the bottleneck network. Then the
UDP will also start using the same bottleneck
link causing congestion. As the congestion
builds packets get both delayed and dropped
on busy links (This can be seen in figure 44).
Notice the queue on the router 2, packets will
be both lost and delayed form this point.
Figure 44 Simulation 3 running (Network is
congested)
The UDP protocol then stops transmitting packets,
and the new RelUDP protocol can be seen resending
the delayed or dropped Packets until the Network
resumes as it was when it started.
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Simulation
4 – A complex network with greater
congestion |
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The fourth simulation consists of exactly
the same network topology as in Simulation
3, but it introduces very high congestion by
setting the rate at which the UDP protocol
sends packets to be very high. The network
becomes highly congested but eventually the
RelUDP resends all necessary packets and the
Network returns to normal. Figure 45 shows
a screenshot of the Protocol running this simulation,
at this point the protocol is recovering form
the high congestion of the network.
Figure 45 Simulation 4 running (recovering
from high congestion)
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