Student Projects in Computer
Networking: Simulation versus
Coding
Leann M. Christianson
Kevin A. Brown
Cal State East Bay
Cal State East Bay
Introduction
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Computer networking is an integral part of
computer science education
Network protocols involve many entities
Creating practical and compelling student
assignments in networking is challenging
Cal State East Bay
Challenges…
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Protocols differ in how they respond to
corruption, errors, and loss, and replication
of results difficult
Algorithm performance may only be apparent
under high load, negatively impacting other
users of the network
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Challenges (cont’d)…
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The differences in the performance of transport
algorithms may only be apparent if the
transmitter and receiver nodes are separated
by large distances or if a large number of
machines are linked to the network
Routing algorithms require communication with
tens to hundreds of other nodes
Cal State East Bay
Challenges (cont’d)…
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Security concerns within a university may
make it difficult to provide access to live
servers with which to interact
Super-user access may be needed to use
commands that report on network performance
Much network code is at the kernel-level
requiring recompilation of the kernel in order to
modify
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Networking
Algorithms are complex
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It is beneficial to provide more than a
description and explanation
Students learn by experimentation
The ability to experiment may be provided in
(at least) two ways
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Experimentation
Two Methods
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Provide a simulation environment
Allow the students to implement the algorithm
themselves and run it on real machines
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Coding Benefits
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Computer Science is similar to engineering
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Computer Scientists need experience applying
what they learn by building workable modules or
programs that implement a key concept
Coding skills enhance career opportunities
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Coding Issues
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Dedicated equipment is needed
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For security
Multiple nodes at great distances must be available
Testing
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Difficult to duplicate conditions such that all students see
identical results
Inducing errors, loss and excess delay is difficult even with a
traffic generator
Internet traffic, error, and loss patterns are not reproducible
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Simulation Software Benefits
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Allows for rapid configuration - WANs, LANs,
intermediary, and host nodes
Protocols can be easily interchanged and tested
Large distances and multiple nodes can be simulated
Errors, losses, and delay rates can be defined to
follow a chosen distribution pattern
Results are reproducible
Dedicated equipment and super user access not
required
Long time periods can be simulated quickly
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Simulation Software Issues
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Requires investment of class time
Simulation model may not accurately reflect real
traffic patterns
May be difficult to reproduce a particular event as
some simulation applications do not allow the user to
modify all simulation entities
Students will not gain experience writing actual
networking code and interacting with live standardsbased servers
Cost, support, and license management must be
considered
Cal State East Bay
Simulation Software
OPNET
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University Program provides
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Free IT Guru software for each student
Runs on Windows XP
Unix version for university
www.opnet.com
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Example 1
TCP vs UDP packet delay
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Simulate client/server communication over an
IP network
Observe the effect of packet size on delay for
both TCP and UDP transport layer protocols
for file transfer
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OPNET: FTP client and server
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TCP vs UDP
Results
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Simulation can be rerun with different packet
sizes
Results can be graphed for easy comparison
TCP packet delay is longer than UDP packet
delay due to the added complexity of the
protocol
Delay to process each TCP packet increases
with packet size
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TCP vs UDP
FTP: Packet Delay
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TCP vs UDP
Simulation Benefits
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Students can easily change parameters such
as link speed, packet size, and background
traffic load and observe how these affect their
initial results
A variety of background application traffic
(web, database, or email) can be chosen
Easy to view and compare results graphically
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TCP vs UDP
Simulation Disadvantages
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Students do not gain valuable coding and
testing experience
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TCP vs UDP
Coding
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Write a client and server program that sends
a small packet back and forth via a TCP
socket 10,000 times
Run program 100 times, noting the round trip
time for a round of 10,000 sends
Graph delay times
Repeat with a pair of programs using UDP
sockets
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TCP vs UDP
Coding Benefits
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Provides experience with socket
programming
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Often a first for CS majors
Allows students experience with the software
lifecycle
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develop, run, test, and document results
Cal State East Bay
TCP vs UDP
Coding Disadvantages
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Difficult to generate a consistent level of background
traffic
Inability to control the actions of other users
competing for network resources
Programming languages (C++ or Java) and operating
systems (Unix or Windows) will affect delay times
Takes additional time to import results to Excel and
create graphs
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Example 2
Routing Convergence Time
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Convergence is the time it takes for routes
between network nodes to stabilize after start
up or after a link has gone down
Common routing algorithms such as Open
Shortest Path First (OSPF), the Routing
Information Protocol (RIP), or others can be
used
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RIP Routing Convergence
Simulation
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Create a network of router nodes configured
to use a particular routing algorithm (RIP)
Evaluate the routing tables created by the
routing algorithm and trace a path between
two nodes.
Break a link and run the simulation again
Determine the routing table convergence time
after a link is broken
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OPNET: Routing Convergence
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Routing Table: node 0 after 8 sec
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Routing
Simulation Benefits
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Rapid and easy configuration
Routing tables are automatically created
Can “break” links and rerun the simulation
easily
Simulation runs quickly
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Routing Convergence
Simulation Disadvantages
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Students do not gain experience implementing
a routing algorithm on their own
Difficult to calculate the exact convergence
time due to timing of simulation events
Some routing protocols are not offered
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Routing Convergence
Coding
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Provide an input file with nodes, distances, and
weights for initial topology
Implement a routing algorithm on the topology
and run the program until convergence
Output routing tables after convergence
Write an additional program to trace routes
through the tables
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Routing Convergence
Benefits
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Substantial assignment provides a great
coding experience
Allows students experience with the software
lifecycle
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develop, run, test, and document results
Students who complete the project
successfully understand convergence and the
way the routing protocol works
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Routing Convergence
Disadvantages
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Problem is complex and requires a large time
investment
Students get bogged down with the coding
details and lose sight of the purpose of the
assignment
Many give up or fail to write programs that
generate correct results
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Conclusions
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Simulation software allows more
concentration on the performance of the
protocol and allows for an easier visualization
of results
Students are more apt to “play” with their
simulations and experiment beyond the
bounds of the assignment
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Conclusions
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Programming, though viewed by the students
as more difficult, allows them to practice and
gain skills that will be useful in their future
careers
The authors feel that a balance of both
programming and simulation activities is the
best practice
Cal State East Bay
THANK YOU!
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OPNET Lab Manuals
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Brown & Christianson, Lab Manual for Data and Computer
Communications 7/E by William Stallings,Prentice Hall, 2005
Christianson & Brown, Lab Manual for Business Data
Communications 5/E by William Stallings, Prentice Hall, 2005
Brown & Christianson, The Networking and Data
Communications Laboratory Manual, Labs 5-8, edited by
Frances Grodzinsky, Prentice Hall,
http://www.prenhall.com/grodzinsky.
Cal State East Bay
Contact Us…
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[email protected]
[email protected]
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Student Projects in Computer Networking: Simulation …