Student Projects in Computer Networking: Simulation versus Coding Leann M. Christianson Kevin A. Brown Cal State East Bay.

Student Projects in Computer Networking: Simulation versus

Coding

Leann M. Christianson

Kevin A. Brown

Cal State East Bay

Introduction

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

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Challenges…

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)…

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

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Challenges (cont’d)…

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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NetworkingAlgorithms are complex

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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ExperimentationTwo Methods

Provide a simulation environment Allow the students to implement the algorithm

themselves and run it on real machines

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Coding Benefits

Computer Science is similar to engineering– 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

Dedicated equipment is needed – For security – Multiple nodes at great distances must be available

Testing – 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

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

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 standards-based servers

Cost, support, and license management must be considered

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Simulation SoftwareOPNET

University Program provides– Free IT Guru software for each student– Runs on Windows XP– Unix version for university– www.opnet.com

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Example 1TCP vs UDP packet delay

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

OPNET: FTP client and server

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TCP vs UDP Results

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

TCP vs UDPFTP: Packet Delay

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TCP vs UDP Simulation Benefits

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

Students do not gain valuable coding and testing experience

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TCP vs UDP Coding

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

Provides experience with socket programming– Often a first for CS majors

Allows students experience with the software lifecycle

– develop, run, test, and document results

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TCP vs UDP Coding Disadvantages

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

Example 2Routing Convergence Time

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 ConvergenceSimulation

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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RoutingSimulation Benefits

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 ConvergenceSimulation Disadvantages

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 ConvergenceCoding

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 ConvergenceBenefits

Substantial assignment provides a great coding experience

Allows students experience with the software lifecycle– 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 ConvergenceDisadvantages

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

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

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

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THANK YOU!

OPNET Lab Manuals – 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.

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Contact Us…

[email protected] [email protected]

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