Advanced Networking Training for Master Students Through OPNET Projects J. Theunis, P. Leys, J. Potemans1, B. Van den Broeck, E. Van Lil and A. Van de Capelle Katholieke Universiteit Leuven, Division ESAT-Telemic Kasteelpark Arenberg 10, 3001 Leuven-Heverlee E-mail:
[email protected] Abstract OPNET software products can be applied in advanced networking education, providing students a means to gain some practical networking insight. At K.U.Leuven, Belgium, Master students in Electrical Engineering focusing on Telecommunications have to model a realistic business network with OPNET Modeler. This modeling complements the theoretical networking courses.
Afterwards we will comment on the OPNET Modeler tutorial offered to the students in order to get acquainted with the simulation program. Because supervision and control of the students in such self-learning education is a major issue, these topics will be discussed as well. Finally some results obtained by the students will be published. For more information on the design projects, we refer to [5]. The Design Projects Here we will describe the assignments given to the Master students. For more information, readers can have a look at [6].
This paper will focus on different aspects of the modeling assignment. First, the projects will be described extensively. Then, the tutorial written at K.U.Leuven introducing the students to OPNET Modeler will be discussed. Some results from the students will be published as well as additional teaching remarks and supervision issues.
Actually, the design projects consisted out of three parts. The first part was focused on measuring traffic and processing the results. The second part was about analyzing and simulating applications on a real-life network. This was the part were OPNET Modeler had to be used. The third part had nothing to do with the previous two and dealt with self-similar traffic and its impact on a router.
ESAT-Telemic participates in the OPNET University Program for research [1, 2, 3, 4] and educational projects [5]. Introduction Too often, graduate Master students lack practical insight in modern networking. To cope with this lack, K.U.Leuven introduces lab sessions and real-life design projects on networking in the curriculum of Master Studies in Electrical Engineering. The projects are integrated in an advanced course on telecommunication networks. In these hands-on design projects, students have to plan a realistic corporate network, spanning two cities in Europe.
For the simulation part of the projects, the students had to design and analyze a simple corporate business network. The headquarters of the company were located in Rome, and it had three remote offices in Brussels. The remote network consisted of three Juniper backbone routers, interconnected with Fast Ethernet links. One of the routers is connected to the headquarters through a PPP link. At each node in the network of Brussels 25 employees are connected. A simplified version of the network is sketched in Figure 1.
In four weeks of measurements, preceding the OPNET sessions, students have examined the properties of an application that needs to be implemented on the network. They have also created a profile for the background traffic on all the network links. Both the application behavior and the background traffic have to be added to a model of the network in OPNET Modeler. Advanced networking issues such as VoIP and priority queuing are covered as well. OPNET Modeler allowed the students to set up and dimension a real-life network. It offered the students a touch with reality and their future professional job. First of all, we will discuss the design projects themselves. We will go deeper into the assignments the students had to complete.
Figure 1: The corporate business network
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Research Assistant of the Fund for Scientific Research – Flanders (Belgium) (F.W.O.-Vlaanderen).
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The OPNET Modeler Tutorial
The background traffic running between the Juniper routers at the remote network in Brussels was measured and analyzed in an earlier part of the projects, as well as the characteristics of a client-web server-database (C-WS-DB) application [7]. For each node in the Brussels network, two network administrators had to phone frequently to the headquarters in Rome. For this purpose they used a VoIP application with a codec without any compression but with Voice Activity Detection (VAD).
New users to OPNET Modeler can easily be confused and loose courage due to the vast range of features of the program. It takes a while for these newbies to find their way to get an error-free and meaningful simulation up and running. However, due to the limited amount of time the students had to their disposal, we could not throw them into OPNET without any introduction.
From all this information, the students first had to design the capacity of the PPP link. Therefore, they had to: • Build the network topology on a map of Europe. • Include the measured background traffic between the routers. • Add the C-WS-DB application. Each user in Brussels had to be considered as a client, while the database server is located in Rome. A custom task needed to be defined. • Dimension the PPP link so that the usage of the link is between 75% and 80%. • Add the VoIP traffic to the network. Investigate the impact on the response time of the application and the packet loss. Investigate whether delay and jitter of the voice application are acceptable.
For this purpose, we developed an on-line tutorial [9], adapted to the students’ simulation needs. In just a couple of hours, students could run through this step-by-step tutorial and master the OPNET Modeler skills they needed.
A second step was adding QoS to the network. For this purpose, students had to activate priority queuing on the routers. The assignment was to: • Adapt the VoIP application so that its priority is higher than the priority of the C-WS-DB application. • Change the queuing schemes of the Juniper router interfaces so that priority is taken into account.
Another means to keep students awake was encouraging the students to a trial-and-error approach. The solutions to some problems had to be distilled from the given information and hints and the available OPNET documentation.
The tutorial mainly focuses on the basic OPNET Modeler features: creating and configuring a network topology, adding traffic to this topology, using the custom task, setting up custom applications and profiles, interpreting the Simulation Log, getting and analyzing simulation results etc. To avoid the mind numbing effect easy step-by-step tutorials can have, students had to reflect on questions while they completed the tutorial. These questions were about OPNET Modeler itself, technological aspects and simulation insight.
Supervision and Control The design projects are regarded as a kind of ‘coached selfstudy’ assignments. This means students have to complete the assignments mostly by themselves. In these projects, there is more than one path to glory. Bearing all the information from the courses and informational sessions in mind, the Master students have to overcome some rather complicated networking issues on their own.
Another aim of the design projects was to make the students comfortable with the ACE module. Hence, they had to: • Complete some ACE module tutorials. • Create a new application characterization and include the dump file2 of the C-WS-DB application from the measurement project. • Replace the custom task / application / profile used to include the measured application by this ACE traffic file.
Of course, there is a supervision staff supporting the students. Five hours a week, informational sessions are organized, where students can work on their assignments while course assistants are on the spot to answer their questions. During these sessions, new concepts are introduced and the assignments are explained in detail.
Finally, a comparison between the OPNET simulation results and some small analytical calculations was required. The task was to: • Calculate the expected delay introduced by the router in Rome. • Calculate the expected voice and application delay when using priority queuing for voice traffic. • Compare the results obtained from the calculations above with the simulation results from the respective OPNET scenarios.
Apart from these sessions, websites on the course, holding lots of information on the topics, are at the students’ disposal. There is an external website [5] and an internal. Alas, the latter cannot be consulted from outside K.U.LeuvenNet3. Here, students can browse a FAQ and ask for advice. Another important issue concerning this kind of education is the control and motivation of the students. Not all students do realize they have to work from the beginning to the end of the projects. If they don’t, they’ll generate poor results. Therefore, we changed our approach with respect to former academic years
The solutions to all these problems and the workflow had to be bundled in a report. These reports can be consulted online [8]. 2
This dump file was offered to the students during the measurement sessions. The file was generated using ‘tcpdump’ on a GNU/Linux system.
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K.U.LeuvenNet is the private network of K.U.Leuven, connecting all the faculties and university services.
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and introduced milestones in the work flow. The students had to meet these milestones and report their results from time to time. This facilitated an on-time intervention when needed. In order to keep the projects manageable, students were divided in small groups of no more than two students a group. The assignments the different groups had to accomplish had only minor differences. This way students could help each other out while copying was impossible and supervisors could keep track of well and ill performing students. Project Results Here we will present some of the results obtained by the students. For a complete overview of all the simulation results, the interested reader is referred to [8].
Figure 3: Network topology at Rome
A scenario was created in which a remote WAN in Brussels was connected with a PPP link to the headquarters in Rome. The topology in OPNET Modeler was as in Figures 2 and 3.
Figure 4: The load of the PPP link After the dimensioning of the PPP link, VoIP traffic generated by the admins was added. G.711 was used as codec and VAD was enabled. The influence on the behavior of the C-WS-DB application was investigated. As a result, we can see in Figure 5 that the application did not suffer from this additional traffic. Figure 5 shows the response time in seconds of the application under study both before (in blue) and after (in red) VoIP was added. However, as can be seen in Figure 6, the number of packets dropped at the IP layer increased significantly.
Figure 2: The network topology at Brussels At each router in Brussels, a LAN is connected. Two system administrators, making VoIP calls to Rome, can also be distinguished. Each user in the LANs acts as client in the CWS-DB application. The web server is located in Brussels; the database server in Rome.
Although the delay and delay variation of the VoIP calls was sufficiently small, the students investigated whether changing the queuing schemes on the routers to priority queuing improved the quality of the VoIP application. The impact on the C-WSDB application was also examined.
After adding the application traffic to the network, the PPP link could be dimensioned. This resulted in the required load of the link of about 75%, as can be seen in Figure 4.
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Figure 7: End-to-End Delay of the Voice Packets Figure 5: Response Time of the C-WS-DB Application
Figure 8: Response Time of the C-WS-DB Application Figure 6: Traffic Dropped
The same results can be obtained by a simplified analytical calculation of the queuing delay at the router located in Rome. With the FIFO queuing scheme, the VoIP packets suffered a queuing delay of about 20 ms, while with priority queuing, the delay almost vanished and was no more than 3 ms. The impact on the queuing delay of the C-WS-DB application seemed to be negligible.
The results can be found in Figures 7 and 8. Figure 7 shows the End-to-End delay of the VoIP packets without priority queuing (blue) and with priority queuing (red). In the latter case, VoIP was given priority over the C-WS-DB application. This resulted, as could be expected, in a much smaller and more stable delay for the VoIP packets. The QoS for this real-time application was thus significantly increased.
These results showed the students how minor changes to the configuration of a network could influence the overall performance. This forced them to reflect on QoS, priority and link dimensioning, more than any dull theoretical course could have ever achieved.
For the C-WS-DB application, QoS was no major issue. However, as can be seen in Figure 8, the response time of this application almost did not increase when the students accorded a lower priority to it than to the VoIP application. The blue dots show the results with normal FIFO queuing; for the red dots priority queuing was used.
Finally, the students explored the possibilities of the ACE module and used it to include the C-WS-DB application instead of the custom task / application / profile approach. Figure 9 4
[2] B. Van den Broeck, P. Leys, J. Potemans, J. Theunis, E. Van Lil and A. Van de Capelle, “Validation of Router Models in OPNET”, OPNETWORK 2002, Washington D.C., USA, 2002.
depicts the traffic sent and received by the ACE task on the PPP link.
[3] P. Leys, J. Potemans, B. Van den Broeck, J. Theunis, E. Van Lil and A. Van de Capelle, “Use of the Raw Packet Generator in OPNET”, OPNETWORK 2002, Washington D.C., USA, 2002. [4] J. Potemans, J. Theunis, B. Rodiers, B. Van den Broeck, P. Leys, E. Van Lil and A. Van de Capelle, “Simulation of a Campus Backbone Network, a case-study”, OPNETWORK 2002, Washington D.C., USA, 2002. [5] H239 Network Design Projects Homepage: http://www.esat.kuleuven.ac.be/~h239. [6] Simulation sessions of the Network Design Projects: http://www.esat.kuleuven.ac.be/~h239/project2.htm. [7] Measurement sessions of the Network Design Projects: http://www.esat.kuleuven.ac.be/~h239/project1.htm. [8] Reports of the Network Design Projects: http://www.esat.kuleuven.ac.be/~h239/reports.htm.
Figure 9: Traffic Generated by ACE
[9] OPNET Modeler Tutorial for the Network Design Projects: http://www.esat.kuleuven.ac.be/~h239/opnetstart.htm.
Conclusion Practical insight in modern networking is highly important for Master students in all branches of telecommunications education. OPNET Modeler proves to be a handy tool to reach this insight, if an efficient tutorial is provided and coaching of the students is not neglected. In this paper we presented such an example of introducing OPNET in advanced networking courses by means of design projects. Details of the actual assignments were discussed. The OPNET Modeler tutorial developed at K.U.Leuven for these projects was introduced. Student supervision and control are of major importance during such projects. Issues regarding these topics were sketched, as well as hints for those planning to use ‘coached self-study’ assignments. Finally, results from the students were presented. These results made it clear that OPNET Modeler can give students a touch with modern networking reality. Acknowledgments We are indebted to the Flemish government, which partly sponsors this research through the generic university basic research program (GBOU) "End-to-End QoS in an IP Based Mobile Network". References [1] J. Potemans, B. Van den Broeck, Y. Guan, J. Theunis, E. Van Lil and A. Van de Capelle, "Implementation of an advanced traffic model in OPNET Modeler", OPNETWORK 2003, Washington D.C., USA, 2003.
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