The use of Xen Virtualization Technology for the Analysys and Teaching of Communications Protocols

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1 The use of Xen Virtualization Technology for the Analysys and Teaching of Communications Protocols Jose Saldana, Julián Fernández-Navajas, José Ruiz-Mas Communication Technologies Group (GTC) Aragon Institute of Engineering Research (I3A) Dpt. IEC. Ada Byron Building. CPS Univ. Zaragoza Zaragoza, Spain {jsaldana, navajas, Abstract. The European Higher Education Area (EHEA) proposes an education centered on the student, and in the acquisition of competences. The possibility of using complex systems for tests, being able to analyze the interactions between their elements is an interesting experience for learning. For the students that are performing their Final Degree Project in Computer Science, the disposal of an environment including a high number of connected nodes can be useful in order to test applications and protocols. This article presents some experiences related to the use of Xen virtualization while performing these projects, and remarks the competences which can be strengthened. Some use cases, in which the characteristics of the environment are especially interesting, are explained. Finally, virtualization has been found as an interesting technology suitable for students interested on research. Keywords. Virtualization, EHEA, competences, virtual laboratory 1 Introduction After some years of study, many Engineering students of European Higher Education Area (EHEA) have to face their last challenge, i.e. the Final Degree Project. They have to use all the acquired skills and knowledge in order to perform a rigorous work, using a proper methodology. This project can either be oriented to the professional world, or it can be seen as their first research work. The new framework proposes a student-oriented education, in which the acquisition of competences is of the first importance. As a consequence, it is important for the student to be able to analyze a set of systems. The availability of a tool allowing the control of a multi-node network can be interesting in order to test their knowledge and skills. In the concrete case of Computer Science, systems consist of a set of nodes, networks, protocols and applications. The student may need to use a number of connected machines, and this fact may cause budget and control problems because of the number of required nodes. In addition, the possibility of having a complete control over the machines using a protocol, and all the applications, from a single interface, can be an interesting option. This kind of systems, assuming scalability and ease of use, can be an interesting teaching environment with a high potential.

2 In the last years, our group is using Xen virtualization to provide the students with a virtual network including a number of machines in the same physical one. These virtual machines have a complete operating system, and use real protocol stacks. A network scenario can be created, in which every machine has a number of network interfaces (Fig. 1). One of the interfaces is only used for control traffic, i.e. it is used to send the commands indicating the virtual machine the tasks to perform. The rest of the interfaces are used to create a network which corresponds to the emulated scenario. Thus, control and test traffic do not interfere, as they do not share the same links, which could reduce the tests realism. This scheme allows us to provide an isolated scenario which can be used by a single student, who can deploy network tests using a low or mid-end PC, which does not require special hardware features. The scheme has been used for teaching, and also for research and knowledge transfer to enterprises. The article is organized as follows: the next section includes the related works. Section 3 presents some use cases of the virtualization platform. The next section details the competences which can be improved by the use of virtualization, and the paper ends with the conclusions. 2 Related Works Many network testbeds and emulators are used in research and academic contexts [1]. In [2] a comparative of the performance of virtualization solutions was performed. Xen presented good results in terms of performance, linearity and isolation between different machines. This is the main reason for selecting it four our platform. A classification of virtualization technologies can be found in [3]. Regarding educational uses of networks, in [4] the design of a laboratory for practical sessions, allowing a big set of network configurations was presented. The main objective was to permit the students to directly configure the machines, and also the capacity for a number of groups to simultaneously work in the laboratory. Research activities were also supported. Public IP Physical machine Control traffic Virtual network Test traffic Fig. 1. A virtual scenario included in a physical machine

3 Regarding the use of virtualization in an educational environment, in [5] a set of experiences was presented, for both theoretical and practical sessions. Xen was used in some of the tests, especially in the ones related to research. The results of a survey about the knowledge of virtualization technologies, between professors and students were also presented. The best known one was found to be VirtualBox, and Xen was used in a smaller percentage, because of its difficulty for managing graphical environments. The main reported strengths of virtualization were its easiness of installation and management, and its public availability. The main weaknesses are hardware requirements and resource consumption. These results are interesting as, according to our experience, Xen can be a very practical solution when used in long-term work, as Final Degree Project is. Other virtualization technologies which permit graphical environments can be more interesting for practical sessions, due to the fact that they are easier to use, although the control over the systems may be smaller. Finally, in [6] the authors present the migration of a laboratory infrastructure, used for network security teaching, from a real-machine environment to a virtual-machine one, based in Xen. More than 40 virtual machines were included into a physical one, also including network components. The students were not aware of the use of virtualization, as it was totally transparent. The authors remark the advantages of Xen, especially in terms of costs and administrative tasks reduction, which were divided by six. Other advantage of the use of Xen virtualization is that the students can get familiar with a technology which they will later probably use in the professional world. 3 Use Cases of the Platform In order to illustrate the usefulness of the platform, we will explain in this section two use cases in which different protocols can be tested and analyzed by students. First, mobility protocols are analyzed and next an IP telephony system is included in the platform by means of virtual machines. 3.1 Mobility Protocols Some tests using MIPv4 mobility protocol were performed, with the aim of measuring handover delay for multimedia flows. The different elements of the scenario are translated into virtual machines (Fig. 2a). The students are able to observe the difference in terms of delay caused by triangle routing when the mobile node is in the destination network (Fig. 2b). An increase of packet size is also present due to IP-over-IP tunneling. The fact of being able to capture traffic traces at eth or IP level allows the students to observe the ARP messages sent by the home agent using the IP address of the mobile node, once the handover is detected, and the rest of exchanged packets during a handover.

4 Mobile Node Mobility One Way Delay (ms) Home Agent OWD (ms) Correspondent Node (a) Foreign Agent packet number Fig. 2. Mobility scheme and measurement of a handover using the test platform (b) Data center Ext PBX ape52 Office Gateway MySQL ape37 ape Ext Xenbr Xenbr SIP Proxy Gateway ape38 ape ape58 Ext ape36 Softphone ape09 SIP Proxy Xenbr Xenbr10 ape54 Ext 300 Office ape51 Gateway Softphone Ext ape42 ape ape41 Xenbr12 ape57 Xenbr14 SIP Proxy Ext ape Office Ext Office Gateway SIP Proxy Softphone ape55 Softphone ape56 ape11 Ext 301 ape05 Office 1 database IP phone SIP proxy PBX SIP proxy Gateway 183 Session Progress 183 Session Progress 302 Moved Temporarily (a) (b) Fig. 3. IP Telephony system scheme and analysis of SIP protocol flow database SIP proxy Gateway Office i Office j 3.2 Protocols for Real-time Service The virtualization platform has also been used to test a real-time distributed application, i.e. a SIP-based IP telephony system which uses a software PBX and a proxy located in each office. Each element of the system has been emulated using a virtual machine, as shown in Fig. 3a. The system also includes a MySQL database server, which is located at the data center. The proxies are in charge of call admission control, which only permits a certain number of simultaneous calls in an office. The calls can also be redirected when there are not available lines at the destination gateway (Fig. 3b). The availability of a complete system for the use of a single student makes it possible to deeply analyze the protocol and debug configuration files. Virtualization permits the use a scenario including 19 machines, which would not be possible if real hardware was used. 4 Acquisition of Competences In this section we will present the competences which we consider that can be improved by the use of this platform, making reference to the use cases we have explained in previous section. The competences have been mainly extracted from [7].

5 Tidiness, Clarity and Precision. The methodology requires from the student to be especially tidy and methodical so as to manage all the machines included in the system. The machines are controlled via remote sessions, so the students have to clearly identify the ones which they are working with, and which are the traffic generators and destinations. Synchronization is a common problem when measuring network delays in Computer Science. This environment can help the student to be aware of this problem and to find solutions. If synchronization is not correct, the results can be illogical, e.g. the arrival can be previous to the sending of packets. The precision provided in these virtual networks is high, and synchronization can be roughly one millisecond, as the network works at processor speed. This fact implies that the student has to emulate network delays, and also has to add some effects offline, as dejitter delay for voice applications. This helps them to correctly identify and distinguish the different delays present, i.e. processing times, transmission, etc. The integration of online and offline tests is good so as to improve the skills related to tidiness. Analytical Thinking and Skillfulness. It can be frequent for an IT professional to cope with applications that do not work correctly. Different tests have to be then performed, so as to identify the level where the problem is. An error may be at physical level, of it may be caused by routing, NAT, application ports, etc. In the presented scenario the access to all communication levels is granted to the students, so they are able to identify the problem wherever it is. Skill in the use of Tools. The fact of including a number of virtual machines into a single physical one makes it impossible the utilization of graphical interfaces for interacting with machines. These environments have high requirements, so a single machine is not able to execute a number of them. As a result, the student has to use command line interface to control all the machines, and this is also interesting, taking into account that it permits a better control. In addition, command line interface is frequently used by IT professionals in enterprises. There is also an interesting ability, which is the capacity of using script languages in order to automatize repetitive tasks. Initiative and Creativity. The virtual environment permits the use of the same tools present in real machines. But some existing limitations imply the need of emulating some behaviors. In these cases, the students have to use their creativity so as to find a way to reproduce or emulate in the virtual environment a situation which can be found in the real one. As an example, IP mobility was emulated by means of creating a duplicate network interface, which was disconnected from the origin network and simultaneously connected to the destination one, while maintaining its IP address. Other example is the use of netem Linux tool to add network delays, when the bridges that connect machines are not real but only virtual ones working at processor speed. Search for Information. The need of using command line interfaces makes it necessary to install non-commercial applications developed by other research groups. The information about these tools may be scarce, so the student has to ask in forums or even has to write to the authors of the programs. Cooperation and Relate Well to Others. The importance of working in a group is growing, and it is getting more and more importance in enterprise environments. In

6 some occasions, a number of students have had to share the same machine, using different networks of virtual ones. In these cases, they have been able to cooperate in different ways, e.g. a student can be in charge of maintaining the database which is used by the rest, or a virtual machine with a correctly installed and configured application can be copied and used by other student. The finding of ways for sharing of experience is also an interesting competency. Finally, coordination between the students is necessary, as measurements cannot be performed at the same time, due to the fact that all the machines share the same hardware resources. 5 Conclusions This work has presented the advantages of the use of Xen virtualization in the performance of Final Degree Projects or long-term works which can be oriented to education or research. The different competences which can be improved by its use have been analyzed. Xen has been found as a suitable environment for learning, as it permits a good control over the different levels of communications protocols Two use cases have been exposed, showing the interest of this platform so as to permit a high control and capacity of analysis of applications and protocols in systems including a high number of nodes. The advantages of virtualization have been highlighted, showing its interest for providing a complete test environment to students. Acknowledgements. This work has been partially financed by CPUFLIPI Project (MICINN TIN ), MBACToIP Project, of Aragon I+D Agency and Ibercaja Obra Social, Project of Catedra Telefonica, Univ. of Zaragoza. References 1. Göktürk, E.: A stance on emulation and testbeds. In Proc. 21st European Conference on Modelling and Simulation ECMS (2007) 2. Quetier, B., Neri, V., Cappello, F.: Selecting A Virtualization System For Grid/P2P Large Scale Emulation. In Proc. Workshop on Experimental Grid testbeds for the assessment of large-scale applications and tools EXPGRID'06, Paris (2006) 3. Tim Jones, M.: Virtual Linux. An overview of virtualization methods, architectures, and implementations. developerworks/linux/library/l-linuxvirt/ 4. Caicedo, C.E., Cerroni, W.: Design of a computer networking laboratory for efficient manageability and effective teaching. Frontiers in Education Conference. FIE '09. 39th IEEE, pp.1-6, (2009) 5. Fuertes, W., López de Vergara, J. E., Meneses, F.: Educational Platform using Virtualization Technologies: Teaching-Learning Applications and Research Uses Cases. In Proc. II ACE Seminar: Knowledge Construction in Online Collaborative Communities (2009) 6. Lindinger, T., Reiser, H., Felde, N. G.: Virtualizing an IT-Lab for Higher Education Teaching. In für Informatike. V., G., editor, 1. GI/ITG KuVSFachgespräch "Virtualisierung", pp , Paderborn, Germany (2008) 7. Jurse, M., Tominc, P.: Professional competences of graduates as a labour market mechanism for aligning business school curriculum reform with the Bologna declaration principles. Management, 13, (2008)