P O Z NA N UN I V E R S ITY O F TE C H N O LO GY A C A D E M IC J O U R N AL S
No 54 Electrical Engineering 2007
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Bartosz PAWŁOWICZ*
Grzegorz LIPIŃSKI*
UTILIZATION OF VIRTUAL MACHINES IN LABORATORY
STANDS ON EXAMPLE OF SIP EXPRESS ROUTER
APPLICATION
VoIP telephony laboratory stand with SIP server created with utilization of virtual machine has been presented in the paper.
Keywords: VoIP, SIP Express Router, Virtual Machine
1. INTRODUCTION
Utilization of the laboratory stands in different didactic subjects creates the necessity of frequent reconfiguration of the stands, and also of computer equipment of each laboratory stand. One of the largest "threats" for maintenance of failure-free running of computer systems in laboratory is continuous use of the administrator's account because of necessity of frequent reconfiguration of machines’ operating systems. The frequent changes of system functions and configuration are necessary because of necessity for introduction of the students in the subjects of using servers to deliver services such as VoIP telephony, audio and video streaming, e-mail, service users authorization, internet links and also many well-known services from classic the computer network for example file transfer. In such conditions it is proper to make use of advantages of virtual machine engines.
2. VIRTUAL MACHINES
Laboratory computer network presented on Fig. 1 is equipped with five workstations - one for each laboratory stand and one computer for network and workstations remote management. Each laboratory stand may require presence of independent server or servers of services and several clients, and the addition of a series of peripheral equipments such as digital and analog modems, xDSL modems
2007
Poznańskie Warsztaty Telekomunikacyjne Poznań 6 - 7 grudnia 2007 POZNAN UNIVERSITY OF TECHNOLOGY ACADEMIC JOURNALS
or VoIP telephones. In such a case the presented network will not fulfill the requirements of proper number of physical computers in it. This problem can be solved by use virtual machines. Virtual machine is the computer simulated by special-purpose applications such as Virtual Server 2005R2, Virtual PC 2007 or one of application from family VMware.
Fig. 1. The laboratory computer network schematic with graphical presentation of installed workstations and connection between each of them
Possibility of running of several virtual computers on one physical workstation is one of advantages of this type of solution. Quantity of simultaneously running virtual machines is limited by physical components of computer and it depends on
Fig. 2. The example of computer network build with utilization of physical workstations and virtual machines which are "guests" in each physical computer
computational efficiency of processor, the quantity and efficiency of applied RAM memory and hard disk capacity of physical workstation. The advantage of using of virtual machines is that they are recognized in the networks as other physical computers. It denotes that one physical computer can be used to create several servers and several clients in network (Fig. 2). The restoration easiness of working system configuration is the additional advantage of using virtual machines for computers that operate in condition of frequent changes of their configuration [1]. False configuration of operating system can be corrected by restoration working system quickly from image file. It makes possibility for exercising students to have maximum administrative privileges in systems running as virtual machines. Thus, minimum required level of standard user authorizations may be kept in reference to operating systems installed on physical workstations in laboratory.
3. VOIP LABORATORY STANDS
VoIP telephony systems are good example which shows advantages of using virtual machines on laboratory computers. Laboratory network depicted in Fig. 3 is
Fig. 3. VoIP telephony network build around virtual SIP Server – every laboratory stand can be separated network with server and clients
built with use of six physical computers, virtual machines and VoIP telephones. The purpose of such arrangement is to assure that VoIP telephony network with
virtual VoIP server, virtual and physical clients and VoIP phones can be built at each laboratory bench. The use of virtual machines is in this case the ideal solution because it makes possible of running additional virtual VoIP clients application and allows the creation of VoIP telephony network on every laboratory bench [2]. Additional advantage of running SIP server as virtual machine is the possibility of multiple restitution of basic configuration of this server from image file which allows the students to reconfigure it many times during exercises. The possibility of restoration of properly working system configuration is the additional advantage in case of exercising students mistakes that will lead to irreversible damage of virtual machine operating system. The possibility of demonstration of communication between many virtual servers installed in laboratory environment is also a huge advantage.
4. SIP EXPRESS ROUTER APPLICATION
In aim of utilization SIP Express Router software packet as VoIP server there is necessity of having the computer with UNIX family operating system [3]. NetBSD operation system has been chosen to fulfill needs of described laboratory bench. Choice of this system was dictated by its compatibility with virtual machines applications, accessibility of system and applications source packets as well as documentation relating to system installation and configuration. The MS Virtual PC 2007 software was chosen as virtual machine host application [4]. Basic version of NetBSD is sufficient to execute correct installation and configuration of VoIP server [5]. Only packets from groups: base, etc, comp, kernel, text, misc, man are needed. The packet base contains the basic version of system, the etc contains the system configuration files, the kernel is the source of operating system, the text contains necessary text processing tools, the misc contains examples of configuration files with the precise description of configuration procedures, man is the source of system documentation. After installation of operating system, the first thing to do was to configure network interfaces. The beginning of installation of SIP Express Router packet is the next step. NetBSD possesses excellent tools to building packets from external sources, which assure ability of use source packets dedicated to other UNIX family platforms.
This subsystem called pkgsrc was used to compile SIP Express Router from source files. The standard configuration of packet was extended of mySQL database. Its task is the storage information about server users such as login password, email etc. Database administration is possible due to implementation of administrative panel called SERweb, which makes possible the remote management of users' accounts by Internet browser. In order to run remote management the www server (in this case lighttpd) with the PHPprogramming language services must be installed. The correct configuration makes possible the login to remote control panel which runs
in the internet browser after choice of the correct URL. Remote control panel is accessible both for administrator and remaining users.
Fig. 4. An example of screenshots illustrating VoIP telephone and virtual SIP server configuration
The laboratory stand consists of physical workstation, GOODNET vs009 VoIP telephone and virtual machines created with use of MS Virtual PC 2007 application. There was created the local network between workstation, telephone and virtual machines. Owing to this network the communication between all hosts in it is possible. Created network operates on the base of IP protocol. For compatibility test between software platforms there were installed UNIX, Linux and MS Windows operating systems on selected virtual machines. Every system is equipped with SIP communicator proper for his architecture. The students' tasks are SIP server (SIP Express Router) installation and configuration and creation of working VoIP network in range of the laboratory stand (fig. 4).
7. CONCLUSIONS
Virtual machines are effective alternative for use of many physical computers on one laboratory bench. Their advantages are such as the simplicity of restoration of correct operating system configuration, the possibility of giving to the exercising
students full administrative privileges to operating system.Virtual machines create possibility of running of additional clients and servers of services in the network. It expands the functionality of laboratory networks.
REFERENCES
[1] Manufacturer’s site: http://www.microsoft.com/windows/products/winfamily /virtualpc/overview.mspx?wt_svl=20323a&mg_id=20323b
[2] Khasnabish B.: Implementing Voice over IP, John Wiley & Sons, Hoboken New Jersey, 2003.
[3] Developer’s site: http://www.iptel.org/ser
[4] Otey M.: Highs and Lows of Virtual PC 2007, Windows IT Pro, June 2007. [5] Developer’s site: http://www.netbsd.org/
