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Quality of Service Evaluation of Telemedicine 1etwork Design with IEEE 802.11b Technology A.Zambrano1, M.Huerta1, M.Diaz1 , M.de Andrade2 and P.Marchena3 1 Simon Bolivar University/Electronic and Circuit Department, Caracas, Venezuela Cataluña Polytechnic University/ Telematics Engineering Department, Barcelona, Spain 3 Simon Bolivar University/Applied Bioengineering and Biophysics Group (GBBA), Caracas, Venezuela 2
Abstract— Telemedicine 1etworks should meet specific Quality of Service (QoS) requirements to guarantee that the users can work with the supported applications in a reliable manner. Therefore it must be verified that network resources satisfy these requirements especially in wireless networks, due to their channel characteristics: Communication over a wireless link often suffers from limited bandwidth, high error rates and interference from other users on the shared channel. This paper describes the performance evaluation of a simulated Telemedicine 1etwork supporting various applications. To begin with, QoS parameters and transmission data methods are discussed. Subsequently the following subjects are described: simulation methodology, network simulation software used (OP1ET), simulated network and modeled applications. The simulation results suggest that the network does not meet QoS bandwidth and delay requirements when supporting the simultaneous use of all modeled applications in the individual client stations. Further mechanisms are necessary to ensure the required quality. Keywords
Quality of Service, Telemedicine 1etwork, IEEE 802.11b.
I. INTRODUCTION Telemedicine is currently one of the most common applications of telecommunications technology. It is very useful in rural areas where primary health-care centers are usually located in geographically disperse zones, and staffed with low-qualified medical personnel [1]. In rural environments, Telemedicine Networks can interconnect primary health-care centers with hospitals. This makes remote communication between physicians and specialists in the reference hospital possible, allowing them to exchange medical test results, do inter-consultation, share interactive applications, etc [2]. Depending on the environment, Telemedicine Networks can be built using either wired or wireless technology. The main differences between wired and wireless technology are related to the characteristics of the wireless channel, including bandwidth limitations, high error rates and interference from other users on the shared channel. Therefore it is very important to assess how these characteristics of the wireless
channel affect the performance of Telemedicine applications [3]. Nowadays there is a wide range of applications that can be supported by Telemedicine Networks. These can be Real Time (RT) or Store and Forward (SF) Applications which generate data, audio or video streams with different Quality of Service (QoS) requirements on the network. For obtaining the maximum benefit from these new eHealth services, a reliable and timely service to the end users should be guaranteed [4]. A traffic analysis in a simulated Telemedicine Network Design was carried out to verify the attainment of QoS communication network requirements when servicing a certain group of applications of this kind. The simulated Telemedicine Network has been designed for a group of rural health centers in the Baruta and El Hatillo municipalities located in Miranda State, Venezuela. The design includes 15 client stations, 7 repeaters and one central station. The communication technology used in this network was IEEE 802.11b, which is an emerging and attractive solution for providing connectivity to rural health centers, due to its low cost and reasonable rate [5]. Although IEEE 802.11b is designed for best effort services, when used as a Telemedicine Network it should support voice and data communication between primary health center physicians and specialist doctors. The remainder of this paper is organized as follows: Section II discusses Quality of Service regarding communication networks. Section III describes the simulation methodology used for this study. Section IV presents simulation results and analysis. The last section summarizes conclusions. II. QUALITY OF SERVICE Telemedicine applications generate different types of traffic with different requirements that must be guaranteed to provide a good service at user level. The term Quality of Service can be defined as the probability of the telecommunication network to meet a given traffic contract. It can be quantitatively measured in terms of several parameters [6].
O. Dössel and W.C. Schlegel (Eds.): WC 2009, IFMBE Proceedings 25/V, pp. 218–221, 2009. www.springerlink.com
Quality of Service Evaluation of Telemedicine Network Design with IEEE 802.11b Technology
A. Quality of Service parameters The Telemedicine Network requirements are higher today due to advances in Telemedicine applications; they can generate data, audio or video streams with different traffic requirements. Consequently it is necessary to evaluate the performance communication network through the following parameters to guarantee the QoS [4]: Delay (End to End Delay, EED): refers to data delay caused by different factors such as: media access, transmission, propagation, etc. Jitter: difference between consecutive delays. Packet Loss Rate (PLR): ratio of the number of lost packets to the total number of transmitted packets. Lost packets need retransmission. Bandwidth (BW): available data communication resources (for data, audio, video) in link network.
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tools for simulation instrumentation, report generation, and statistical analysis of results. OPNET was used to design an IEEE 802.11 wireless network around Basic Service Sets (BSS), i.e. sets of stations which can communicate directly with each other in ad hoc mode or through wireless access points in infrastructure mode [7]. The OPNET modeler was used to simulate an infrastructure wireless network, subdivided in six different BSS as shown in Figure 1. The network is composed of 15 client stations representing the health centers and the Simon Bolivar University, several repeaters modeled as wireless routers enabling access point functionality and a central station connected to server equipment via an Ethernet connection.
B. Data transmission methods Telemedicine applications can be transmitted in two ways [2]: Store and Forward (SF): it refers to a telecommunication technique in which all the information is saved first and then transferred to the other side. This transmission method does not present high requirements on delay or bandwidth but does not allow packet loss. Real Time (RT): consists in the acquisition and transmission of the information in a simultaneous way. It is very useful in cases of emergency, but requires high network performance on delay and bandwidth. III. SIMULATION METHODOLOGY A. Simulation environment The software used for the network simulations was OPNET 10.5. The OPNET modeler is a powerful communication system simulator developed by OPNET Technologies. It is useful for testing network performance in wired or wireless environments [3]. The OPNET tool provides a hierarchical graphical user interface for the definition of network models. A network is constructed by graphically connecting network nodes via communications links. The OPNET modeler provides an extensive model library, including application traffic models (e.g., HTTP, FTP, E-mail), protocol models (e.g., TCP/IP, IEEE 802.11b, Ethernet) and generation of random variables using a broad set of probability distributions (e.g. exponential, lognormal, pareto). It also provides adequate
Figure 1. Telemedicine Network of Baruta and el Hatillo municipalities
In each wireless station the following parameters were configured: channel transmission, BSS identifier (BSSID), minimal signal level required (sensibility) corresponding in this case to the value needed by the wireless card of the selected network equipment, throughput (11 Mbps), and Equivalent Isotropically Radiated Power (EIRP). Further, the Application and Profile OPNET modules were configured. The application module defines which applications are supported by the network: web browsing, FTP, videoconference, audio, etc. The profile module describes how the users employ the applications defined in the Application Configuration Module [8]. B. Types of services simulated. The purpose of the simulation was to test the performance of the designed IEEE 802.11b network when supporting different types of applications with different QoS requirements on the communication network, such as guaranteed bandwidth, delay, jitter and error rate. Guaranteeing these QoS requirements in a 802.11b WLAN is very challenging due the noisy and variable
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physical layer (PHY) characteristics [9]. The simulated network should support the following Telemedicine Applications:
Application type Bandwidth Web > 32 kbps
Delay < 100 ms
PLR < 15%
FTP
> 64 kbps
< 180 s
384 kbps Voice over IP (G.729) > 16 kbps
