Evaluation of QoS for Different Voice Schemes in Wireless LAN using OPNET Modular Navdeep Singh Chauhan 1, Loveljeet Kaur 2, Ajit Singh Walleh 3 Abstract In last few years there has been significant growth in the area of wireless communication. Quality of Service (QoS) has become an important consideration for supporting variety of applications that utilize the network resources. These applications include voice over IP, multimedia services, like, video streaming, video conferencing etc. IEEE 802.11/ WLAN is a network which is designed with quality of service in mind. This paper focuses on evaluate quality of service for different voice schemes implemented by the WLAN network. First, it presents the details of the quality of service architecture in WLAN network. For evaluation, a WLAN network developed based on popular network simulator opnet 14.0, is used. Various real life scenarios for different voice schemes are setup in the simulation environment. Parameters that indicate quality of service, such as, throughput, packet loss, retransmission attempt, network load and average delay, are analyzed for evaluation interactive voice is used as traffic scheme for simulate in WLAN. Index Terms IEEE 802.11, QoS, WLAN I. INTRODUCTION WLAN stands for Wireless local area network. It is the technology aimed to provide wireless data access over short distances. It is based on Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard [1], [2]. The technology provides basic Internet Protocol (IP) connectivity to the user. The variety of applications used in IP networks has increased tremendously in the recent years. Various multimedia applications along with the common email, file transfer and web browsing applications are becoming increasingly popular. These applications send large audio and video streams with variable bandwidth and delay requirements. On the other hand, remote monitoring of critical services, electronic commerce and banking applications, as well as, network control and signaling do not need strict bandwidth guarantees due to the bursty nature of the data transfer. Instead, these applications require reliable and prompt packet routing. The presence of different kinds of applications in a network, results in heterogeneous traffic load. The traffic from different applications may require certain type of quality of service. In this paper, the Quality of Service (QoS) as prescribed in the WLAN networks is studied. 1 BHSBIET/IT, Lehragaga, India Email: Navdeepkhiva@yahoo.com 2 SLIET/CSE, Longowal, India Email:{ Loveljeetchauhan87, }@yahoo.com 3 BHSBIET/ECE, Lehragaga,India Email:{walleh_ajit,}@rediffmail.com 110 As packets travel within a wireless network such as WLAN, they experience the following problems: Delay, jitter, out-of-order delivery, packet loss or error. There is no formal definition of Quality of service. QoS, in the field of telephony, was defined in 1994 in the International Telecommunication Union (ITU) Recommendation E.800. This definition is very broad, listing 6 primary components: Support, Operability, Accessibility, Retain ability, Integrity and Security. In 1998, the ITU published a document discussing QoS in the field of data networking. The term Quality of Service refers to the probability of the telecommunication network meeting a given traffic contract. In the field of packet-switched networks and computer networking it is used informally to refer to the probability of a packet succeeding in passing between two points in the network. Although the name suggests that it is a qualitative measure of how reliable and consistent a network is, there are a number of parameters that can be used to measure it quantitatively. These include throughput, transmission delay or packet delay, delay retransmission attempt, percentage of packets lost etc. The IEEE 802.11 standard includes the QoS mechanism in the Medium Access Control (MAC) layer (layer 2) architecture. It defines service flows which can map to different applications. This enables end-to-end IP based QoS. Among other things, the MAC layer is responsible for scheduling of bandwidth for different users. The MAC layer performs bandwidth allocation based on user requirements as well as their QoS profiles. The standard is designed to support a wide range of applications. These applications may require different levels of QoS. To accommodate these applications, the 802.11 standard has defined three different type of access categories having different priorities. These are summarized in TABLE I.
Figure 1. WLAN architecture in OSI reference model This paper focuses on the evaluation of QoS in WLAN networks. The details of the implementation of QoS in the WLAN network architecture will be presented. To evaluate the QoS parameters simulation based on the popular network simulator opnet 14.0 is used. Various parameters that determine QoS of real life usage scenarios and traffic flows of applications is analyzed. The goal is to compare different types of voice schemes with respect to the QoS parameters, such as, throughput, retransmission attempt, average delay network load and packet loss etc. In this research we can use three different type of voice schemes. These schemes are PCM quality voice, GSM(Global System for Mobile Communication) quality voice and LOW quality voice. II. QOS ARCHITECTURE IN WLAN WLAN works in the lower two layers of OSI model. First one is the physical layer which takes care of transmission of bits through a communication channel by defining electrical, mechanical and procedural specifications. Second one is data link layer which is sub-divided into two layers: Logical link layer (LLL) and Medium Access Control layer (MAC).Only MAC layer is considered as wireless LAN functions. MAC layer provides different priorities to different type of applications, users or data flows and guaranties certain level of performance in WLAN network. These priority details are shown in table I. In this paper we use three different types of voice schemes. According to priorities, MAC layer assigns them interactive voice as a traffic stream. In next section we detail studies of various QoS parameters. These parameters are delay, packet loss, retransmission attempt, throughput and network load. A. Throughput III. QOS PARAMETERS Throughput refers to how much data can be transferred from one location to another in a given amount of time. It is used to measure the performance of hard drives and RAM, as well as internet and network connections. Throughput is a measure of data rate (bits per second) generated by theapplication. B. Retransmission Attempts Total number of retransmission attempts by all WLAN MACs in the network until either packet is successfully transmitted or it is discarded as a result of reaching short or long retry limit. This factor plays an important role in performance of WLAN. C. Data Drop Another name of Data Drop is Packet Loss or Corruption rate. Packet loss is the failure of one or more transmitted packets to arrive at their destination. This event can cause noticeable effects in all types of digital communications. The effects of packet loss: In text and data packet loss produces errors. 111
In videoconferencing environments it can create jitter. In pure audio communications, such as VOIP, it can cause jitter and frequent gaps in received speech. D. Average Delay Average Delay is a technical term that can have a different meaning depending on the context. It can relate to networking, electronics or physics. In general it is the length of time taken for the quantity of interest to reach its destination. In computer networks, average delay is the amount of time it takes for the head of the signal to travel from the sender to the receiver over a medium. It can be computed as the ratio between the link length and the propagation speed over the specific medium. Average delay = d/s where d is the distance and s is the wave propagation speed. In this research we use twenty nodes and a single WLAN server to make a perfect network model. All nodes communicate with each other through WLAN sever. The simulation experiments are carried out using OPNET (version 14.5) on windows platform. For this simulation, data rate of 11 Mbps is chosen. The various MAC and PHY parameter values used in our experiment are according to IEEE 802.11e default values given in the Table II. Then run the simulation for 5 minutes for each scenario and then compared the results obtained from them. Figure 1.2 shows a sample network model. E. Network Load Network load define the total load on WLAN. Different applications have different effect on network load. Network load also depends upon the type and size of data. For example, for real time applications load will be high as compare to other type of data. IV. SIMULATION SCENARIO Creating a simulation scenario that is equivalent to real world scenario is the first step of simulation. In this simulation, the wireless topology considered of several wireless stations and one base station in wireless LAN. All wireless stations are located such that every station is available to detect a transmission from any other station, and there is no mobility in the station in the system. This means that our results will not be impact by mobility and phenomenon such as hidden node problem. V. SIMULATION RESULTS Following are the Comparative metrics for Voice application by using variations in quality of voice such as GSM quality speech, low quality speech and PCM quality speech. Following are the graphs that show Throughput of voice application by using different quality speech, Media access delay of voice application by using different quality speech, Data drop of voice application by using different quality speech, Retransmission attempt of voice application by using different quality speech, End to end delay of voice by using different quality speech and Network load of voice application by using different quality speech. Figure 2. a sample network model 112
A. Throughput C. Data Drop Figure 3. Throughput of Voice Application In Figure 3 we can see the throughput of GSM quality is higher than the throughput of low quality voice and PCM quality voice. The throughput of low quality voice is lying between the GSM quality and PCM quality voice. The throughput of PCM quality voice is less than both other voice schemes. B. Media Access Delay Figure 5. Data Drop of Voice Application. In Figure 5 we can see that the Data drop in the case of PCM quality is much more than other voice schemes there is slight difference b/w GSM quality voice & low quality voice schemes. Data Drop of GSM quality is slightly larger than low quality voice scheme. It means that data drop increases as the increasing of voice celerity or voice quality. D. Retransmission Attempts Figure 4. Media Access Delay of Voice Application. In Figure 4 we can see that Media Access Delay for PCM quality voice is larger than the other schemes while Media Access Delay of GSM quality voice scheme is lying between PCM quality and low quality voice. Low resolution voice having minimum delay. Thus, Media Access Delay increases according to voice quality. Figure 6. Retransmission Attempt of Voice Application. In Figure 6 we can see that retransmission attempts in the case of low quality voice scheme is less than other voice quality schemes. Retransmission attempt in the case of PCM quality voice is slightly larger than GSM quality voice scheme. Retransmission attempts in the case of PCM quality are higher than other schemes. 113
E. End to End Delay CONCLUSION The results shows that while increasing the quality of voice the QoS parameters such as Network Load, Delay, Data Drop and Retransmission Attempts also increased. FUTURE WORK In our scenario the nodes and servers are stationary in the network. Future work may be done by using moveable Infrastructure of wireless LAN and eliminate Hidden node problem in wireless LAN. Hidden problem is that two device A and C communicating with node B but unaware of each other. Figure 7. End to End Delay of Voice Application. In Figure 7 we can see that End to End delay in the case of PCM quality is slightly larger than the other schemes. Low quality voice having Less End to End delay from other voice schemes. End to End Delay of GSM quality voice is overlapped with PCM quality schemes. F. Network Load Figure 9. Hidden node problem REFERENCES Figure 8. Network Load of Voice Application. In Figure 8 we can see that the network load of PCM quality voice is higher than the other voice schemes. Network load on low quality voice is less than all other voice schemes. Network load of GSM quality voice is between the other two Voice schemes. [1]Andrew S. Tanenbaum, Computer Networks, 4th Edition, Pearson Edu.2007. [2]Behrouz A Forouzan, Data Communications and Networking, 4th Edition, Tata McGraw Hill, 2006. [3]Sunghyun, Del, Sai, Mangold S. IEEE 802.11 e ontentionbased channel access (EDCF) performance evaluation, IEEE International Conference on In, vol. 2, pp. 1151-1156, 2003. [4]Choi S. and Shin K. G., A cellular local area network w i t h QoS guarantees for heterogeneous traffic, Proceedings IEEE Infocom 97, pp. 1032-1039, Kobe, Japan, April 1997. [5]Comer, D. Computer Networks, Upper Saddle River, NJ: Prentice Hall, 2004. [6]Crow Brian P., Widjaja Indra, Kim Jeong Geun, Prescott T. Sakai, IEEE 802.11 Wireless Local Area Networks,IEEE Communications Magazine, September 1997. [7]Draft Standard IEEE 802.11, Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, November 1999. 114