IJCSNS International Journal of Computer Science and Network Security, VOL.11 No.1, January 2011 36 Manuscript received January 5, 2011 Manuscript revised January 20, 2011 Impact of Various VoIP and Video Traffics to Performance of Aggregation with Fragment Retransmission (AFR) in WLAN Teuku Yuliar Arif and Riri Fitri Sari Electrical Engineering Department, Engineering Faculty, University of Indonesia, Depok, Indonesia Summary Agregation With Fragment Retransmision (AFR) is a frame transmission scheme that can improve the efficiency and the throughput of MAC layer in WLAN 802.11n. In this paper, we studied the performance of AFR scheme when various VoIP and video traffics transmitted over WLAN. The purpose of this work is to know how the number of connections, packet size and fragment size of VoIP and video traffics influence the throughput and the delay performance of frame transmission. We used G.711, G.723a and G.729 format as VoIP traffics and H.264/MPEG-4 AVC format as video traffics which used 768 Kbps, 2 Mbps, 4 Mbps, 10 Mbps and 20 Mbps video bit rate. We used network simulator 2 (NS-2) with AFR module to simulate VoIP and video trafics over WLAN and measured each traffic performance. Simulation results show that throughput of MAC layer with AFR scheme will saturate when 70 connections of G.711 were transmitted. The transmission delay of G.723a and G.729 will be optimum when each traffic aggregated in 512 bytes of frame size. Simulation results also show that the throughput of AFR scheme is 70 Mbps and the delay is 0.025 ms when 30 H.264 video connections with 2 Mbps bit rate were transmiited. We have found the fragment and frame sizes that will give optimum throughput and the delay performance in AFR MAC scheme. Key words: WLAN 802.11n, AFR, Performance, VoIP, Video 1. Introduction Today, Wireless Local Area Network (WLAN) technology based on IEEE 802.11 standard has rapidly developed and widely deployed as wireless Internet access in office, home and public location. On the other hand, the requirement of multimedia applications such as Voice over IP (VoIP) and video also have improved which multimedia application needed to high bit rate and low latency. For example, VoIP application that used G.711, G.723a and G.729 codec format will need a low and constant latency [1,2,3], video H.264/MPEG-4 Advanced Video Coding (AVC) with DVD quality format will need to 9,8 Mbps bit rate and H.264 with HDTV quality format will need 20 Mbps bit rate [4,5]. The latest standard of WLAN is IEEE 802.11n released in late of 2009, it can support up to 600 Mbps data rate at PHY layer [6]. Certainly this standard is very potensial to be used to trasmit VoIP and video traffics. But high data rate at PHY layer will not automatically improve MAC layer throughput because it depend on the mechanism in MAC layer itself. A research [7] shows that efficiency of IEEE 802.11 MAC layer will be decreased when PHY data rate increased. This occured while PHY data rate increased cousing faster transmission of MAC frame payload. Overhead such as PHY headers and contention time typically do not decrease at the same rate and thus begin to dominate frame transmission times. To support the requirement of higher throughput MAC layer in WLAN IEEE 802.11n, Tianji Li et al. [7] introduced a new frame transmission mechanism called Aggregation With Fragment Retransmission (AFR). In AFR scheme, multiple packets recieved from the upper layer will be aggregated into a big frame before transmission. If the packet size is larger than fragment treshold size then the packet is devided into fragments before being aggregated. If the error occured during transmission, then only the fragments of the frame that had beed corrupted will be retrasmitted. Therefore the AFR scheme can improve the throughput of MAC layer with small overhead. Several papers reported the performance of MAC layer with AFR scheme and other schemes [8,9,10,11,12]. However the performance of AFR MAC mechanism when used to transmit VoIP and video traffic have not clearly described. For example for the standard format such as G.711, G.723a and G.729 in VoIP traffics format, and H.264/MPEG-4 AVC in video traffic format, with various bit rate, resolution size and the number of frame per second. It is importan to know the behavior of the throughput and the delay of each VoIP and video traffic format while transmitting over WLAN with AFR MAC scheme. The transmission depends on the number of video connections, frame size and fragment size. The aims of this study are to gain the size of fragment and the size of the frame use by AFR scheme to get the optimal performance for each VoIP and video traffic format over WLAN. The reminder of this paper is organized as follows. On Section II, we explain the AFR MAC scheme which include the aggregation scheme and the theoretical background of AFR performance. Section III describe the overview of VoIP and video traffics format, Section IV