IJCSES International Journal of Computer Sciences and Engineering Systems, Vol.3, No.3, July 2009 CSES International ⓒ2009 ISSN 0973-4406 1                                     Monji ZAIDI, Ridha OUNI, Jamila BHAR and Rached TOURKI Electronic and Micro-Electronic Laboratory (EμE, IT-06) FSM, Monastir, Tunisia ridha.ouni@ipeim.rnu.tn Abstract Wireless local area networks (WLAN) have seen rapid growth and deployment in the recent years. It has become the state-of-the art campus networking option in many academic and corporate campuses. As Wi-Fi technology becomes ubiquitous, it is important to understand trends in the usage of these networks. As the mobile clients are moving from one access point to another, the convectional layer-2 handoff consumes more time in the channel-scanning process. The proposed handoff mechanism for mobility management is designed to minimize the handoff latency in IEEE 802.11 wireless local area network. It reduces the discovery phase according to two models extended from the basis model. There are two methods to implement Handoff functions in the MAC layer. The first method is CPU-based solution. It uses software for protocol analysis and CPU, such as DSP, for process management. It is more flexible in design stage and easy to modify, however the low processing speed and the higher cost present its major weakness. The second method means that all functions are processed by hardware circuits. The advantage of this method is circuit reconfiguration and processing speed very high, but it needs long developed time. We propose the last method to implement handoff functions in the MAC layer. Key words: Handoff, Latency, MAC, 802.11, Mobility, FPGA. 1. Introduction IEEE 802.11 based wireless LANs have seen a very fast growth in the last few years [1]. Voice over IP (VoIP) is one of the most promising services to be used in mobile devices over wireless networks [2]. One of the main problems in VoIP communication is the handoff latency introduced when moving from one Access Point (AP) to another [3]. Then, the amount of time needed for the handoff in 802.11 environments is too large for seamless VoIP communications [4]. The definition of new mobile network architectures able to improve the Internet experience to the mobile users is becoming the primary objective of the wireless research community. The future 4G access technologies will inevitably have to cooperate with the existing cellular environments (e.g. 3G) and indoor environments (e.g. 802.11 WLAN). These technologies have been developed for provisioning different specific services and thus they widely vary in terms of bandwidth, latencies, coverage capability, etc. The complementariness of these radio access technologies can be an advantage, in order to offer adaptive and flexible services to mobile users. The incompatibilities between heterogeneous systems will be overcome by using both new hardware solutions (for example FPGAs solutions for providing physical layer reconfigurability) and new software solutions (algorithms and protocols for providing mobility management across heterogeneous systems). We were able to reduce the handoff latency using extended handoff mechanisms, with modifications being limited to mobile devices and compatible with standard 802.11 behaviors. This paper is organized as follow. Section 2 presents a wireless communication environment based on IEEE 802.11 standard. In section 3, we describe the existing layer-2 handoff mechanism. In section 4, we detail handoff mechanisms proposed for campus wide networks. The simulation, analysis and synthesis are dealt in Section 5. Finally, section 6 concludes the paper. 2. IEEE 802.11 Standards There are currently three IEEE 802.11 standards [5]: 802.11 a, b and g. The 802.11a standard operates in the 5 GHz ISM band. It uses a total of 32 channels of which only 8 do not overlap. Both 802.11b and 802.11g standards operate in the 2.4 GHz ISM band and use 11 among the 14 possible channels. While 802.11b can operate up to a maximum rate of 11 Mbit/sec, the 802.11g and 802.11a standards can operate up to a maximum rate of 54 Mbit/sec. The 802.11g standard is backwards-compatible with the 802.11b standard while the 802.11a standard, because of the different ISM band, is not compatible with the two other.