VoIP capacity over multiple IEEE 802.11 WLANs.

Chan, An.Thesis (M.Phil.)--Chinese University of Hong Kong, 2007.Includes bibliographical references (leaves 80-84).Abstracts in Chinese and English.Chapter Chapter 1 --- Introduction --- p.1Chapter 1.1 --- Motivations and Contributions --- p.1Chapter 1.2 --- Related Works --- p.3Chapter 1.3 --- Organization of the Thesis --- p.4Chapter Chapter 2 --- Background --- p.5Chapter 2.1 --- IEEE 802.11 --- p.5Chapter 2.1.1 --- Basic IEEE 802.11 Standards --- p.5Chapter 2.1.2 --- Types of Networks --- p.7Chapter 2.2 --- Voice over IP (VoIP) Codecs --- p.8Chapter 2.3 --- VoIP over WLAN --- p.9Chapter 2.3.1 --- System Architecture of VoIP over WLAN --- p.9Chapter 2.3.2 --- VoIP Capacity over an Isolated WLAN --- p.10Chapter Chapter 3 --- VoIP Capacity over Multiple WLANs --- p.12Chapter 3.1 --- Topology Settings and Assumptions --- p.12Chapter 3.2 --- Low VoIP Capacity Found in NS2 Simulations --- p.16Chapter 3.3 --- Applying Frequency Channel Assignment --- p.18Chapter Chapter 4 --- Clique Analysis and Call Admission Control --- p.21Chapter 4.1 --- Conflict Graph Model and Cliques --- p.21Chapter 4.2 --- Cliques in Multi-Cell WLANs --- p.22Chapter 4.3 --- Clique-Based Call Admission Control Algorithm --- p.24Chapter 4.3.1 --- Algorithm Description --- p.24Chapter 4.3.2 --- Algorithm Performance Evaluation --- p.27Chapter 4.3.3 --- Clique-Based Admission Control in Three-Frequency- Channel WLAN --- p.29Chapter Chapter 5 --- Time Division Multiple Access (TDMA) on IEEE 802.11MAC --- p.32Chapter 5.1 --- Coarse-Grained Time-Division Multiple Access (CTDMA) --- p.33Chapter 5.1.1 --- Basic Ideas of CTDMA --- p.33Chapter 5.1.2 --- Conflict Graph Modeling of CTDMA --- p.35Chapter 5.1.3 --- Parameter Values in CTDMA --- p.41Chapter 5.2 --- Possible Realization of TDMA on 802.11 Standards --- p.47Chapter Chapter 6 --- Coloring Problem in Wireless Networks: A Theoretical Treatment --- p.52Chapter 6.1 --- Coloring of One-Dimensional Linear Network --- p.53Chapter 6.1.1 --- Network with Same Link Length --- p.53Chapter 6.1.2 --- Network with Variable Link Length --- p.54Chapter 6.2 --- Coloring of Two-Dimensional Network --- p.63Chapter Chapter 7 --- Conclusion --- p.66Appendices --- p.69References --- p.8

Analysis and Performance Evaluation of IEEE 802.11 WLAN

With fast deployment of wireless local area networks VoIP over IEEE 802.11 wireless local area network (WLAN) is growing very fast and is providing a cost effective alternative for voice communications. WLANs were initially set up to handle bursty nonreal time type of data traffic. Therefore, the wireless access protocols initially defined are not suitable for voice traffic. Subsequently, updates in the standard have been made to provision for QoS requirements of data, especially the real time traffic of the type voice and video. Despite these updates, however, transmitting voice traffic over WLAN does not utilize the available bandwidth (BW) efficiently, and the number of simultaneous calls supported in practice is significantly lower than what the BW figures would suggest. Several modifications have been proposed to improve the call capacity, and recently isochronous coordination function (ICF) was introduced to mitigate the problem of low call capacity. The proposed modified ICF which further improves the performance in terms of the call capacity. The proposed scheme uses multiplexing and multicasting in the downlink to substantially increase the call capacity

IMPROVING QoS OF VoWLAN VIA CROSS-LAYER BASED ADAPTIVE APPROACH

Voice over Internet Protocol (VoIP) is a technology that allows the transmission of voice packets over Internet Protocol (IP). Recently, the integration of VoIP and Wireless Local Area Network (WLAN), and known as Voice over WLAN (VoWLAN), has become popular driven by the mobility requirements ofusers, as well as by factor of its tangible cost effectiveness. However, WLAN network architecture was primarily designed to support the transmission of data, and not for voice traffic, which makes it lack ofproviding the stringent Quality ofService (QoS) for VoIP applications. On the other hand, WLAN operates based on IEEE 802.11 standards that support Link Adaptive (LA) technique. However, LA leads to having a network with multi-rate transmissions that causes network bandwidth variation, which hence degrades the voice quality. Therefore, it is important to develop an algorithm that would be able to overcome the negative effect of the multi-rate issue on VoIP quality. Hence, the main goal ofthis research work is to develop an agent that utilizes IP protocols by applying a Cross-Layering approach to eliminate the above-mentioned negative effect. This could be expected from the interaction between Medium Access Control (MAC) layer and Application layer, where the proposed agent adapts the voice packet size at the Application layer according to the change of MAC transmission data rate to avoid network congestion from happening. The agent also monitors the quality of conversations from the periodically generated Real Time Control Protocol (RTCP) reports. If voice quality degradation is detected, then the agent performs further rate adaptation to improve the quality. The agent performance has been evaluated by carrying out an extensive series ofsimulation using OPNET Modeler. The obtained results of different performance parameters are presented, comparing the performance ofVoWLAN that used the proposed agent to that ofthe standard network without agent. The results ofall measured quality parameters hav

A multiplex-multicast scheme that improves system capacity of voice-over-IP on wireless LAN by 100%

Voice-over-IP (VoIP) is.an important application on the Internet. With the emergence of WLAN technology and its various advantages compared with the traditional wired LAN, it is fast becoming the 'last-mile' of choice for the overall Internet infrastructure. This work considers the support of VoIP over 802.11b WLAN. We show that although the raw WLAN capacity can potentially support more than 500 VoIP sessions, various overheads bring this down to only 12 VoIP sessions when using GSM 6.10 codec. We propose a novel multiplexing scheme for VoIP which exploits multicasting over WLAN for the downlink VoIP traffic. This scheme can achieve nearly 100% improvement in system capacity. In addition, we present results showing that the delay and delay jitter introduced by the proposed scheme are small. We believe that the scheme can reduce the blocking probability of VoIP sessions in an enterprise WLAN significantly.published_or_final_versio