A Novel Packet Aggregation Mechanism for Enhancing VoIP Performance on IEEE 802.11 Wireless Mesh Networks

In 802.11 Wireless Mesh Network (WMN), bandwidth will be wasted much for transferring VoIP flows since each voice frame must contain relatively large amount of protocol data. “Packet Aggregation” mechanism can be applied to merge the voice data of multiple VoIP flows into one frame for transmission. It reduces the waste on bandwidth and increases the maximum number of successful VoIP calls. In addition, the mechanism “MCF controlled channel access” (MCCA) defined in 802.11 standard can be used to obtain better QoS than adopting default EDCA mechanism. In MCCA, mesh stations which wants to transfer VoIP flows can reserve time intervals of the medium for transmission and this reservation will be advertised to their neighbors. It is why MCCA causes less medium contentions than EDCA. In this paper, a mechanism to transfer VoIP flows in IEEE 802.11 WMN by MCCA with packet aggregation scheme is proposed. The effectiveness of the proposed mechanism is shown by simulation results. In addition, the problem named as Routing-Packet Aggregation / De-aggregation-Scheduling optimization problem (abbr. RPADS problem) derived from the proposed mechanism is also studied. A heuristic algorithm for RPADS problem to maximize the total number of supported calls is also proposed

VoIP Capacity Evaluation in IEEE 802.11e WLAN Environment

In this report, we present an analytical model for VoIP capacity in IEEE 802.11e WLAN. We illustrate performance results relative to typical codec rates of G.711 PCM (64 kbit/s), G.729 (8 kbit/s) and G.723 (6.3 kbit/s). G.729 and G.723 allow a greater capacity than G.711 which is constrained by throughput. This greater capacity is at the expense of small quality degradation due to the delay increase since G.729 and G.723 codecs are more delay sensitive than G.711. In our study we analyse the occurrence of CAPs (Controlled Access Periods) during the Contention Period (CP) and its effect of a promising increase in the VoIP over WLAN capacity. We also show that high data rates (up to 54 Mb/s) allow important VoIP capacity (up to 400 G.711 VoIP calls, 997 G.729 VoIP calls and 1045 G.723 VoIP calls)

Performance evaluation of real-time schedulers for HCCA function in IEEE 802.11e wireless networks

IEEE 802.11 standard for wireless networks recently has been enhanced with IEEE 802.11e amendment to this protocol which introduces Quality of Service support. It provides differentiation mechanisms at the Medium Access Control layer, using two additional access functions: the Enhanced Distributed Channel Access (EDCA) function and the HCF Controlled Channel Access (HCCA) function. The EDCA function is based on a distributed control and enables prioritized channel access while the latter requires centralized scheduling and allows the applications to negotiate parameterized service guarantees. Only HCCA mechanism is suitable for serving traffic streams with real-time requirements such as multimedia applications and Voice Over IP. The IEEE 802.11e standard does not specify a mandatory HCCA scheduling algorithm, while it offers a reference scheduler. In this paper we analyze four HCCA schedulers which are alternative to the reference one and which offer real-time guarantees. A performance evaluation through simulation is conducted to show the main differences between the considered schedulers, including the reference one

Quality of service differentiation for multimedia delivery in wireless LANs

Delivering multimedia content to heterogeneous devices over a variable networking environment while maintaining high quality levels involves many technical challenges. The research reported in this thesis presents a solution for Quality of Service (QoS)-based service differentiation when delivering multimedia content over the wireless LANs. This thesis has three major contributions outlined below: 1. A Model-based Bandwidth Estimation algorithm (MBE), which estimates the available bandwidth based on novel TCP and UDP throughput models over IEEE 802.11 WLANs. MBE has been modelled, implemented, and tested through simulations and real life testing. In comparison with other bandwidth estimation techniques, MBE shows better performance in terms of error rate, overhead, and loss. 2. An intelligent Prioritized Adaptive Scheme (iPAS), which provides QoS service differentiation for multimedia delivery in wireless networks. iPAS assigns dynamic priorities to various streams and determines their bandwidth share by employing a probabilistic approach-which makes use of stereotypes. The total bandwidth to be allocated is estimated using MBE. The priority level of individual stream is variable and dependent on stream-related characteristics and delivery QoS parameters. iPAS can be deployed seamlessly over the original IEEE 802.11 protocols and can be included in the IEEE 802.21 framework in order to optimize the control signal communication. iPAS has been modelled, implemented, and evaluated via simulations. The results demonstrate that iPAS achieves better performance than the equal channel access mechanism over IEEE 802.11 DCF and a service differentiation scheme on top of IEEE 802.11e EDCA, in terms of fairness, throughput, delay, loss, and estimated PSNR. Additionally, both objective and subjective video quality assessment have been performed using a prototype system. 3. A QoS-based Downlink/Uplink Fairness Scheme, which uses the stereotypes-based structure to balance the QoS parameters (i.e. throughput, delay, and loss) between downlink and uplink VoIP traffic. The proposed scheme has been modelled and tested through simulations. The results show that, in comparison with other downlink/uplink fairness-oriented solutions, the proposed scheme performs better in terms of VoIP capacity and fairness level between downlink and uplink traffic

Voice-over-IP (VoIP) over wireless local area networks (WLAN).

Wang Wei.Thesis (M.Phil.)--Chinese University of Hong Kong, 2004.Includes bibliographical references (leaves 80-83).Abstracts in English and Chinese.Chapter Chapter 1 --- Introduction --- p.1Chapter 1.1 --- Motivations and Contributions --- p.1Chapter 1.2 --- Organization of the Thesis --- p.4Chapter Chapter 2 --- Background --- p.6Chapter 2.1 --- IEEE 802.11 --- p.6Chapter 2.1.1 --- Distributed Coordination Function (DCF) / Point Coordination Function (PCF) --- p.7Chapter 2.1.2 --- Types of Networks --- p.8Chapter 2.1.3 --- The 802.11 MAC Sublayer Protocol --- p.9Chapter 2.1.4 --- Why CSMA/CA for Wireless LAN? --- p.11Chapter 2.2 --- Voice over IP (VoIP) --- p.13Chapter 2.2.1 --- Speech Codec --- p.13Chapter 2.2.2 --- The H.323 Standard --- p.13Chapter 2.3 --- Related Work --- p.15Chapter 2.3.1 --- Capacity limits of VoIP over WLAN --- p.16Chapter 2.3.2 --- Methods for increasing VoIP capacity over WLAN --- p.16Chapter 2.3.3 --- Interference between traffic of VoIP and other applications --- p.18Chapter Chapter 3 --- VoIP Multiplex-Multicast Scheme --- p.20Chapter 3.1 --- System Architecture --- p.20Chapter 3.2 --- Packet Multiplexing and Multicasting --- p.22Chapter 3.3 --- Header Compression --- p.24Chapter 3.4 --- Connection Establishment --- p.29Chapter Chapter 4 --- Capacity Analysis --- p.31Chapter 4.1 --- VoIP Capacity Analysis for 802. 11b --- p.31Chapter 4.1.1 --- Capacity of Ordinary VoIP over WLAN --- p.32Chapter 4.1.2 --- Capacity of Multiplex-Multicast Scheme over WLAN --- p.33Chapter 4.2 --- "VoIP Capacity Analysis for 802,11a and 802.11g" --- p.34Chapter 4.3 --- VoIP Capacity with VBR Sources --- p.38Chapter 4.4 --- Simulations --- p.38Chapter Chapter 5 --- Delay Performance --- p.41Chapter 5.1 --- Access Delay --- p.42Chapter 5.2 --- Extra Delay Incurred by the Multiplex-Multicast Scheme --- p.47Chapter Chapter 6 --- VoIP Co-existing with TCP Interference Traffic --- p.49Chapter 6.1 --- Ordinary VoIP co-existing with TCP over WLAN --- p.49Chapter 6.1.1 --- Problem Caused by TCP Interference --- p.49Chapter 6.1.2 --- Solutions --- p.52Chapter 6.2 --- M-M VoIP coexisting with TCP over WLAN --- p.53Chapter 6.3 --- 802.11e --- p.56Chapter 6.3.1 --- EDCA --- p.56Chapter 6.3.2 --- ACK Policies --- p.58Chapter 6.3.3 --- VoIP over EDCA --- p.58Chapter Chapter 7 --- Experimental Validation --- p.61Chapter 7.1 --- Transmission Errors --- p.61Chapter 7.2 --- Prototype Implementation --- p.62Chapter Chapter 8 --- VoIP over Ad Hoc Networks --- p.65Chapter 8.1 --- Mobile Ad Hoc Networks (MANET) and Wireless Distributed System (WDS) --- p.65Chapter 8.2 --- The M-M Scheme in WDS --- p.67Chapter 8.2.1 --- Modified System Architecture --- p.67Chapter 8.2.2 --- Delay Performance --- p.68Chapter 8.2.3 --- Analysis of M-M Scheme in WDS --- p.69Chapter 8.2.4 --- Capacity Improvement --- p.70Chapter 8.2.5 --- Delay Improvement --- p.71Chapter 8.2.6 --- Spectrum Reuse --- p.71Chapter Chapter 9 --- Conclusions --- p.76References --- p.8

Impact of Background Traffic on Speech Quality in VoWLAN

This paper describes measurements of the impact of background traffic on speech quality in an environment of WLANs (IEEE 802.11). The simulated background traffic consists of three types of current traffics in telecommunication networks such as data transfer service, multimedia streaming service, and Web service. The background traffic was generated by means of the accomplished Distributed Internet Traffic Generator (D-ITG). The impact of these types of traffic and traffic load on speech quality using the test sequence and speech sequences is the aim of this paper. The assessment of speech quality is carried out by means of the accomplished Perceptual Evaluation of Speech Quality (PESQ) algorithm. The proposal of a new method for improved detection of the critical conditions in wireless telecommunication networks from the speech quality point of view is presented in this paper. Conclusion implies the next application of the method of improved detection of critical conditions for the purpose of algorithms for link adaptation from the speech quality point of view in an environment of WLANs. The primary goal of these algorithms is improving speech quality in the VoWLAN connections, which are established in the competent link