Application-aware scheduling for VoIP in Wireless Mesh Networks

Wireless Mesh Networks (WMNs) are seen as a means to provide last mile connections in Next Generation Networks (NGNs). Because of their auto configuration capabilities and the low deployment cost WMNs are considered to be an efficient solution for the support of multiple voice, video and data services in NGNs. This paper looks at the optimal provision of resources in WMNs for Voice over IP (VoIP) traffic, which has strict performance requirements in terms of delay, jitter and packet loss. In WMNs, because of the challenges introduced by wireless multi hop transmissions and limited resources, providing performance quality for VoIP comparable to the voice quality in the traditional circuit switched networks is a major challenge. This paper analyses different scheduling mechanisms for TDMA based access control in mesh networks as specified in the IEEE 802.16 2004 WiMAX standard. The performance of the VoIP applications when different scheduling mechanisms are deployed is analysed on a variety of topologies using ns 2 simulation and mathematical analysis. The paper concludes that on demand scheduling of VoIP traffic typically deployed in 802.11 based WMNs is not able to provide the required VoIP quality in realistic mesh WiMAX network scenarios and is therefore not optimal from a network operator’s point of view. Instead, it is shown, that continuous scheduling is much better suited to serve VoIP traffic. The paper then proposes a new VoIP aware resource coordination scheme and shows, through simulation, that the new scheme is scalable and provides good quality for VoIP service in a wide range of network scenarios. The results shown in the paper prove that the new scheme is resilient to increasing hop count, increasing number of simultaneous VoIP sessions and the background traffic load in the network. Compared to other resource coordination schemes the VoIP aware scheduler significantly increases the number of supported calls

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

Supporting Internet Access and Quality of Service in Distributed Wireless Ad Hoc Networks

In this era of wireless hysteria, with continuous technological advances in wireless communication and new wireless technologies becoming standardized at a fast rate, we can expect an increased interest for wireless networks, such as ad hoc and mesh networks. These networks operate in a distributed manner, independent of any centralized device. In order to realize the practical benefits of ad hoc networks, two challenges (among others) need to be considered: distributed QoS guarantees and multi-hop Internet access. In this thesis we present conceivable solutions to both of these problems. An autonomous, stand-alone ad hoc network is useful in many cases, such as search and rescue operations and meetings where participants wish to quickly share information. However, an ad hoc network connected to the Internet is even more desirable. This is because Internet plays an important role in the daily life of many people by offering a broad range of services. In this thesis we present AODV+, which is our solution to achieve this network interconnection between a wireless ad hoc network and the wired Internet. Providing QoS in distributed wireless networks is another challenging, but yet important, task mainly because there is no central device controlling the medium access. In this thesis we propose EDCA with Resource Reservation (EDCA/RR), which is a fully distributed MAC scheme that provides QoS guarantees by allowing applications with strict QoS requirements to reserve transmission time for contention-free medium access. Our scheme is compatible with existing standards and provides both parameterized and prioritized QoS. In addition, we present the Distributed Deterministic Channel Access (DDCA) scheme, which is a multi-hop extension of EDCA/RR and can be used in wireless mesh networks. Finally, we have complemented our simulation studies with real-world ad hoc and mesh network experiments. With the experience from these experiments, we obtained a clear insight into the limitations of wireless channels. We could conclude that a wise design of the network architecture that limits the number of consecutive wireless hops may result in a wireless mesh network that is able to satisfy users’ needs. Moreover, by using QoS mechanisms like EDCA/RR or DDCA we are able to provide different priorities to traffic flows and reserve resources for the most time-critical applications

Packet aggregation for voice over internet protocol on wireless mesh networks

>Magister Scientiae - MScThis thesis validates that packet aggregation is a viable technique to increase call ca-pacity for Voice over Internet Protocol over wireless mesh networks. Wireless mesh networks are attractive ways to provide voice services to rural communities. Due to the ad-hoc routing nature of mesh networks, packet loss and delay can reduce voice quality.Even on non-mesh networks, voice quality is reduced by high overhead, associated with the transmission of multiple small packets. Packet aggregation techniques are proven to increase VoIP performance and thus can be deployed in wireless mesh networks. Kernel level packet aggregation was initially implemented and tested on a small mesh network of PCs running Linux, and standard baseline vs. aggregation tests were conducted with a realistic voice tra c pro le in hop-to-hop mode. Modi cations of the kernel were then transferred to either end of a nine node 'mesh potato' network and those tests were conducted with only the end nodes modi ed to perform aggregation duties. Packet ag- gregation increased call capacity expectedly, while quality of service was maintained in both instances, and hop-to-hop aggregation outperformed the end-to-end con guration. However, implementing hop-to-hop in a scalable fashion is prohibitive, due to the extensive kernel level debugging that must be done to achieve the call capacity increase.Therefore, end-to-end call capacity increase is an acceptable compromise for eventual scalable deployment of voice over wireless mesh networks

MeshScan: a Fast and Efficient Handoff Scheme for IEEE 802.11 Wireless Mesh Networks

As a next generation network solution, Wireless Mesh Networks (WMN) provides fast Internet access to a large area, which is from university campus to city scale. In order to provide an uninterrupted Internet experience to a mobile client, a process called handoff is required to maintain the network connection from one Mesh Node (MN) to another MN. Ideally, handoff should be completely transparent to mobile users. A critical application like VoIP will require a handoff capability that transfers a call from one mesh node (MN) to another in less than 50 msec. However the current IEEE 802.11 standards do not address the handoff well. Studies have revealed that standard handoff on IEEE 802.11 WLANs incurs a latency of the order of hundreds of milliseconds to several seconds. Moreover, the discovery step in the handoff process accounts for more than 99% of this latency. The study addresses the latency in the discovery step by introducing an efficient and powerful client-side scan technique called MeshScan which replaces the discovery step with a unicast scan that transmits Authentication Request frames to potential MNs. A prototype of MeshScan has been developed based on the MadWifi WLAN driver on Linux operating systems. The feasibility of MeshScan to support fast handoff in WMNs has been demonstrated through extensive computer simulations and experiments under same given conditions. The results from the simulations and experiments show that the latency associated with handoff can be reduced from seconds to a few milliseconds by using the MeshScan technique. Furthermore, it is shown that MeshScan can continue to function effectively even under heavy traffic loads