Vertical Handover Management for VoIP Session over Brodband Wireless Networks

Today, wireless LAN (IEEE802.11g/n) has been the dominant wireless network that can provide high data rates in a \ud limited coverage area. While emerging mobile WiMAX (IEEE802.16e) can provide a wireless broadband access to \ud mobile users in a wide coverage area. These two different technolgies will co-exist while complementing each other in \ud some regions, hence, a mobile node (MN) with dual interfaces traverses and executes many handovers (HOs) between \ud 802.11g and 802.16e. Meanwhile, there is a huge demand for Voice over IP (VoIP) service over wireless networks. \ud However, VoIP is a delay and loss sensitive application, hence, VoIP session is more likely to be deteriorated during \ud HO between 802.11g and 802.16e. In order to maintain quality of VoIP session during HO, we proposed Vertical \ud Handover Management (VHM) for VoIP session that focuses on HO initiation and decision strategy according to the \ud wireless link condition and congestion state of wireless networks. The VHM exploits request to send (RTS) retries and \ud round trip time (RTT) between an MN and an access point in an 802.11g interface as well as a carrier to interference \ud noise ration (CINR) level and MN???s queue length of an 802.16e interface as HO triggers. We then conducted simulation \ud experiments to evaluate the effectiveness of our proposed VHM using QualNet 4.5. Our simulation results show that \ud our proposed VHM can preserve the quality of VoIP session during such HO

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

Handover Management for VoWLAN Based on Estimation of AP Queue Length and Frame Retries

Switching a communication path from one Access Point (AP) to another in inter-domain WLANs is a critical challenge for delay-sensitive applications such as Voice over IP (VoIP) because communication quality during handover (HO) is more likely to be deteriorated. To maintain VoIP quality during HO, we need to solve many problems. In particular, in bi-directional communication such as VoIP, an AP becomes a bottleneck with the increase of VoIP calls. As a result, packets queued in the AP buffer may experience a large queuing delay or packet losses due to increase in queue length or buffer overflow, thereby causing the degradation of VoIP quality for the Mobile Nodes (MNs) side. To avoid this degradation, MNs need to appropriately and autonomously execute HO in response to the change in wireless network condition, i.e., the deterioration of wireless link quality and the congestion state at the AP. In this paper, we propose an HO decision strategy considering frame retries, AP queue length, and transmission rate at an MN for maintaining VoIP quality during HO. Through simulation experiments, we then show that our proposed method can maintain VoIP quality during HO by properly detecting the wireless network condition