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

Muhammad NISWAR

IEICE TRANSACTIONS on Information and Systems   Vol.E92-D    No.10    pp.1847-1856
Publication Date: 2009/10/01
Online ISSN: 1745-1361
DOI: 10.1587/transinf.E92.D.1847
Print ISSN: 0916-8532
Type of Manuscript: Special Section PAPER (Special Section on New Technologies and their Applications of the Internet)
Category: Wireless Network
handover,  AP queue length,  frame retries,  transmission rate,  VoIP,  multi-rate WLAN,  

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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.