Class Hijacking in Differentiated Services Wireless Networks

Abstract

Wireless networks have a variety of advantages making them very popular in many appli-cations. IEEE 802.11 Wireless Local Area Network (WLAN) is one of the most widely de-ployed wireless network technologies in the world today. As the use of wireless networks in-creases, so does the demand for better service in terms of less delay for voice and video traffic. The IEEE 802.11e standard was introduced to enhance the support of time sensitive applica-tions (QoS) such as video streaming and voice over the internet protocol (VoIP) in modern WLANs. The access mechanism of IEEE 802.11e, referred to as Enhanced Distributed Chan-nel Access (EDCA), assigns to different types of data traffic different priorities based on the QoS requirements of the traffic, and for each priority it uses a different set of medium access parameters to introduce QoS support. The differentiation is realized in each wireless node by grouping traffic flows into categories implemented as priority queues. The criterion for this flow aggregation is based on marking the flows at the network level and inserting frames into the appropriate queues. These queues are called Access Categories (ACs). IEEE 802.11e de-fines four Access Categories (ACs): AC_VO (voice traffic), AC_VI (video traffic), AC_BE (best effort traffic) and AC_BK (background traffic). AC_VO and AC_VI constitute the mul-timedia ACs and AC_BK and AC_BE are called non-multimedia ACs. Inserting low-priority frames into high priority queues will influence the service levels of the multimedia packets. These “invading” frames can be the cause of dramatic network QoS deterioration that may alter (under certain circumstances) completely the functionality of IEEE 802.11e downgrading it to the legacy IEEE 802.11 DCF behavior. The marking procedure typically takes place at layer-3 of the protocol stack. However, one may intervene at this marking process and abuse the class-based functionality to the benefit of low priority traffic. The act of intentionally al-tering the marking on low priority frames in order for them to receive increased priority is called Class Hijacking. The main topic in this thesis is to investigate class hijacking and de-velop a MAC-layer mechanism to confront it. By enhancing the EDCA QoS mechanism in an effective and optimal way, it is possible to detect signs of hijacked traffic and ultimately re-instate the standard EDCA functionality. The effectiveness of the proposed solution is demon-strated by means of simulation.