Sobre la Justicia en las Redes IEEE 802.11e: Desincronización de su Mecanismo de Acceso al Medio (On the unfairness in IEEE 802.11e networks: Desynchronization of its medium access mechanism)

Elena Lopez-Aguilera (elopez@entel.upc.edu), Jordi Casademont (jordi.casademont@entel.upc.edu), Josep Cotrina (jcotrina@entel.upc.edu)


Departamento de Ingeniería Telemática, Universitad Politècnica de Catalunya
This paper appears in: Revista IEEE América Latina

Publication Date: Oct. 2007
Volume: 5,   Issue: 6 
ISSN: 1548-0992


Abstract:
Since the advent of the first IEEE 802.11 standard, several papers have proposed means of providing QoS to IEEE 802.11 networks and evaluate various traffic-prioritization mechanisms. Nevertheless, studies on the assignment of AIFS times defined in IEEE 802.11e reveal that the various priority levels work in a synchronized manner. The studies show that, under large loads of high-priority traffic, EDCA starves low-priority frames, which is undesirable. We argue that QoS traffic needs to be prioritized, but users sending best-effort frames should also obtain the expected service. High-priority traffic can also suffer performance degradation when using EDCA because of heavy loads of low-priority frames. Thus, we have proposed a mechanism based on desynchronizing the IEEE 802.11e working procedure. It prevents stations that belong to different priority classes from attempting simultaneous transmission, prioritizes independent collision groups and achieves better short-term and long-term channel access fairness. We have evaluated the proposal based on extensive analytical and simulation results. It prevents the strangulation of low-priority traffic, and, moreover, reduces the degradation of high-priority traffic with the increased presence of low-priority frames.

Index Terms:
Access Protocols, Wireless LAN.   


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