Technical Report 2002-022

Coping with Communication Gray Zones in IEEE 802.11b based Ad hoc Networks

Henrik Lundgren, Erik Nordström, and Christian Tschudin

June 2002

Our experiments with IEEE 802.11b based wireless ad hoc networks show that neighbor sensing with broadcast messages introduces "communication gray zones": in such zones data messages cannot be exchanged although the HELLO messages indicate neighbor reachability. This leads to a systematic mismatch between the route state and the real world connectivity, resulting in disruptive behavior for some ad hoc routing protocols. Concentrating on AODV we explore this issue and evaluate three different techniques to overcome the gray zone problem. We present quantitative measurements of these improvements and discuss the consequences for ad hoc routing protocols and their implementations.

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