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Even though hot spots and mesh networks increasingly realize the long-standing vision of ubiquitous Internet access, our understanding of wireless protocols and system is still in its infancy. To analyze and debug the current and new protocols, packet-level accurate information of protocol status is crucially needed. Thus, this paper introduces PaPMo (Packet accurate Protocol Monitor), an active monitoring tool that captures snapshots of the protocol status as packets pass through the different layers and over distributed nodes. By merging and correlating the captured information, PaPMo is able to provide packet-level accurate information of deployed wireless network behavior that is currently available only via simulations. We show that PaPMo is able to correlate MAC-layer events, such as packet loss due to queue overflow, with TCP congestion control behavior at the accuracy of microseconds and with high fidelity. [ABSTRACT FROM AUTHOR]