ACK Spoofing on MAClayer Rate Control: Attacks and Defenses Abstract   In wireless 802.11 networks, MAClayer rate control mechanisms such as Minstrel have an important role in selecting an appropriate transmission rate to maximize throughput andor to minimize frame loss. Transmitting at a higher rate in good channel quality achieves high throughput, but it achieves a low or zero throughput if the channel quality is bad. In many MAClayer rate control mechanisms, the selection of transmission rates depends on link quality metrics calculated based on MAClayer acknowledgements (ACKs) of the successful transmissions of data frames. We found that injecting forged ACKs to acknowledge lost data frames can mislead most rate control mechanisms to select an unsustainable transmission rate resulting in frame losses. Due to the lack of protection of ACKs, the sender cannot detect and avoid this attack. In this paper, we develop a MAClayer ACK spoofing mechanism and design experiments to exploit such a vulnerability in 802.11 networks. We analyze this vulnerability in different attack models for wellknown MAClayer rate control mechanisms. Our experiment results show that the spoofing attack can reduce the throughput to zero by tricking the sender to believe the highest rate should be used even when the channel quality is bad. To address this issue, we present a defense mechanism that is effective and lightweight. Experiment results confirm the effectiveness of the proposed solution with low communication overhead.

Fair and efficient resource allocation in IEEE 802.11ah WLAN with heterogeneous data rates Abstract   For dense wireless LANs (WLANs), IEEE 802.11ah has specified restricted access window (RAW) as the channel access scheme. Here the competing stations (STAs) are divided into groups and STAs belonging to each group attempt to access the channel during their designated RAW slot by invoking the distributed coordination function (DCF) protocol. This paper describes an analytical model to evaluate the throughput performance of IEEE 802.11ah WLAN, when STAs use distinct data rates and the RAW mechanism is implemented for medium sharing. When STAs are grouped randomly (i.e., without considering their data rates), a group will contain STAs operating at distinct data rates. Since all these STAs simultaneously contend for channel access based on DCF protocol, the throughput of high data rate STAs are downequalized to that of lower data rate STAs; thus the aggregate network throughput is degraded significantly. To resolve the resulting performance anomaly problem, we consider data rate based grouping where STAs operating at the same data rate are grouped together. We describe an algorithm for implementing data rate based grouping at the access point (AP). Further, we describe an analytical procedure to find the network throughput under data rate based grouping. Through numerical and experimental investigations, we establish that data rate based grouping can significantly improve the aggregate network throughput performance, as compared to the conventional random grouping strategy. Further, we use Jainxe2x80x99s fairness index (JFI) to establish that data rate based grouping can also provide fair resource allocation among the STAs operating at distinct data rates, by ensuring that all the competing STAs in the network achieve throughput proportional to their data rates.