4 Acceleration Software/Hardware
In addition to the basic services specified in the 802.11 standard, manufacturers
often include acceleration hardware and software to increase performance
gains and to support future standards prior to ratification. Enhancement
techniques currently deployed to improve data transmission rates include
data compression, frame bursting, overhead management, and client-to-client
transfer [5]. The use of proprietary enhancement techniques can help distinguish
among devices. For example, the frame bursting technique, which is
based on the proposed 802.11e standard, unpacks short data packets and rebundles
them into a larger packet. An RI with frame bursting technology
would exhibit di?®erent timing features by generating larger packets and less
frequent management and control overhead tra?±c than an RI without frame
bursting.
5 Using Rate Switching to Detect Unauthorized Nodes
To illustrate a technique for distinguishing among heterogeneous sensors, we
focus on the implementation of the rate switching algorithm as an attribute
within the RI. Rate switching is a service that is required by the 802.11
standard, but its implementation is unspecified. Additionally, it is not a con-
figurable service and it would be di?±cult to conceal its influence on tra?±c
without altering the hardware or driver software. By analyzing the di?®erences
in implementation of the rate switching algorithm we can establish an identity
for the radio interface of a sensor.
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