These events wield a certain behavior in the
communication stream that can be observed and measured by parameters,
such as the occurrence and duration of gaps between data packets, types of
packets, and size of packets. Di?®erences in the implementation of these services
will cause a di?®erent influence on the behavior of the tra?±c that can be
exploited to distinguish between RIs. We exploit this fact in our experimental
evaluation (see Section 7).
4.3 Configuration of the Radio Interface
The 802.11 standard supports the dynamic configuration of the RI to tune
its behavior to be conducive to a variety of environments. Examples of con-
figurable parameters include request-to-send (RTS) threshold, fragmentation
threshold, transmit power, and power save mode. Di?®erent settings of these
parameters can alter the behavior of tra?±c. For example, the RTS threshold
sets the data packet size for which to trigger the request-to-send/clear-to-send
(RTS/CTS) handshake to reserve the wireless link prior to data transmission.
The RTS/CTS handshake is overhead that widens the inter-arrival time between
data packets. An RI with the RTS threshold set to a lower value will
trigger the RTS/CTS handshake more frequently than an RTS threshold with
a higher value. As a result, the packets??™ inter-arrival time would be larger and
this phenomenon would occur more often than for the higher RTS threshold.
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Chapter 18 Unauthorized Sensor Node Identification
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