Hardware Reference
In-Depth Information
Figure 2-3. Advertising and scanning
The scan interval and scan window parameters define how often and for how long a
scanner device will listen for potential advertising packets. As with the advertising in‐
terval, those values have a deep impact on power consumption, since they directly relate
to the amount of time the radio must be turned on.
The specification defines two basic types of scanning procedures:
Passive scanning
The scanner simply listens for advertising packets, and the advertiser is never aware
of the fact that one or more packets were actually received by a scanner.
Active scanning
The scanner issues a Scan Request packet after receiving an advertising packet. The
advertiser receives it and responds with a Scan Response packet. This additional
packet doubles the effective payload that the advertiser is able to send to the scanner,
but it is important to note that this does
not
provide a means for the scanner to send
any user data at all to the advertiser.
Figure 2-4
illustrates the difference between passive and active scanning.
