Hardware Reference
In-Depth Information
not depend on types of advertising packets. Instead, the type of connection establish‐
ment procedure used depends on the kind of filtering the central imposes on those
incoming packets:
Auto connection establishment procedure
With this single-step procedure, the host populates a white list (see
“White Lists”
on page 23
) with an array of known peripheral devices and then instructs the con‐
troller to connect to the first one detected. Generally speaking, this procedure is
useful when the central already knows a limited set of devices and does not have a
preference for which one to connect to.
General connection establishment procedure
This two-step procedure is commonly used to connect to a new, unknown periph‐
eral. The central starts by scanning without a white list, accepting all incoming
advertising packets. For each peripheral detected, the application then needs to
decide whether to connect to it or to continue to the next one. To do so, the appli‐
cation can prompt the user or parse advertising data included in the received ad‐
vertising packet. Once a peripheral is chosen, the central connects to it using the
direct connection establishment procedure.
Selective connection establishment procedure
This procedure is identical to the general connection establishment procedure, with
the exception that the host uses a white list of previously known devices to filter
incoming advertising packets. This can be useful in certain cases in which the user
should choose which of several known peripherals to connect to.
Direct connection establishment procedure
This standard single-step connection establishment procedure connects the central
to one particular peripheral. The host uses the Link Layer to initiate a connection
to one single device, identified by its Bluetooth Address, without previous knowl‐
edge of its presence. The procedure can fail if the targeted peripheral is not available
or is not in a connectable mode.
It is worth reiterating that a central host has two different ways to initiate a connection.
The first method requires two steps: first scanning and then connecting directly to a
device (by specifying its Bluetooth Address) detected during the scanning phase. The
second method skips the explicit scanning step and instead uses the controller to select
one or more devices to connect to, without previous knowledge of whether they are
actually nearby.
Additional GAP Procedures
GAP defines a few other procedures that are relevant only to already established con‐
nections, and which are commonly used:
