Hardware Reference
In-Depth Information
Bluetooth Device Address
The fundamental identifier of a Bluetooth device, similar to an Ethernet Media Access
Control (MAC) adddress, is the
Bluetooth device address
. This 48-bit (6-byte) number
uniquely identifies a device among peers. There are two types of device addresses, and
one or both can be set on a particular device:
Public device address
This is the equivalent to a fixed, BR/EDR, factory-programmed device address. It
must be registered with the IEEE Registration Authority and will never change
during the lifetime of the device.
Random device address
This address can either be preprogrammed on the device or dynamically generated
at runtime. It has many practical uses in BLE, as discussed in more detail in
“Address
Types” on page 44
.
Each procedure must be performed using one of the two, to be specified by the host.
Advertising and Scanning
BLE has only one packet format and two types of packets (
advertising
and
data
packets),
which simplifies the protocol stack implementation immensely. Advertising packets
serve two purposes:
• To broadcast data for applications that do not need the overhead of a full connection
establishment
• To discover slaves and to connect to them
Each advertising packet can carry up to 31 bytes of advertising data payload, along with
the basic header information (including Bluetooth device address). Such packets are
simply broadcast blindly over the air by the advertiser without the previous knowledge
of the presence of any scanning device. They are sent at a fixed rate defined by the
advertising interval, which ranges from 20 ms to 10.24 s. The shorter the interval, the
higher the frequency at which advertising packets are broadcast, leading to a higher
probability of those packets being received by a scanner, but higher amounts of packets
transmitted also translate to higher power consumption.
Because advertising uses a maximum of three frequency channels and the advertiser
and the scanner are not synchronized in any way, an advertising packet will be received
successfully by the scanner only when they randomly overlap, as shown in
Figure 2-3
.
