GAP (Advertising and Connections) - Getting Started with Bluetooth Low Energy - page 50

GAP Service
The final item that GAP includes as part of its section in the core specification is the
GAP Service, a mandatory GATT service that every device must include among its
attributes (see “Attribute Protocol (ATT)” on page 26 ). The service is freely accessible
(read-only) to all connected devices with no security requirements whatsoever, and it
contains the following three characteristics:
Device Name characteristic
This contains the same user-readable UTF-8 string that can also be included in the
Device Name AD Type described in Table 3-3 . This is the characteristic read to
perform the name discovery procedure in “Additional GAP Procedures” on page 42 .
Appearance characteristic
This 16-bit value associates the device in which it is included with a certain generic
category (phone, computer, watch, sensor, etc.) and is typically used by the GATT
client to display an icon that represents the given category. This characteristic can
also be made available in the advertising packet with the Appearance AD Type.
Peripheral Preferred Connection Parameters (PPCP) characteristic
Once the central has established a connection with the peripheral, it can (although
it has no obligation to) then read the value of this characteristic and perform a
connection parameter update procedure (described in “Additional GAP Proce‐
dures” on page 42 ) to change the connection's parameters to values that are agree‐
able to the peripheral.
Chapter 4 explores GATT services and characteristics in more detail, along with all of
the procedures that allow BLE devices to exchange user data over an established con‐
nection.