Product Specs

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You can easily see that it is possible for a device to be a GATT server and a GATT

client at the same time. While it is most common for the slave (peripheral) device to be

the GATT server only and the master (central) device to be the GATT client, this is

not required. The GATT functionality of a device is logically separate from the

master/slave role. The master/slave roles control how the BLE radio connection is

managed, and the client/server roles are dictated by the storage and flow of data.

1.1.3 Profiles

A GATT database implements one or more profiles, and each profile is made up of

one or more services, and each service is made up of one or more characteristics.

Figure 5.

GATT servers can implement as many profiles, services, and characteristics as needed

by the product, figure 5. When using a non-standard profile, a 128bit UUID is required

and must be provided by the peripheral producer offering this unique profile. You can

also adhere to any Bluetooth SIG profiles (services, and characteristics) currently

supported, in which case the profile UUID is 16bit long. Every BLE device acting as a

GATT server must implement the official Generic Access service. This includes two

mandatory characteristics: Device Name and Appearance.

1.1.4 Attributes and Characteristics

Remember that a service is made up of one or more characteristics. However, one

characteristic may be comprised of many different attributes.

Each attribute is given a unique numerical handle which the GATT client may use to

reference, access, and modify it. Every characteristic has one main attribute which

allows access to the actual value stored in the database for that characteristic. When

you “write a value to a characteristics” or “read the value of the characteristic” you are

doing read and write operations on the main data attribute (of said characteristic).