Link layer and GAP

[rushin]

hello there i have basic question about BLE. what is difference between link layer and GAP?? i know about host and controller. but in both layer there is advertisement and scanning. then what is difference between them??

[endnode]

Hi rushin. Link and GAP (Generic Access Profile) are two layers of the BT Smart (LE) stack which are living on top of each other. If you are using Generic Access Profile (it's optional but most of the applications today are deployed on top of GAP - which is the last layer which is considered as part of certified BT Smart stack) then your stack is definitely implementing Link layer which is sitting just on top of Physical layer (actual radio waves).

I guess some deeper study of LE stack will be necessary if you want to understand these details but in a nutshell:

• Link layer keeps the data flow and in BLE it defines most of the basic terms such Advertising, Scanning, Connection, Address, Packet, Packet Data Unit, Master/Slave topology, frequency hopping etc.
• GAP is very high level layer which is already saying what "role" is the device able to play (Observer, Broadcaster, Peripheral, Central) and what "profile" it adopts (meaning what GATT client/server methods will be available and what Services/Characteristics/Descriptors objects - standard or proprietary - will live there and what "procedures" they will support).

On top of these GAP profiles live real applications. Some of them can be just simple set of rules how to work with these objects (e.g. "Temperature" app will just take care to keep one GATT value updated with the temperature data), some of them can be pretty complex. That's up to you...

Cheers Jan

[KETAN_PATEL]

where i get the details about each and every profile like GAP,GATT etc.. thank you.

[endnode]

You are now speaking about core Bluetooth Low Energy stack layers and principles. Are you asking "where to learn how BLKE works?" The answer is "in BT SIG Core specification" but because that has almost 3000 pages and even not all of them are relevant to LE it's not the best starting point. Luckily BLE is so wide spread today that you can get brief introductions to BLE stack and architecture all over the internet, you can see introductions at basically every big vendor/system:

[endnode]

• Nordic
• Microsoft for Windows
• Android
• Texas Instruments\
• CSR
• Cypress ...

[KETAN_PATEL]

Thank you endnode