Logical Link Control and Adaptation Layer Protocol

[Roei]

Hi,

I understand that BLE Logical Link Control and Adaptation Layer Protocol is responsible for protocol multiplexing capability.

Can you please explain what kind of protocol multiplexing occurs?

Thanks!

[ovrebekk]

Hi

Generally the L2CAP is doing multiplexing between host level protocols in the Bluetooth stack. 

In the old 'classic Bluetooth' days there were a large number of host protocols that could be used at the same time, as illustrated here, but this was greatly simplified in Bluetooth Low Energy. 

In BLE there are basically only the SMP and the ATT protocols that will be multiplexed through the L2CAP, since all higher levels profiles in BLE are implemented through the GATT and ATT layers:

The only exception to this is when using L2CAP connection oriented channels, allowing you to communicate directly with the link layer without going through the GATT and ATT, but this is not a very common use case (in part because there is little extra performance to gain by doing this). 

The L2CAP is also doing packet fragmentation/defragmentation in order to allow the host level protocols to use longer packets than the physical or link layer can handle. 

Best regards
Torbjørn