How to discover RFCOMM channel number for one bluetooth device?

[dw]

If i know the bt mac address of one bluetooth device, and I know it
support RFCOMM with one serial profile, how could I discover the
device RFCOMM channel? I have to try from 1 - 31.
Any suggestion?

[Matthias Ringwald]

Hi dw,

the easiest one for a particular device would be to run the sdp browse tool in linux, or just pair it to the Mac and check Bluetooth Explorer or record the pairing process with the PacketLogger tool. It (mostly) good job of deciphering the Bluetooth data packets (like show you the RFCOMM channel in the response to the SDP request)

If you need to do it programmatically, here's a binary blob to ask for SPP profile and retrieve attributes 1-4. 

uint8_t sdpQuerySPP[] =

{

    0x06, 0x00, 0x06, 0x00, 0x0F, 0x35, 0x03, 0x19,

    0x11, 0x05, 0xFF, 0xFF, 0x35, 0x05, 0x0A, 0x00, 0x01, 0x00, 0x04, 0x00

};

Matthias Ringwald

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