Multiplexing problem


#1

Hey guys, I know it is bad to ask after just a day of trying to implement the multiplexer protocol, but time pushes me to do it.
I have a very basic problem: after sending AT+CMUX=0 I have 3 seconds to communicate and the modem stops responding at all. During these 3 seconds I can freely send SABM frames to open the control channel and 2 other channels, communicate with AT commands, all works, but when the 3 seconds are over… thats all. Like a demo version :wink:

What I do is use the SABM to open the channels, then start sending UIH frames on the channel 1, nothing else. Is there a magic thing I’m missing?

Thanks


#2

Hi,

SABM frame should be sent to open control channel, and other DLC channels after AT+CMUX=0 command is executed successfully. UA frames should received in

response . Firmware will send a MSC control frame over control channel (and also expects a response for the frame), indicating that the DLC channel is ready to receive and

send frames. DLC channel is considered as faulty by the firmware if no response frame is received.

Regards,
Paruthiv


#3

Thanks for the response, I’ve actually found whats wrong with it - DTR! If I don’t keep it high, which I can on the development board, but not in the device I’m working with, cmux dies in 3 seconds. That happens on wismo tho, working good on q2686.