Establishing a PPP link over a CMUX channel on a HL6528


I have an embedded device that establishes 2 channels via CMUX to a WS6318 modem. One is used for standard AT commands while the other is used to establish a PPP connection to send data. This works perfectly.

I have recently acquired an “AirPrime - HL6528RDx - Firmware” modem to replace the WS6318, however I believe I am struggling setting up the CMUX channels correctly. HDLC1 works with AT commands, but HDLC2 which is first used for some AT setup before being passed over to the PPP module, falls over! Part of the way through the LCP Link Negotiation the modem stops responding.

The CMUX command I’m using is this: “AT+CMUX=0,0,1,255,10,0,15” which, on the WS6318, is enough to then just open the HDLC channels. If I just use this on the HL6528RDx chip then the HDLC2 channel acks all my open channel requests and HDLC1 works for 2 AT command requests and then the modem stops responding.

With the HL6528RDx I found I got further if I also sent a DLC parameter negotiation message per channel before opening HDLC0, HDLC1 and HDLC2. However as I stated above, HDLC2, which handles the PPP link setup eventually stops showing responses from the modem. Note that when I stop getting responses from the modem over HDLC2, the HDLC1 channel is still working perfectly with AT requests.

Does anyone have the magic runes for “AT+CMUX” or the DLC parameter negotiation message values that the HL6528RDx modem works with?

Many thanks

Topic moved to the correct section


After further investigation it turns out to be a PPP link establishment issue as it appears to do the same thing without setting up CMUX channels.

The HL6528RDx establishes a PPP connection with Windows 7, so it’s looking like a problem with our RTOS’s PPP module.

The same PPP module works perfectly with the WS6318 modem though.

Does anyone know of any differences between the WS6318 and the HL6528RDx with respect to their PPP expectations?