3G/4G modem configuration (MC7700) problems with PPP and error: CHAT: Invalid d



  • Hi all,

    I have built a custom image that has added support for the MC7700 Sierra Airprime internal 3G/4G modem.  I am using the Nanobsd build on an Alix router board.

    The devices are detected and I correctly see a number of /dev/cuaU0.0 - /dev/cuaU0.3 devices as expected.
    I am able to use the PPP command to query the modem and get some modem information out, so I am happy that the card is working.

    However I can't seem to get the modem to connect due to the error in the ppp log of pfsense:

    CHAT: Invalid dial init string.
    

    Unfortunately I don't really know much at all about 3g modems or PPP so struggling a bit with the required knowledge.  I have configured pfsense to use the device /dev/cuaU0.2 as the modem as this is teh device using the PPP command line util I can get modem information from such as:

    
    Current Time:  976          Temperature: 22
    Bootup Time:   1          Mode:        ONLINE
    System mode:   GSM             PS state:    Not attached
    GSM band:      GSM900
    GSM channel:   75
    GMM (PS) state:DEREGISTERED        PLMN SEARCH
    MM (CS) state: IDLE                NO IMSI
    
    Serving Cell:  75 (GSM 900    )
    RX level (dBm):-96.1875          LAC:         00A0 (160)
    GPRS State:    GPRS IDLE           Cell ID:     0000022A (554) 
    

    The rest of the error log snippet is below:

    Jan 1 01:17:41	ppp: [opt2_link0] CHAT: +CGDCONT=1,"IP","general.t-mobile.uk"
    Jan 1 01:17:41	ppp: [opt2_link0] CHAT: Detected Hayes compatible modem.
    Jan 1 01:17:41	ppp: [opt2_link0] CHAT: Dialing server at *99#...
    Jan 1 01:17:41	ppp: [opt2_link0] CHAT: ATDT*99#
    Jan 1 01:17:41	ppp: [opt2_link0] CHAT: Invalid dial init string.
    Jan 1 01:17:41	ppp: [opt2_link0] MODEM: chat script failed
    Jan 1 01:17:41	ppp: [opt2_link0] Link: DOWN event
    Jan 1 01:17:41	ppp: [opt2_link0] LCP: Down event
    Jan 1 01:17:41	ppp: [opt2_link0] Link: reconnection attempt 13 in 4 seconds
    

    Any help is much appreciated.

    Thanks


  • Netgate Administrator

    Reading some blog and forum posts, possibly that modem needs atd instead of atdt to dial. No idea how you'd change that but maybe you could test it from the command line.

    Steve



  • @stephenw10:

    Reading some blog and forum posts, possibly that modem needs atd instead of atdt to dial. No idea how you'd change that but maybe you could test it from the command line.

    Steve

    Thanks, I did wonder if it was something like that.

    I'll try that from the PPP term.


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