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skl 08-14-2011 05:37 PM
Cannot establish a ppp link over a gsm 0710 mux (n_gsm) tty
 
Hello

I have a GSM modem (UBLOX Leon100) that I want to be able to receive SMS and keep a data connection using ppp - concurrently. So I have setup the n_gsm module according to the nice description (n_gsm.txt) found with 3.0.1. kernel release. I am using the n_gsm module from this release. My linux host is a Freescale IMX25 ARM based unit.

At first glance this works fine because I am able to create four virtual ttys (ttygsm1-4) from my physical tty. I can, concurrently, fire up four minicom terminals on each virtual tty and launch AT commands with no problem.

---

Welcome to minicom 2.2

OPTIONS: I18n
Compiled on Aug 10 2011, 13:08:56.
Port /dev/ttygsm4

Press CTRL-A Z for help on special keys
at+fmm
LEON-G100

OK

---

HOWEVER, when I want to fire up pppd (here using service wrapper) on a single virtual tty (/dev/ttygsm4) it fails. If I enable debug and dump in /etc/ppp/options this is what the log says:

root@InnBox-NOIID ~$ /etc/rc.d/init.d/ppp start
Starting the ppp daemon:
pppd options in effect:
debug # (from /etc/ppp/options)
dump # (from /etc/ppp/options)
/dev/ttygsm4 # (from /etc/ppp/peers/gprs)
115200 # (from /etc/ppp/peers/gprs)
lock # (from /etc/ppp/options)
connect /etc/ppp/chat/gprs-chat.sh # (from /etc/ppp/peers/gprs)
crtscts # (from /etc/ppp/options)
noaccomp # (from /etc/ppp/peers/gprs)
nopcomp # (from /etc/ppp/peers/gprs)
novj # (from /etc/ppp/peers/gprs)
novjccomp # (from /etc/ppp/peers/gprs)
noipdefault # (from /etc/ppp/peers/gprs)
defaultroute # (from /etc/ppp/peers/gprs)
usepeerdns # (from /etc/ppp/peers/gprs)
nobsdcomp # (from /etc/ppp/peers/gprs)

root@InnBox-NOIID ~$ cat /var/log/messages
(...)
Jan 1 01:28:45 InnBox-NOIID local2.info chat[1008]: send (ATDT*99***1#^M)
Jan 1 01:28:45 InnBox-NOIID local2.info chat[1008]: expect (CONNECT)
Jan 1 01:28:45 InnBox-NOIID local2.info chat[1008]: ^M
Jan 1 01:28:45 InnBox-NOIID local2.info chat[1008]: ATDT*99***1#^M^M
Jan 1 01:28:45 InnBox-NOIID local2.info chat[1008]: CONNECT
Jan 1 01:28:45 InnBox-NOIID local2.info chat[1008]: -- got it
Jan 1 01:28:45 InnBox-NOIID local2.info pppd[1000]: Serial connection established.
Jan 1 01:28:45 InnBox-NOIID local2.debug pppd[1000]: using channel 21
Jan 1 01:28:45 InnBox-NOIID local2.info pppd[1000]: Using interface ppp0
Jan 1 01:28:45 InnBox-NOIID local2.notice pppd[1000]: Connect: ppp0 <--> /dev/ttygsm4
Jan 1 01:28:45 InnBox-NOIID user.debug kernel: [ 5325.550000] PM: Adding info for No Bus:ppp0
Jan 1 01:28:46 InnBox-NOIID local2.debug pppd[1000]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0xe9d66b93>]
Jan 1 01:28:49 InnBox-NOIID local2.debug pppd[1000]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0xe9d66b93>]
Jan 1 01:28:52 InnBox-NOIID local2.debug pppd[1000]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0xe9d66b93>]
Jan 1 01:28:55 InnBox-NOIID local2.debug pppd[1000]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0xe9d66b93>]
Jan 1 01:28:58 InnBox-NOIID local2.debug pppd[1000]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0xe9d66b93>]
Jan 1 01:29:01 InnBox-NOIID local2.debug pppd[1000]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0xe9d66b93>]
Jan 1 01:29:04 InnBox-NOIID local2.debug pppd[1000]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0xe9d66b93>]
Jan 1 01:29:07 InnBox-NOIID local2.debug pppd[1000]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0xe9d66b93>]
Jan 1 01:29:10 InnBox-NOIID local2.debug pppd[1000]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0xe9d66b93>]
Jan 1 01:29:13 InnBox-NOIID local2.debug pppd[1000]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0xe9d66b93>]
Jan 1 01:29:16 InnBox-NOIID local2.warn pppd[1000]: LCP: timeout sending Config-Requests
Jan 1 01:29:16 InnBox-NOIID local2.notice pppd[1000]: Connection terminated.
Jan 1 01:29:16 InnBox-NOIID user.debug kernel: [ 5356.600000] PM: Removing info for No Bus:ppp0
Jan 1 01:29:17 InnBox-NOIID local2.notice pppd[1000]: Modem hangup
Jan 1 01:29:17 InnBox-NOIID local2.debug pppd[1000]: LCP: Down event in state 1!
Jan 1 01:29:17 InnBox-NOIID local2.info pppd[1000]: Exit.

---

As can be seen the chat script successfully reaches the CONNECT (yes, AT commands also works on virtual ttys) but after this there is no answer to the LCP ConfReq, and eventually a timeout occurs.

Changing tty parameter from virtual tty (/dev/ttygsm4) to physical tty (/dev/ttymxc2) have the result that pppd works fine with this configuration on the physical tty (no muxing, obviously)

(The physical tty is configured for HW handshaking in accordance with the pppd crtscts setting)

To get closer to understanding this we setup a testing environment to log all bytes on each side of the serial line where COM4 is the host imx25 and COM20 is the GSM UBLOX LEON 100.

The interesting part is the last part around where the LCP ConfReq are send - wrapped in the gsm 0710 protocol with F9 start stop frames.
---

8/12/2011 12:46:02.708 [COM4] - 41
8/12/2011 12:46:02.709 [COM20] - 41 54 0D
8/12/2011 12:46:02.756 [COM4] - 54 0D 0D 0A 4F 4B 0D 0A 41
8/12/2011 12:46:02.853 [COM20] - 41
8/12/2011 12:46:02.868 [COM4] - 54
8/12/2011 12:46:02.869 [COM20] - 54 0D
8/12/2011 12:46:02.900 [COM4] - 0D 0D 0A 4F 4B 0D 0A 41
8/12/2011 12:46:09.841 [COM20] - 41
8/12/2011 12:46:09.857 [COM4] - 54
8/12/2011 12:46:09.857 [COM20] - 54 0D
8/12/2011 12:46:09.889 [COM4] - 0D 0D 0A 4F 4B 0D 0A 41 54
8/12/2011 12:46:10.081 [COM20] - 41 54 2B 43 4D
8/12/2011 12:46:10.129 [COM4] - 2B 43 4D
8/12/2011 12:46:10.129 [COM20] - 55 58
8/12/2011 12:46:10.145 [COM4] - 55 58 3D
8/12/2011 12:46:10.145 [COM20] - 3D 30 2C
8/12/2011 12:46:10.177 [COM4] - 30 2C
8/12/2011 12:46:10.177 [COM20] - 30 2C 30
8/12/2011 12:46:10.209 [COM4] - 30 2C 30
8/12/2011 12:46:10.209 [COM20] - 2C
8/12/2011 12:46:10.225 [COM4] - 2C 31 32
8/12/2011 12:46:10.225 [COM20] - 31 32 37 2C
8/12/2011 12:46:10.257 [COM4] - 37 2C
8/12/2011 12:46:10.257 [COM20] - 32 35 33 2C
8/12/2011 12:46:10.305 [COM4] - 32 35 33 2C 33
8/12/2011 12:46:10.306 [COM20] - 33 2C 32 35 34
8/12/2011 12:46:10.337 [COM4] - 2C 32 35
8/12/2011 12:46:10.353 [COM20] - 2C 30 2C
8/12/2011 12:46:10.369 [COM4] - 34 2C 30
8/12/2011 12:46:10.384 [COM20] - 30 0D
8/12/2011 12:46:10.385 [COM4] - 2C 30 0D 0D 0A 4F 4B 0D 0A
8/12/2011 12:46:13.462 [COM20] - F9 03 3F 01 1C F9
8/12/2011 12:46:13.495 [COM4] - F9 03 73 01 D7 F9
8/12/2011 12:46:14.516 [COM20] - F9 07 3F 01 DE F9 F9 03 EF 09 E3 05 07 0D FB F9 F9 03 EF 09 E3 05 07 01 FB F9 F9 07 53 01 3F F9
8/12/2011 12:46:14.580 [COM4] - F9 07 73 01 15 F9 F9 01 EF 09 E1 05 07 0D 9A F9 F9 01 EF 09 E1 05 07 01 9A F9
8/12/2011 12:46:14.612 [COM20] - F9 0B 3F 01 59 F9
8/12/2011 12:46:14.627 [COM4] - F9 0B 73 01 92 F9 F9 01 EF 09 E1 05 0B 0D 9A F9
8/12/2011 12:46:14.628 [COM20] - F9 03 EF 09 E3 05 0B 0D FB F9 F9 03 EF 09 E3 05 0B 01 FB F9 F9 0B 53 01 B8 F9
8/12/2011 12:46:14.660 [COM4] - F9 01 EF 09 E1 05 0B 01 9A F9
8/12/2011 12:46:14.676 [COM20] - F9 07 53 01 3F F9 F9 0F 3F 01 9B F9 F9 03 EF 09 E3 05 0F 0D FB F9
8/12/2011 12:46:14.708 [COM4] - F9 0F 73 01 50 F9 F9 01 EF 09 E1 05 0F 0D 9A F9
8/12/2011 12:46:14.724 [COM20] - F9 03 EF 09 E3 05 0F 01 FB F9 F9 0F 53 01 7A F9
8/12/2011 12:46:14.740 [COM4] - F9 01 EF 09 E1 05 0F 01 9A F9
8/12/2011 12:46:14.756 [COM20] - F9 0B 53 01 B8 F9 F9 07 53 01 3F F9 F9 13 3F 01 96 F9 F9 03 EF 09 E3 05 13 0D FB F9
8/12/2011 12:46:14.788 [COM4] - F9 13 73 01 5D F9 F9 01 EF 09 E1 05 13 0D 9A F9
8/12/2011 12:46:14.820 [COM20] - F9 03 EF 09 E3 05 13 01 FB F9 F9 0F 53 01 7A F9
8/12/2011 12:46:14.836 [COM4] - F9 01 EF 09 E1 05 13 01 9A F9
8/12/2011 12:46:14.852 [COM20] - F9 13 53 01 77 F9 F9 0B 53 01 B8 F9 F9 0F 53 01 7A F9 F9 13 53 01 77 F9 F9 13 53 01 77 F9 F9 13 3F 01 96 F9 F9 03 EF 09 E3 05 13 0D FB F9
8/12/2011 12:46:24.764 [COM4] - F9 01 EF 09 E1 05 13 0D 9A F9 F9 13 73 01 5D F9 F9 13 1F 01 BC F9 F9 13 1F 01 BC F9 F9 13 73 01 5D F9 F9 03 EF 09 E1 05 13 0D FB F9
8/12/2011 12:46:24.779 [COM20] - F9 03 EF 09 E3 05 13 05 FB F9
8/12/2011 12:46:24.796 [COM4] - F9 01 EF 09 E1 05 13 05 9A F9
8/12/2011 12:46:24.811 [COM20] - F9 03 EF 09 E3 05 13 01 FB F9
8/12/2011 12:46:24.812 [COM4] - F9 01 EF 09 E1 05 13 01 9A F9
8/12/2011 12:46:25.844 [COM20] - F9 03 EF 09 E3 05 13 0D FB F9
8/12/2011 12:46:25.862 [COM4] - F9 01 EF 09 E1 05 13 0D 9A F9
8/12/2011 12:46:25.972 [COM20] - 41 54 2B 43 50 49 4E 3F 0D F9 13 EF 03 41 9C F9 F9 13 EF 03 54 9C F9
8/12/2011 12:46:26.102 [COM4] - F9 11 EF 03 41 FD F9
8/12/2011 12:46:26.116 [COM20] - F9 13 EF 03 5A 9C F9
8/12/2011 12:46:26.118 [COM4] - F9 11 EF 03 54 FD F9 F9 11 EF 03 5A FD F9 F9 11 EF 03 0D FD F9 F9 01 EF 0B E3 07 13 0C 01 79 F9 F9 11 EF 0D 0D 0A 4F 4B 0D 0A 17 F9
8/12/2011 12:46:26.164 [COM20] - F9 13 EF 03 0D 9C F9 F9 03 EF 0B E1 07 13 0C 01 18 F9 F9 13 EF 03 41 9C F9 F9 13 EF 03 54 9C F9
8/12/2011 12:46:26.201 [COM4] - F9 11 EF 03 41 FD F9
8/12/2011 12:46:26.218 [COM20] - F9 13 EF 03 0D 9C F9
8/12/2011 12:46:26.234 [COM4] - F9 11 EF 03 54 FD F9 F9 11 EF 03 0D FD F9 F9 11 EF 0D 0D 0A 4F 4B 0D 0A 17 F9
8/12/2011 12:46:26.260 [COM20] - F9 13 EF 03 41 9C F9 F9 13 EF 03 54 9C F9
8/12/2011 12:46:26.283 [COM4] - F9 11 EF 03 41 FD F9 F9 11 EF 03 54 FD F9
8/12/2011 12:46:26.295 [COM20] - F9 13 EF 03 2B 9C F9 F9 13 EF 03 43 9C F9
8/12/2011 12:46:26.315 [COM4] - F9 11 EF 03 2B FD F9 F9 11 EF 03 43 FD F9
8/12/2011 12:46:26.326 [COM20] - F9 13 EF 03 46 9C F9 F9 13 EF 03 55 9C F9
8/12/2011 12:46:26.343 [COM4] - F9 11 EF 03 46 FD F9 F9 11 EF 03 55 FD F9 F9 11 EF 03 4E FD F9
8/12/2011 12:46:26.375 [COM20] - F9 13 EF 03 4E 9C F9 F9 13 EF 03 3D 9C F9 F9 13 EF 03 31 9C F9
8/12/2011 12:46:26.394 [COM4] - F9 11 EF 03 3D FD F9 F9 11 EF 03 31 FD F9
8/12/2011 12:46:26.404 [COM20] - F9 13 EF 03 0D 9C F9
8/12/2011 12:46:26.422 [COM4] - F9 11 EF 03 0D FD F9 F9 11 EF 0D 0D 0A 4F 4B 0D 0A 17 F9
8/12/2011 12:46:26.452 [COM20] - F9 13 EF 03 0D 9C F9
8/12/2011 12:46:26.470 [COM4] - F9 11 EF 03 0D FD F9
8/12/2011 12:46:31.480 [COM20] - F9 13 EF 03 41 9C F9 F9 13 EF 03 54 9C F9 F9 13 EF 03 5A 9C F9
8/12/2011 12:46:31.515 [COM4] - F9 11 EF 03 41 FD F9 F9 11 EF 03 54 FD F9
8/12/2011 12:46:31.528 [COM20] - F9 13 EF 03 0D 9C F9
8/12/2011 12:46:31.547 [COM4] - F9 11 EF 03 5A FD F9 F9 11 EF 03 0D FD F9 F9 11 EF 0D 0D 0A 4F 4B 0D 0A 17 F9
8/12/2011 12:46:31.576 [COM20] - F9 13 EF 03 41 9C F9 F9 13 EF 03 54 9C F9
8/12/2011 12:46:31.595 [COM4] - F9 11 EF 03
8/12/2011 12:46:31.608 [COM20] - F9 13 EF 03 0D 9C F9
8/12/2011 12:46:31.611 [COM4] - 41 FD F9 F9 11 EF 03 54 FD F9 F9 11 EF 03 0D FD F9 F9 11 EF 0D 0D 0A 4F 4B 0D 0A 17 F9
8/12/2011 12:46:31.656 [COM20] - F9 13 EF 03 41 9C F9 F9 13 EF 03 54 9C F9 F9 13 EF 03 2B 9C F9
8/12/2011 12:46:31.691 [COM4] - F9 11 EF 03 41 FD F9 F9 11 EF 03 54 FD F9
8/12/2011 12:46:31.704 [COM20] - F9 13 EF 03 43 9C F9 F9 13 EF 03 47 9C F9
8/12/2011 12:46:31.723 [COM4] - F9 11 EF 03 2B FD F9 F9 11 EF 03 43 FD F9
8/12/2011 12:46:31.736 [COM20] - F9 13 EF 03 44 9C F9
8/12/2011 12:46:31.739 [COM4] - F9 11 EF 03 47 FD F9
8/12/2011 12:46:31.752 [COM20] - F9 13 EF 03 43 9C F9 F9 13 EF 03 4F 9C F9
8/12/2011 12:46:31.771 [COM4] - F9 11 EF 03 44 FD F9 F9 11 EF 03 43 FD F9
8/12/2011 12:46:31.800 [COM20] - F9 13 EF 03 4E 9C F9
8/12/2011 12:46:31.803 [COM4] - F9 11 EF 03 4F FD F9 F9 11 EF 03 4E FD F9
8/12/2011 12:46:31.816 [COM20] - F9 13 EF 03 54 9C F9
8/12/2011 12:46:31.819 [COM4] - F9 11 EF 03 54 FD F9
8/12/2011 12:46:31.833 [COM20] - F9 13 EF 03 3D 9C F9 F9 13 EF 03 31 9C F9 F9 13 EF 03 2C 9C F9
8/12/2011 12:46:31.851 [COM4] - F9 11 EF 03 3D FD F9 F9 11 EF 03 31 FD F9
8/12/2011 12:46:31.880 [COM20] - F9 13 EF 03 22 9C F9
8/12/2011 12:46:31.883 [COM4] - F9 11 EF 03 2C FD F9
8/12/2011 12:46:31.897 [COM20] - F9 13 EF 03 49 9C F9
8/12/2011 12:46:31.899 [COM4] - F9 11 EF 03 22 FD F9 F9 11 EF 03 49 FD F9
8/12/2011 12:46:31.915 [COM20] - F9 13 EF 03 50 9C F9 F9 13 EF 03 22 9C F9 F9 13 EF 03 2C 9C F9
8/12/2011 12:46:31.947 [COM4] - F9 11 EF 03 50 FD F9 F9 11 EF 03 22 FD F9 F9
8/12/2011 12:46:31.960 [COM20] - F9 13 EF 03 22 9C F9
8/12/2011 12:46:31.963 [COM4] - 11 EF 03 2C FD F9
8/12/2011 12:46:31.976 [COM20] - F9 13 EF 03 6D 9C F9
8/12/2011 12:46:31.979 [COM4] - F9 11 EF 03 22 FD F9 F9 11 EF 03 6D FD F9
8/12/2011 12:46:31.992 [COM20] - F9 13 EF 03 64 9C F9 F9 13 EF 03 61 9C F9
8/12/2011 12:46:32.011 [COM4] - F9 11 EF 03 64 FD F9 F9 11 EF 03 61 FD F9
8/12/2011 12:46:32.024 [COM20] - F9 13 EF 03 2E 9C F9
8/12/2011 12:46:32.027 [COM4] - F9 11 EF 03 2E FD F9
8/12/2011 12:46:32.040 [COM20] - F9 13 EF 03 69 9C F9 F9 13 EF 03 74 9C F9
8/12/2011 12:46:32.059 [COM4] - F9 11 EF 03 69 FD F9 F9 11 EF 03 74 FD F9
8/12/2011 12:46:32.072 [COM20] - F9 13 EF 03 73 9C F9 F9 13 EF 03 70 9C F9
8/12/2011 12:46:32.091 [COM4] - F9 11 EF 03 73 FD F9 F9 11 EF 03 70 FD F9 F9 11 EF 03 6C FD F9
8/12/2011 12:46:32.108 [COM20] - F9 13 EF 03 6C 9C F9 F9 13 EF 03 61 9C F9 F9 13 EF 03 74 9C F9
8/12/2011 12:46:32.138 [COM4] - F9 11 EF 03 61 FD F9 F9 11 EF 03 74 FD F9
8/12/2011 12:46:32.169 [COM20] - F9 13 EF 03 66 9C F9 F9 13 EF 03 6F 9C F9
8/12/2011 12:46:32.173 [COM4] - F9 11 EF 03 66 FD F9
8/12/2011 12:46:32.185 [COM20] - F9 13 EF 03 72 9C F9
8/12/2011 12:46:32.187 [COM4] - F9 11 EF 03 6F FD F9 F9 11 EF 03 72
8/12/2011 12:46:32.216 [COM20] - F9 13 EF 03 6D 9C F9 F9 13 EF 03 2E 9C F9 F9 13 EF 03 64 9C F9 F9 13 EF 03 6B 9C F9
8/12/2011 12:46:32.260 [COM4] - FD F9 F9 11 EF 03 6D FD F9 F9 11 EF 03 2E FD F9 F9 11 EF 03 64 FD F9 F9 11 EF 03 6B FD F9 F9 11 EF 03 22 FD F9
8/12/2011 12:46:32.280 [COM20] - F9 13 EF 03 22 9C F9 F9 13 EF 03 0D 9C F9
8/12/2011 12:46:32.315 [COM4] - F9 11 EF 03 0D FD F9 F9 11 EF 0D 0D 0A 4F 4B 0D 0A 17 F9
8/12/2011 12:46:32.328 [COM20] - F9 13 EF 03 41 9C F9 F9 13 EF 03 54 9C F9 F9 13 EF 03 44 9C F9
8/12/2011 12:46:32.363 [COM4] - F9 11 EF 03 41 FD F9 F9 11 EF 03 54 FD F9
8/12/2011 12:46:32.376 [COM20] - F9 13 EF 03 54 9C F9 F9 13 EF 03 2A 9C F9 F9 13 EF 03 39 9C F9
8/12/2011 12:46:32.402 [COM4] - F9 11 EF 03 44 FD F9 F9 11 EF 03 54 FD F9 F9 11 EF 03 2A FD F9
8/12/2011 12:46:32.410 [COM20] - F9 13 EF 03 39 9C F9 F9 13 EF 03 2A 9C F9
8/12/2011 12:46:32.428 [COM4] - F9 11 EF 03 39 FD F9 F9 11 EF 03 39 FD F9
8/12/2011 12:46:32.442 [COM20] - F9 13 EF 03 2A 9C F9 F9 13 EF 03 2A 9C F9
8/12/2011 12:46:32.460 [COM4] - F9 11 EF 03 2A FD F9 F9 11 EF 03 2A FD F9
8/12/2011 12:46:32.474 [COM20] - F9 13 EF 03 31 9C F9
8/12/2011 12:46:32.476 [COM4] - F9 11 EF 03 2A FD F9
8/12/2011 12:46:32.490 [COM20] - F9 13 EF 03 23 9C F9 F9 13 EF 03 0D 9C F9
---> CONNECT from GSM UBLOX modem
8/12/2011 12:46:32.508 [COM4] - F9 11 EF 03 31 FD F9 F9 11 EF 03 23 FD F9 F9 11 EF 03 0D FD F9 F9 01 EF 0B E3 07 13 8C 01 79 F9 F9 01 EF 0B E3 07 13 86 01 79 F9 F9 11 EF 17 0D 0A 43 4F 4E 4E 45 43 54 0D 0A E6 F9
8/12/2011 12:46:32.554 [COM20] - F9 03 EF 0B E1 07 13 8C 01 18 F9 F9 03 EF 0B E1 07 13 86 01 18 F9
8/12/2011 12:46:32.556 [COM4] - F9 01 EF 0B E3 07 13 8C 01 79 F9
8/12/2011 12:46:32.571 [COM20] - F9 03 EF 0B E1 07 13 8C 01 18 F9 F9 03 EF 09 E3 05 13 05 FB F9
8/12/2011 12:46:33.610 [COM4] - F9 01 EF 09 E1 05 13 05 9A F9
---> host imx sends 10 LCP ConfReqs - they are never received at the GSM Ublox modem side
8/12/2011 12:46:34.614 [COM20] - F9 13 EF 5B 7E FF 7D 23 C0 21 7D 21 7D 21 7D 20 7D 34 7D 21 7D 24 7D 21 28 7D 22 7D 26 7D 20 7D 20 7D 20 7D 20 7D 25 7D 26 88 95 8C 9D 36 7D 20 7E FE F9 F9 13 EF 5B 7E FF 7D 23 C0 21 7D 21 7D 21 7D 20 7D 34 7D 21 7D 24 7D 21 28 7D 22 7D 26 7D 20 7D 20 7D 20 7D 20 7D 25 7D 26 88 95 8C 9D 36 7D 20 7E FE F9 F9 13 EF 5B 7E FF 7D 23 C0 21 7D 21 7D 21 7D 20 7D 34 7D 21 7D 24 7D 21 28 7D 22 7D 26 7D 20 7D 20 7D 20 7D 20 7D 25 7D 26 88 95 8C 9D 36 7D 20 7E FE F9 F9 13 EF 5B 7E FF 7D 23 C0 21 7D 21 7D 21 7D 20 7D 34 7D 21 7D 24 7D 21 28 7D 22 7D 26 7D 20 7D 20 7D 20 7D 20 7D 25 7D 26 88 95 8C 9D 36 7D 20 7E FE F9 F9 13 EF 5B 7E FF 7D 23 C0 21 7D 21 7D 21 7D 20 7D 34 7D 21 7D 24 7D 21 28 7D 22 7D 26 7D 20 7D 20 7D 20 7D 20 7D 25 7D 26 88 95 8C 9D 36 7D 20 7E FE F9 F9 13 EF 5B 7E FF 7D 23 C0 21 7D 21 7D 21 7D 20 7D 34 7D 21 7D 24 7D 21 28 7D 22 7D 26 7D 20 7D 20 7D 20 7D 20 7D 25 7D 26 88 95 8C 9D 36 7D 20 7E FE F9 F9 13 EF 5B 7E FF 7D 23 C0 21 7D 21 7D 21 7D 20 7D 34 7D 21 7D 24 7D 21 28 7D 22 7D 26 7D 20 7D 20 7D 20 7D 20 7D 25 7D 26 88 95 8C 9D 36 7D 20 7E FE F9 F9 13 EF 5B 7E FF 7D 23 C0 21 7D 21 7D 21 7D 20 7D 34 7D 21 7D 24 7D 21 28 7D 22 7D 26 7D 20 7D 20 7D 20 7D 20 7D 25 7D 26 88 95 8C 9D 36 7D 20 7E FE F9 F9 13 EF 5B 7E FF 7D 23 C0 21 7D 21 7D 21 7D 20 7D 34 7D 21 7D 24 7D 21 28 7D 22 7D 26 7D 20 7D 20 7D 20 7D 20 7D 25 7D 26 88 95 8C 9D 36 7D 20 7E FE F9 F9 13 EF 5B 7E FF 7D 23 C0 21 7D 21 7D 21 7D 20 7D 34 7D 21 7D 24 7D 21 28 7D 22 7D 26 7D 20 7D 20 7D 20 7D 20 7D 25 7D 26 88 95 8C 9D 36 7D 20 7E FE F9 F9 03 EF 09 E3 05 13 01 FB F9
8/12/2011 12:47:04.576 [COM4] - F9 01 EF 0B E3 07 13 8C 01 79 F9 F9 01 EF 09 E1 05 13 01 9A F9 F9 11 EF 0D 0D 0A 4F 4B 0D 0A 17 F9 F9 03 EF 09 E1 05 13 01 FB F9
8/12/2011 12:47:04.585 [COM20] - F9 03 EF 0B E1 07 13 8C 01 18 F9

---

Since I'm not really an expert in the gsm 3GPP TS 07.10 protocol here are my questions: Why are the LCP ConfReq never received on the GSM Ublox modem? Us it due to the 0710 protocol, e.g some n_gsm control channel signaling? Is it due to a missing pppd setting? Is it a ppp kernel or application issue? Or is it a bug in the GSM modem SW?
Has anybody had a successful experience in setting up a ppp connection from a host to a GSM UBLOX modem (or another modem) using muxed ttys?

Any help or hint to solving this issue is highly appreciated!

Thank you!

Svend Lindholm

Software Architect

Inntrasys
Email skl@inntrasys.com
Web www.inntrasys.com

skl 08-16-2011 04:21 AM
One update to narrow down the search for answers:

Looking at the 07.10 protocol trace it seems that the linux host (imx25) sends a Modem Status Command to the GSM modem with the following contents:

Modem Status Command CR=1
Lngt=2
DCLI=4
EA=1, FC=0, RTC=1, RTR=0, IC=1, DV=1

I have no clue of the origin - but - apparently - this Modem Status Command tells the GSM modem to be silent. Nevertheless pppd continues to send LCP ConfReqs afterwards, could it be when switching from inline chat (AT commands) to binary ppp protocol that the issue occurs?

Seems like all the modules pppd, n_gsm, chat works fine on a module base - but when integrated they fail...

skl 08-17-2011 02:02 PM
Another finding:

If I leave out the following lines in pppd (2.2.4) it works.
[connect_tty () in tty.c]

(...)
/* set line speed, flow control, etc.;
clear CLOCAL if modem option */
#if 0
if (real_ttyfd != -1)
set_up_tty(real_ttyfd, 0);
#endif
(...)

Regarding a root cause fix I am not sure and I need some advice.

Is it a new flag for pppd (e.g. nottyreconfig) which is true for muxed ttys, and false otherwise, or is it at kernel level (n_gsm) where n_gsm somehow re-initiates the connection?

I would imagine the latter to make the fix apply for any app using a muxed tty.

bpringlemeir 07-06-2012 09:54 AM
Some suggestions.
 
The 'n_gsm' module has a parameter 'debug'. You can set it through /sys/modules/n_gsm/parameters/debug. Try the value '2' and it should ignore DCD status. Also, you can use noctrrts. You might also need to configure your modem with 'AT' commands to ignore these lines as well as DTR. Finally, there is usually AT+CGDCONT and AT+CGATT that you may need to use. Your network topology is not entirely clear. Usually, your gsm modem will connect to the ISPs network. You have to know what the data mode is for the AT+CGDCONT command. Are you IP,IPV6,PPP,etc? You can try the pppd 'passive' option and see if the remove side sends you anything.

Hope some of that help.

edit: I guess it is not the AT+CGATT and AT+CGDCONT as your connection works with the pppd commented. It is definitely the pppd configuration or the remote GSM config. Try 'AT&D', etc and pppd commands like 'local', 'nocrtscts', etc.

freedreamer 02-21-2013 01:16 PM
Hi guys ,

Same problem here... trying to enable n_gsm on fedora 16 with pppd but no luck.
The pppd works correctly if used without the mux.

Any ideas? I've been using wvdial to set up the pppd.

Marco

pragma 02-27-2015 06:52 PM
I have encountered the same problem with a Telit GE865 QUAD modem mounted on an embedded ISEE board.
In CMUX mode the modem wouldn't reply to LCP config requests.

I have solved it by using the Svend's hint about the set_up_tty() call in pppd. It turns out that
the offending call is actually setdtr(tty_fd, 1) at the beginning of set_up_tty(). It's called
twice: once before the chat script and once after the chat script. The second call seems to
freak out the modem somehow. I simply disabled the call when the local flag is set to 0 (the second time)
and it started to work.

Another hint: newer versions of the Telit modem firmware seem to support the AT#CMUXMODE command
which can disable sensitivity to DTR changes when CMUX is in effect. I haven't had the opportunity
to try it myself as updating the firmware was not an option but I think it might help too.

--

Szymon Tomasz Stefanek

zanget 02-15-2017 08:53 AM
hi, skl
im facing the same problem exactly as you have done, as the log reads :
LCP: timeout sending Config-Requests
but it doesnot work with your magic by modify connect_tty.


I just want to know, how did you find out :
it seems that the linux host (imx25) sends a Modem Status Command to the GSM modem with the following contents:

Modem Status Command CR=1
Lngt=2
DCLI=4
EA=1, FC=0, RTC=1, RTR=0, IC=1, DV=1

what's the clue???


thanks in advance.


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