Modem tools

Here I have two little scripts:

1. bin/modem-monitor, which uses the control connection to display (and log) runtime modem information.
2. bin/con2, to keep the connection up.

Modem monitor

The script bin/modem-monitor finds the proper ttyUSB device, reads data from it and display it. Uses the additional port, so works well with pppd etc.

Example output:

Path         : /dev/ttyUSB4
Device       : huawei E3131 rev. 21.158.13.00.209 IMEI=353101043024719
Device lock  : unlocked
RSSI / RSCP  : -95 / -91 dBm, ECIO = -3 dBm :), RSSI=9
SIM status   : valid, data only
Network      : MegaFon, CellID: 8160074, +sms, +cb, LTE
Operators    : no data
Connected for: 7:09:58 IP address: 100.127.194.46
Traffic      : 1490.83 mb received, 2496.47 mb sent
Speed        : 0.48 dl, 1.84 ul
Top speed    : 4.86 dl, 2.35 ul
Last error   : none
Last update  : 2020-03-14 20:16:48

Here you can see:

• Port being used.
• Device identification data, lock status.
• Signal quality, obtained using the best available method.
• Network status, cell ID.
• Operators (needs to be started before connecting).
• Traffic statistics, speed.
• Last update (to be sure that it doesn't just hang).

RSSI, network mode and ISP changes are logged into a separate file, which looks like this:

2020-06-20 21:34:27 19 9 4 25001
2020-06-20 21:34:37 20 9 4 25001
2020-06-20 21:34:47 17 9 4 25001
2020-06-20 21:35:07 20 9 4 25001

Connection manager

I use a mobile connection and have two SIM cards from different operators, for falback purpose. They fail at times, modem hangs, other shit happens. I got so fucked up by managing all this crap manually on my Linux server, that I wrote this little program bin/con2, which does the following:

1. Waits for a USB device with one of pre-configured ids.
2. Sends USB mode switch for devices in wrong mode.
3. Creates a symlink /dev/modem to the proper TTY.
4. Gets SIM card id, matches it to the ISP name.
5. Runs pppd to connect to the selected ISP.
6. If pppd fails due to modem error, resets the modem: first with AT^RESET, if not working -- with a USB reset.
7. Reconnects with a delay of 5 seconds.

Config file is read from ~/.config/con2.toml and looks like this:

valid_devices = [
    '12d1:1506',
]

switch_devices = [
    '12d1:14fe',
    '12d1:1f01',
]

[iccid_map]
"89701983875679234987" = "mts"

Command output:

$ bin/con2
2020-06-20 21:57:53,344 INFO Read config from /root/.config/con2.toml
2020-06-20 21:57:53,433 INFO Using device with usbid 12d1:1506 as /dev/ttyUSB0
2020-06-20 21:57:53,436 INFO Hard reset with: usbreset /dev/bus/usb/001/099
2020-06-20 21:57:53,440 INFO Sending AT^ICCID? to /dev/ttyUSB0
2020-06-20 21:57:53,940 DEBUG modem response: AT^ICCID?
2020-06-20 21:57:53,951 DEBUG modem response: ^ICCID: 89701983875679234987
2020-06-20 21:57:53,972 INFO Sim card 89701983875679234987 found, using ISP mts.
2020-06-20 21:57:56,179 INFO pppd: chat:  Jun 20 21:57:56 CONNECT
2020-06-20 21:57:56,183 INFO pppd: Script /usr/sbin/chat -v -f /etc/ppp/peers/mts.chat finished (pid 3994), status = 0x0
2020-06-20 21:57:56,188 INFO pppd: Serial connection established.
2020-06-20 21:57:56,191 INFO pppd: using channel 140
2020-06-20 21:57:56,194 INFO pppd: Using interface ppp0
2020-06-20 21:57:56,207 INFO pppd: Connect: ppp0 <--> /dev/modem
2020-06-20 21:57:57,192 INFO pppd: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x23159fd8> <pcomp> <accomp>]
2020-06-20 21:57:57,196 INFO pppd: rcvd [LCP ConfReq id=0x1 <accomp> <pcomp> <asyncmap 0x0> <mru 1500> <magic 0x548> <auth chap MD5>]
2020-06-20 21:57:57,199 INFO pppd: No auth is possible
2020-06-20 21:57:57,204 INFO pppd: sent [LCP ConfRej id=0x1 <auth chap MD5>]
2020-06-20 21:57:57,209 INFO pppd: rcvd [LCP ConfAck id=0x1 <asyncmap 0x0> <magic 0x23159fd8> <pcomp> <accomp>]
2020-06-20 21:57:57,213 INFO pppd: rcvd [LCP ConfReq id=0x2 <accomp> <pcomp> <asyncmap 0x0> <mru 1500> <magic 0x548>]
2020-06-20 21:57:57,217 INFO pppd: sent [LCP ConfAck id=0x2 <accomp> <pcomp> <asyncmap 0x0> <mru 1500> <magic 0x548>]
2020-06-20 21:57:57,222 INFO pppd: sent [IPCP ConfReq id=0x1 <addr 0.0.0.0> <ms-dns1 0.0.0.0> <ms-dns2 0.0.0.0>]
2020-06-20 21:57:57,226 INFO pppd: rcvd [IPCP ConfReq id=0x1]
2020-06-20 21:57:57,230 INFO pppd: sent [IPCP ConfNak id=0x1 <addr 0.0.0.0>]
2020-06-20 21:57:57,234 INFO pppd: rcvd [IPCP ConfNak id=0x1]
2020-06-20 21:57:57,238 INFO pppd: sent [IPCP ConfReq id=0x2 <addr 0.0.0.0> <ms-dns1 0.0.0.0> <ms-dns2 0.0.0.0>]
2020-06-20 21:57:57,242 INFO pppd: rcvd [IPCP ConfReq id=0x2]
2020-06-20 21:57:57,247 INFO pppd: sent [IPCP ConfAck id=0x2]
2020-06-20 21:57:57,249 INFO pppd: rcvd [IPCP ConfNak id=0x2 <addr 10.212.26.107> <ms-dns1 217.66.153.254> <ms-dns2 217.66.153.250>]
2020-06-20 21:57:57,250 INFO pppd: sent [IPCP ConfReq id=0x3 <addr 10.212.26.107> <ms-dns1 217.66.153.254> <ms-dns2 217.66.153.250>]
2020-06-20 21:57:57,253 INFO pppd: rcvd [IPCP ConfAck id=0x3 <addr 10.212.26.107> <ms-dns1 217.66.153.254> <ms-dns2 217.66.153.250>]
2020-06-20 21:57:57,254 INFO pppd: Could not determine remote IP address: defaulting to 10.64.64.64
2020-06-20 21:57:57,258 INFO pppd: local  IP address 10.212.26.107
2020-06-20 21:57:57,261 INFO pppd: remote IP address 10.64.64.64
2020-06-20 21:57:57,264 INFO pppd: primary   DNS address 217.66.153.254
2020-06-20 21:57:57,266 INFO pppd: secondary DNS address 217.66.153.250
2020-06-20 21:57:57,269 INFO pppd: Script /etc/ppp/ip-up started (pid 4442)
2020-06-20 21:57:57,271 INFO pppd: Script /etc/ppp/ip-up finished (pid 4442), status = 0x0

I normally run this script on an Alpine Linux server, using supervisord, with a config like this:

[program:pppd]
command = /root/bin/con2
directory = /root
autorestart = true
startsecs = 0
startretries = 1000000
restartpause = 5
user = root