Scripts to monitor cellular connection for 4G LTE RPi on OpenWrt

conmon.sh

#!/bin/sh

# Internet Monitoring Script for QMI Modem
# Modem: Quectel EG25-G

# Script inspired from conmon.sh in ROOter project.
# https://www.ofmodemsandmen.com/

# What is most likely to happen in my experience is modem gets a new IP from ISP, randomly, and interface does not update, therefore outbound traffic stops
# This script will cover both scenarios

# Scenario 1: Obtain new IP by forcing udhcpc to get new address. Verify address with AT command IP. If not the same, repeat until IP is the same
# Scenario 2: IPs are the same, outbound traffic not working, reset modem

# But so far, easier to only implement Scenario 2, and by that, resetting the modem when there is any connection issue

# At worst case scenario, router restart

# Define variables

GCOM_DIR="/etc/gcom"
CPORT=2
RST_CNT=0
RST_CNT_FLR=2
PKT_LOSS_FLR=40
SLEEP_TIME=30
SLEEP_PLUS=10
SLEEP_CNT=0
SLEEP_CNT_FLR=3
TRCK_IP="8.8.8.8"

# Define functions

# unused function, for now
restart_udhcpc() {

    udhcpc_pid=$(pidof udhcpc)
    /bin/kill -SIGUSR2 $(udhcpc_pid)
    /bin/kill -SIGUSR1 $(udhcpc_pid)
    
}

log() {
	logger -t "conmond" "$@"
}

get_modem_ip() {

    # run gcom script
    export ATCMD="AT+CGPADDR"
    local ATRES=$(comgt -d "/dev/ttyUSB$CPORT" -s $GCOM_DIR/run-at.gcom)

    # parse variable output, return modem IP
    local modem_ip=$(echo $ATRES | cut -d "," -s -f2 | cut -d "\"" -s -f2)

    log "Obtained Modem IP: $modem_ip using command $ATCMD"

    unset ATCMD
    echo $modem_ip

}

get_wwan0_ip() {

    local wwan0_ip=$(ip addr show wwan0 | grep 'inet ' | cut -d' ' -f6 | cut -d "/" -s -f1)
    log "Obtained wwan0 IP: $wwan0_ip"

    echo $wwan0_ip
}

reset_modem() {

    export ATCMD="AT+CFUN=4;+CFUN=1,1"
    comgt -d "/dev/ttyUSB$CPORT" -s $GCOM_DIR/run-at.gcom

    log "Modem reset with command $ATCMD"
    unset ATCMD

}

check_rsts_reboot() {

    if [ "$RST_CNT" -gt "$RST_CNT_FLR" ]; then
        log "Modem Reset $RST_CNT times failed to restart internet. Rebooting now ..."
        reboot -f
    fi

}

check_internet() {

    # Perform Ping Test to check for connectivitiy issues
    # Ping Test Fails > Obtain IP (v4) of interface and check against IP from AT command

    initial_wwan0_ip=$(get_wwan0_ip)
    pkt_loss=$(ping -c 5 $TRCK_IP | tail -2 | head -1 | awk '{print $7}' | sed 's/.$//')

    if [ -z $pkt_loss ]; then
        pkt_loss=100
    fi

    if [ "$pkt_loss" -gt "$PKT_LOSS_FLR" ]; then

        check_rsts_reboot
        RST_CNT=$((RST_CNT+1))

        log "$pkt_loss% is greater than $PKT_LOSS_FLR%, Internet Down"
        log "Initiate modem reset $RST_CNT"

        reset_modem
        sleep $SLEEP_TIME

        modem_ip=$(get_modem_ip)
        wwan0_ip=$(get_wwan0_ip)

        while [ -z "$modem_ip" ] && [ "$SLEEP_CNT" -lt "$SLEEP_CNT_FLR" ]
        do
            log "Sleep $SLEEP_PLUS until Modem IP resolves"
            sleep $SLEEP_PLUS
            modem_ip=$(get_modem_ip)
            SLEEP_CNT=$((SLEEP_CNT+1))

        done

        SLEEP_CNT=0

        while [ -z "$wwan0_ip" ] && [ "$SLEEP_CNT" -lt "$SLEEP_CNT_FLR" ]
        do
            log "Sleep $SLEEP_PLUS until wwan0 IP resolves"
            sleep $SLEEP_PLUS
            wwan0_ip=$(get_wwan0_ip)
            SLEEP_CNT=$((SLEEP_CNT+1))

        done

        if [ -z "$modem_ip" ] || [ -z "$wwan0_ip" ]; then

            check_rsts_reboot
            RST_CNT=$((RST_CNT+1))

            log "Modem IP: $modem_ip or wwan0 IP: $wwan0_ip is empty | Initiate subsequent modem reset $RST_CNT"
            reset_modem
            sleep $SLEEP_TIME

            check_internet

        elif [ "$modem_ip" = "$wwan0_ip" ]; then

            log "Modem IP: $modem_ip and wwan0 IP: $wwan0_ip match | Retest with ping"
            check_internet

        else

            check_rsts_reboot
            RST_CNT=$((RST_CNT+1))

            log "Modem IP: $modem_ip and wwan0 IP $wwan0_ip do not match | Initiate subsequent modem reset $RST_CNT"

            reset_modem
            sleep $SLEEP_TIME

            check_internet

        fi

    else

        log "Internet operational with IP: $initial_wwan0_ip"
        exit 0

    fi

}

check_internet

# be sure to write number of reconnects to file (append latest reconnect with timestamp, regardless of reconnect method used)

crontab

*/5 * * * * /etc/conmon.sh

run-at.gcom

opengt
 set com 115200n81
 set comecho off
 set senddelay 0.05
 waitquiet 1 0.2

:start
let f=25

let $x=$env("ATCMD")
if $x="" goto error
send $x
send "^m"
let t=time()+f
gosub getresult
if $s="^mTIMEOUT ERROR" print $s
:continue
exit 0

:error
print "No ATCMD var set"
exit 1

:getresult
get 1 "^m" $s
let x=len($s)
if x=0 let $s="^mTIMEOUT ERROR"
else print $s
if $s="^jOK" return
if $mid($s,0,6)="^jERROR" return
if $mid($s,0,8)="^jCOMMAND" return
if $mid($s,0,11)="^j+CME ERROR" return
if time()>t return
goto getresult