Raspberry Pi /etc/network/interfaces with Sierra Wireless 305

connect

''	at+cfun=1
OK	at+cgdcont=3,"IP","tfdata"
OK	at!scdftprof=3
OK	at!scprof=3,"",0,0,0,0
OK	at!scact=1,3
OK

disconnect

''	at!scact=0,3
OK

interfaces

auto lo 
iface lo inet loopback

auto eth0
allow-hotplug eth0 
iface eth0 inet dhcp

auto wlan0
allow-hotplug wlan0
iface wlan0 inet dhcp 
wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf
iface default inet dhcp

auto wwan0
allow-hotplug wwan0
iface wwan0 inet dhcp
	pre-up /etc/modemctl/modem-up.sh
	post-down /etc/modemctl/modem-down.sh

modem-down.sh

#!/bin/sh
set -eu

echo 'modem-down: Shutting down modem'
sudo chat -e -f /etc/modemctl/disconnect < /dev/ttyUSB2 > /dev/ttyUSB2

modem-up.sh

#!/bin/sh
set -eu

echo 'modem-up: Starting modem'
sudo chat -e -f /etc/modemctl/connect < /dev/ttyUSB2 > /dev/ttyUSB2