Carambola2 and gprs modem

i have problem with Carambola2 (with Openwrt) and gprs modem (sim800) connected to Carambola2 by usb/uart converter.
My network settings:

config interface ‚loopback’
option ifname ‚lo’
option proto ‚static’
option ipaddr ‚’
option netmask ‚’

config globals ‚globals’
option ula_prefix ‚fda2:3253:ccc0::/48’

config interface ‚lan’
option type ‚bridge’
option ifname ‚eth0’
option proto ‚static’
option netmask ‚’
option ip6assign ’60’
option ipaddr ‚’
option dns ‚’

config interface ‚gsm’
option proto ‚3g’
option device ‚/dev/ttyUSB0’
option service ‚gprs_only’
option apn ‚playmetric’
option dialnumber ‚99**1#’
option ipv6 ‚auto’
option auto ‚0’

config interface ‚eth’
option ifname ‚eth1’
option proto ‚dhcp’

when i do 'ifup gsm' interface goes up without problem. But when i try ping i get few positive response and OpenWRT hangs. After few seconds Carambola2 restarting.

Can you get any log messages?

That is the problem. After 'ping' hangs, i cannot do anything. Even console (by USB/UART) hangs.

Can you run an output of the log on console, and then begin pings?

You should get the last messages.