Modem Device Statistics RXBytes and TxBytes is always 0

[Ana Rodriguez Lopez <rodrilopez ana gmail com>]

Hi,

I am experiencing a problem with the Device.Statistics interface of my
modem. It always shows RxBytes and TxBytes equal 0.

:~# dbus-send --system --print-reply
--dest=org.freedesktop.NetworkManager
/org/freedesktop/NetworkManager/Devices/21
org.freedesktop.DBus.Properties.GetAll
string:'org.freedesktop.NetworkManager.Device.Statistics'
method return time=1517851680.451055 sender=:1.8 -> destination=:1.219
serial=57018 reply_serial=2
   array [
      dict entry(
         string "RefreshRateMs"
         variant             uint32 0
      )
      dict entry(
         string "TxBytes"
         variant             uint64 0
      )
      dict entry(
         string "RxBytes"
         variant             uint64 0
      )
   ]

:~# nmcli -f all d
DEVICE    TYPE      STATE     
DBUS-PATH                                   CONNECTION 
CON-UUID                             
CON-PATH                                           
eth0      ethernet  connected 
/org/freedesktop/NetworkManager/Devices/2   Ethernet   
66d1285e-9905-4991-99c8-25fa3b3aa08b 
/org/freedesktop/NetworkManager/ActiveConnection/70
usb0      ethernet  connected 
/org/freedesktop/NetworkManager/Devices/4   UsbHost    
66d1285e-9905-4991-99c8-25fa3b3aa08a 
/org/freedesktop/NetworkManager/ActiveConnection/1 
cdc-wdm0  gsm       connected 
/org/freedesktop/NetworkManager/Devices/21  ModemGSM   
baa2af1b-e21e-7bcf-f1ac-1a775c46ddc3 
/org/freedesktop/NetworkManager/ActiveConnection/69
sit0      iptunnel  unmanaged 
/org/freedesktop/NetworkManager/Devices/3   --         
--                                   
--                                                 
lo        loopback  unmanaged 
/org/freedesktop/NetworkManager/Devices/1   --         
--                                    --    


In `/proc/net/dev` the number of transmited an received bytes
increasesfor the wwan0 device:

Inter-|   Receive                                                |  Transmit
 face |bytes    packets errs drop fifo frame compressed
multicast|bytes    packets errs drop fifo colls carrier compressed
  sit0:       0       0    0    0    0     0          0         0       
0       0    0    0    0     0       0          0
  eth0: 3215382   30910    0    0    0     0          0         0  
970029    4037    0    0    0     0       0          0
    lo: 2574458   11351    0    0    0     0          0         0 
2574458   11351    0    0    0     0       0          0
  usb0: 6374036   32031    0    0    0     0          0         0 
5811383   25347    0    0    0     0       0          0
 wwan0:  167057     841    0    0    0     0          0         0  
358321     981    0    0    0     0       0          0


Is this broken?

Thanks,

Ana