The Sierra Wireless MC8705 mPCIE modem provide HSDPA/3G wireless connectivity, these modems by default use a different 'Direct IP' primary connection method to earlier modems in the range.

We'll start by installing the udev rule (20-modem-8705.rules) in /etc/udev/rules.d from the modem rule pack

This sets up shortcut references to allow us to consistently identify which of the ttyUSBx ports do which functions

root@raspberrypi:~# ls -l /dev/modem*
lrwxrwxrwx 1 root root 7 Jan  1  1970 /dev/modemAT -> ttyUSB4
lrwxrwxrwx 1 root root 7 Jan  1  1970 /dev/modemS0 -> ttyUSB1
lrwxrwxrwx 1 root root 7 Jan  1  1970 /dev/modemS1 -> ttyUSB2
lrwxrwxrwx 1 root root 7 Jan  1  1970 /dev/modemS2 -> ttyUSB3
lrwxrwxrwx 1 root root 7 Jan  1  1970 /dev/modemS3 -> ttyUSB4

Note the absence of a modemPPP link, this is because, the modem is in a configuration mode where there is only one AT command port available on this model.

We can bring the PPP connection channel back by re-enabling it using modem configuration commands via the AT command set below :

at!entercnd="A710"
at!udusbcomp=?
at!udusbcomp=3
at!reset

Setting 2 is the default, retaining only the wwan0 direct IP interface and the single AT command port

Setting 3 gives both PPP, AT & wwan0 ports

Setting 5 is similar to setting 2 but gives an eth1 port rather than a wwan0 port.

To make a direct IP data connection the modem should be sent a series of AT commands to the modemAT port, below shows an example using minicom with the modem in setting 3

# minicom -D /dev/modemAT

In this sequence this is what each command does:

Setup profile 1 apn details:
at+cgdcont=1,"IP","pp.vodafone.co.uk"

Set profile 1 to be non-autoconnect type:
at!scprof=1,"",0,0,0,0

Manual connect statement (takes about 3 seconds to complete) :
at!scact=1,1

Check that the cellular network interface has been assigned an IP address:
at!scpaddr=1

Now when we check the interfaces we see that the connection has been established and the interface has been assigned the IP address seen above, now all we need to do is alter the routing to use the modem.

To disconnect from the network issue "at!scact=0,1" to the AT command port

In setting mode 3 the PPP interface can be used as normal (albeit at a lower data rate)

Sierra Wireless Help Note

Using MC8705 under Linux Blog Post