Hi,
2009/11/13 Chris Pitchford <of...@intrepid.cx>:
Is the line discipline so much of an issue when using ppp connected to a
fake tty? could that not be handed on the proxy side inside ofono?
I've not tried it on a non-tty but it definitely should work modulo
potential bugs that need to be squashed. It's supposed to work.
However by using a separate process to do ppp you add overhead. The
original idea in ofono as well as in other projects (think OpenMoko)
was to have both ppp and multiplexing in the kernel to avoid the
context switches when a lot of data is being sent, but this is not
very portable and causes lots of other problems. Having both in a
single non-kernel process is going to be almost as fast and much more
portable at the expense of reimplementing part of pppd.
I've had another thought.. and it doesn't push for pppd, but it introduces
another idea.
When connecting to an APN for MMS services, there is the possibility of a
clash of IP addresses both with other APN connections and with other
internet connections (for example wifi)..
For example: wlan0 192.168.1.20/24 default gw 192.168.1.250
ppp0/tun0: 10.1.1.1 <=> 10.255.255.255
and the MMSC (to which the phone will need to communicate to send/receive
MMS) is 192.168.1.20
bam.. it clashes with a locally assigned IP address and therefore no
policy routing will allow a process to reach 192.168.1.20 via the MMS
interface (or atleast not with excessive engineering)
Other clashes may cause problems too..
To solve the problem, the MMS environment could be run in its own kernel
network name space. This means the ppp/tun interface would be separate
from the other interfaces.. this removes the clashing IP address space
problem.
If pppd were used, it could be "wrapped" in a different address space
meaning the ppp interface would be localised to an environment that
carried out all of the MMS communications. What's more, the work would
require no change to the existing global address space.. it very neatly
keeps the main environment seperate from the MMS environment that requires
its own gateway and IP address space..
I appreciate the chances of a clash are slim, but with telcos using
RFC-1918 and home users mainly using the same the chances of a clash are
far above zero (and I hear it is a problem for iphone users.. no dig at
iphones but a colleage reports seeing MMS traffic over his wireless
connection.. not confirmed but still)
So, if ofonod is responsible for creating tun interfaces, I'm not sure it
would be possible to isolate them within their own name space and
therefore allow concurrent "internet" and "mms" access via two different
connections..
I'm still formulating my thoughts on this one, but I hope it is food for
thought!
cp
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