how network-manager chose connection?

[Pierre-Marie Coron <pierremarie coron gmail com>]

Hello everybody,

I'm just coming from forum.ubuntu-fr.org (topic :
http://forum.ubuntu-fr.org/viewtopic.php?pid=3589852#p3589852 for
french users) and the suggest me to ask my question here.
I explain my problem : I'm using ubuntu 10.04 and I have 3 way to
connect to internet  : one though a network area connected to a
satellite modem, one is using a GPRS key and the last one is using a
56K modem.
The connection though satellite modem has a speed witch decrease
according to the data volume exchange.
I noticed that network-manager chose the kind of connection according
to the speed and so prefer use an ethernet connection than use a
wireless connection if both are avialable.
Can we change this order? Or can we affect a kind of connection for a
kind of software?
I want to make a proxy server who chose the connection according to
the aviability of it or the kind of protocol witch is using.
For exemple instant messaging don't need a big bandwidth but streaming
yes so  instant messaging could be used though 56k modem or GPRS key
instead of  using the ethernet connection.
I already see documentation about QoS software like wondershaper but
it is made for one connection.
I hope my message is clear and i apologize for my poor English.

Best regards

PM