PPP to UMTS provider && incoming traffic (TCP, UDP)

[Matthias Apitz]

El día Tuesday, January 17, 2012 a las 11:43:15PM +0100, Maciej Milewski escribió:

> Dnia wtorek, 17 stycznia 2012 20:08:48 Matthias Apitz pisze:
> > Hello,
> > 
> > I'm used to connect my FreeBSD 10-CURRENT netbook to Internet via PPP;
> > the provider in question is a German O2 UMTS provider; so far so good,
> > i.e. all is working as it should: outbound HTTP, SSH, SMTP (I'm just
> > sending this mail through such a connection), ...
> > 
> > what does not work is VoIP; the call is established via SIP (using a
> > STUN server), but remote audio RTP packages are not coming down; I
> > checked this with TCPDUMP: only upstream RTP is send, no incoming UDP;
> I observed similar problem with L2TP VPN and for me it looks that they are 
> blocking incoming/returning UDP traffic in public APN.
> On the server side I see both incoming and outgoing traffic but device 
> complains that it's unable to connect. If I switch to local wireless network 
> then everthing works fine. I suspect that's because they are selling 
> special(money) APNs.

Thanks for your feedback; I think too, that UDP downstream is blocked if
there is not upstream UDP initialized for the same socket pair; and VoIP
is using different UDP ports for up- and downstream media (audio).

What I'm wondering is, how does Skype works (which is fine with my UMTS
provider at the same time), have to check this with TCPDUMP...

	matthias
-- 
Matthias Apitz
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