[asterisk-users] VPN As SIP Tunneling?

[Anselm Martin Hoffmeister]

Am Montag, den 11.12.2006, 18:48 -0500 schrieb Barry Fawthrop:
> Hi Anselm
> Thanks for your input
> Yes I was thinking of using OpenVPN so it was good to hear your experiences
> I'm not so much concerned with the encryption of traffic etc..
> But the Level of QoS.
> If my IP Phone set QoS and the VoIP Termination provider's * PBX sets QoS
> 
> And we now connected via a VPN tunnel. We should be able to guarantee 
> Quality due to the Tunnel.

No, that is not true because you have no control over the tunnel
packets. For an analogy, you can buy yourself first-class tickets for a
transatlantic flight, but that will not help the plane you sit in to
skip queue on the airport to take off earlier. You still have to rely on
the underlying transport.

> The main issue is would I expect a higher latency ?

Compared to non-VPN: Yes, latency is to be expected a little higher. It
will probably not matter much though because it should be a magnitude
smaller of the latency incurred by DSL links and the like. Someone
(googled for numbers) claims the typical increase in roundtrip time to
be less than 5 msec.

> and (2) If I were using a 1 Mbps connect would I have less bandwidth due 
> to overheads. That where I could do
> 8 concurrent calls x 115 bps 920 kbps  I could now only do 6  or will I 
> still be able to do 8 ?

I cannot say. I would expect a bandwidth overhead of 7% to 8%, from the
numbers I saw on the web, so 7 streams could be OK, _possibly_ 8. You
will have to try out.

A question though is why you have 115kpbs/call/sec - that is quite
significantly above ISDN call quality (64kbps/call/sec). You could
always use less "fat" codecs... if your phones support those.
alaw or ulaw should be supported by nearly all devices out there... and
as uncompressed codecs are even below the numbers you gave. GSM
restricts quality a lot, but you could nearly transport a GSM stream
over an avian carriers link ( http://www.faqs.org/rfcs/rfc1149.html )
SCNR

Best regards,
Anselm