16 Mar
2004
16 Mar
'04
5:30 p.m.
Switching is not possible with symmetric NAT. But if only one of the
clients is behind symmetric NAT, you don't need an rtpproxy, if the
other client can act as "passive" client.
see
http://www.softarmor.com/wgdb/docs/draft-ietf-sipping-nat-scenarios-00.txt
section 2.2.1.6 Receiving an Invitation to a Session
a=active, a=passive
Klaus
Simon Barber wrote:
My confusion over symmetric / cone NAT. But does look
possible to
communicate between symmetric NATs in many cases - but first starting
with RTP proxy or TURN. Using the RTP proxy to learn which class of
symmetric NAT you have, and predicting the port allocation - then
switching to direct communication if the port prediction test gives good
results.
Simon
Jiri Kuthan wrote:
At 07:16 PM 3/15/2004, Simon Barber wrote:
possible way to get through symmetric NAT without
permanent rtpproxy.
Initiate the connection using rtpproxy, as normal. Now, learn the udp
port the NAT is sending RTP from. Now send a re-invite to both
parties, and switch the stream to the udp port the NAT is using,
instead of the rtpproxy. This will only work if the NAT uses the same
external ip/port pair when the same internal ip/port pair is used
Which is non-symmetric NAT. Symmetric NATs are only traversable the way
Klaus described.
-jiri
(and I'm expecting that most sip phone will
reuse the same internal
ip/port pair when you re-invite). Apparently some NATs do this.
(although I'm not a NAT expert - I have only read a few papers on the
subject).
Simon
Klaus Darilion wrote:
--
Jiri Kuthan http://iptel.org/~jiri/
You can't overcome symmetric NAT with STUN.
To traverse a symmetric
NAT you need:
- A SIP proxy with NAT traversal (nathelper module)
- An RTP proxy (or an generic TURN server and a SIP UA which
supports TURN)
- A symmetric SIP UA (symmetric SIP & symmetric RTP)
regards,
Klaus
> Hi,
> Can someone please help me if my dialer does not support symmetric
> signalling, is there anyway to go through symmetric nat through
> the server
> or configure from the server that asking the dialer to point to a STUN
> server before reaching the UA. Please help........
> regards, shirley
>
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