[JDEV] Videoconferencing with jabber / Re: [speex-dev]Videoconferencing with speex and jabber

Matthias Wimmer m at tthias.net
Wed Nov 26 04:01:04 CST 2003

Hi Carsten!

Carsten Breuer schrieb am 2003-11-25 23:41:45:
> they can split the internet from the internal net. Have you ever tried 
> to get Netmeeting running over a linux gateway running on a 486DX4100 
> without the need to switch of your firewall. It is completly a mess.

Yes I have ... that what H.323 Gatekeepers are for.

Do you think the ITU has choosen UDP as a transport for the media data
if they wouldn't have had a good reason? TCP has many disadvantages for
for real time data because of the build in error recovery and flow
control. TCP is just not made for real time data.

And UDP/TCP is the point. You need the Gatekeeper for H.323 and the
proxy for SIP not because they don't have external servers (in fact they
can have), but because it's often hard to cross NAT with UDP packets as
there is no connection for which the NAT router can know how do deliver
incoming IP packets.

There are not much techniques available to solve this problem (beside
the Gatekeeper/Proxy on the NAT system). Possibilities include:
- using TCP - problems see above. Sometimes it's implemented that the
  TCP connection is dropped as soon as there should be incoming traffic
  on it but you don't get it and a new TCP connection is esablished. But
  this results in much bigger sound quality problems - you hear these
  reconnects as small interruptions and/or noise.
- Using any sort of a proxy on the NAT: Gatekeepers, proxies, SOCKS, ...

Tot kijk

Fon: +49-(0)70 0770 07770       http://matthias.wimmer.name/
HAM: DB1MW                      xmpp:mawis at charente.de
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