Re: [GnomeMeeting-list] Bandwidth limitations in GM

[Craig Southeren <craigs postincrement com>]

On Wed, 16 Jun 2004 23:09:28 +0200
Kilian Krause <kk verfaction de> wrote:

..deleted

> > Also, when I open the GM preferences, there is a form box containing a 
> > number for Maximum video bandwidth of ___ kB/s under the "Codecs... 
> > Video Codecs" tab, but I cannot seem to set it to higher than 100 kB/s 
> > even though our network connection and gatekeeper are capable of much 
> > more.
> 
> That's an OpenH323 limitation.

There is no such OpenH323 limitation, but it could be a GM bug.

If this value is the max bandwidth that is passed to H323EndPoint, then
you need to know that H323Endpoint expects the value in multiple of
100bps, so 100,000 actuallty represents 10,000,000.

If you want to know why, then read on.....

OpenH323 allows a user to indicate a bandwidth limit in the H323EndPoint
in order drive the algorithm that chooses codecs when a call is started.
For example, if the user indicates that they have a bandwidth of 50kbps,
then OpenH323 will not choose G.711, even if it is available to both
endpoints, because that codec requires 64kpbs. This stops users from
getting crappy calls when they don't have the bandwidth, and it mirrors
a similar feature in NetMeeting (and most other clients)

Unfortunately, this limitation does not work well when video codecs are
used, because it uses the bandwdith of the maximum possible video
quality at the specified frame rate, not the dynamic bandwidth as
determined by the actual frame rate or scene complexity. So, normally,
we don't recommend that applications use this value - unless they are
only using audio.

Unless the application specifies a value, OpenH323 will use a default
bandwidth of 10Mbps (i.e. Ethernet speed) which will result in selecting
the highest bandwidth codec (and presumably also highest quality codec)
that can be agreed upn between the two endpoints.

The H.323 specification uses this value in multiples of 100 bps, so a
value of 100,000 actually means 10 times that. Hence, a value of 100,000
actually means 10 x 100,000 = 10,000,000 bps

   Craig

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