[h323plus] Dynamic Bandwidth Management!!

Simon Horne s.horne at packetizer.com
Wed Jan 23 03:17:47 EST 2008

Just a quick check of the source code shows that flowcontrol is only
partially implemented. It is recieved by the stack and accessed via the
H323Connection::OnH245FlowControl() and does go back to the codec however
doesn't reach the plugin codecs themselves. There appears to be no sending
part in the library. I will put this on the to-do list.

Just a note DiffServ is implemented by default in the h323plus library. All
audio/video capability exchanges contain a transport capability component
containing diffserv values. The default values are 46 audio and 26 video and
seem to work quite well with wireless networks

These can be changed by static members


-----Original Message-----
From: h323plus-bounces at lists.packetizer.com
[mailto:h323plus-bounces at lists.packetizer.com]On Behalf Of Paul E. Jones
Sent: Wednesday, January 23, 2008 5:46 PM
To: Abhishek Rohilla; h323plus at lists.packetizer.com
Subject: Re: [h323plus] Dynamic Bandwidth Management!!


I do not know what the H323 Plus software has, but there are procedures
defined for H.323 and facilitated with RTCP information to help control
bandwidth.  For example, if packet loss is observed by looking at RTCP
reports, then an H.323 device could use the "flow control" command, "request
mode", or even close and open a channel that uses a lower bit-rate codec.

The problem, though, is that while a mode shift can be made to a lower
bit-rate codec, there are dangers in doing the reverse.  I mentioned in my
previous e-mail that what can happen is that devices get into a constant
state of increasing and decreasing bandwidth usage based RTCP feedback.

One possible way to help mitigate that is to utilize a Gatekeeper to
allocate and revoke bandwidth to a terminal.  This works acceptable well,
unless you have a network connection that is utilized by other applications.
And, in fact, most network connections are used by a multiplicity of
applications.  As a consequence, using the Gatekeeper for bandwidth
management is often non-workable.

There are two tools to help address this issue, and those are RSVP and
DiffServ.  We are presenting defining Recommendations for the use of both
RSVP and DiffServ within H.323 systems, with the initial recommendations
expected to be approved in May 2008.  Using these tools will generally work
well if you can control the end-to-end network and/or your service provider
will provide some kind of service agreement and honor your DiffServ packet
markings accept RSVP requests and use DiffServ or other means to increase
the likelihood that your packets will arrive at the remote end as desired.

In short, this is not a simple issue of H.323 or any particular stack like
H323 Plus or the IP link, but rather a whole system problem that requires
coordination and cooperation to work.


----- Original Message -----
From: Abhishek Rohilla
To: h323plus at lists.packetizer.com
Sent: Wednesday, January 23, 2008 1:09 AM
Subject: [h323plus] Dynamic Bandwidth Management!!


By dynamic bandwidth management I mean that when a video call is in progress
, the bandwidth keeps on increasing or decreasing, So does h323+ takes care
of that and keeps the bitrate of encoder in control by some means.Suppose
encoder is producing more no of bits for a frame than can be send on currnet
available bandwidth. how does H323 deal with that?

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