[h323plus] Master/Slave and SessionIDs

Paul E. Jones paulej at packetizer.com
Mon May 19 17:56:54 EDT 2008


Simon,

Many also use SessionID = 3 for fax, too.

To use other SessionIDs, the master must assign them as per H.245:

"The sessionID is a unique RTP or T.120 Session Identifier in the
conference. It is used by the
transmitter to refer to the session to which the logical channel applies.
Only the master can create
the session identification. By convention, there are three primary sessions.
The first primary session
with a session identification of 1 is the audio session, the second primary
session with a session
identification of 2 is the video session, and the third primary session with
a session identification
of 3 is the data session. A slave entity can open an additional session by
providing a session
identification of 0 in the openLogicalChannel message. The master will
create a unique session
identification and provide it in the openLogicalChannelAck message."

The problem here is the Tandberg device proposes the use of '3' ... that's
perfectly valid.  But, if you are the master device, you should reject it
with master/slave conflict or some such.  In truth, addressing this can be
quite tricky.

Paul

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> -----Original Message-----
> From: h323plus-bounces at lists.packetizer.com [mailto:h323plus-
> bounces at lists.packetizer.com] On Behalf Of Simon Horne
> Sent: Friday, May 16, 2008 8:31 PM
> To: Niek Kooij; h323plus at lists.packetizer.com
> Subject: Re: [h323plus] Master/Slave and SessionIDs
> 
> 
> Typically SessionID 1 to 3 are reserved for Audio,Video and Data. To me
> data
> means T.120. Unlike H.239 which clearly states the session ID must not
> be
> 1,2 or 3 the H.224 specification does not state whether it can use 3
> (for
> data) or must use a higher number. This is clearly a grey area however
> if
> you offer a session ID of 4 then the tandberg device should honor that
> request with the same session ID and not 3. To my way of thinking this
> is a
> bug in tandberg equipment. If you are not going to use T.120 then
> changing
> the default H.224 session id to 3 should not affect anything too much.
> 
> Simon
> 
> > -----Original Message-----
> > From: h323plus-bounces at lists.packetizer.com
> > [mailto:h323plus-bounces at lists.packetizer.com]On Behalf Of Niek Kooij
> > Sent: Friday, May 16, 2008 10:50 PM
> > To: h323plus at lists.packetizer.com
> > Subject: [h323plus] Master/Slave and SessionIDs
> >
> >
> > Hi,
> >
> > I am trying to get the h224/h281 data channel to work with Tandberg
> > equipment and ran into some problems. It turns out this has to do
> with
> > sessionId's. The current implementation lets the connection/endpoint
> > create an h281handler which will handle both in- and outgoing h224
> RTP.
> > The problem is that my H323Endpoint will usually begin with opening
> the
> > logical channel and assigns DefaultH224SessionID = 4 as sessionID.
> Later
> > on the Tandberg endpoint wants to open a channel but then with
> sessionId
> > 3! This results in the construction of a new RTP_Session which will
> > never be used (cause the h281handler is allready constructed and has
> its
> > RTP_Session set).
> > Can anybody tell me what the "right" way would be to solve this
> problem?
> > Should the incoming and outgoing h224 channels have the same
> sessionID?
> > My current solution is to change DefaultH224SessionID to 3 but this
> will
> > probably result into problems when more data channels need to be
> > openend...
> >
> > Thanks,
> >
> > Niek
> >
> 





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