<s>
H.239	B-Application
is	O
an	O
ITU-T	O
recommendation	O
from	O
the	O
H.32x	O
Multimedia	O
Communications	O
 '	O
macrofamily	O
of	O
standards	O
for	O
multimedia	O
communications	O
over	O
various	O
networks	O
.	O
</s>
<s>
The	O
H.239	B-Application
recommendation	O
is	O
titled	O
"	O
Role	O
management	O
and	O
additional	O
media	O
channels	O
for	O
H.3xx-series	O
terminals	O
"	O
.	O
</s>
<s>
H.239	B-Application
builds	O
on	O
the	O
ITU-T	O
'	O
s	O
H.32x	O
(	O
which	O
includes	O
H.323	B-Protocol
)	O
and	O
H.245	B-Application
series	O
of	O
standards	O
,	O
called	O
"	O
recommendations	O
"	O
by	O
the	O
ITU	O
.	O
</s>
<s>
Tandberg	O
introduced	O
the	O
ability	O
to	O
send	O
a	O
computer	O
or	O
video	O
presentation	O
along	O
with	O
a	O
video	B-Application
teleconference	I-Application
session	O
in	O
2000	O
with	O
their	O
"	O
DuoVideo	O
"	O
feature	O
in	O
February	O
2000	O
.	O
</s>
<s>
The	O
ITU-T	O
published	O
this	O
technology	O
as	O
Recommendation	O
H.239	B-Application
in	O
July	O
2003	O
.	O
</s>
<s>
A	O
traditional	O
videoconference	B-Application
has	O
an	O
audio	O
channel	O
,	O
a	O
video	O
channel	O
and	O
an	O
optional	O
data	O
channel	O
.	O
</s>
<s>
H.239	B-Application
defines	O
rules	O
and	O
messages	O
for	O
establishing	O
an	O
additional	O
video/graphics	O
channel	O
,	O
often	O
to	O
transmit	O
a	O
PC	O
graphics	O
presentation	O
or	O
video	O
from	O
a	O
document	O
camera	O
,	O
while	O
still	O
transmitting	O
the	O
video	O
of	O
the	O
presenter	O
.	O
</s>
<s>
For	O
presentations	O
in	O
multipoint	O
conferencing	O
,	O
H.239	B-Application
defines	O
token	O
procedures	O
to	O
guarantee	O
that	O
only	O
one	O
endpoint	O
in	O
the	O
conference	O
sends	O
the	O
additional	O
video	O
channel	O
which	O
is	O
then	O
distributed	O
to	O
all	O
conference	O
participants	O
.	O
</s>
<s>
The	O
signaling	O
for	O
H.239	B-Application
is	O
defined	O
in	O
a	O
way	O
which	O
simplifies	O
implementation	O
of	O
gateways	B-Application
between	O
H.323	B-Protocol
and	O
H.320	O
.	O
</s>
<s>
When	O
an	O
H.323	B-Protocol
call	O
is	O
connected	O
,	O
signaling	O
defined	O
in	O
H.245	B-Application
is	O
used	O
to	O
establish	O
the	O
set	O
of	O
capabilities	O
for	O
all	O
connected	O
endpoints	O
and	O
MCUs	B-Protocol
.	O
</s>
<s>
When	O
the	O
set	O
of	O
capabilities	O
includes	O
an	O
indication	O
that	O
H.239	B-Application
presentations	O
are	O
supported	O
,	O
a	O
connected	O
endpoint	O
can	O
choose	O
to	O
open	O
an	O
additional	O
video	O
channel	O
.	O
</s>
<s>
contains	O
encoded	O
video	O
from	O
a	O
computer	O
's	O
video	O
output	O
at	O
XGA	B-Device
resolution	O
.	O
</s>
