Hi Craig and Damien,
Was there ever a follow-up or wrapup session writeup, or conclusions
from this conference? In testing the openh323-based/pwlib-based
application ohphoneX (which is otherwise regarded as a blessing by
this community), a study by a serious but friendly commercial MCU
vendor (Codian) found the following defects, as listed below.
I'd like to know whether these problems are in the openh323 or pwlib
layers, and thus common to GnomeMeeting, for example, or specific to
the otherwise very nice ohphoneX implementation.
Apologies to Mark Blake for quoting his e-mail without permission, but
I think these are things that ought to be addressed by the ohphoneX/GM
developers and user community and should not have to be worked around
by vendors:
On Jan 18, 2005, at 12:03 PM, Mark Blake wrote:
Although all the endpoint manufacturers attempt to adhere to the the
various standards the quality with which they manage to do so varies
tremendously from manufacturer to manufacturer. For instance of “the
big two” endpoint manufacturers we have seen something like 10x more
bugs with one than the other. Typically these are real bugs that are
not just a matter of interpretation. However there is almost always a
work-around of some sort - so our code has quite a lot of stuff that
attempt to detect various bugs in real time and implement
work-arounds!
In the specific case of OhphoneX we managed to find the following
major bugs / issues in only about 15 minutes of testing
1) Bad H.263 bitrate advertisment
2) Inability to cope with some H.261 fragmented packets
3) Incorrect timestamps on H.261 media
4) H.261 encoder only uses I-macroblocks
5) OhphoneX does not correctly issue fast update requests in all
cases.
So (1) is why H.263 calls do not work
(2) is what was causing the corrupt video with H.261 but (3) would
also be sufficient to cause major problems even if (2) were fixed.
(4) is not a bug as such but means that OhphoneX is only using the
most basic form of H.261 encoding which means it will need roughly
10x the bandwidth for the same quality of video compared to a “full”
H.261 encoder.
(5) means that OhphoneX has poor resilience to packet loss / bad
network conditions.
(2) and (3) are worked around in the forthcoming MCU build John
previously mentioned. This is sufficient for H.261 video to work ok.
On Jan 11, 2005, at 6:03 PM, Craig Southeren wrote:
To all,
The German Unix Users Group is holding the second annual Free
Software/Open Source Telephony-Summit n Geilenkirchen, Germany this
weekend and early next week. Myself and many other developers and
users
will be attending the event. If anyone is interested in attending,
please see the web page at:
http://www.guug.de/veranstaltungen/telephony-summit-2005/
Craig
----------------------------------------------------------------------
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Craig Southeren craigs postincrement com / craigs voxgratia org
Phone: +61 243654666 ICQ: #86852844
Fax: +61 243673140 MSN: craig_southeren hotmail com
Mobile: +61 417231046 Jabber: craigs jabber voxgratia org
Post Increment - Consulting & Services
http://www.postincrement.com
Vox Gratia - The Open Source VoIP portal http://www.voxgratia.org
Raving Of A Strange Mind - the VoIP blog
http://www.southeren.com/blog
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