Video on TCP, Audio on UDP, why?

Perhaps somebody out there can explain this to me. It would seem that the
most common problem people are having with MSN Messenger is the audio
whereas the video seems robust (for the most part). From what I could
determine, the video connection is via a defined TCP port value (80 or
9000) whereas the audio is a UDP stream of varying port value from 5004
upwards. Why wasn't the audio put into a separate, defined TCP port value
as well? I would think most of these audio problems would go away if that
were done, right? Anybody care to shed some light on this?

Jonathan
Mon Nov 03 15:52:03 CST 2003

Greetings,

In MSN Messenger 3.x, when voice was introduced, it actually was on a specific TCP port (6901
to be exact). With the release of MSN Messenger 4.x and Windows Messenger 4.x (at that
point, not separate applications like today), Universal Plug and Play (UPnP) support was
added, and the dynamic range added (5004-65535 UDP). Also note that with Windows Messenger
4.x, video capabilities were added as well, which use the same port range (this video mode is
known as 'Video Conference' in MSN Messenger 6.x) but only for Windows XP users (still a
restriction). With the release of MSN Messenger 6's 'Webcam' component, we have port 9000
and 80 TCP for the 'Webcam' feature.

It really makes little difference which port is being utilized to do this, as simply
forwarding the port number, or "opening" the port will *not* solve the problems. The only
reason you see less problems with the Webcam component is that is does *not* need to
establish a direct two-way connection between two users as the audio component does. The
Webcam component can use a relay server (that is, use a central server to receive and
transfer) so that both sides do not need to connect (indeed file transfer in MSN Messenger
6.x can do something similar).
____________________________________________
Jonathan Kay
Microsoft MVP - MSN Messenger/Windows Messenger
Associate Expert
http://www.microsoft.com/windowsxp/expertzone/
Messenger Resources - http://messenger.jonathankay.com

"Press Ctrl-Alt-Del Now" <3finger_ms_solution@reboot.now> wrote in message
news:Xns94288BACF82663fingermssolutionreb@198.80.55.250...
> Perhaps somebody out there can explain this to me. It would seem that the
> most common problem people are having with MSN Messenger is the audio
> whereas the video seems robust (for the most part). From what I could
> determine, the video connection is via a defined TCP port value (80 or
> 9000) whereas the audio is a UDP stream of varying port value from 5004
> upwards. Why wasn't the audio put into a separate, defined TCP port value
> as well? I would think most of these audio problems would go away if that
> were done, right? Anybody care to shed some light on this?

Jone
Tue Nov 04 05:10:28 CST 2003

Press Ctrl-Alt-Del Now wrote:
> Perhaps somebody out there can explain this to me. It would seem
> that the most common problem people are having with MSN Messenger is
> the audio whereas the video seems robust (for the most part). From
> what I could determine, the video connection is via a defined TCP
> port value (80 or 9000) whereas the audio is a UDP stream of varying
> port value from 5004 upwards. Why wasn't the audio put into a
> separate, defined TCP port value as well? I would think most of
> these audio problems would go away if that were done, right? Anybody
> care to shed some light on this?

It seems like a sensible thing to use UDP since there is less overhead. UDP
will not retransmitt lost packets. If you loose a packet in the audio
stream, you don't need it half a second later anyway.
TCP will retransmitt a lost packet. With video they probably only send the
changes since last picture. If you loose a packet the picture would look
rather strange. I'm sure they transmitt a complete picture at regular
interval, but still.
Even if the audio is UDP it could have been fixed port number. Why MS chose
to use this UPnP crap instead of some other way that really works behind
NAT, I don't know. There should have been an option to turn off UPnP in
messenger and use fixed ports. Instead they adviece people to turn off the
firewall!
MS has the upper hand in this "messenger market" since it's preinstalled
with XP, but they are going to loose if they don't release a version that
works soon.

--
Jone Tytlandsvik
http://tytlandsvik.no
mailto: firstname at lastname dot no

Press
Tue Nov 04 12:41:26 CST 2003

"Jone Tytlandsvik" <jone@tiscali.no> wrote in
news:bo81fl$1a8nsg$1@ID-107013.news.uni-berlin.de:

> Press Ctrl-Alt-Del Now wrote:
>> Perhaps somebody out there can explain this to me. It would seem
>> that the most common problem people are having with MSN Messenger is
>> the audio whereas the video seems robust (for the most part). From
>> what I could determine, the video connection is via a defined TCP
>> port value (80 or 9000) whereas the audio is a UDP stream of varying
>> port value from 5004 upwards. Why wasn't the audio put into a
>> separate, defined TCP port value as well? I would think most of
>> these audio problems would go away if that were done, right? Anybody
>> care to shed some light on this?
>
> It seems like a sensible thing to use UDP since there is less
> overhead. UDP will not retransmitt lost packets. If you loose a packet
> in the audio stream, you don't need it half a second later anyway.
> TCP will retransmitt a lost packet. With video they probably only send
> the changes since last picture. If you loose a packet the picture
> would look rather strange. I'm sure they transmitt a complete picture
> at regular interval, but still.
> Even if the audio is UDP it could have been fixed port number. Why MS
> chose to use this UPnP crap instead of some other way that really
> works behind NAT, I don't know. There should have been an option to
> turn off UPnP in messenger and use fixed ports. Instead they adviece
> people to turn off the firewall!
> MS has the upper hand in this "messenger market" since it's
> preinstalled with XP, but they are going to loose if they don't
> release a version that works soon.
>

That's what I was getting at too. Ok, so use UDP for audio but just like
what you said, why the random port value? It could of easily been a
single port or a small block of port values, say 5 or 10. The only thing
I can think of is a marketing ploy to sell and promote UPnP. You'd think
in today's world of Internet security that they would be creating and
promoting products which are firewall friendly, especially since it is
their OS which is targeted with all of these worms and virii so often.
Sometimes you just got to wonder...