Trying to connect to a Viewstation

Hello,

I have a problem:

At work we have a Video Conferencing Device, a Polycom Viewstation
V500.
It is in the DMZ of our 3com Superstack firewall but to avoid problems
we are allowing all traffic in and out.

With a laptop running Windows XP and a Logitech Quickcam Pro 4000 I
can connect with Netmeeting to the Polycom from the LAN and from my
home in the Netherlands.
At home I have cable internet (4000/512) with a Motorola modem and a
SMC wireless router (NAT, UPnP enabled).

When I take this laptop to a colleague in his office in France the
following happens.
- On the laptop we can see and hear the office but the sound stops and
the image freezes after approx. 10 seconds.
- At the Polycom we see a black screen with the name of the caller.
After a minute the connection is terminated automatically.

In France we use ADSL (1024/256) with a Netopia Cayman 3341 router.
(NAT, uPnP enabled)
The router manual explicitly states, netmeeting connections are
possible without making any changes to the configuration.
Only changes to be made were those allowing incoming calls to get
relayed to the computer behind the NAT. After doing this placing a
call from the Polycom has the same result.
The Internet provider, Nerim, claims to block nothing.

Also from the colleague's home the result is the same. He has a
Wanadoo ADSL connection (1024/128) with a Sagem 3202 wireless router
(NAT, uPnP enabled).

Does anyone have a clue?

Regards,

Piet.
.

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