Help 3G problem

[jpbbricole]

Hi guys

I have a 3G connection problem, I try to reach aweb server behind a 3G router:
Parameters are:
HTC Desire Android 2.2.2
ASUS TF101 Android 3.2.1
Browser: Dolphin Browser HD or standard HTC and or ASUS browser
3G Router 3G Vololink VA122-Q

In this configuration:
[HTC Desire]~~~<3G>~~~~~~~~~~~~~~~~~~~~~~~~~~~<Cloud>~~~<3G>~~~[3G Router]---<LAN>---(WEB Server)
I almost alwaysHTTPError503 -Service unavailable
From Time to Time ( ~1/20), the communication is ok.

In these configurations:
[HTC Desire]~~~<Wifi>~~~[FAI Router]~~~~~~~~~~<Cloud>~~~<3G>~~~[3G Router]---<LAN>---(WEB Server)
[ASUS TF101]~~~<Wifi>~~~[HTC Desire]~~~<3G>~~~<Cloud>~~~<3G>~~~[3G Router]---<LAN>---(WEB Server)
[iPhone 4]~~~<3G>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~<Cloud>~~~<3G>~~~[3G Router]---<LAN>---(WEB Server)
no problem.

Where to look?
Android 2 problem, HTCproblem, Timeoutproblem?
Thanks foryour help.