In the Converged Conference 3.0 solution, no matter whether the multimedia cascade mode or the MCU center mode is used, all the audio and video media streams of the Web client need to be forwarded by the USM/MS system as a proxy? Correct or Wrong

The U1900 system is connected to the PSTN through a digital trunk. In U1900, phone A cannot call user B's On mobile phone, user B can call back phone A normally. Which of the following reasons may cause this failure? () (single choice)

If IP phone A fails to register with U1900, which of the following situations will not be the cause of the registration failure? ()

Regarding call bills and billing scenarios, which of the following statements is correct () (multiple choice)