VoIP is to digitize the voice signal, compress, encode and package it, transmit it through the network, and then decompress it to restore the digital signal to sound for the other party to hear.

All incoming calls to the 400 switchboard number are transferred to the preset fixed telephone, mobile phone or call center line. The 400 telephone switchboard is only responsible for handling incoming calls, not outgoing calls. Telephone charges are shared by enterprises and users who dial 400, and callers only pay local telephone charges. The 400 hotline embodies the sense of enterprise service and is a symbol of credibility and strength.

With the increasing use of VoIP, the security problem of VoIP has become increasingly prominent. Security is an indispensable part of VoIP. How to protect the privacy of VoIP voice information has become a problem to be overcome in the development of VoIP. VoIP encryption is a technical means to ensure the security of VoIP, including IPSec, secure real-time transport protocol SRTP and virtual private network.

On the other hand, the callback mode only consumes a little traffic to transmit signals to the server before connection, about 2KB at a time. After the connection, the server will call back, so the whole call process no longer needs to consume traffic, which is suitable for people to use when they go out. Suppose you are in a different place and we use the callback mode, then your mobile phone must be connected.