The SIP protocol, VOIP protocol is commonly used
SIP is an application layer control protocol that can be used to establish, modify, and terminate multimedia sessions (or conference), such as the Internet phone, SIP can also invite participants to existing session, such as the multi-party conference, the media can convenient in an existing session (or delete), with the increase of the SIP display supports name mapping and redirection services, this is used to support personal mobile business - you can use a unique external signs and don't have to care about their actual network site,
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