Video conference, about SIP call problems

First of all, SIP is a protocol, video conferencing usually have 2 kinds of protocols, a H.323 one is SIP, SIP will be the next generation of communication protocols, but now has not yet become the industry standard, SIP need to be registered in the network gate or SIP servers can be used normally, of course, you point-to-point calls to both sides to use the SIP protocol do not need to be registered, the most simple benefit is that you do not need to enter a complex IP address. The advantage of the simple only tube is that you do not have to enter the complex IP address, you only need to enter the GK or SIP server to assign you the number on the line.