什么是sip服务器？
also called a sip proxy, a sip server manages call sessions. it can setup sessions/calls with multiple endpoints, end a call, transfer a call, and put callers on hold. note that the server itself doesn’t actually make or receive calls  it just manages the connected parties.
though the exact amount of bandwidth will depend on the number of users, the general rule of thumb for hosted pbx is 90 kilobits per second per caller. this means if you were on a call with three people on the same hosted pbx platform, you’d need 270 kilobits of bandwidth.