PureVPN’s Value Bundle Offer: Internet Kill Switch, NAT Firewall & Auto-Protocol Features http://www.purevpn.com/blog/purevpns-value-bundle-offer-internet-kill-switch-nat-firewall-auto-protocol-features/
SIP (Session Initiation Protocol) is the protocol used by VoIP (Voice over Internet Telephony) systems to manage the VoIP phone calls. Because VoIP calls work differently from ordinary circuit-switched phone calls, different protocols are used to accomplish basic tasks such as establishing and terminating phone calls.
Internet Protocol (IP) and Private Branch Exchange (PBX) is a telephone switching system which allows each user to have Internet access, VoIP communications and traditional telephone communications using one data feed. Start understanding this type of business solution by looking PBX systems. http://www.phonepower.com/business-plans.aspx PBX phone system