SIP is an excellent option for organizations that desire to expand existing communication systems.
SIP, when used in conjunction with intercom stations, allows end users to easily expand enterprise communication by bridging the gap between the Voice over IP phone system and the intercom. SIP is the Session Initiation Protocol. Although two SIP devices can talk directly to each other, they generally will use an intermediary system that acts as a SIP proxy.
SIP is a very flexible protocol that has great depth. It was designed as a general-purpose method to set up real-time multimedia sessions between groups of participants. And now it can be used to combine intercom stations and phones into one system.