So we designed the protocol by assuming that an IP Phone has minimum call control functionality and user interface. Text base message SPCP's messages are containers of plain text. SPCP is extensible and easy to debug. And TCP has a capability of recovering missing packets. Authentication is necessary for preventing illegal access to an IP Phone.
Authentication also allows user dependent services.
Then it can work with a gateway or a terminal adaptor which handle multiple calls. An IP Phone can use HD storage on a computer as an extra storage device. More complex process can be handled by exchanging programmed scripts as media data. Those are designed to be flexible in order to accommodate various types of IP Phones. X- Optional Figure 2.