2.3.13.1 Phone Device Life Cycle
TSPI version negotiation follows a simple model as described in the following diagram.
A schematic view of version negotiation is shown. The TAPI DLL passes the Service Provider the range of versions it understands. The Service Provider compares this with the range of versions it understands to determine the range of overlap. The Service Provider returns any value (usually the highest) in the range of overlap as the result of the negotiation.