Incoming Calls

The Incoming Call Request message is generated by the FEP to indicate an incoming call (ring) immediately following the ring or after the FEP has processed the user information. If the NTS wants to answer the call, it sends an Incoming Call Reply message. This instructs the FEP to answer the call and negotiate the connect speed. After the FEP makes the connection, it can determine (based on the connect speed) how large a receive window it wants and how long it will take to process the data it does receive. The amount of time required to process data is called the Packet Processing Delay (PPD). The FEP responds back with an Incoming Call Connected message containing its receive window size and PPD value.