When a host system sends a command to the receiver, the receiver uses its internal SAASM or M-Code module to decrypt the GPS signals. The results are then repackaged into ICD-GPS-153 messages. The host never sees the raw classified keys.

B-286466,B-286466.2 [Protest of Air Force Rejection of ... - GAO

The protocol ensures the 1 Pulse Per Second (1 PPS) signal aligns perfectly with the time information in the binary messages.

This protocol provides a standardized method for transferring time, position, and status data, ensuring interoperability between DoD GPS equipment (like the GB-GRAM) and communication systems such as SINCGARS (Single Channel Ground and Airborne Radio System). A Comprehensive Guide to the ICD-GPS-153 (GSSIP) Protocol 1. What is the ICD-GPS-153 Protocol?