At its core, ICD-GPS-153 is an that defines the message format and functional requirements for a digital data interface. It is often referred to as part of the GPS Standard Serial Interface Protocol (GSSIP) suite.

To obtain the complete specification (e.g., ICD-GPS-153C), developers often must submit a GPS Technical Library Document Request through the U.S. Coast Guard Navigation Center . ICD-GPS-153 vs. NMEA-0183 ICD-GPS-153 Primary Use Military/Industrial Timing & Emulation Consumer/Marine Navigation Data Format Binary/Structured ASCII (GSSIP) ASCII "Sentences" Common Messages Time Transfer, Current Status $GPGGA, $GPRMC, $GPVTG Accessibility Controlled/Restricted Fully Public Interface Control Documents - GPS.gov

The protocol typically includes several critical message formats designed for specific synchronization tasks: