The term IRIG signals is used to refer to a whole group of serial timecodes, which use a continuous stream of binary data to transmit information on date and time. The individual time code formats can be distinguished by the signal characteristics, e.g. modulated versus unmodulated, which require different ways of signal transmission, by the data rate, and by the kind of information included in the transmitted data.
Back in 1956 the TeleCommunication Working Group (TCWG) of the American Inter Range Instrumentation Group (IRIG) was mandated to standardize different time code formats, resulting in IRIG Document 104-60. The latest revision is IRIG Standard 200-04 which is the current version specifying some new codes which also transmit a year number. IRIGB is widely used to synchronize systems in Substation Automation Systems (SAS) and in Defence and Aerospace. Nowadays, it is quite frequent combining IEEE 1588 systems with IRGIB systems. The following diagram maps as an example the functionalities of SoC-e timing related IPs of SAS equipment related to synchronization.