e signal together (commonly 1PPS and ToD). There are ITU-T standards for some of these signals, but there are also many historical and proprietary signals. One example of the former is the Inter-Range Instrumentation Group (IRIG) signal types frequently used in the power industry. The other option to output these signals is to use PTP to carry the time and phase and optionally the frequency. The frequency, if not carried by the PTP, can be carried with SyncE or as a separate sig- nal (for example 2 MHz or 10 MHz). If so, then these devices must be equipped with an Ethernet packet interface to carry the PTP and optional SyncE. This makes the PRTC simultaneously a grandmaster and PRTC (sometimes written as PRTC+GM). For the telecoms market, many implementations of PRTC are based on a GNSS receiver, with an embedded GM that uses SyncE for frequency. Their PTP output is compliant with one of the tele- com profiles of PTP, and SO they are known as Telecom Grandmasters (T-GM) and combined as PRTC+T-GM sources. They are available in PRTC-A or PRTC-B performance levels and come in many form factors, even down to a small form-factor pluggable (SFP). They can be deployed in a central location with a PRC as backup or versions with fewer features (cheaper) can be placed out at the cell site. Chapter 9 and "Chapter 11. 5G Timing Solutions", provide detailed coverage of options and trade- offs to consider when selecting and situating a PRTC to best meet your specific needs. As introduced earlier in the "Clocks" section, 1PPS stands for 1 pulse per second and is an electrical signal used to carry phase. It is most commonly a square wave or, alternatively, a pulse of configur- able length (between 100 ns and 500 ms). As the name suggests, the signal has a period of 1 second and the midpoint of the leading edge is defined as the significant instant. Clause 19 of the ITU-T recommendation G.703 specifies the physical and electrical characteristics of the 1PPS interface. The details are specified for both a 100-Ohm V.11-based signal