 clock. In this case it defines the performance at the output of the combined PRTC and T-GM func- tion, i.e., the precision time protocol (PTP) messages. So, G.8272 basically specifies the accuracy with which the PRTC provides a reference time signal traceable to a recognized time standard, normally Coordinated Universal Time (UTC). As men- tioned in the scope, there are two cases: Where the PRTC provides only physical signals for frequency, phase, and time-commonly the 1PPS, ToD, and 10-MHz signals outlined in "Chapter 3. Synchronization and Timing Concepts", and "Chapter 7. Precision Time Protocol" Where the PRTC is combined with a PTP grandmaster and the frequency, phase, and time is distributed with PTP packets from the device directly The requirements for accuracy include both cases, although in the second case, one is obviously measuring the error of the T-GM as well as that of the PRTC itself. But the recommendation makes no allowance for that; the limits are the same, although in the combined case, the time error samples are measured through a moving-average low-pass filter. There are two classes of device covered in this recommendation: PRTC-A and PRTC-B. The time output of PRTC-B is more accurate than that of PRTC-A, SO it is better suited to those applications where more accurate time is required. This is covered in much more depth in "Chapter 10. Mobile Timing Requirements", and "Chapter 11. 5G Timing Solutions", when addressing timing in the mo- bile front-haul network. Generally, PRTC-B is achieved by using GNSS receivers with enhanced capabilities as well as being located where there is better control of the environment, especially temperature. This recommendation includes the following main topics and appendix: Constant time offset compared to the reference time (say, UTC) when locked Phase error (wander and jitter) produced at the output of the device, which is specified (for wander) as MTIE and TDEV masks for both classes of device Phase and time as well as frequency interfaces, defining the cha