 Refer to the section "Time Error" of Chapter 5 for fur- ther details on MTIE and TDEV. dTEH Peak-to-peak measurements of TE are used for measuring the dTEH component of dTE. Note that "peak-to-peak" means the difference between the lowest peak (minimum ob- served value) and the highest peak (maximum observed value) of TE. This is specified in nanoseconds. The limits for max|TE|, dTEL and dTEH are specified in ITU-T G.8271.1 (FTS network), G.8273.2 (T-BC and T-TSC clocks), G.8273.3 (T-TC clock), and G.8273.4 (PTS/APTS clock) recommendations. 9.3.1 Asymmetry The major problem with asymmetry is that it accumulates the further along the chain that a timing signal has traveled. Unless the asymmetry is known and constant, then once it is present, it cannot be undone or compensated for. This accumulation is not necessarily the same with PDV because the PTP master port on the BC regenerates the PTP message stream; therefore, the PDV is effectively "reset" to zero. Inserting BC clocks is a good solution available for phase/time profiles, not only for resetting the PDV but also for avoiding an excessive build up in asymmetry (since the PTP mes- sages do not pass through the BC). The options to mitigate against asymmetry are somewhat limited and include Compensation: Any asymmetry that is known to be fixed (an example is differences in cable length) can be measured and compensated for by configuration on the slave clock. Avoidance: Not allowing asymmetry to accumulate in the first place is a solution. This means selecting components and elements that are expressly designed to avoid it. The same applies to the transport technology because some transport types are inherently asymmetric. PTP/timing awareness: This really is a form of avoidance. When a network element allows time to transit via a non-packet hardware mechanism, then it avoids adding excessive asym- metry that it would suffer from the normal processes of packet switching inside the NE. PDV avoidance: When PDV arises in a node, that is a problem. But the bigger i