 oscillators and their impact on ac- curacy, stability, and precision of the clock recovery. Recommended practice dictates using a good stratum 3E oven-controlled crystal oscillator (OCXO) (or temperature-compensated crys- tal oscillator [TCXO] as the next-best option) as an oscillator when building good synchronous equipment. 12.1.1 Time- and Phase-Aware Clock With phase synchronization now a key requirement for mobile networks, the hardware and software designs of NEs have evolved to be aware of time and phase. Although time and phase can be car- ried via PTP packets alone, the network timing engineer might encounter different situations where just packet-based time/phase transfer might not be good enough. "Chapter 11. 5G Timing Solu- tions", covers many alternate deployment topologies. To support multiple different network topologies of mobile networks, NEs are expected to support a variety of ways to accept time and phase from external sources. These sources can include a GNSS receiver (providing both time and phase) and/or dedicated ports for time of day (ToD) and 1PPS input. If the system contains an embedded GNSS receiver, an antenna port on the front panel can be dir- ectly connected to an external antenna. The receiver will provide both ToD and 1PPS signals (in ad- dition to the 10-MHz frequency signal) for the NE to generate PTP and SyncE. These signals are almost always internal to the device, SO it is very difficult to monitor the signal between the receiver and the SETS device. The NE is also expected to support dedicated 1PPS, 10-MHz, and ToD ports to receive respective signals from an external clocking and timing source. For measurement reasons, the NE should also support using these ports as output as well as input. Figure 12-3 shows the hardware components and signal paths of a time-/phase-aware NE. Local TOD and Phase-Aware Equipment oscillator Front panel Front panel ports Ethemet Frequency interfaces & phase (In out) receiver recovery (PLLs) 1PPS/Phase (In out) Synchronized (In out) Timestampi