affected by their nondeterministic nature, packet network elements have large buffers and deep queues of packets. In summary, the following factors contribute to the PDV of packets: Queuing for output, especially when multiplexed with traffic containing very long frames (thou- sands of bytes), which cannot be interrupted once it starts being transmitted. Low-frequency noise, such as diurnal effects. Packet traffic load is quite dynamic and can be filtered to some extent, but long-term effects are almost impossible to filter out. Transmission reasons such as modulation and demodulation, waiting for transmission time slots, buffering, and the inherent delay characteristics of different transport technologies. Routing and rerouting. Path sharing techniques and load balancing such as interface bundling and multipath load sharing. Congestion or contention at some resource or interface and the associated QoS mechanisms to deal with it. Other errors such as packet error, reordering, fragmentation, and even packet loss. For further reference material, G.8261.1 specifies the hypothetical reference model and the PDV network limits applicable when frequency synchronization is carried via packets. G.8263 provides a lot of mathematical treatment, especially Appendix I, "Packet delay variation noise tolerance-test- ing methodology." G.8263 clause 7, "Packet delay variation noise tolerance," has related coverage of PDV. 9.3.1 Packet Selection and Floor Delay Even using SyncE to solve the PDV problems for frequency recovery, PDV is still a problem for the phase/time component because it leads to asymmetrical delay due to shifting traffic loads in un- aware nodes. In fact, to recover an accurate phase and time, the discovery of a true delay floor in both directions is more critical than ever. For the frequency PTP case, it was just sufficient that the delay be somewhat constant and only in the master to slave direction. The message that completes the journey in the delay floor time has traveled between master and slave in the min