Timing devices are increasingly becoming ‘just another network device’. Many have the capability to offer multiple timing services across a multi-port device, even delivering more than one time base service per port. There is an issue to bear in mind when delivering multiple services. The most common protocols – PTP (Precision Time Protocol) and NTP (Network Time Protocol) – use distinctly different time bases.
Time Base Differentiation
This isn’t a huge issue as most devices get their time from satellite signals, then calculate their own time base, So, if PTP and NTP have different time bases the system clock can deliver the right time base to the right requirement. PTP delivers Atomic Time (TAI) whereas NTP delivers UTC. Which, although based on Atomic Time, takes the changes in the Earth’s rotation into account. So, ‘Leap Seconds’ can be added or taken away every six months if necessary.
So, mixing NTP and PTP on the same port of a timing device is best avoided for that reason. However, you should be mindful that each port may not have the same functionality and independence across a multiport device. As a result, it may be that the TAI/UTC issue can apply to a cluster of ports as well as just one.
Given the multi-port nature of these devices, there will be straightforward ways to mitigate this issue but forewarned is forearmed!
Summary
When implementing an accurate timing signal in your infrastructure, it’s important to keep this in mind. Two of the most prevalent protocols – PTP and NTP – use different time bases. Avoid situations where more than one protocol is sharing the same port. That way your timing won’t be affected by a problem that’s easily avoided!
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