UTC Offset

Enhanced PTP User Guide (UG1602)

Document ID
UG1602
Release Date
2022-10-18
Revision
1.0 English

The UTC offset (TAI - UTC) is conveyed to PTP slave clocks from a PTP master clock within the Sync or FollowUp messages. The UTC valid flag (UTCV) indicates whether the UTC offset time is considered valid by a master device and therefore should be used by a PTP slave device.

In the sfptpd configuration file, the ptp_utc_valid_handling option identifies the action taken with the UTC offset value by sfptpd.

Table 1. UTC Handling
Value Description
default If UTCV is set, use UTC, otherwise do not.
ignore Ignore the UTC valid flag. Always apply the UTC offset.
prefer Prefer master clocks that set the UTCV flag above those that do not.
require Do not accept PTP messages from master clocks that do not set the UTCV flag.
override <seconds> Ignore the UTC valid flag and UTC offset value set by the master clock. Use only the value set by the override option.
Important: You must ensure the override <seconds> value is set to the correct UTC offset. The UTC offset increments on the occasion of each leap second.