Requested revision
| Standard: | IEEE Std 802.1AS-2020 | Clause: | 10.2.10.3 |
| Clause title: | State diagram | ||
Rationale for revision
In the SEND_SYNC_INDICATION block of the ClockMasterSyncOffset state machine (Figure 10-6), the computation of clockSourcePhaseOffset for the case where selectedState[0]==PassivePort is not correct. The computation accounts only for the seconds portion of masterTime and, in addition, subtracts from this the full syncReceiptTime rather than the seconds portion. Investigation of this indicated that the full computation was present in 802.1AS-2011. Comment 165 against 802.1AS-Rev/D6.0 indicated that sourceTime (in the version of this equation in 802.1AS-2011) should be changed to masterTime. The comment was accepted; however, apparently a portion of this equation was accidentally deleted when addressing comment 165 and/or other comments related to this figure. The result was that, while masterTime did appear in D7.0, a portion of the equation was no longer present. The equation currently reads:
clockSourcePhaseOffset = masterTime.seconds – syncReceiptTime;
The equation should read:
clockSourcePhaseOffset = (masterTime.seconds – SyncReceiptTime.seconds)*(109)*(1<<16) +
(masterTime.fractionalNanoseconds – SyncReceiptTime.fractionalNanoseconds);
Proposed text
In the SEND_SYNC_INDICATION block of Figure 10-6, replace:
clockSourcePhaseOffset = masterTime.seconds – syncReceiptTime;
By:
clockSourcePhaseOffset = (masterTime.seconds – SyncReceiptTime.seconds)*(10^9)*(1<<16) +
(masterTime.fractionalNanoseconds – SyncReceiptTime.fractionalNanoseconds;
(Note: The quantity “10^9” should be written in the document as 10 with 9 as a superscript, i.e., exponent; it is written as “10^9” here because the maintenance database does not allow superscripts.)
Impact on existing networks
This change will cause clockSourcePhaseOffset to be computed correctly. This will result in the correct value for the phase difference between the synchronized time (i.e., current GM time) and the ClockMaster time for the current PTP Relay Instance.
Originator
| Name: | Geoffrey M. Garner | Email: | gmgarner@alum.mit.edu |
| Affiliation: | Huawei | ||
| Submitted: | 2021-08-18 | ||