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Requested revision
Standard:IEEE Std 802.1AS-2020Clause:16.5.3.2.2
Clause title:CSN TLV
Rationale for revision
Table 16-1, which shows the CSN TLV, contains the field rxTime. However, in the description in 16.5.3.2.2.6, the name of the field is upstreamTxTime. The name upstreamTxTime is more descriptive of what the quantity actually represents, and in fact was the name of the field in 802.1AS-2011 (the analogous table in 802.1AS-2011 was Table E.1, and in that table the field was labeled upstreamTxTime. It appears that the name was changed to rxTime in the Table around draft D0.4 of 802.1ASbt (this was a planned amendment to 802.1AS-2011; it was later decided to develop a revision instead). There were no ballots at the time, and no emails or presentations on this topic have been found. It is not known why the change was made, but it appears to be incorrect. In addition, the CSN TLV contains the field domainNumber, which was not present in 802.1AS-2011. Since domainNumber is already carried in the PTP common header, it is not clear why it was added to the CSN TLV. The addition was made around draft D0.5 of 802.1ASbt, i.e., this change was separate from the change of upstreamTxTime to rxTime. However, there were no ballots at the time, and no presentations or emails on this have been found. It is not known why the change was made.
Proposed text
Change ‘rxTime’ to ‘upstreamTxTime’ in Table 16-1. Discuss whether to take any action on the domainNumber field. Note that removing domainNumber cause a problem for backward compatibility because it is now published in 802.1AS-2020. On the other hand, leaving this field in the TLV causes no harm other than the transmission of one extra octet over the CSN; one approach could be to simply leave this field in the TLV.
Impact on existing networks
There is no impact on existing networks if rxTime is changed to upstreamTxTime in Table 16-1. If domainNumber is left in the TLV, there is no impact on existing networks. If domainNumber is removed from the TLV, there could be a backward compatibility problem.
Originator
Name:Geoffrey M. GarnerEmail:gmgarner@alum.mit.edu <mailto:gmgarner@alum.mit.edu>
Affiliation:Huawei (Consultant)
Submitted:2020-10-29