Hi Richard,
Thank you for your feedback. I want to explain why we chose to add TAB to your
BC implementation rather than adding a new type of device. A TAB is
mathematically equivalent to a TC but is functionally equivalent to a BC. More
specifically, a TAB has the following BC attributes:
- A TAB participates in the BMC selection.
- A TAB has port state.
- A TAB has a separate logSyncInterval dataset member for each port.
It’s the last point that I think needs further clarification. Under clause
10.2.4 ‘Per-port global variables’ of the IEEE Std 802.1AS™-2011 standard, the
following per port variables are defined:
10.2.4.3 currentLogSyncInterval: the current value of the logarithm to base 2
of the mean time interval, in seconds, between the sending of successive
time-synchronization event messages (see 10.6.2.3).
10.2.4.4 initialLogSyncInterval: the initial value of the logarithm to base 2
of the mean time interval, in seconds, between the sending of successive
time-synchronization event messages (see 10.6.2.3).
10.2.4.5 syncInterval: a variable containing the mean time-synchronization
event message transmission interval for the port.
Clause 10.6.2.3 ‘time-synchronization event message transmission interval’ adds
the following note:
NOTE—The value of initialLogSyncInterval is the value of the sync interval when
the port is initialized. The value of the sync interval may be changed, e.g.,
if the port receives a Signaling message that carries a message interval
request TLV (see 10.5.4.3), and the current value is stored in
currentLogSyncInterval. The value of the sync interval can be reset to the
initial value, e.g., by a message interval request TLV for which the value of
the field timeSyncInterval is 126, see 10.5.4.3.7.
Based on these clauses, it’s clear that each port maintains its own sync
interval setting and needs to maintain its own sync interval timer. It’s also
clear that when the slave port of a TAB receives a sync event, that message is
not immediately sent out on downstream ports. Rather, the configured sync
interval for a given port must be adhered to.
Regards,
Rodney Greenstreet
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