H3C Technologies H3C SR8800 - Manual (Page 96)

84
SSM level of the reference source
SSM, also known as synchronization quality marker, indicates the synchronization timing signal level on
a synchronization timing transmission link.
The priority of SSM level of the reference source, ranging from high to low, includes:
• PRC—G.811 clock signal.
• TNC—G.812 transit node clock signal.
• LNC—G.812 local node clock signal.
• SETS—SDH device clock source signal.
• unknown—Unknown synchronization quality.
• DNU—Cannot be used as a clock source.
NOTE:
The reference source whose SSM level is DNU cannot be used as a clock source.
Working mode of the clock monitoring module
The clock monitoring module can be configured to work in either of the following two modes:
Manual mode
In this mode, the clock source is configured manually. The clock monitoring module does not
automatically switch the clock source, but just tracks the primary reference source. If the primary
reference source is lost, the clock monitoring module enters a holdover state.
Auto mode
In auto mode, the clock source is automatically selected by the system. When the primary clock source
is lost or not available, the clock monitoring module selects another clock source based on the following
rules:
• If SSM level is not activated, the clock source is determined by reference source priority. If two
reference sources have the same priority, the clock source is selected according to the reference
source number (1 to 18). When the reference source with the highest priority is lost, the next
available reference source with the highest priority is selected. When the former clock source
becomes available, the system switches to that clock again.
• If SSM is activated, the clock source is decided by the SSM level. If two reference sources have the
same SSM level, the reference source priority takes effect, in the way described above.
NOTE:
The following clock sources are excluded in clock selection (when SSM is activated):
• Clock sources whose signals are lost.
• Clock sources whose priority is 255.
• Clock sources whose SSM level is DNU (DoNotUse).
Working mode of the port clock
Depending on the source of the port clock, a port supports two modes of clocks: