Basic System Configuration Guide System Management
Edition: 01 3HE 11010 AAAC TQZZA 265
After the quality level values have been associated with the system timing inputs, the
two reference inputs and the external input timing ports are processed by the system
timing module to select a source for the SSU. This selection process is described
below.
• Before an input can be used as a potential timing source, it must be enabled
using the ql-selection command. If ql-selection is disabled, then the priority
order of the inputs for the Synchronous Equipment Timing Generator (SETG) is
the priority order configured under the ref-order command.
• If ql-selection is enabled, then the priority of the inputs is calculated using the
associated quality level value of the input and the priority order configured under
the ref-order command. The inputs are ordered by the internal relative quality
level (shown in the middle row in Table 30) based on their associated quality
level values. If two or more inputs have the same quality level value, then they
are placed in order based on where they appear in the ref-order priority. The
priority order for the SETG is based on both the reference inputs and the
external synchronization input ports.
• Once a prioritized list of inputs is calculated, the SETG and the external
synchronization output ports are configured to use the inputs in their respective
orders.
• Once the SETG and external synchronization output ports priority lists are
programmed, then the highest-qualified priority input is used. To be qualified, the
signal is monitored to ensure that it has the expected format and that its
frequency is within the pull-in range of the SETG.
6.4.9.1.1 SSM/ESMC QL Transmission
If a port is using the SETG output as its timing reference, the port transmits the SSM
corresponding to the QL of the SETG.
On the port that is selected as the reference for the SETG, the port transmits the
DNU/DUS value in the SSM/ESMC.
If a BITS port is selected as the reference for the SETG, both BITS ports transmit
DNU/DUS value.
An Ethernet port with a copper SFP always transmits DNU/DUS when SSM is
enabled on the port. When SSM is enabled on a copper-based RJ45 Ethernet port,
DNU/DUS is transmitted if the port phy-tx-clock is not configured as master. When
SSM is enabled on a copper-based RJ45 Ethernet port and the port phy-tx-clock is
configured as master, the port transmits the SSM value corresponding to the
determined by the SSU.
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