Alcatel 1850 TSS-320 Technical Handbook page 139

• In SDH there is one T4/T5 selection process controlling and keeping aligned SEL_A on
SLCCRU copy A and B (protected mode); the selection of the output clock from the active copy
is done by PSF card. Selection of the internal oscillator is supported (holdover and free-running
states).
The quality information can be also allocated (if the source signal does not support SSM) or overruled by
provisioning.
All the output signals generated with the internal clock are marked with same SSM value with the following
two exceptions:
• The source being selected as the timing source for internal synchronization sends the SSM "do
not use" for preventing potential creation of a timing loop in the network.
• A forced transmit SSM = "do not use" is configured for that port
In accordance to ETSI prETS 300 417-6 standard if the received SSM changes without triggering the
selection process (because it is still the best quality available in QL-enabled mode) this change is
forwarded to the transmit SSM in less than 200 ms; if the received SSM changes and this triggers the
selection process the new selection and the new SSM is performed within 500 ms; if the holdover mode
is entered the requirement is 2000 ms.
In addition to the generic "QL-enabled/disabled" modes also"ADM-with-SSU" mode is possible
In this configuration the selection is made among derived reference clocks of STM-N inputs for generating
the external reference clock output (T4/T5) which is used to synchronize the SSU. The output signal of
the SSU is configured as the timing source (T3 or T6) of the highest priority for selection of the timing
source for the internal synchronization.
Technical Handbook Common
Functional Description
Alcatel 1850 TSS-320 Rel. 1.1
8DG 07734 AAAA Edition 01 137/270