Selecting The Reference Selection Mode - Symmetricom TSG-3800 Series User Manual

value. The operator may also set the port to disregard the received SSM and always
output the provisioned SQL. The SQL received or provisioned is passed to the
frame generators for determining the output SSM when in Locked mode. If inputs
are not receiving SSMs and are provisioned below the selected clock's stratum
level, the clock enters holdover.
SSMs and Clock and Frame Generator Modules
The Clock modules compare their holdover SQLs to the reference SQL. If the clock
SQL is better than the reference SQL, the clock enters holdover. If the reference
SQL is equal to or better than the clock SQL, the clock operates normally.
When an input has been provisioned to SSMs On or SSM Mode Auto, the
TSG-3800 determines if a received SSM is a valid SQL. The TSG-3800 interprets
the SQLs listed in the SQL table
unrecognized. According to GR-378, if an input has been receiving a valid SSM and
then receives an invalid SSM, the input fails. When a valid SSM is received and
re-qualified, the fault automatically clears. However, if the SSM remains invalid and
the signal is ESF or E1, the operator can clear the alarm using the "Input #.# SSM
Mode Auto" command.
The Frame Generators take the input SQL from the reference input and convert it to
the appropriate SSM for output. The operator may override this by placing the
framer in manual mode and then entering the output SSM directly (both T1 and E1).
If the Clock module associated with the Frame Generator is in holdover, the Frame
Generator outputs the clock's holdover SQL. With the bypass Frame Generator (PN
23478486-000-0) and backplane, when both clocks are in warmup or have failed
and the SSM is set to STU, the signal from input 1.1 or 2.1.1 can be used to
generate the output.
If the received T1 SSM does not have an E1 match, the E1 Frame Generator
outputs the Stratum Unknown (STU) message. The operator should be able to
provision the input to PRS, STU, ST2, and ST3.

Selecting the Reference Selection Mode

The TSG-3800 can choose input references using one of three modes:
Priority – bases the reference selection on the port's provisioned priority.
Secondary criteria is the SSM information.
SSM – bases the reference selection on received or provisioned SSM, then
priority and position.
Best – bases the reference selection on the weight derived from the input
stability calculations. Secondary criteria are the priority and SSM information.
Priority Mode
In Priority Mode, the provisioned Priority is the first criteria when selecting a
reference.The selection order is as follows:
12778474-002-2 Revision F – March 2004
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
Selecting the Input Reference Signal
(Table 3-1); any other SSM is considered
Operating the TSG-3800
TSG-3800 User's Guide 85