Ds1 Freq/Clk Slips - Fluke 635 User Manual

2-9.

DS1 Freq/Clk Slips

DS1 Freq
Clk Slips
T1
DS1 Freq
When the DS1 frequency result is selected (using the RESULTS keys), the test
set displays the frequency (in Hz) of the DS1 signal. If the DS1 frequency
deviates from the nominal (1.544 MHz ± 50 Hz), the red FREQDEV LED
illuminates to indicate that a DS1 frequency deviation is occurring. A
frequency deviation of greater than ± 50 Hz indicates that the clock source is
becoming unstable and has an unacceptable variation.
Clk Slips
In order for a T1 circuit to perform properly, the TX clock (from the CPE)
must be synchronized with the receive clock (from the central office). If a
variation of these clocks exists, errors will result. The clock-slip parameter is
used to verify clock synchronization. The test setup for a clock-slip
measurement between the Tx and Rx side of a T1 span is described in section
3-10 of this manual.
Timing tests may also be performed to either side of the span when a T1
reference clock (stratum) is used. If a bipolar clock or a T1 signal is present at
both the REF and RX receivers, the test set compares the two inputs and
declares clock slips (if they are out of phase). If an external reference clock is
not available, the unit will automatically compare the receiver clock to the
internal, 5-ppm, 1.544-MHz clock source.
Clock slips is a loop-timing parameter that shows the total number of clock
counts that the reference and receiver clocks have deviated from since the test
began (or from the last restart). A positive number indicates that the reference
clock is faster than the receive clock. A negative number indicates that the
receive clock is faster than the reference clock.
RB Int
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1544000Hz
0
CSU
2
abn09f.eps
2-7