External Clock Reference Alarm Handling
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Transcript of External Clock Reference Alarm Handling
External Clock Reference Alarm Handling
Alarm Description:This alarm is reported when a BTS fails to perform clock synchronization because external reference
clock signals are lost, when the reference clock is unavailable, or when there is a large frequency
offset between the reference clock and the local oscillator.
Alarm
ALM-26262 External Clock Reference Problem, Specific Problem= Excessive Frequency Difference
between Clock Reference and Local Crystal Oscillator
Possible Cause1. Transmission quality unstable. Transmission instability is the major cause of this alarm.
2. Clock Source Lost.
3. WMPT/GTMU board is faulty; the frequency output of the crystal oscillator can’t trace and
lock the upper level reference clock which leads to clock reference alarm.
4. Configuration issue.
Handling Procedure
3G SITE
Step 1. Check clock status. The PLL status should be equal to LOCKED to clear the alarm which means that the local oscillator is getting its clock from the source. From the result below, the clock is in Free
running instead of Locked.
%%DSP CLKSTAT: SN=7;%%
Display System Clock Status
---------------------------
Cabinet No. = 0
Subrack No. = 0
Slot No. = 7
Current Clock Source = Line Clock
Current Clock Source State = Frequency Deviation
Clock Working Mode = Manual
PLL Status = Free running
(Number of results = 1)
--- END
NOTE: Please check PLL status reference on the last pag.
Step 2. Check the clock resource. Check other sites of the RNC if also experiencing clock problem. If majority of sites are normal, clock resource is working without any problem, if not check the RNC
interface board and clock source.
Step 3. Check if there is fault or sync issue in the transmission network.
Step 4. Modify the value of the Current DA to adjust the value of the frequency offset to zero. Theoretically we can only adjust the frequency offset from -19 to 19.
1. Open the Maintenance Client for the NodeB. Click on the MAINTENANCE and expand the
REALTIME SPECIFIC MONITORING Tree to get on the CLOCK TEST.
2. Double click on the CLOCK TEST. A window will prompt up. Set Cabinet No = 0, Subrack No =
0, Slot No = 7 (WMPT board) and then click OK. This will show the current frequency
offset/difference of the internal oscillator to the source clock. You can choose the chart
graph to see how the frequency offset move when you adjust the current DA value. You
should adjust the current DA to make the difference as close to zero.
3. Display the CLOCK DA and take note of the Current DA value.
%%DSP CLKDA: SN=7;%%
Display Clock DA
----------------
Cabinet No. = 0
Subrack No. = 0
Slot No. = 7
Initial DA = 32316
Center DA = 32029
Current DA = 32029
(Number of results = 1)
--- END
4. Use the formula below to calculate for the value of the new current DA to adjust the
Frequency difference to 0.
New Current DA Value = Current DA – (65535/40 Hz) * Ave. Frequency Offset
5. Modify the value of the current DA with the result from the formula. You can change further
the DA value until the difference is almost 0.
%%MOD CURRDA: SN=7, DA=37760;%%
--- END
%%MOD CURRDA: SN=7, DA=37595;%%
--- END
6. When the difference is almost 0, modify the Center DA according to the Current DA. List the
clock record to check on the PLL status. It takes time before the clock will locked to the
source (about 2 – 3 hours), the alarm will clear after this time. (The PLL status will be
changed from Free Running Capture Fast Tracking Locked, see reference on the last
page)
%%MOD CENTERDA: SN=7, DA=37595;%%
--- END
%%LST CLKRECORD: SN=7;%%
List Clock Record
-----------------
Time PLL Status Current DA Center DA
2012-07-06 10:42:25 DST Fast tracking 37595 37595
2012-07-06 10:30:53 DST Free running 37760 32029
2012-07-06 10:30:19 DST Free running 38582 32029
2012-07-06 10:29:29 DST Free running 36945 32029
2012-05-27 03:26:39 DST Free running 32029 32029
2012-05-27 03:26:39 DST Free running 32029 32029
2012-05-27 01:56:44 DST Fast tracking 32029 32029
2012-05-27 01:51:43 DST Free running 32029 32029
2012-05-27 01:51:43 DST Free running 0 32029
(Number of results = 18)
--- END
7. We can forced the clock to Fast track the source by setting the clock working mode to Free
Running then setting back to Manual.
%%LST CLKMODE:;%%
List Clock Working Mode
-----------------------
Clock Working Mode = Manual
Selected Clock Source = Line Clock
Clock Source No. = 0
(Number of results = 1)
--- END
%%SET CLKMODE: MODE=FREE;%%
--- END
%%SET CLKMODE: MODE=MANUAL, CLKSRC=LINECLK;%%
--- END
%%LST CLKRECORD: SN=7;%%
List Clock Record
-----------------
Time PLL Status Current DA Center DA
2012-07-06 10:55:56 DST Fast tracking 37595 37595
2012-07-06 10:54:51 DST Fast tracking 37432 32029
2012-07-06 10:54:08 DST Fast tracking 36940 32029
2012-07-06 10:42:25 DST Fast tracking 37760 32029
2012-07-06 10:30:53 DST Free running 37760 32029
2012-07-06 10:30:19 DST Free running 38582 32029
2012-07-06 10:29:29 DST Free running 36945 32029
2012-05-27 03:26:39 DST Free running 32029 32029
2012-05-27 03:26:39 DST Free running 32029 32029
2012-05-27 01:56:44 DST Fast tracking 32029 32029
2012-05-27 01:51:43 DST Free running 32029 32029
2012-05-27 01:51:43 DST Free running 0 32029
(Number of results = 18)
--- END
8. We can see that the alarm will clear in few minutes but the clock working state will stay to
Fast Tracking until it is locked to the source. If after sometime and the clock cannot locked to
the external source the clock state will come back to the Free running state and the alarm
will reappear.
%%LST CLKRECORD: SN=7;%%
List Clock Record
-----------------
Time PLL Status Current DA Center DA
2012-07-06 13:28:27 DST Locked 37616 37595
2012-07-06 12:58:17 DST Locked 37615 37595
2012-07-06 12:58:17 DST Locked 37595 37595
2012-07-06 10:55:56 DST Fast tracking 37595 37595
2012-07-06 10:54:51 DST Fast tracking 37432 32029
2012-07-06 10:54:08 DST Fast tracking 36940 32029
2012-07-06 10:42:25 DST Fast tracking 37760 32029
2012-07-06 10:30:53 DST Free running 37760 32029
2012-07-06 10:30:19 DST Free running 38582 32029
2012-07-06 10:29:29 DST Free running 36945 32029
2012-05-27 03:26:39 DST Free running 32029 32029
2012-05-27 03:26:39 DST Free running 32029 32029
2012-05-27 01:56:44 DST Fast tracking 32029 32029
2012-05-27 01:51:43 DST Free running 32029 32029
2012-05-27 01:51:43 DST Free running 0 32029
(Number of results = 21)
--- END
Step 5. Reset/ replace the WMPT board.
2G SITE
Same principle works with 2G but the alarm handling is slightly different.
Step 1. Modify the value of the Current DA to locked the BTS clock to the external source.
1. Open the BSC LMT. On the BTS Device Panel, right click on the GTMU and select QUERY
BOARD INFORMATION. We can see that the Clock is free oscillating (same with Free running
in 3G). Clock Source is TRACE BSC CLOCK which means that the BTS gets its clocking from the
BSC through Abis Link.
2. Right click again on the GTMU then select MAINTAIN CLOCK. Take note of the Clock Factory
Value and the Current DA value.
3. Modify the Current DA value by running the command below. Set the Calibration Value to
the Clock Factory Value.
%%SET BTSCLKPARA: IDTYPE=BYID, BTSID=187, CN=0, SRN=0, SN=6, CLKMOD=BSCCLK, TRCRNGLMT=DISABLE, CALVAL=1901;%
%
RETCODE = 0 Execution succeeded.
--- END
4. Then save the BTS clock by running the command below.%%SAV BTSCLKPARA: IDTYPE=BYID, BTSID=187;%%
--- END
5. Wait until the alarm clears and check on the clock working state to change to Locked. It will
be changed from Free Oscillation Capture Locked.
6. If the clock working state changed to Locked then we can enable back the Clock Source to
the BSC clock and setting the calibration value to the current DA value.%%SET BTSCLKPARA: IDTYPE=BYID, BTSID=187, CN=0, SRN=0, SN=6, CLKMOD=BSCCLK, TRCRNGLMT=ENABLE, CALVAL=2285;%%
--- END
7. Save again the BTS clock by running the command below.%%SAV BTSCLKPARA: IDTYPE=BYID, BTSID=187;%%
--- END
PLL State Mode
1. Free Running
If no reference clock source is configured of the reference clock sources are unavailable, the
PLL works in free running state.
If there’s an available reference clock source, the BSC judges the reference clock source for
260 seconds. If the source remains stable for more than 260 seconds, the PLL shifts to quick
capture state. Otherwise, the PLL still works in free running state.
2. Quick Capture
If the reference clock source is available and remains stable for a period (longer than 400
seconds for a GPS source or 200 seconds for any source other than the GPS source), the PLL
shifts to tracking state.
If the reference clock is lost, the PLL shifts back to free running state.
3. Fast Tracking
4. Locked
Difference between CENTER and CURRENT DA
When the NE clock works in Free running mode, the current DA will be changed according to the
Center DA. If the NE uses a clock source, the current DA changes with the frequency of the clock
source. If the external clock source stays locked for seven consecutive days, this shows that the clock
source is very stable. In this case the clock module overwrites the center DA with the current DA.