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New Member

Clock Source Errors

Can any one Please asssit :

I've got a POS link on a 7609 Flexwan Module connecting via a Sonet Network connecting to a remote 12410 GSR.

Problem is: i have configured both ends to clock from Line but the OSR keeps reverting back to internal.

with the show controller command , it indicates a change back to internal , Reason S1.

Has anyone had this problem before ? any suggestion ?

What exactly is the S1 Error ?

Find below output of Show controller:

SHOSR01#sh controllers pos 7/0/0 details



LOF = 1 LOS = 1 BIP(B1) = 4843


AIS = 1 RDI = 1 FEBE = 6321445 BIP(B2) = 2105609


AIS = 22 RDI = 22 FEBE = 193111 BIP(B3) = 206445

PLM = 5 UNEQ = 10 TIM = 0 TIU = 0

LOP = 0 NEWPTR = 699 PSE = 4053218 NSE = 21

Active Defects: None

Active Alarms: None

Alarm reporting enabled for: SF SLOS SLOF B1-TCA LAIS LRDI B2-TCA PAIS PLOP PRDI B3-TCA

Line alarm trigger delay = 100 ms

Path alarm trigger delay = 100 ms

Framing: SONET


COAPS = 6 PSBF = 1

State: PSBF_state = False

Rx(K1/K2): 00/00 Tx(K1/K2): 00/00

Rx Synchronization Status S1 = 0F

S1S0 = 02, C2 = CF

Remote aps status (none); Reflected local aps status (none)



State: RDOOL_state = False


Remote hostname : ESGSR01

Remote interface: POS1/0

Remote IP addr :

Remote Rx(K1/K2): F9/FF Tx(K1/K2): 08/00

50CE4880: 45534753 52303100 00000000 ESGSR01.....

50CE4890: 00000000 00000000 00000000 504F5331 ............POS1

50CE48A0: 2F300000 00000000 00003130 2E313336 /0........10.136

50CE48B0: 2E32342E 31330000 00004639 46463038 .24.13....F9FF08

50CE48C0: 30300D0A 00..

BER thresholds: SF = 10e-3 SD = 10e-6

TCA thresholds: B1 = 10e-6 B2 = 10e-6 B3 = 10e-6

Clock source: internal

Clock source changed to : internal Reason : S1


Re: Clock Source Errors

Rx Synchronization Status S1 = 0F " indicate Don't Use for synchronization regarding to the standard ITU G.704:

As noted above the "show controller" output seems to indicate that the clock source was indeed set to be internal..

So the root cause of the issue is SPA is not ignoring Rx Synchronization Status S1 and changing clock source to internal

New Member

Re: Clock Source Errors


Thanks .

I actually digged up a command " fos flag s1 ignore " which seems to change the clocking back to line.

Apparently on some Cisco IOS , the Router reverts to Internal if it recieves an S1 bit ???

Question is : is it safe to ignore the S1 Bit ?

New Member

Re: Clock Source Errors


although I'm a little late and you solved the problem on your own this information could be helpful.

The S1 byte indicates the clock quality in sdh/sonet networks. You received 0xf (1111) which is known as "don't use for synchronization" in sdh world. So it should be investigated why the connected sdh-equipment sends oxf. Most probably the sdh-equipment will have a clock-problem itself or it is just misconfigured. If you ignore the s1 byte you will clock from a line which should not be used for clocking in sdh world. but I think this won't bring you in trouble because the clock you receive will be good enough for the pos interface.

Further information of how clocking works can be found here:

If you don't want to use the ignore s1 byte command you could try to fix the problem in the sdh network. If you receive a better S1 byte (as for example 0x2 or 0x4) you would be on the safe side.

best regards


New Member

Re: Clock Source Errors


I was talking about sdh networks because I wasn't aware of the fact you were using SONET. So replace all sdh in my last post by SONET in order to fit my answer to your question.



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