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New Member

Clocking guidelines

Hi,

In order to recover signal from the line, receiver must have some reference signal (just to correctly detect 0s & 1s send by far-end).

I can imagine that if I set clocking to 'line' on the controller, then it tries to build this reference signal based on the signal itself.

If I set clocking to 'internal' it possibly somehow calculates the reference signal based on the link speed (E1 / T1 /...).

There should be two basic scenarios:

1). clocking is provided by telco between my two routers with controllers. In such scenario I should use clock line as they should send good quality signal (very low stratum). Is there any justification for putting internal (even if I use better clock)?

2). how building reference signal (clocking) works for channelized circuits (e.g. T3 channelized to T1s with clocking set to internal on T3 level, but line on T1 level)?

3). should the values always be symmetric (either line-line, or internal-internal) depending if telco provides clocking or not?

4).what does it exactly mean that telco provides clocking signal (see my first three sentences re how I understand this all works).

Thanks for answers & providing reference documents to better study this area.

Mariusz

2 REPLIES
Cisco Employee

Clocking guidelines

1). clocking is provided by telco between my two routers with  controllers. In such scenario I should use clock line as they should  send good quality signal (very low stratum). Is there any justification  for putting internal (even if I use better clock)?

[upinder]

The Cisco router or for that matter the edge device is supposed to be a stratum 4 device. when you do internal you shall be generating clock yourself and if the oscilator on the card cannot sync with the TDM you shall have slips etc on the card. that is the reason why its always recommended for the edge routers be on line instead.

2). how building reference signal (clocking) works for channelized  circuits (e.g. T3 channelized to T1s with clocking set to internal on T3  level, but line on T1 level)?

[Upinder]

are you talking on SONET ? what card you have in mind ? the best thing is to look at the CCO document for configuration.  At the level on T3 and SONET you have to have equipemnt such as ONS to do the T1 splitting. Mostly SP will have this expenisve equipment   in that way you are better off doing internal at both levels. can you elaborate on the ques if the above does not make sense to you.

3). should the values always be symmetric (either line-line, or internal-internal) depending if telco provides clocking or not?

[Upinder]

SP (internal) ----------edge_router(line)

rare cases if you cannot get rid of slips y ou can try this is a troubleshoting step :

SP (line) ----------edge_router(internal)

But this is not a advisable solution as the card oscillator is not supposed to be used in this fashion.

4).what does it exactly mean that telco provides clocking signal (see my  first three sentences re how I understand this all works).

[Upinder]

think of the data traffic has to be put in each time slot. this goes back  to your netwoking class and topic of TDM

Regards,

~upinder sujlana (usujlana)

New Member

Clocking guidelines

Hi Upinder,

First of all - thank yuo for provided feedback. It was really helpful, but still wondering on one thing:

clocking line - it means that the oscilation signal is built based on the received signal (0s and 1s which creates data itself)

clocking internal - it means that the oscilation signal is built based on external (looking from access perspective) clocking signal and based on that 0s and 1s are determined.

Now, as telco should use the best available clocking available, just wondering in which scenarios it might fail (i.e. my "external" oscillaton signal will be better from the one created based on incoming signal). Is it for low signal quality (0s are so close to 1s so that I cannot build reference signal correctly)? What else can cause slippage?

p.s. re the configuration, I had in mind for example ESR-4OC3-ChSTM-1 & ESR-6CT3 .

Thanks, Mariusz

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