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  • Performance paramaters PJC+ and PJC-

    From Najam Saleem@21:1/5 to All on Thu Jun 27 03:27:12 2019
    Hello everyone!

    Could anyone tell about some details of PJC+ and PJC-. How these number can be used to analyse the performance of a signal.

    Regards,
    Najam Saleem

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  • From Huub van Helvoort@21:1/5 to All on Sun Jun 30 22:46:39 2019
    Hello Najam,

    You ask:

    Could anyone tell about some details of PJC+ and PJC-.
    How these number can be used to analyse the performance of a signal.

    Pointer Justifications (PJ) occur when the network clock (or local
    system clock) are not synchronised.

    PJ's are counted per second, 15 minutes and 24 hours PJC.
    PJC+ if the reference clock is slower, PJC- if it is faster.

    if the PJC+ and PJC- are equal during a period it means there
    is some wander on the clocks, this may be due to temperature
    differences, or the stability of the reference clock.

    Best regards, Huub.



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  • From Najam Saleem@21:1/5 to Huub van Helvoort on Mon Jul 1 03:44:13 2019
    On Monday, July 1, 2019 at 1:46:42 AM UTC+5, Huub van Helvoort wrote:
    Hello Najam,

    You ask:

    Could anyone tell about some details of PJC+ and PJC-.
    How these number can be used to analyse the performance of a signal.

    Pointer Justifications (PJ) occur when the network clock (or local
    system clock) are not synchronised.

    PJ's are counted per second, 15 minutes and 24 hours PJC.
    PJC+ if the reference clock is slower, PJC- if it is faster.

    if the PJC+ and PJC- are equal during a period it means there
    is some wander on the clocks, this may be due to temperature
    differences, or the stability of the reference clock.

    Best regards, Huub.



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    Dear Huub,

    Thanks for the kind reply.

    Will be very grateful if I can have a reply on few questions in reference to above discussion:

    1- How many PJCs are considered within acceptable limit?
    2- If there are lot of PJCs (+ or -) what type of service degradation one can experience (If any).

    Thanks in anticipation.

    Regards,
    Najam Saleem

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  • From Huub van Helvoort@21:1/5 to You on Sun Aug 4 13:05:30 2019
    Hello Najam,

    You replied:

    Will be very grateful if I can have a reply on few questions in reference to above discussion:

    1- How many PJCs are considered within acceptable limit?

    In clause 8.1.3. of ITU-T Recommendation G.707 the pointer justification process is described.

    A pointer justification action occurs when there is a difference of
    ± 3 bytes (24 bits) between system clock and client clock.

    For SDH the network-client tolerance value is ± 4.6 ppm.
    This means that after transport of 1 million bits, a difference up to
    4.6 bits is acceptable.

    With this you can calculate how often a pointer justification can occur.

    2- If there are lot of PJCs (+ or -) what type of service degradation one can experience (If any).

    Also in clause 8.1.3 of G.707 you will see that in case e positive
    or negative justification occurs there is no loss of information.
    Only when there is excessive pointer justification (e.g. more often
    than once in three SDH frames) information is lost.

    Best regards, Huub.


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