Sonet Pointer justification Concept

Discussion in 'VHDL' started by ekavirsrikanth@gmail.com, Mar 13, 2008.

  1. Guest

    Hi ALL,

    If any one working on Sonet STS-N framer/deframer IP devleopment
    please help me in understanding the concept of Pointer Justification.

    1. when the SPE data is in slow rate that the STS-1 frame Positive
    Stuffing will take care of this problem but what my question is as we
    are inverting some ofthe bytes in the H1 & H2 (positiving Stuffing)
    and adding one extra byte after H3 byte which does not carry any info
    but included to delay by one BYTE how it will rectify the prbolem of
    slow data rate Sync with the STS-1 data rate.

    I know it looks odd sending this quiery to this site but some of them
    have knowledge in Sonet IP development...i am looking forward for
    them....


    Thanks
    kil
    , Mar 13, 2008
    #1
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  2. wrote:
    > I know it looks odd sending this quiery to this site but some of them
    > have knowledge in Sonet IP development...i am looking forward for
    > them....


    You could have considered sending this to the comp.dcom.sdh-sonet newsgroup, but
    I guess you're in luck: some of us are indeed familiar with SONET/SDH.


    > 1. when the SPE data is in slow rate that the STS-1 frame Positive
    > Stuffing will take care of this problem but what my question is as we
    > are inverting some ofthe bytes in the H1 & H2 (positiving Stuffing)
    > and adding one extra byte after H3 byte which does not carry any info
    > but included to delay by one BYTE how it will rectify the prbolem of
    > slow data rate Sync with the STS-1 data rate.


    An STS1SPE carries 85*9=765 data bytes (9 of which are overhead), and in an
    AU3/STS1 mapping gain 2 stuff columns for a total of 87*9=783 bytes. The
    location of the start of this STS1SPE is carried in H1 & H2 (which implies the
    pointer value there can be between 0 and 782), with a 0 pointer indicating the
    start of the STS1SPE (J1 location) is located right behind the H3 bytes.

    If the datarate of the STS1SPE is too slow, you need to insert a stuff byte into
    the STS1 payload to compensate. This is done using a positive stuffing combined
    with a pointer increase.

    Let's say your pointer value is 5, and you wish to do a positive stuffing:
    In frame 1, you invert the I (increase) bits of your pointer to indicate a
    pointer increase, and insert a stuff byte (usually value 0) after the H3 byte;
    then you continue with sending your STS1SPE data as normal.
    Starting frame 2, you send pointer value 6. You are not allowed to start a new
    stuffing until after frame 4.

    A slow rate basically means that your STS1SPE does not provide enough data to
    fill your STS1. By inserting a stuff byte into your frame (during which you
    don't read from your STS1SPE buffer) you allow your STS1SPE to catch up. Since
    the start of your frame will now be one position later in the frame, your
    pointer has to be increased.

    A similar story goes for fast rate, where you use H3 to send an extra byte of
    your STS1SPE frame, invert the D (decrease) bits in your pointer in frame 1, and
    decrease your pointer by 1.

    Hope this helps.

    Kind regards,

    Pieter Hulshoff
    Pieter Hulshoff, Mar 13, 2008
    #2
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  3. Symon Guest

    wrote:
    > Hi ALL,
    >
    > If any one working on Sonet STS-N framer/deframer IP devleopment
    > please help me in understanding the concept of Pointer Justification.
    >
    >
    > Thanks
    > kil


    Kil,
    You need to read and understand ITU-T G.707. There are sections for each of
    the pointers, AU-n, TU-3, etc., and these include detailed step-by-step
    guides to exactly how the frequency justification works.
    HTH., Syms.
    Symon, Mar 13, 2008
    #3
  4. On Thu, 13 Mar 2008 11:27:39 -0000, "Symon" <>
    wrote:

    > wrote:
    >> Hi ALL,
    >>
    >> If any one working on Sonet STS-N framer/deframer IP devleopment
    >> please help me in understanding the concept of Pointer Justification.
    >>
    >>
    >> Thanks
    >> kil

    >
    >Kil,
    >You need to read and understand ITU-T G.707. There are sections for each of
    >the pointers, AU-n, TU-3, etc., and these include detailed step-by-step
    >guides to exactly how the frequency justification works.
    >HTH., Syms.


    BTW, all released ITU-T Recommendations are now available for free
    download, thanks to a policy change within the ITU.

    G Series here:
    http://www.itu.int/rec/T-REC-G/e

    The last time I did anything with pointers, I needed G.783 as well as
    G.707. (I don't recall exactly what I got from G.783 though.)

    Regards,
    Allan
    Allan Herriman, Mar 13, 2008
    #4
  5. Guest

    On Mar 13, 10:01 am, Allan Herriman <> wrote:
    > On Thu, 13 Mar 2008 11:27:39 -0000, "Symon" <>
    > wrote:
    >
    > > wrote:
    > >> Hi ALL,

    >
    > >> If any one working on Sonet STS-N framer/deframer IP devleopment
    > >> please help me in understanding the concept of Pointer Justification.

    >
    > >> Thanks
    > >> kil

    >
    > >Kil,
    > >You need to read and understand ITU-T G.707. There are sections for each of
    > >the pointers, AU-n, TU-3, etc., and these include detailed step-by-step
    > >guides to exactly how the frequency justification works.
    > >HTH., Syms.

    >
    > BTW, all released ITU-T Recommendations are now available for free
    > download, thanks to a policy change within the ITU.
    >
    > G Series here:http://www.itu.int/rec/T-REC-G/e
    >
    > The last time I did anything with pointers, I needed G.783 as well as
    > G.707.  (I don't recall exactly what I got from G.783 though.)
    >
    > Regards,
    > Allan


    Hi ALL,

    Thanks you all for your valuble responses. I will try to gothrough the
    ITU Docs..... to have a clear understanding...

    Regards
    kil
    , Mar 14, 2008
    #5
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