Sonet Pointer justification Concept

[ekavirsrikanth]

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

 

[Pieter Hulshoff]

> 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

 

[Symon]

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.

 

[Allan Herriman]

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

 

[ekavirsrikanth]

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