Dear Sir,

[TM1]<--------->[ADM]<--------->[TM]

If the clock of Terminal Mux [TM1] is f1 & the clock of [ADM] is f2
(f1>f2), then whether ADM will do +ve pointer justification OR -ve
pointer justification??

In this case whether [TM1] will also do the justification?? That is if
[ADM] is doing +ve justification, i guess [TM1] should do -ve
justification for the reverse direction. Pl clarify me sir.

Thanks & Regds

Satheesh

Hi Satheesh,

You wrote:

> [TM1]<--------->[ADM]<--------->[TM]
> 
> If the clock of Terminal Mux [TM1] is f1 & the clock of [ADM] is f2
> (f1>f2), then whether ADM will do +ve pointer justification OR -ve
> pointer justification??

f1>f2 means more bits are transported using f1 than using f2,
so the justification has to be positive to give extra bytes for
the extra bits.

> In this case whether [TM1] will also do the justification?? That is if
> [ADM] is doing +ve justification, i guess [TM1] should do -ve
> justification for the reverse direction. Pl clarify me sir.

Yes, you are correct, if both f1 and f2 are totally independent
(which should be an exception, because the S in SDH and Sonet
stands for Synchronous!) then the TM shall have the same amount
of -ve justifications as the ADm does +ve justifications.

Cheers, Huub.

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If the TM1 is sending excess bits (because f1 is higher), then how ADM
will provide extra bytes for receiving the incoming excess bits in
case of +ve justification? The main confusion is during +ve
justification, 3 bytes after H3 are stuffed which can't carry any
useful info, whereas for -ve justification, H3 bytes can be used for
holding the additional incoming bits from TM1. Pl clarify sir.

In ITU-T G.707, it is stated that if the VC rate is less than the STM
rate, then the justification will be +ve, otherwise it will be -ve.

Hello Satheesh,

> If the TM1 is sending excess bits (because f1 is higher), then how ADM
> will provide extra bytes for receiving the incoming excess bits in
> case of +ve justification? The main confusion is during +ve
> justification, 3 bytes after H3 are stuffed which can't carry any
> useful info, whereas for -ve justification, H3 bytes can be used for
> holding the additional incoming bits from TM1. Pl clarify sir.

There is a buffer used with write frequency f1 and read frequency f2.
If the read and write counters are too close together an extra byte
is read. The byte is put in the H3 byte and the pointer is incremented.

See for a live demo http://www.lagrit.etsmtl.ca/seminaires/SonetFlash/
select menu 7a.

> In ITU-T G.707, it is stated that if the VC rate is less than the STM
> rate, then the justification will be +ve, otherwise it will be -ve.

Correct, in your case the received STM rate is f1 and the
internal VC rate is f2.

Cheers, Huub.

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Always remember that you are unique...just like everyone else...

Huub,

>> If the TM1 is sending excess bits (because f1 is higher), then how ADM
>> will provide extra bytes for receiving the incoming excess bits in
>> case of +ve justification? The main confusion is during +ve
>> justification, 3 bytes after H3 are stuffed which can't carry any
>> useful info, whereas for -ve justification, H3 bytes can be used for
>> holding the additional incoming bits from TM1. Pl clarify sir.
> 
> There is a buffer used with write frequency f1 and read frequency f2.
> If the read and write counters are too close together an extra byte
> is read. The byte is put in the H3 byte and the pointer is incremented.

Actually, I think Satheesh is correct here: if extra bytes are placed in the H3 byte, then the pointer will be decremented.

Kind regards,

Pieter Hulshoff

Hallo Pieter,

You wrote:

>>> If the TM1 is sending excess bits (because f1 is higher), then
>>> how ADM will provide extra bytes for receiving the incoming
>>> excess bits in case of +ve justification? The main confusion is
>>> during +ve justification, 3 bytes after H3 are stuffed which
>>> can't carry any useful info, whereas for -ve justification, H3
>>> bytes can be used for holding the additional incoming bits from
>>> TM1. Pl clarify sir.
 >>
>> There is a buffer used with write frequency f1 and read frequency
>> f2. If the read and write counters are too close together an extra
>> byte is read. The byte is put in the H3 byte and the pointer is
>> incremented.
> 
> Actually, I think Satheesh is correct here: if extra bytes are placed
> in the H3 byte, then the pointer will be decremented.

Indeed, I answered too fast.

In case f1 is higher rate as f2 the VC clock is faster than the
AUG clock. By putting bytes in the H3 bytes there will be more
bytes of the VC in the AUG frame.
But the number of bytes in the VC frame does not change so
this requires the decrementing of the pointer, a -ve
justification.

See clause 8.1.3 of G.707 and figures 8.4 and 8.6.


M.vr.gr. Huub.

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