Differences between TU-3 and TUG-3

[Michelot]

Bonsoir Huub,

In the section 7.2.2 of G.707 we can read that "The TU-3 consists of
the VC-3 with a 9-byte VC-3 POH and the TU-3 pointer".

I would think that it is TUG-3 and not TU-3 as it is noted in the
figure just below.

And this figure doesn't mention where is TU-3, contrary to the title
"multiplexing of a TU-3 via a TUG-3".

Another point, is it important to indicate "via" instead of "in"?

I understand that TU-3 is only VC-3 with the 3 bytes of the TU-3
pointer. Thus, we can't really represent TU-3 by an homogenous block
of (9 x 85 + 3) bytes, with VC-3 floating into.

In fact, I woul think that VC-3 doesn't float in TU-3 but in TUG-3. Is
it correct?

Thanks very much to clarify my brain on these basic SDH points.

When the new G.707 version is planned to be published?

Best regards,
Michelot

[Bert Klaps]

Hi Michelot,

Post by Michelot
In the section 7.2.2 of G.707 we can read that "The TU-3 consists of
the VC-3 with a 9-byte VC-3 POH and the TU-3 pointer".
I would think that it is TUG-3 and not TU-3 as it is noted in the
figure just below.

No, the TU-3 does not include the fixed stuff bytes, while
the TUG-3 does: the TUG-3 is a structure of 9 rows by 86 columns.

Post by Michelot
And this figure doesn't mention where is TU-3, contrary to the title
"multiplexing of a TU-3 via a TUG-3".

That would be sort of difficult to do: the TU-3 is not a
contiguous structure. It consists of a VC-3 and the TU-3
pointers pointing to it.
So in a sense it's there in the figure (the fixed stuff
could have been marked differently).

Post by Michelot
Another point, is it important to indicate "via" instead of "in"?

Not really, but it is a subtle indication that the TUG-n
(or AUG-n) are not network layers. They're just auxiliary
concepts to explain the multiplexing scheme.
So a TUG/AUG is not the end-target of the multiplexing,
only a network layer like VC-n is, hence "via" a TUG/AUG
and not "in/into"...

Post by Michelot
I understand that TU-3 is only VC-3 with the 3 bytes of the TU-3
pointer. Thus, we can't really represent TU-3 by an homogenous block
of (9 x 85 + 3) bytes, with VC-3 floating into.

Correct.

Post by Michelot
In fact, I woul think that VC-3 doesn't float in TU-3 but in TUG-3. Is
it correct?

Correct.

Post by Michelot
Thanks very much to clarify my brain on these basic SDH points.
When the new G.707 version is planned to be published?

The 01/07 version is listed as in-force on the website but not
published yet.
It also wasn't pre-published?...
Anyway, IIRC the new version is mainly a consolidation of corrigenda
and amendments.

Regards,
Bert

PS In-force pdf versions of the ITU-T recommendations are now
available free of charge:
http://www.itu.int/ITU-T/newslog/Trial+Period+For+Free+ITUT+Recommendations+Starts.aspx

[Michelot]

Bonsoir Bert,

=====
I lost my message, I write it again. Sorry if it is twice!
=====

Very happy to hear you (euh!... only the sound of your writing).

Post by Bert Klaps
No, the TU-3 does not include the fixed stuff bytes, while
the TUG-3 does: the TUG-3 is a structure of 9 rows by 86 columns.

You're right, the section 7.2.2 is fully correct. I don't know to
read. I mixed the 9-byte POH with the 9-byte pointer + stuff. Sorry
for that.

Post by Bert Klaps
That would be sort of difficult to do: the TU-3 is not a
contiguous structure. It consists of a VC-3 and the TU-3
pointers pointing to it.
So in a sense it's there in the figure (the fixed stuff
could have been marked differently).

I propose to try to be more accurate, if possible.

The TU-3 unity consists of a 3-byte pointer from the VC-4 clock,
associated with VC-3 from a clock not compulsorily synchronous from
the VC-4 clock. So, as you say, TU-3 is not a contiguous structure. We
can represent it as a pointer separated from the VC-3, by pointing the
different clock origin.

On the contrary, TUG-3 is a contiguous structure from a unique VC-4
clock, with the fixed stuff, and where we can find in its payload the
VC-3 thanks to the TU-3 pointer.

Thus, the difference between TU-3 and TUG-3 is not only a question of
fixed stuff, and we can have 2 distinctly representations.

Post by Bert Klaps
So a TUG/AUG is not the end-target of the multiplexing,
only a network layer like VC-n is, hence "via" a TUG/AUG
and not "in/into"...

Thanks for that very interresting augument.

Post by Bert Klaps
PS In-force pdf versions of the ITU-T recommendations are now
available free of charge:http://www.itu.int/ITU-T/newslog/Trial+Period+For+Free+ITUT+Recommend...

It's a good thing. The quality and the serious of these documents have
to be known from more people. We have all of thus to benefit of the
spreading of these recommendations. Let's hope it stays free of
charge, I will give this information all around me.

The TU-12 is for the VC-12 similar to TU-3 for the VC-3. Normally, we
couldn't represent TU-12 as a contiguous structure of 9 x 4 bytes per
125 µs. The Vn byte is from the VC-4 clock which can't be synchronous
to the VC-12 clock. However, we can see in the figure 7-11 such a
contiguous structure.

Thanks for your opinion.
Best regards,
Michelot

[Huub van Helvoort]

Bonnuit Michelot,

Post by Michelot

Post by Bert Klaps
That would be sort of difficult to do: the TU-3 is not a
contiguous structure. It consists of a VC-3 and the TU-3
pointers pointing to it.
So in a sense it's there in the figure (the fixed stuff
could have been marked differently).

I propose to try to be more accurate, if possible.
The TU-3 unity consists of a 3-byte pointer from the VC-4 clock,
associated with VC-3 from a clock not compulsorily synchronous from
the VC-4 clock. So, as you say, TU-3 is not a contiguous structure. We
can represent it as a pointer separated from the VC-3, by pointing the
different clock origin.

And apart from the pointer there is is the payload; a VC-3 which
is a contiguous structure.

Post by Michelot
On the contrary, TUG-3 is a contiguous structure from a unique VC-4
clock, with the fixed stuff, and where we can find in its payload the
VC-3 thanks to the TU-3 pointer.

Where the TU-3 pointer is also contained in the TUG-3.

Post by Michelot
Thus, the difference between TU-3 and TUG-3 is not only a question of
fixed stuff, and we can have 2 distinctly representations.

The fixed stuff is only necessary to fill the empty space left
after filling the TUG-3 with TU-3 pointer and TU-3 payload.
The TU-3 pointer points to the start of the VC-3 in the TU-3
payload.

If you look at figure 7-3/G.707 you will see the representation
of the AUG-1, AU-4 and VC4.
figure 7-7/G/707 is drawn a little different.

If it would have been drawn similat to figure 7-3 then on top
there would have been the 9 row * 85 column (1 POH and 84 payload)
VC-3, next a three byte pointer area and a 9 * 85 rectangular area
in which the VC-3 floats, and at the bottom a 9 * 86 rectangular
area that will be filled with the TU-3 pointer, the TU-3 payload
area, and the fixed stuff.

Cheers, Huub.

[Michelot]

Bonjour Huub and Bert,

Post by Huub van Helvoort
If you look at figure 7-3/G.707 you will see the representation
of the AUG-1, AU-4 and VC4.
figure 7-7/G/707 is drawn a little different.
If it would have been drawn similat to figure 7-3 then on top
there would have been the 9 row * 85 column (1 POH and 84 payload)
VC-3, next a three byte pointer area and a 9 * 85 rectangular area
in which the VC-3 floats, and at the bottom a 9 * 86 rectangular
area that will be filled with the TU-3 pointer, the TU-3 payload
area, and the fixed stuff.

Great! now it's very clear.

So, my clarification is passed by 2 facts :

(1) The figure 7-7 which could be developped as in the figure 7-3

(2) The statement as it is written in the section 7.2.2 "TU-3 consists
of the VC-3 with a 9-byte VC-3 POH and the TU-3 pointer" which has to
be interpreted as: TU-3 consists of the TU-3 pointer and a payload in
which the TU-3 pointer points to the start of the VC-3.

TU-3 is not really a set of 2 separate elements, the VC-3 from one
side and, from the other side, the TU-3 pointer. In a book I have,
from Caballero, this confusion is maintained.

Thanks Huub and Bert for that very interresting talks.
Best regards,
Michelot