RE: [PWE3] comments on draft-ietf-pwe3-requirements-03.txt

[Sasha Vainshtein <Sasha@AXERRA.com>]

Yaakov and all,
Please see comments inline.

With best regards,
                                   Sasha Vainshtein
email:     sasha@axerra.com <mailto:sasha@axerra.com> 
tel:       +972-3-7659993 (office)
           +972-8-9254948 (res.)
           +972-58-674833 (cell.)
 


> -----Original Message-----
> From: Yaakov Stein [mailto:yaakov_s@rad.co.il]
> Sent: Tuesday, October 08, 2002 4:43 PM
> To: Alexander Vainshtein
> Cc: pwe3@ietf.org; Ron Cohen; neil.2.harrison@bt.com; 
> stbryant@cisco.com
> Subject: RE: [PWE3] comments on draft-ietf-pwe3-requirements-03.txt
> 
> 
> Sasha, 
> 
> > What you are trying to say is that the basic elements of a 
> > certain hierarchy do not belong to it.
> > Sounds strange to me.
> 
> As Ron pointed out SONET/SDH multiplexes PDH signals
> (e.g. OC-1 was devised to transport a DS3).
>
I will use the SDH terms for clarity even when referring to "SONET/SDH".

Contrary to what Ron pointed out, SONET/SDH does _not_ directly
multiplex E1, DS1 or DS3. Strictly speaking (and I assume that
this is _your_ position) it _multiplexes_ administrative units (AU) and
tributary units (TU) .
AUs are multiplexed in a _synchronous way_ (i.e. are always
positioned at the same place relative to the SDH frame boundary);
TUs are multiplexed in a _synchronous_  way too, but relative to the
boundary of a high order VC. High order VCs are _floating_ within
their respective AUs, while low-order VCs are _floating_ within their
respective TUs.
This _multiplexing_ scheme does _not_ depend on payload of virtual
containers:
they may carry PDH signals, ATM packets or POS frames - just to name
a few options. And some containers may be left unequipped. 
> 
> So do you propose calling a DS3 - SDH?
> That would sound stranger!
> 
As I have just said, DS3 (or, for that matter, DS1 or E1) signals are 
_not_ multiplexed per se in SONET/SDH. They are just _mapped_ into 
appropriate virtual containers: DS3 and E3 are mapped into VC3, E1 
is mapped into VC12 and DS1 is mapped into VC-11. 
POS frames and ATM cells can be mapped into any 
In other words, these signals are no more part of the SDH(ierarchy) 
that ATM cells or POS packets. On the other hand, AUs, TUs and VCs 
are part of this hierarchy. 

The details (including reference to multiplexing, aligning and mapping) 
can be found in G.707, Fig. 6.1 "Multiplexing Structure".

> The input doesn't matter. It is the technology used to 
> multiplex that matters.
>
Correct. That is why DS3 (which _directly_ multiplexes DS1 and E1), DS1 and
E1 belong
to a hierarhy that is commonly referred to as PDH. And that is why VC4, VC12
etc.
belong to a hierarchy that is commonly referred to as SDH.
>
> Y(J)S
> 
>  
> 
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