Subject: Re: [Fwd: use ideas from, but not true aal]

From: [email-masked]
Date: Mon, 15 Apr 2002 10:11:16 -0700

> I would say that working with packets carrying fixed amount of
> payload is an advantage. E.g.:

True.  It can be fixed if you want, but still arbitrary, i.e. not 
restricted to an integer multiple of anything.  Or it can be dynamic. 
Either way, it's as flexible as you can get, with little cost to achieve 
this.

> 1. If you are dealing with unstructured E1 or T1, there is no framing to
> preserve -
>    the framing bits are carried as part of the payload. 
>

> 2. If you are dealing with N*DS0, you can consider the framer as a kind 
of
> codec
 
I agree.  In both of these cases, the problem solves itself.  Therefore, 
the proposed structure pointer in the PW header can be unused in such 
cases, or used but irrelevant, or made optional.  I guess this is a 
detail.

> 3. When it comes to combining N*DS0 with Channel-Associated Signaling 
(CAS),
>    you can treat it in several ways:

Yes, you can either put the signaling in separate packets, or as part of a 
structure.  I suggested the latter based on Mr. Stein's comments in more 
than one posting (I'll just quote one of these) where he says, "Isn't it a 
lot easier to leave the TDM stream alone?
Leave the bits where they are and forget about all the details." I defer to others with regard to knowledge of TDM, but it seems to me that 
the two of you disagree on the issue of whether the structure concept is a 
"natural" one, or is artificial.  Even defining the terms natural and 
artificial is probably a bit difficult, but it would be very helpful if 
Mr. Stein and Mr. Vainshtein could come to an agreement on the validity of 
the above quotation.

> As mentioned above, there are two sources of complexity:
> a) Creation of an intermediate structure to carry across the PSN at
>    ingress and its interpretation at egress. IMHO your proposal
>    does not address this problem
> b) AAL1-specific complexity. I agree that if the structure must be
>   carried, your proposal looks simpler. 

To me, the best idea is to transmit everything as naturally as possible, 
and add the minimum necessary overhead in the PW header in order to 
perform this robustly.  This was the basis for my suggestion, and that's 
why I believe the AAL1-specific complexity ought to be eliminated, but a 
PW-header structure pointer maintained.  But as for (a) above, my 
understanding was that we weren't artificially producing anything that 
wasn't there already, and that indeed (to quote another email) "We leave 
the bits where they were (we don't even care whether they are there or 
not)."  Perhaps Mr. Stein can clarify this.

Thank you.  It has occurred to me that a "Barrack compromise" would sound 
really good on my resume.  So come on guys!  ;-)

-Craig