RE: LCAS and draft-mannie-ccamp-gmpls-lbm-tdm-00.txt

["Mannie, Eric" <Eric.Mannie@ebone.com>]

Hello Maarten

> LCAS is added to the networks to resize the pipe over which e.g. Ethernet
packets flow in a hitless manner. The A and Z endpoints need therefore to be
synchronised at frame level. There is no alternative in the control plane
which
can support this.

We know that perfectly and we never said the opposite. It is not because we
speak about GMPLS that there is no transport plane anymore.

GMPLS-LBM discusses two issues both the control plane issues and the
necessary relationship with the transport plane (i.e. how to achieve the
synchronization in a similat manner as LCAS using transport plane features).

To be clear, GMPLS-LBM proposed also a solution for the frame
synchronization.




-----Original Message-----
From: Maarten Vissers [mailto:mvissers@lucent.com]
Sent: Monday, November 19, 2001 12:20 PM
To: Mannie, Eric
Cc: 'Stephen Trowbridge'; ccamp; q11/15; t1x1.5; Dimitri Papadimitriou
Subject: Re: LCAS and draft-mannie-ccamp-gmpls-lbm-tdm-00.txt


Eric,

LCAS is added to the networks to resize the pipe over which e.g. Ethernet
packets flow in a hitless manner. The A and Z endpoints need therefore to be
synchronised at frame level. There is no alternative in the control plane
which
can support this.

Looking at your simple example, I get the impression that you do not fully
understand the use of the UNEQ value in C2/V5. The UNEQ value in C2/V5 is
generated by the HOVC/LOVC connection function (see G.783) as part of the
UNEQ
VC-n signal generation process. The UNEQ value is not generated by the path
termination function or its associated adaptation function. An adaptation
function alsways generates an equipped-specific signal label (>= 2).

So, as soon as the fabrics in the to be setup connection have setup their
matrix
connections, the VC-n path termination function will receive an
equipped-specific signal label value, and consequently clears its UNEQ
defect.

I.e. the assumptions underlying your steps 2 to 6 are incorrect and not
aligned
with the SDH specifications in ITU-T.

Regards,

Maarten



"Mannie, Eric" wrote:
> 
> Hello Stephen
> 
> > GMPLS-LBM and LCAS ARE solutions to different problems.
> 
> No, please see explanations below.
> 
> > If you use LBM and change the mappings at the two ends without some
> coordination such as LCAS, you will have a glitch to the traffic
> (I think this is simple enough).
> 
> No, please see below (C2 or V5 transition).
> 
> >The compare/contrast discussion of LBM and LCAS is appropriate not
> >because LCAS is "sacred", but because you are comparing apples to
> >oranges. Statements in this document such as "One drawback of LCAS is .."
> >are unnecessary and inappropriate in this context, since LBM does
> >NOT solve the problem LCAS was designed to solve. Perhaps if you
> >were solving the SAME problem better, this would be OK, but this
> >is not the case.
> 
> No, please see below.
> 
> Simple example:
> 
> 1) you first signal an additional VC/SPE to the destination (via a Path).
> 2) the destination knows exactly which VC/SPE is added (via the label).
> 3) the new VC is unequipped (indicated in POH C2 (for HOVC)),
>    so the VC/SPE is not yet added to concatenated signal.
> 4) then, you wait at the source for a confirmation from the destination
> (i.e. Resv).
> 5) the source "equip" the VC/SPE and sends.
> 6) the destination sees in the POH that the VC is "equipped" (transition).
> 
> The difference between LCAS and LBM is that LCAS uses an additional
explicit
> indication in the overhead to say "this is the payload" to use. LBM
doesn't
> change the SDH/SONET overhead, while LCAS changes the SDH/SONET overhead
:-)
> 
> LCAS uses a new field in the POH (CTRL) to know when the new VC
transitions
> to a significant payload. LBM proposes to do the same simply by looking at
> the C2 (for HOVC) transition - regular SDH/SONET field that will change
> anyway and that is used to indicate the type of payload.
> 
> To be more precise about LCAS (I copy from the LCAS specification, section
> 6.3.1): "The first container frame to contain payload data for the new
> member shall be the container frame immediately following the container
> frame that contained the last bit(s) (i.e. the CRC) of the control packet
> with NORM/EOS message for that member" (the LCAS control packet).
> 
> So, LCAS waits for the last bit of the appropriate LCAS control packet in
> the POH with the appropriate transition of its CTRL field. LBM waits
simply
> for the appropriate C2 (for HOVC) or V5 (for LOVC) transition in the POH
> (don't change SDH/SONET).
> 
> By the way, this is version 0 of the draft and it was just posted.
> 
> Suggestions, technical comments and improvements are welcome.
> 
> I would appreciate if people could first read and speak before shooting
> directly :-)
> 
> Kind regards,
> 
> Eric
> 
> -----Original Message-----
> From: Stephen Trowbridge [mailto:sjtrowbridge@lucent.com]
> Sent: Friday, November 16, 2001 7:49 PM
> To: Mannie, Eric
> Cc: 'Maarten Vissers'; ccamp; q11/15; t1x1.5; Dimitri Papadimitriou
> Subject: Re: LCAS and draft-mannie-ccamp-gmpls-lbm-tdm-00.txt
> 
> Eric,
> The point of my earlier email (items again below, this time with
> numbers) was not to prompt the comment "#3 is out of scope, therefore
> it is a choice between #1 and #2" (my parsing of recent statements).
> 
> The issue (and I think the reason for Maarten's strong reaction) is this:
> GMPLS-LBM and LCAS are NOT different solutions to the same problem.
> GMPLS-LBM and LCAS ARE solutions to different problems.
> (I hope this is not too subtle for non-native English speakers).
> 
> LCAS is a method to hitlessly change the mappings at the two
> ends of a virtually concatenated trail to increase or decrease the
> bandwidth. It does not say anything about how components to be
> added or removed from the virtually concatenated "bundle" are
> set up or taken down.
> 
> LBM talks about how to set up or take down those added or removed
> components, but not about the details of changing the mapping (other
> than that it is done after the new components are successfully
> established.
> 
> If you use LBM and change the mappings at the two ends without some
> coordination such as LCAS, you will have a glitch to the traffic
> (I think this is simple enough).
> 
> The compare/contrast discussion of LBM and LCAS is appropriate not
> because LCAS is "sacred", but because you are comparing apples to
> oranges. Statements in this document such as "One drawback of LCAS is .."
> are unnecessary and inappropriate in this context, since LBM does
> NOT solve the problem LCAS was designed to solve. Perhaps if you
> were solving the SAME problem better, this would be OK, but this
> is not the case.
> 
> Time to try to be constructive:
> - I think most of the current discussion of LCAS should be removed from
> this document. It is irrelevant since LCAS solves a different problem than
> LBM. To say that one is "better" than the other would only be meaningful
> if they were solving the same problem (can you really say that LBM solves
> problem A better than LCAS solves problem B?).
> - LCAS can be a good informative reference as a way to hitlessly modify
> the size of a virtually concatenated trail.
> - Clarify in the scope that the current draft describes the use of LBM
> without LCAS, which results in a traffic glitch when bandwidth is
modified.
> Indicate that the use of LCAS to hitlessly negotiate the changes to
> the size of virtually concatenated pipes after LBM sets up new
component(s)
> or before LBM takes down old component(s) is a topic for further study
> and perhaps to be addressed in a future version of the draft.
> 
> Regards,
> Steve
> 
> Steve Trowbridge wrote:
> > 1. Can you use LBM without LCAS? Yes, if you don't mind a glitch to
> > the traffic.
> >
> > 2. Can you use LCAS without LBM? Yes, if you don't care whether the
> > control plane knows that the different LSPs are part of the same
> > circuit.
> >
> > 3. Can you use LCAS WITH LBM? Hopefully yes, and this would seem to
> > be the preferred method for many applications.
> 
> "Mannie, Eric" wrote:
> >
> > Hello Maarten,
> >
> > >Any sentence in which LCAS and ASON/GMPLS are compared shows a lack of
> > >understanding of LCAS's objective (my very strong opinion).
> >
> > Sorry, do you mean that it is forbidden to speak about your LCAS
document
> > and to compare GMPLS and LCAS functionalities ?
> >
> <snip, to save BW>