Re: comments on ID-draft-bernstein-ccamp-gmpls-vcat-lcas

[Huub van Helvoort <hhelvoort@chello.nl>]

Hello Trevor,

You replied:

> Thanks for the clarifications, see in-line for responses.

OK, I have added my response [hvh2] and sipped the parts
where we agree.

> > Section 3.2:
> >
> > Is Fixed synonymous with no-LCAS ?
>
> [hvh] No, not necessarily, in this case the client signal will
>        not change its bandwidth. LCAS can be used for resilience.
> [tw]	Accepted that this is possible. However I still think the reader
> could be forgiven for assuming that Fixed = non-LCAS-capable and Dynamic
> = LCAS-capable; so perhaps this needs to be clarified in the text.

[hvh2] OK that can be done.

> > If so, then in the Fixed co-routed scenario, there can be no graceful 
> > degradation in the event of a failure.
> [tw] I have a typo here is should say Fixed diversely-routed instead of
> Fixed co-routed
>
> [hvh] a mis-connection is also a failure
> [tw]	but a mis-connection won't cause a hit, since this will occur at
> set-up, but I agree that if LCAS is present then graceful degradation
> can be achieved in the event of a signal degrade.

[hvh2] I don't agree, mis-connections can also occur after set-up,
       e.g. when a crossconnect is wrongly provisioned and changed
       an existing connection.

> > A hitless decrease can
> > in certain circumstances, be achieved by using a signal degrade to
> > trigger the LCAS remove operation.
>
> [hvh] how do you provision/achieve a signal degrade?
> [tw]	G.806 clause 10.1.1.2 shows "P-Xv_AI_TSD = P_AI[1.. XMR]_TSD"
> and "P-Xv/P-X-L_A_Sk_MI_TSDEnable" as inputs to the "LCAS-capable
> virtual concatenated path adaptation sink function P-Xv/P-X-L_A_Sk", and
> the text says "The MI_TSDEnable input controls whether the sink function
> uses AI_TSD[i] indications as contributors for signalling defective
> members back to the LCAS source function (MI_TSDEnable = true) or
> whether it ignores AI_TSD[i] indications altogether (MI_TSDEnable =
> false)."

[hvh2] this is the enabling of the TSD to be a trigger. What I dis
       mean is that it is impossible to force a signal degrade (e.g.
       by introducing bit errors on purpose).
       Maybe we should only mention that hitless decrease is guaranteed
       when a member is removed (and LCAS is enabled).


> > Dynamic, diversely routed: A dynamic VCAT group, transported over 
> > at least two diversely routed subsets of member signals.  The 
> > intent here is dynamic resizing and resilience (but differential
> > delay may be a limiting factor). Graceful degradation is 
> > possible in the event of a TSD (Trail Signal Degrade) on a VCG
> > member(s)
>
> [hvh] graceful degradation is a feature of LCAS, it is not necessary
>        to mention it here explicitly
> [tw]	It's equally (if not more) relevant to mention it here than in
> the fixed scenario.

[hvh2] see my previous comment

> >   The LCAS in-band 
> > signaling step is taken first to take the component out of the 
> > group as the result of a remove command from the LCAS controller; the 
> > permanently removed member will then be in the IDLE state.
>
> [hvh] mentioning only one of the LCAS states will create confusion
>        and is irrelevant to GMPLS
> [tw]	OK so take out the mention of the DNU state (4.1.3.1) and IDLE
> (4.1.3.2). In fact perhaps 4.1.3.1 could be combined with 4.1.3.2 as
> follows: -
>
> 4.1.3		Permanent removal of a VCG member
>
> A VCG member can be permanently removed from the VCG either following a
> temporary removal (due to a failure) or as the result of a management
> command.
> The LCAS in-band signaling step is taken first to take the component out
> of the group, either the temporary removal or as the result of a
> management command.

[hvh2] good suggestion

> > This permanent removal procedure is only applicable to 
> > LCAS-capable-VCAT.
>
> [hvh] the paragraph replaced by the latter sentence contains more
>        relevant detail and should be kept intact.
> [tw]	The introduction to section 4 states that it (section 4) is "in
> support of the LCAS procedure". So I don't quite see how the sentence
> that I deleted is relevant to LCAS since it deals with the "VCAT only"
> interface. 	

[hvh2] you missed the word "and" in quoting, so section 4 describes
       extentions for diversely routed paths and (extentions) in
       support of LCAS". So the detail given in the paragraph is
       relevant for making the distinction between VCAT with and
       without LCAS.

Cheers, and have a nice weekend, Huub.

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