comments on ID-draft-bernstein-ccamp-gmpls-vcat-lcas -- was Re: Polling for new WG I-Ds

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

Hello Trevor,

You wrote:

> I have read the ID-draft-bernstein-ccamp-gmpls-vcat-lcas-04.txt
> I have the following questions and comments:

See my comments in-line [hvh]

> 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.

> If so, then in the Fixed co-routed scenario, there can be no graceful
> degradation in the event of a failure.

[hvh] a mis-connection is also a failure

> This is more applicable to the dynamic, diversely-routed scenario (and
> in fact could apply to the dynamic co-routed scenario, although this is
> far more unlikely).

[hvh] see my previous comment

> Regarding 'graceful degradation in the event of a failure': surely this
> is a misnomer ? Graceful degradation can only be achieved if the VCG
> capacity is hitlessly decreased. A full blown failure on any VCG member
> will cause a hit to the traffic, albeit temporary. 

[hvh] agree

> 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?

> Suggested text for 3.2 (partial)
>
> Fixed, diversely routed: A fixed bandwidth VCG, transported over 
>       at least two diversely routed subsets of member signals.  In this 
>       case, the subsets are link-disjoint over at least one link of the 
>       route.  The intent here is more efficient use of network resources
>
>       (no unique route has the required bandwidth), (note 
>       that differential delay may be a limiting factor).

[hvh] I don't agree, LCAS can provide resilience, I agree that the
      degradation is not graceful

> 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

> Section 4
>
> Typo on second line of last paragraph: VC4-7v should be VC-4-7v.

[hvh] OK

> Section 4.1.3
>
> G.7042 section 6.4 addresses VCG capacity decrease (temporary removal
> due to member failure) and section 6.5 addresses VCG capacity decrease
> (permanent removal). Each of these has distinct meanings and I think
> that this ID should make that distinction also, or at least be more
> pedantic in the use of 'removal'.
>
> Perhaps (as far as GMPLS is concerned) there is only the need to address
> the VCG capacity decrease (permanent removal), since the 'temporary
> removal' is an autonomous action performed by the LCAS protocol and does
> not require any management intervention.

[hvh] the temporary removal description was in previous versions
      of this draft, because (as you mention) this draft concerns
      GMPLS it was removed to avoid confusion.

> Suggested text for 4.1.3: -
>
> 4.1.3. Decreasing VCG capacity 
>
> VCG capacity can be decreased in two ways
> o	Temporary removal of a VCG member(s) due to failure
> o	Planned permanent removal of a VCG member(s) which requires
> management intervention
>
> 4.1.3.1	Temporary Removal of a VCG member
>
> This is an autonomous action performed by the LCAS protocol whenever a
> failure occurs on an active VCG member(s). The relevant VCG member will
> then be in the DNU state.
>
> There is no management intervention required to perform this operation.
>
> This member can then be permanently removed from the VCG. (4.1.3.2)
>
> 4.1.3.2		Planned permanent removal of a VCG member
>
>    The procedure to remove a component signal is similar to that used to
>
>    add components as described in Section 4.1.2.  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

>    LCAS signaling is described in [ITU-T-G.7042] 
>
>    In this case, the NVC value is decremented by 1 and the timeslot 
>    identifier for the dropped component is removed from the ordered list
>
>    in the Generalized Label.  
>
> 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.

> Best regards,
>
> Trevor
>
> Trevor Wilson
> Nortel Networks

Kind regards, Huub van Helvoort.

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