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RE: comments on ID-draft-bernstein-ccamp-gmpls-vcat-lcas -- was Re: Polling for new WG I-Ds
Thanks for the clarifications, see in-line for responses.
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From: Huub van Helvoort [mailto:firstname.lastname@example.org]
Sent: 16 August 2006 19:02
Cc: Wilson, Trevor (IRE07:Q840)
Subject: comments on ID-draft-bernstein-ccamp-gmpls-vcat-lcas -- was Re:
Polling for new WG I-Ds
> 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.
[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.
> 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
[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.
> 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.
> 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 =
> 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
> case, the subsets are link-disjoint over at least one link of
> route. The intent here is more efficient use of network
> (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
[tw] We are converging here (as usual); see my previous
> 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
[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.
> Section 4
> Typo on second line of last paragraph: VC4-7v should be VC-4-7v.
> 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.
[tw] I'm all for avoiding confusion -- see next comment.
> 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
> 188.8.131.52 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
> This member can then be permanently removed from the VCG. (184.108.40.206)
> 220.127.116.11 Planned permanent removal of a VCG member
> The procedure to remove a component signal is similar to that used
> 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
[tw] OK so take out the mention of the DNU state (18.104.22.168) and IDLE
(22.214.171.124). In fact perhaps 126.96.36.199 could be combined with 188.8.131.52 as
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
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
> 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
> in the Generalized Label.
> This permanent removal procedure is only applicable to
[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"
> Best regards,
> Trevor Wilson
> Nortel Networks
Kind regards, Huub van Helvoort.
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