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[mpls] Re: Y.1720 liased text

  • From: Huub van Helvoort <hhelvoort@chello.nl>
  • Date: Fri, 26 Jan 2007 13:09:46 +0100
  • Cc: mpls@ietf.org, stbryant@cisco.com, pwe3@ietf.org, ghani.abbas@ericsson.com
  • User-Agent: Thunderbird 1.5.0.9 (Windows/20061207)

Hello Neil,

You responded:

> Thanks Huub, 
> 
> Can you clarify how the S bit is set when this 1+1 seq no. field is
> used? 

I checked the appendix II twice (because my left eye is still 10%),
I could not find any text referring to setting the S bit.
I only see that the 4 octet sequence number is placed right
after the shim header.

> What is puzzling me is this sentence in the text Stewart
> extracted from Y.1720/Appendix 11:
> 
> "Note that packet 1+1 can be provided at any level of the hierarchy of a
> nested LSP."
> 
> I sort-of read this as there can be a set of nested LSPs (hence
> concatenated MPLS headers) and that the protection mechanism can be
> applied to any one of these within such a stack.  Am I reading this
> right?

I agree with your reading.

> If I am, then please see my concerns of yesterday on this
> thread....which, in essence, is querying what happens if there is
> misconnectivity and the LSP carrying the 1+1 Seq No. stuff arrives at
> some arbitrary LSR.....how will that LSR parse/interpret the fields it
> sees?
> 
> I have no background on Y.1720, so my apologies if I am asking a dumb
> question.

There are no dumb questions, only dumb answers. Maybe this is one:

This morning I did some further investigating where the text originates
and found it in the IETF archives:
http://www.watersprings.org/pub/id/draft-nagarajan-ccamp-mpls-packet-protection-00.txt

It was also discussed on the MPLS WG list and there I found the
answer to your concerns expressed above (provided by yourself ;-)

http://cell.onecall.net/mhonarc/mpls/2002-Apr/msg00211.html

Cheers, Huub.

-- 
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