[mpls] Indicators in the stack and ancillary data after the BoS

Loa Andersson <loa@pi.nu> Tue, 15 June 2021 12:31 UTC

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From: Loa Andersson <loa@pi.nu>
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Subject: [mpls] Indicators in the stack and ancillary data after the BoS
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Design Team,

When the Associated Channel first were desing it was assume that one 
associated channel per packet would be enough for the future.

The rules for where the GAL (indicator for an associated channel) should 
be located in the stack and that there could only be one GAL in the 
stack was strictly specified.

Now we are where the development has taken us to a point where the GAL 
can be found aqt almost any position in the stack.

Further changes are discussed.

- As label stack has been growing there is a risk that some LSRs that
   need to find the GAL might find that the GAL is below readable depth.
   The proposed remedy is to allow entering a copy of the first GAL
   higher in the stack, i.e. more than one GAL in the stack point to the
   same ACH.

- It has also been discussed to carry more than one ACH after the BoS,
   i.e. you'll need more than one different GALs in the stack pointing to
   different ACH's.
   (I think the if this statement is true that would require a "slight",
   but backwards compatible redesign of the GAL.)

- It has also been discussed to carry more then set of (the ACH is one)
   ancillary data after the BoS, and e.g. FAI, GAL, EHI, OAM indicator,
   etc. mixed in the label stack.

The issue is that the set of ancillary data after the BoS might will 
interfere and that we need a strong mechanism to find the ancillary data 
that "belongs to" a certain indicator.

I think that we first need to decide what is required and after that
design a solution.

The correctness of statements about need to be verified and if necessary 



Can someone tell me if I should use anxillary or ancillary?


Loa Andersson                        email: loa@pi.nu
Senior MPLS Expert                          loa.pi.nu@gmail.com
Bronze Dragon Consulting             phone: +46 739 81 21 64