[mpls] Re: PSD technical issues

[Tony Li <[e-mail]>]

[WG chair hat: off]

Hi Haoyu,


> <HS> So we have only three cases to consider: pseudowire, detnet, and BIER.
> If only the egress node needs to process them, they can be located after PSD.
> If the intermediate nodes also needs to process them, then they can be normally parsed and followed by PSD. I didn't look into those use cases in detail. Can anybody tell me why the above suggestion doesn't work.


BIER is the interesting case, as it’s multicast and definitely requires intermediate nodes to examine the BIER information and act on it.

Placing MNA PSD after the BIER header requires that all nodes have an intimate knowledge of BIER and its variable length encapsulation. Finding the PSD header would be dependent on first correctly parsing BIER.

This dependency is most unfortunate as it makes the entire architecture brittle and tightly coupled.  We would much rather have things be loosely coupled and allow one protocol to be independent of other protocols. Unfortunately, no mechanism was put in place for this when we started MPLS, so we want to do what we can to avoid these dependencies.

Regards,
Tony