[mpls] Example of MPLS RLD with IOAM Trace in PSD

[Rakesh Gandhi <[e-mail]>]

Hi WG,



There were some comments regarding how MPLS Readable Label Depth (RLD) can
affect pre-allocated IOAM trace data carried in MNA PSD.



Using an example:

For 10 hops with 10 LSEs (sub-total 40 bytes)

+ 2 LSEs for MNA in MPLS header (sub-total 48 bytes)

+ 2 words for PSD Headers (sub-total 56 bytes)

+ 10 words of pre-allocated IOAM space for recording 4-byte timestamp
fraction (sub-total 96 bytes)

+ adding 4-byte IOAM Namespace (sub-total 100 bytes or 25 words)



This means the *first midpoint* will *need 100-byte (or 25-word) RLD* to
record 32-bit timestamp fraction in MNA IOAM PSD for 10-hop SR path, right?



If a midpoint node supports *RLD of 128-byte*, MPLS can support per-hop
delay measurement use-case for 10-hop SR-path using IOAM trace option
(pre-allocated).



Are we missing anything?



Thanks,

Rakesh



P.S.



Following MNA use-case draft lists IOAM Pre-allocated trace option use-case.

   -
   https://www.ietf.org/archive/id/draft-ietf-mpls-mna-usecases-10.html#name-in-situ-oam



Following MNA draft defines a PSD solution for this use-case.

   - https://datatracker.ietf.org/doc/html/draft-gandhi-mpls-mna-ioam-dex-01