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

[Rakesh Gandhi <[e-mail]>]

Hi Tony,

In your example, that midpoint would not have updated the IOAM data
(timestamp in this case) due to the RLD reachability. This just means, IOAM
data is missing from the node that it is not capable of.

P.S. RLD would be much higher than 64-byte in reality, but ok for the sake
of discussion.
P.S. Nodes (or operators) enabling the IOAM encapsulation would have some
knowledge of RLDs and could enable IOAM accordingly.

thanks,
Rakesh



On Thu, Jun 27, 2024 at 11:54 AM Tony Li <[e-mail]> wrote:

> [WG chair hat: off]
>
> Hi Rakesh,
>
> I’m missing some point that I think you’re trying to make.
>
> Suppose that a node in this network only has an RLD of 64 octets (i.e., 16
> LSE equivalents).  Won’t there be a perfomance issue?
>
> It seems to me that the further down we push data, the more likely we are
> to run into issues.
>
> T
>
>
> On Jun 27, 2024, at 8:35 AM, Rakesh Gandhi <[e-mail]> wrote:
>
> 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
>
>
>
>
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