Re: [Detnet] Magnus Westerlund's Discuss on draft-ietf-detnet-mpls-11: (with DISCUSS)

[Stewart Bryant <[e-mail]>]

> On 8 Sep 2020, at 16:09, Magnus Westerlund via Datatracker <[e-mail]> wrote:
> 
> Another point on 4.2.2.2:
> 
> When configured, the
>   implementation MUST track the sequence number contained in received
>   d-CWs and MUST ensure that duplicate (replicated) instances of a
>   particular sequence number are discarded.
> 
> That second MUST I think is possible to meet given that one discard all packets
> outside of the current window where one have information if a packet sequence
> number have been forwarded or not. Given that a very late packet beyond the
> amount of state for the flow likely anyway have little utility that is likely
> the right choice. However, I think it needs to be made explicit that this is
> okay.

Yes we need to make sure that when we are tracking sequence numbers, packets outside the window are discarded.

I am not sure how common the re-order option will be. In latency centric applications I suspect that re-order will not happen. I am also concerned about how a high performance implementation would do a re-order, so I suspect that this will only be applied to relatively slow flows that are processed by a classical pure software implementation. In turn I am not sure if we will ever see that in an MPLS network. So whilst the design has capability, I am not sure how profitable it is to drill down into the detail with some operational experience. I don’t think we need to do a lot of hand holding, since those that understand their actual requirement will understand how to do this, or soon work it out, and I so not see any interoperability issues per se with the text as it is.

- Stewart