Re: Tsvart early review of draft-ietf-manet-dlep-credit-flow-control-09

On Tue Feb 27 00:30:28 +0000 2024, Black, David wrote:
> Hi Eric,
> 
> Thanks for jumping in ...
> 
> > I think it should be possible to have a "graceful" reduction in the Credit Window with something along the lines of:
> Ok ...
> 
> > "The modem MAY, at its discretion, after sending the Session Update Message with one or more Credit Window Initialization Data Items
> > that decrease the Credit Window Max Size, continue processing received packets that match the indicated FIDs with an unmodified
> > Credit Window Max Size that arrive before the modem receives the corresponding Session Update Response Message.  However,
> > during this time no additional credits for those FIDs are issued.  After the router's Session Update Response Message is received,
> > the modem waits for each affected window to drain until it reaches the new Credit Window Max Size.
> > At this point the modem resumes issuing credits for that FID, limited by the new Credit Window Max Size."
> > 
> > Misbehaving routers that send packets in the absence of credits will still result in those packets being dropped.
> > But, otherwise, we avoid dropping packets at the receiver simply as a side effect of the change.
> 
> If that's the desired effect, then "MAY, at its discretion" is entirely too weak. The new text needs to begin with
> "The modem SHOULD ..." and would benefit from a little rearrangement, e.g.:
> 
>    After sending the Session Update Message with one or more Credit Window Initialization Data Items that decrease
>    the Credit Window Max Size, the modem SHOULD continue processing received packets that match the indicated FIDs,
>    fit within the window for the unmodified Credit Window Max Size and arrive before the modem receives the corresponding
>    Session Update Response Message. 

Yes, the stronger wording seems appropriate here.

> The rest of the text assumes that the window size won't decrease to or below the new max size before the response
> message arrives.  While that's certainly the likely behavior, it won't always be the case.  So instead of:
> 
>    However,   during this time no additional credits for those FIDs are issued.  After the router's Session Update Response Message is received,
>    the modem waits for each affected window to drain until it reaches the new Credit Window Max Size.
>    At this point the modem resumes issuing credits for that FID, limited by the new Credit Window Max Size."
> 
> I'd suggest:
> 
>    The modem SHOULD NOT issue additional credits for each affected FID until the associated affected
>    Window has drained to be less than the new Credit Window Max Size, regardless of whether sufficient
>    draining occurs before or after the modem receives that corresponding Session Update Response Message.
> 
> I think that one sentence covers both cases and using "SHOULD NOT" makes the point clearer.

I agree with your wording here, also.

Thanks,

Eric