Re: [tcpm] RACK - variable explanation

[Neal Cardwell <[e-mail]>]

On Thu, Nov 22, 2018 at 7:25 AM Felix Weinrank <[e-mail]> wrote:
>
> Hey RACK authors,
>
> we're evaluating the nuts and bolts of RACK in its current version and
> we are missing variable explanations.
> Most of the variables are listed and explained in section 5 (Definitions
> of variables) but at least two are missing.

Thanks for pointing these out! We'll add these in the next draft.

> SND.UNA

The RACK draft uses the SND.UNA and SND.NXT notations from the TCP RFC
(from https://tools.ietf.org/html/rfc793#section-3.3 on page 25):

   SND.UNA = oldest unacknowledged sequence number

   SND.NXT = next sequence number to be sent

> RACK.dupthresh << This is where we're stuck

This is using the DupThresh term from RFC 6675, "A Conservative Loss
Recovery Algorithm Based on Selective Acknowledgment (SACK) for TCP"
(from https://tools.ietf.org/html/rfc6675 on page 4):

   We define a variable "DupThresh" that holds the number of duplicate
   acknowledgments required to trigger a retransmission.  Per [RFC5681],
   this threshold is defined to be 3 duplicate acknowledgments.

> And I think this paragraph from section 5 needs two cosmetic newlines:
> "RACK.reo_wnd_persist" is the number of loss recoveries before
> resetting RACK.reo_wnd "RACK.dsack" indicates if a DSACK option has
> been received since last RACK.reo_wnd change "RACK.pkts_sacked"
> returns the total number of packets selectively acknowledged in the
> SACK scoreboard.

Thanks for pointing out the missing newlines! We will try to get that
formatting cleaned up in the next rev.

thanks,
neal