Re: Proposed extension for delayed acknowledgments

[Maxime Piraux <[e-mail]>]

Hi Jana,

Enabling sender-side control of the receiver behaviour is also part of 
our efforts with PQUIC <pquic.org>. We propose a new paradigm for 
deploying new extensions to QUIC. For some use-cases, instead of 
defining a standard wire format enabling the control of specific 
mechanisms, we propose to directly inject code that implements the 
required feature.

More concretely, adding a custom ack policy requires replacing a single 
function (aka protocol operation) in PQUIC. The protocol operation 
is_ack_needed determines whether sending an ack is required. An example 
of the code that could be injected to change the packet tolerance to 10 
and the max ack delay to 10ms can be found below.

/* The function returns whether an ack is needed for a given packet 
context */
protoop_arg_t is_ack_needed(picoquic_cnx_t *cnx)
{
     uint64_t current_time = (uint64_t) cnx->protoop_inputv[0]; /* 
Current time in microsec */
     picoquic_packet_context_enum pc = (picoquic_packet_context_enum) 
cnx->protoop_inputv[1];
     picoquic_path_t *path_x = (picoquic_path_t*) cnx->protoop_inputv[2];
     picoquic_packet_context_t *pkt_ctx = &path_x->pkt_ctx[pc];

     protoop_arg_t ack_needed = 0;
     uint64_t packet_tolerance = 10;  /* 10 packets */
     uint64_t max_ack_delay = 10000;  /* 10 ms */

     if (pkt_ctx->ack_needed) {
         if (pkt_ctx->highest_ack_sent + packet_tolerance <= 
pkt_ctx->first_sack_item.end_of_sack_range ||
             pkt_ctx->highest_ack_time + max_ack_delay <= current_time) {
             ack_needed = 1;
         }
     }

     return ack_needed;
}

Our approach can also be used to deploy an extension defining new frames 
as explained in [PQUIC]. Every time that there will be an interest in 
enabling the dynamic modification of a particular QUIC mechanism, having 
a common interface to inject code will shorten the time to deploy and 
experiment with those modifications.

[PQUIC]: Quentin De Coninck, François Michel, Maxime Piraux, et al. 
Pluginizing QUIC. SIGCOMM 2019. https://dl.acm.org/authorize?N680239

Maxime

Le 23/01/20 à 22:50, Jana Iyengar a écrit :
> Hi all,
>
> Ian and I have proposed an extension to enable sender-side control of
> acknowledgement frequency: draft-iyengar-quic-delayed-ack-00
> <https://datatracker.ietf.org/doc/draft-iyengar-quic-delayed-ack/>.
>
> The problem this extension solves was originally discussed in #1978
> <https://github.com/quicwg/base-drafts/issues/1978>, where we agreed that
> this might be best done in an extension. The desire to reduce the frequency
> of acknowledgements was more recently brought up and discussed in #3304
> <https://github.com/quicwg/base-drafts/issues/3304>, where it seemed clear
> that there was interest in working on this now. This proposed extension is
> a result.
>
> This is an individual draft. Please feel free to use the following github
> repo, which is NOT the working group's repo, for filing issues and
> discussion pertaining to the draft:
> https://github.com/janaiyengar/ack-frequency
>
> - jana
>