Re: Updated DATAGRAM -03 draft

[Christian Huitema <[e-mail]>]

On 7/15/2019 3:03 AM, Robin MARX wrote:
> Hello Tommy,
>
> Good to see the updated draft.
> I do wonder about the decision to enforce congestion control for
> DATAGRAM frames and the effect this will have on the gaming use case. 
> As also discussed in Prague, real-time gaming often requires a set
> update rate frequency (e.g., 30-60 messages per second) for
> responsiveness. 
> I wonder if congestion controlling the frames (e.g., delaying/dropping
> them) will produce some weird edge cases that really mess with this
> setup. 
> It's a bit difficult to assess because the messages are usually
> relatively small (though they could be mixed with larger messages,
> e.g., RPCs) and you could make the argument that, if there is actual
> congestion, the packets will be dropped in the network either way. 
> You could also say that custom game-focused implementations will just
> ignore the text and do their own logic as needed.
>
> So I'm not sure the text needs changes, I just wanted to mention that
> it might not be optimal for the real-time gaming use case and that it
> might be capable footgun with some weird edge cases if people do stick
> to the text.


Not really. If the network is congested and the video game still
persists sending frequent messages the most likely outcome will be
queuing and losses, and thus bad game play. The proper behavior in a
congested network is to switch to a low bandwidth mode of some kind --
maybe a lower frame rate, or a lower resolution. This is pretty much the
same issue as voice or video over IP: if the network is congested, it
makes sense to use a higher compression rate. With congestion control,
the application can detect the upset of congestion and adopt these
strategies. That's generally much better than to just passively accept
queues and losses.

-- Christian Huitema