Re: [quicwg/base-drafts] Packet number echo with variable-length numbering (#391)

[Brian Trammell <[e-mail]>]

> I think it's ok to provide an RTT measurement less frequently when little data is flowing

The issue here is that each direction isn't providing an RTT measurement; it's providing a measurement only for the component of the RTT between the observation point and one endpoint. Referring to the illustration, an observation point close to the receiver in an asymmetric flow gets the RTT component toward the receiver far more often than the RTT component toward the sender. 

> The removal of STOP_WAITING and acking acks results in sending a retransmittable frame with an ack approximately once per RTT. So both directions should get an RTT estimate approximately once per RTT.

Ah, right. Sorry, still thinking in TCP terms. Okay, so Option 2 echoes on (practically) a superset of Option 1. 

FWIW I continue to share your apprehension about making this non-optional. I like the idea of allowing application/user veto, which is only possible when the packet number echo is redundant with the ACK frames.

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