Subject: RTT sampling on retransmissions

From: Arvid Picciani <[email-masked]>
Date: Sat, 21 Jul 2018 16:20:30 +0200

Hi,

UpdateRtt in https://tools.ietf.org/html/draft-ietf-quic-recovery-13#section-3.5.5
does seem to calculate the RTT from an ack on any packet, even if the
packet was resent.

1. In a TLP event The oldest packet is resent and the sent_time reset
to the current time.
2. Eventually that packet is acked, because the network was just slow.
3. RTT is calculated from the last sent_time (which was the time it was resent).
4. RTT is way too small now, leading to lots of timeouts.

what am i missing here?

https://tools.ietf.org/html/rfc6298 section 2 specifically says that
RTT must NOT be calculated from retransmissions. Is a "retransmitted"
bit in the quic-recovery left as exercise to the reader or should
retransmissions actually never be passed to OnPacketSent?

/b/

---

From: Ian Swett <[email-masked]>
Date: Sat, 21 Jul 2018 12:44:56 -0400

QUIC doesn't retransmits packets.  If data needs to be retransmitted
because it's lost, it's sent in a new packet with a new packet number.  The
new packet number prevents issues with ambiguity.

See recovery section 2(particularly 2.1.2) for more details:
https://tools.ietf.org/html/draft-ietf-quic-recovery-13#section-2

On Sat, Jul 21, 2018 at 10:23 AM Arvid Picciani <[email-masked]> wrote:

> Hi,
>
> UpdateRtt in
> https://tools.ietf.org/html/draft-ietf-quic-recovery-13#section-3.5.5