Re: [quicwg/base-drafts] split fast retransmit modes (#1226)

[Subodh Iyengar <[e-mail]>]

siyengar commented on this pull request.



> @@ -209,20 +224,19 @@ reordering of packets in the network.
 
 The RECOMMENDED initial value for kReorderingThreshold is 3.
 
-We derive this default from recommendations for TCP loss recovery {{?RFC5681}}
-{{?RFC6675}}. It is possible for networks to exhibit higher degrees of
-reordering, causing a sender to detect spurious losses. Detecting spurious
-losses leads to unnecessary retransmissions and may result in degraded
-performance due to the actions of the congestion controller upon detecting
-loss. Implementers MAY use algorithms developed for TCP, such as TCP-NCR
-{{?RFC4653}}, to improve QUIC's reordering resilience, though care should be
-taken to map TCP specifics to QUIC correctly. Similarly, using time-based loss
-detection to deal with reordering, such as in PR-TCP, should be more readily
-usable in QUIC. Making QUIC deal with such networks is important open research,
-and implementers are encouraged to explore this space.
+#### Time-based Fast Retransmit
+
+Using time-based loss detection to deal with reordering, such as in PR-TCP,

maybe add a reference to PR-TCP here?

> @@ -846,6 +843,29 @@ DetectLostPackets(largest_acked):
     else if (loss_time == 0 && delay_until_lost != infinite):
       loss_time = now() + delay_until_lost - time_since_sent

i think this might be cleaner to split this up to the end of the loop.

it looks like the intention is to the early retransmit timer to be the loss time of the first packet not lost by packet ordering. It might be cleaner like

```
 last_unacked = largest_acked.packet_number
 foreach (unacked < largest_acked.packet_number):
     ....
     last_unacked = unacked
 if (last_unacked < largest_acked.packet_number) :
    lost_time = now() + delay_until_lost - sent_packets[last_unacked].time_since_sent
```

and similarly in the other one as well

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