Subject: Re: [quicwg/base-drafts] Why min CWND of 2 instead of 1 (#3586)

From: ianswett <[email-masked]>
Date: Tue, 05 May 2020 15:31:55 -0700

@ianswett pushed 1 commit.

1e67d0fb1c81085c81ab5812621111608d824cdf  Update draft-ietf-quic-recovery.md

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From: ianswett <[email-masked]>
Date: Tue, 05 May 2020 15:33:04 -0700

b32ab8c350ac15b92b520f7a3b15f7415b22083b  Update draft-ietf-quic-recovery.md

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From: Jana Iyengar <[email-masked]>
Date: Tue, 05 May 2020 15:46:15 -0700

@janaiyengar commented on this pull request.

> @@ -245,6 +245,15 @@ QUIC specifies a time-based definition to ensure one or more packets are sent
 prior to a dramatic decrease in congestion window; see
 {{persistent-congestion}}.
 
+### The Minimum Congestion Window is 2 Packets

```suggestion
### The Minimum Congestion Window is Two Packets
```

> +QUIC recommends that the minimum congestion window be 2 packets instead
+of the 1 packet minimum in TCP. A 2 packet minimum congestion window avoids
+waiting for a probe timeout (see {{pto}}) every time a single packet is lost.
+A minimum of 2 packets also avoids waiting for a delayed acknowledgement, which
+can substantially decrease throughput, particularly if the max_ack_delay is
+larger than the round trip time.

```suggestion
TCP uses a minimum congestion window of one packet, but this can be fragile
in practice. Loss of a single packet sent with that window limits the sender to
waiting for a PTO ({{pto}}) to recover from that loss, which can be a
substantial period of time depending on the amount of backoff. Sending a
single data packet also increases the chances of incurring additional latency
when a receiver delays its acknowledgement. QUIC therefore recommends that
the minimum congestion window be two packets. While this increases network
load, it is considered safe, since the sender will still reduce its sending rate
exponentially under persistent congestion ({{pto}}).
```

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From: ianswett <[email-masked]>
Date: Tue, 05 May 2020 15:47:02 -0700

b270451746cc6ae9655ceb30281de6bf6bbdb628  Update draft-ietf-quic-recovery.md

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From: ianswett <[email-masked]>
Date: Tue, 05 May 2020 15:55:03 -0700

9f773931b7c57a232ef9a9814fb664832eb7436e  Update draft-ietf-quic-recovery.md

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From: ianswett <[email-masked]>
Date: Tue, 05 May 2020 15:56:59 -0700

c5b9e72880734f6e9e54bcbbd0339d72bdded5bc  Update draft-ietf-quic-recovery.md

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From: Jana Iyengar <[email-masked]>
Date: Tue, 05 May 2020 15:59:25 -0700

> +a single packet sent with that window causes the sender to waiting for a PTO
+({{pto}}) to recover from that loss, which is much longer than a round trip.

```suggestion
that single packet means that the sender needs to waiting for a PTO
({{pto}}) to recover, which can be much longer than a round-trip time.
```

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From: Jana Iyengar <[email-masked]>
Date: Tue, 05 May 2020 16:00:01 -0700

@janaiyengar approved this pull request.

LGTM, modulo one suggestion

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From: ianswett <[email-masked]>
Date: Tue, 05 May 2020 16:00:23 -0700

9a69f882ff119ab34608b3a750ddc7f4639f3ec1  Update draft-ietf-quic-recovery.md

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From: ianswett <[email-masked]>
Date: Tue, 05 May 2020 16:02:15 -0700

Merged #3586 into master.

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