Re: [quicwg/base-drafts] Document TCP RTO vs QUIC PTO (#3441)

[Jana Iyengar <[e-mail]>]

janaiyengar commented on this pull request.



> @@ -228,6 +228,23 @@ QUIC endpoints measure the delay incurred between when a packet is received and
 when the corresponding acknowledgment is sent, allowing a peer to maintain a
 more accurate round-trip time estimate (see Section 13.2 of {{QUIC-TRANSPORT}}).
 
+### Probe Timeout Replaces RTO and TLP
+
+QUIC uses a probe timeout (see {{pto}}), with a timer based on TCP's
+RTO timeout.  QUIC PTO includes the peer's max_ack_delay in the calculation,

```suggestion
RTO period computation.  QUIC's PTO period includes the peer's maximum expected acknowledgement delay (max_ack_delay, Section XX),
```

> @@ -228,6 +228,23 @@ QUIC endpoints measure the delay incurred between when a packet is received and
 when the corresponding acknowledgment is sent, allowing a peer to maintain a
 more accurate round-trip time estimate (see Section 13.2 of {{QUIC-TRANSPORT}}).
 
+### Probe Timeout Replaces RTO and TLP
+
+QUIC uses a probe timeout (see {{pto}}), with a timer based on TCP's
+RTO timeout.  QUIC PTO includes the peer's max_ack_delay in the calculation,
+instead of relying upon a fixed minimum RTO.  Unlike TCP's RTO, which collapses

```suggestion
instead of using a fixed minimum period.  Unlike TCP, which collapses
```

> @@ -228,6 +228,23 @@ QUIC endpoints measure the delay incurred between when a packet is received and
 when the corresponding acknowledgment is sent, allowing a peer to maintain a
 more accurate round-trip time estimate (see Section 13.2 of {{QUIC-TRANSPORT}}).
 
+### Probe Timeout Replaces RTO and TLP
+
+QUIC uses a probe timeout (see {{pto}}), with a timer based on TCP's
+RTO timeout.  QUIC PTO includes the peer's max_ack_delay in the calculation,
+instead of relying upon a fixed minimum RTO.  Unlike TCP's RTO, which collapses
+the congestion window upon expiry, QUIC does not change the congestion window

```suggestion
the congestion window upon expiry of an RTO, QUIC does not change the congestion window
```

> @@ -228,6 +228,23 @@ QUIC endpoints measure the delay incurred between when a packet is received and
 when the corresponding acknowledgment is sent, allowing a peer to maintain a
 more accurate round-trip time estimate (see Section 13.2 of {{QUIC-TRANSPORT}}).
 
+### Probe Timeout Replaces RTO and TLP
+
+QUIC uses a probe timeout (see {{pto}}), with a timer based on TCP's
+RTO timeout.  QUIC PTO includes the peer's max_ack_delay in the calculation,
+instead of relying upon a fixed minimum RTO.  Unlike TCP's RTO, which collapses
+the congestion window upon expiry, QUIC does not change the congestion window
+and instead allows sending probe packets whenever the timer expires.  This is

```suggestion
and instead sends probe packets whenever the timer expires.  This is
```

> @@ -228,6 +228,23 @@ QUIC endpoints measure the delay incurred between when a packet is received and
 when the corresponding acknowledgment is sent, allowing a peer to maintain a
 more accurate round-trip time estimate (see Section 13.2 of {{QUIC-TRANSPORT}}).
 
+### Probe Timeout Replaces RTO and TLP
+
+QUIC uses a probe timeout (see {{pto}}), with a timer based on TCP's
+RTO timeout.  QUIC PTO includes the peer's max_ack_delay in the calculation,
+instead of relying upon a fixed minimum RTO.  Unlike TCP's RTO, which collapses
+the congestion window upon expiry, QUIC does not change the congestion window
+and instead allows sending probe packets whenever the timer expires.  This is
+similar to TCP with F-RTO, but it does allow more packets to be sent when the
+congestion window was not fully utilized when the probe timeout expires. Though

I don't think this is similar to F-RTO... I would remove this previous sentence.

> @@ -228,6 +228,23 @@ QUIC endpoints measure the delay incurred between when a packet is received and
 when the corresponding acknowledgment is sent, allowing a peer to maintain a
 more accurate round-trip time estimate (see Section 13.2 of {{QUIC-TRANSPORT}}).
 
+### Probe Timeout Replaces RTO and TLP
+
+QUIC uses a probe timeout (see {{pto}}), with a timer based on TCP's
+RTO timeout.  QUIC PTO includes the peer's max_ack_delay in the calculation,
+instead of relying upon a fixed minimum RTO.  Unlike TCP's RTO, which collapses
+the congestion window upon expiry, QUIC does not change the congestion window
+and instead allows sending probe packets whenever the timer expires.  This is
+similar to TCP with F-RTO, but it does allow more packets to be sent when the
+congestion window was not fully utilized when the probe timeout expires. Though
+this is slightly more aggressive than TCP RTO, it's less aggressive than if the
+connection was not application limited.

I'm not sure I understand this last sentence... how is app-limited relevant here?

> @@ -228,6 +228,23 @@ QUIC endpoints measure the delay incurred between when a packet is received and
 when the corresponding acknowledgment is sent, allowing a peer to maintain a
 more accurate round-trip time estimate (see Section 13.2 of {{QUIC-TRANSPORT}}).
 
+### Probe Timeout Replaces RTO and TLP
+
+QUIC uses a probe timeout (see {{pto}}), with a timer based on TCP's
+RTO timeout.  QUIC PTO includes the peer's max_ack_delay in the calculation,
+instead of relying upon a fixed minimum RTO.  Unlike TCP's RTO, which collapses
+the congestion window upon expiry, QUIC does not change the congestion window
+and instead allows sending probe packets whenever the timer expires.  This is
+similar to TCP with F-RTO, but it does allow more packets to be sent when the
+congestion window was not fully utilized when the probe timeout expires. Though
+this is slightly more aggressive than TCP RTO, it's less aggressive than if the
+connection was not application limited.
+
+A single packet loss at the tail does not indicate persistent congestion, so
+QUIC defines a time-based definition (see {{persistent-congestion}}) to

```suggestion
QUIC specifies a time-based definition (see {{persistent-congestion}}) to
```

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