Re: [quicwg/base-drafts] MinRTT for the path (#2919)

Jana Iyengar <notifications@github.com> Mon, 13 January 2020 21:32 UTC

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Subject: Re: [quicwg/base-drafts] MinRTT for the path (#2919)
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janaiyengar commented on this pull request.

s/path/network path

> @@ -249,11 +249,10 @@ more accurate round-trip time estimate (see Section 13.2 of {{QUIC-TRANSPORT}}).
 At a high level, an endpoint measures the time from when a packet was sent to
 when it is acknowledged as a round-trip time (RTT) sample.  The endpoint uses
 RTT samples and peer-reported host delays (see Section 13.2 of
-{{QUIC-TRANSPORT}}) to generate a statistical description of the connection's
-RTT. An endpoint computes the following three values: the minimum value
-observed over the lifetime of the connection (min_rtt), an
-exponentially-weighted moving average (smoothed_rtt), and the variance in the
-observed RTT samples (rttvar).
+{{QUIC-TRANSPORT}}) to generate a statistical description of the path's RTT.

```suggestion
{{QUIC-TRANSPORT}}) to generate a statistical description of the network path's RTT.
```

> @@ -295,16 +294,22 @@ retain sufficient history is an open research question.
 
 ## Estimating min_rtt {#min-rtt}
 
-min_rtt is the minimum RTT observed over the lifetime of the connection.
-min_rtt is set to the latest_rtt on the first sample in a connection, and to the
-lesser of min_rtt and latest_rtt on subsequent samples.
+min_rtt is the minimum RTT observed for a given path.  min_rtt is set to the

```suggestion
min_rtt is the minimum RTT observed for a given network path.  min_rtt is set to the
```

>  
 An endpoint uses only locally observed times in computing the min_rtt and does
 not adjust for host delays reported by the peer.  Doing so allows the endpoint
 to set a lower bound for the smoothed_rtt based entirely on what it observes
 (see {{smoothed-rtt}}), and limits potential underestimation due to
 erroneously-reported delays by the peer.
 
+The RTT for a path may change over time.  If a path's actual RTT decreases,

```suggestion
The RTT for a network path may change over time.  If a path's actual RTT decreases,
```

> @@ -333,11 +338,10 @@ endpoint:
   min_rtt.  This limits the underestimation that a misreporting peer can cause
   to the smoothed_rtt.
 
-On the first RTT sample in a connection, the smoothed_rtt is set to the
-latest_rtt.
+On the first RTT sample for a path, the smoothed_rtt is set to the latest_rtt.

```suggestion
On the first RTT sample for a network path, the smoothed_rtt is set to the latest_rtt.
```

>  
 smoothed_rtt and rttvar are computed as follows, similar to {{?RFC6298}}.  On
-the first RTT sample in a connection:
+the first RTT sample for a path:

```suggestion
the first RTT sample for a network path:
```

>  
 An endpoint uses only locally observed times in computing the min_rtt and does
 not adjust for host delays reported by the peer.  Doing so allows the endpoint
 to set a lower bound for the smoothed_rtt based entirely on what it observes
 (see {{smoothed-rtt}}), and limits potential underestimation due to
 erroneously-reported delays by the peer.
 
+The RTT for a path may change over time.  If a path's actual RTT decreases,
+the min_rtt will adapt immediately on the first low sample.  If the path's

```suggestion
the min_rtt will adapt immediately on the first low sample.  If the network path's
```

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