Subject: [quicwg/base-drafts] Safety issue during incipient persistent congestion episode (#3259)

From: Praveen Balasubramanian <[email-masked]>
Date: Mon, 18 Nov 2019 15:52:26 -0800

"When an ACK frame is received that establishes loss of all in-flight packets sent over a long enough period of time, the network is considered to be experiencing persistent congestion." 

QUIC declares persistent congestion only upon receipt of an ACK for a packet sent after entering loss recovery. This means that the cwnd will remain large and usable even if there is prolonged network silence with packets outstanding. If the state of the transport was application limited, this can cause a large burst on the network. 

In TCP, an RTO causes immediate drop of the cwnd to min_cwnd. 

Ideally QUIC should drop the cwnd in the same timescale as TCP would. Typically minrto for the Internet is 200 msec or 300 msec (and larger if the RTT is larger).

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