quicwg/ack-frequency

Can IMMEDIATE_ACK be sent in 0-RTT?

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This seems like it might be important because you're not allowed to send an ACK_FREQUENCY frame to tune any parameters and the remembered values might not be suited for the new connection?

Today the text is quite clear:

Endpoints MUST NOT remember the value of the min_ack_delay transport parameter
they received for use in a subsequent connection. Consequently, ACK_FREQUENCY
frames cannot be sent in 0-RTT packets, as per {{Section 7.4.1 of QUIC-TRANSPORT}}.

Part of the reason for not persisting the min_ack_delay TP is because everytime it changes, 0-RTT would fail.

I don't have a strong opinion on this, but it is a design change if we decided to allow it. Are you proposing we allow it in 0-RTT?

The spec is clear about ACK_FREQUENCY, but it doesn't say anything about IMMEDIATE_ACK. So I think we just want to say MUST NOT for both.