Re: [quicwg/base-drafts] Does it make sense to try 0-RTT after Retry? (#2842)

Kazuho Oku <> Tue, 25 June 2019 10:45 UTC

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From: Kazuho Oku <>
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Subject: Re: [quicwg/base-drafts] Does it make sense to try 0-RTT after Retry? (#2842)
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> Since we can assume that most (all?) server implementation will drop 0-RTT packets when sending a Retry, the only reasonable thing to do for a client is to treat all 0-RTT packets as lost and retransmit them. Considering that, it would make sense to require servers to drop all Retry packets from the first flight, as @kazuho suggests.

Thank you for suggesting a path forward.

I think my weak preference goes to something slightly different.

I think we are in agreement that most if not all the servers would not buffer the 0-RTT packets carrying the original DCIDs when they send Retrys. It makes sense to acknowledge the fact in the specification and suggest clients to retransmit 0-RTT data it has already sent.

What I am not sure is if there is a reason to forbid servers from buffering such 0-RTT packets.

>From client's point of view, sending 0-RTT data once per connection is an optimization. Retransmitting 0-RTT data when the server sends a Retry is further optimization. If we think that way, servers that buffer 0-RTT packets when sending a Retry has increased chance of utilizing 0-RTT data. Compared to that, there is no reason to mandate servers to drop 0-RTT packets.

To summarize, I think all we need to clarify is that servers responding with Retries are likely to discard 0-RTT packets that carry the original DCIDs and therefore that retransmitting 0-RTT data makes sense. But nothing more.

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