Re: Unrecoverable loss pattern

[Christian Huitema <[e-mail]>]

On 2/25/2018 4:58 PM, Marten Seemann wrote:

> @Nick: The server did get all handshake packets, please see 1. in my
> description. It's the server's ACK for the FINISHED message that is
> lost, not the FINISHED message itself.
> @Martin: Yes, it is, but I don't think there's anything problematic
> about the language in this paragraph. Since the server received ACKs
> for all the handshake messages it sent, it makes sense to not open
> unencrypted packets any more.

See https://github.com/quicwg/base-drafts/issues/829 and
https://github.com/quicwg/base-drafts/issues/1018 for  discussion of
related issues.

Picoquic manages these issues by handling "ACK of ACK". Normally, it
will send ACK frames that acknowledge all packets received so far,
potentially with a long list of ACK ranges. So if an ACK is lost, the
next ACK will repeat the information that it carried. The list is only
pruned when an "ACK of ACK" is received.

In your example, if the FINISHED message is not acknowledged, the client
will retransmit the stream zero data containing the FINISHED message in
a new Handshake packet. The server will have to send an ACK of that
packet, and the ACK range will also cover the previous packet. There is
no problem for sending that ACK. You cannot acknowledge a protected
packet in a clear text message, but nothing prevents you from
acknowledging clear text packets in protected messages.

-- Christian Huitema