Subject: RE: Transport in 0-RTT connections for high BDP: opt-in

From: <[email-masked]>
Date: Wed, 13 Mar 2019 14:08:50 +0000

Hi Jana,

IMO, the semantic of BDP_data and early_data don’t differ so much.
early_data works well for the web use case. There are cases like p2p (the client connects and it is the server which sends most of the data first) where the current 0-RTT is inefficient because the reduction of the time to service (TTS) relies on the optimization of the egress.

A client on a slow-to-reestablish session needs to prepare very few resource (memory …). By consequence a server willing to maximize the throughput during the re-establishment of a such connection should prepare the client side. BDP_data and its companion’s ticket are there for 3 usages:

·         BDP_data signals the intend of the server;

·         BDP_data informs the client of the order of magnitude of the optimization;

·         The usage of the session ticket to re-establish is an opt-in signal of the client;

It is up to the client to opt-in. As examples, constrained devices on slow-to-reestablish connections may opt-in the to reduce the duration of the connection and save power, on the other side, very constrained devices may not be able to opt-in because they have too few memory…

Satcom requires an additional signal like BDP_data. It will not optim the first TLS or QUIC connection but will securely reduce the TTS when the session will reestablish.

Regards
Emile

De : Jana Iyengar [mailto:[email-masked]]
Envoyé : mercredi 13 mars 2019 04:42
À : STEPHAN Emile TGI/OLN
Cc : Martin Thomson; [email-masked]; [email-masked]; Kazuho Oku
Objet : Re: Transport in 0-RTT connections for high BDP: opt-in

Emile,

The client does not need to be told that the server is going to use a large window in this connection, the server is free to choose any congestion window without notifying the client. As has been already been noted, the server can remember and use a large window using an opaque token, and a token that is opaque to the client does not need standardization.

What else does the client need to know from the server here?

-  jana

On Fri, Mar 8, 2019 at 12:51 AM <[email-masked]<mailto:[email-masked]>> wrote:

My view differs a bit.

In TLS1.3, the early_data extension field specifies the signaling for tuning the egress part of the 0-RTT traffic.

In https://tools.ietf.org/html/draft-kuhn-quic-0rtt-bdp-00, we discuss the usage of the same signaling for tuning the 0-RTT traffic sent by the server. It is a transport concern common to TCP and QUIC.

A client cannot read the content of the opaque ticket it stores on the behalf of the server. By consequence we have to define a new extension field to be sure the client opt in. The client will not use this ticket if it rejects the option.

Emile

-----Message d'origine-----
De : QUIC [mailto:[email-masked]<mailto:[email-masked]>] De la part de Martin Thomson
Envoyé : jeudi 7 mars 2019 22:26
À : [email-masked]<mailto:[email-masked]>
Objet : Re: Transport in 0-RTT connections for high BDP

As you say, this is a congestion control topic, not as much a QUIC-specific one.  And you are equally correct that this does not require standardization of any signaling to use it.

However, we have typically attempted to document congestion control strategies.  So in that spirit, it's a fine thing to do.

All that said, we explicitly decided to not address this particular question early in our process.  Saving information about congestion window from one connection so that it could be used to jump-start the next connection was a feature cut from HTTP/2 as well.

On Fri, Mar 8, 2019, at 08:04, Kazuho Oku wrote:

> Thank you for writing the draft.

> I think the approach is fine, though I wonder if we need to a

> specification for this.

> The server has the freedom to store whatever it wants in a session

> ticket. Therefore, I do not see why we need to define an extension.

> Also, it has been my understanding that token (sent by NEW_TOKEN

> frame) is a better place for storing the RTT observed in last

> connection. This is because token is a per-path information that is

> updated per each path, compared to session tickets that are expected

> to rarely be updated mid-connection.

> 2019年3月7日(木) 19:36 Kuhn Nicolas <[email-masked]<mailto:[email-masked]>>:

> > Hi,

> > We have uploaded a draft that describes a solution to improve QUIC’s performance during 0-RTT establishment in a high BDP context.

> > https://tools.ietf.org/html/draft-kuhn-quic-0rtt-bdp-00

> > Abstract

> >    0-RTT is designed to accelerate the throughput at the establishment

> >    of a connection.  There are cases where 0-RTT alone does not improve

> >    the time-to-service.

> >    This memo discusses a solution where a fundamental characteristic of

> >    the path is learned during the 1-RTT phase and shared with the 0-RTT

> >    phase to accelerate the initial throughput during subsequent 0-RTT

> >    connections.

> > Would it be possible to have a small slot to present it during the next IETF meeting?

> > Kind regards,

> > Nico & Emile

> --

> Kazuho Oku

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