Return-Path: X-Original-To: quic-issues@ietfa.amsl.com Delivered-To: quic-issues@ietfa.amsl.com Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id BF995120848 for ; Wed, 19 Feb 2020 23:57:46 -0800 (PST) X-Virus-Scanned: amavisd-new at amsl.com X-Spam-Flag: NO X-Spam-Score: -8 X-Spam-Level: X-Spam-Status: No, score=-8 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, HTML_MESSAGE=0.001, MAILING_LIST_MULTI=-1, RCVD_IN_DNSWL_HI=-5, SPF_HELO_NONE=0.001, SPF_PASS=-0.001] autolearn=ham autolearn_force=no Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (1024-bit key) header.d=github.com Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id SShvlXhVUZmq for ; Wed, 19 Feb 2020 23:57:45 -0800 (PST) Received: from out-11.smtp.github.com (out-11.smtp.github.com [192.30.254.194]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id F3EB312083A for ; Wed, 19 Feb 2020 23:57:44 -0800 (PST) Date: Wed, 19 Feb 2020 23:57:43 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=github.com; s=pf2014; t=1582185464; bh=lHORat+bDl4lSTLgVe6Eg5pfNcT6Rl3GlzjTV6kDfeo=; h=Date:From:Reply-To:To:Cc:In-Reply-To:References:Subject:List-ID: List-Archive:List-Post:List-Unsubscribe:From; b=WTNSpn/xxLS2G9rhcPEoivAr8VpwO1aYyS03YGNJ2RplBEVU8yxXR/QenNA6KOLDM h0GnREJVcpKvCDQJjp+PJFDv87JVl1cXCvBEZ1wAM7ODmdoNBCBGxaqemu5k0mXUeG oxFLUBtGS87QWiE+drgZE+jJbsSUx6ym/OsBoodY= From: Kazuho Oku Reply-To: quicwg/base-drafts To: quicwg/base-drafts Cc: Subscribed Message-ID: In-Reply-To: References: Subject: Re: [quicwg/base-drafts] max_packet_size in 0-RTT (#3447) Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="--==_mimepart_5e4e3bf7df414_2b3f3fe38a6cd95c30555b"; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: list X-GitHub-Sender: kazuho X-GitHub-Recipient: quic-issues X-GitHub-Reason: subscribed X-Auto-Response-Suppress: All X-GitHub-Recipient-Address: quic-issues@ietf.org Archived-At: X-BeenThere: quic-issues@ietf.org X-Mailman-Version: 2.1.29 List-Id: Notification list for GitHub issues related to the QUIC WG List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 20 Feb 2020 07:57:47 -0000 ----==_mimepart_5e4e3bf7df414_2b3f3fe38a6cd95c30555b Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit @martinduke > I would like someone to articulate what harm is done if the server were to accept 0-RTT when the max_packet_size has decreased. Consider the case where the original value of max_packet_size was 9000, and client sending 0-RTT packets of 9000 bytes. If the server's max_packet_size goes down to 1280 and the server accepts 0-RTT, the client would consider the 0-RTT packets it has sent to be lost. I think that would halve CWND (to 5 MTU) and we'd exit slow start. This negative impact is likely to be greater than the benefit we'd get from 0-RTT. That said, I am not sure if I like the framing of the discussion, or the current definition of `max_packet_size`. I think we might be conflating the maximum size of QUIC packets and the maximum size of UDP datagrams, and I might argue that what matters in reality is the size of UDP datagrams. As `max_packet_size` is a limit at the QUIC packet level, the transport draft allows a sender to send (and therefore requires a receiver to not discard) a UDP datagram that contains multiple QUIC packets being colesced, each of those QUIC packets being as large as `max_packet_size`. A server might send a UDP datagram that is 3x of `max_packet_size` (datagram consisting of full-sized Initial, Handshake, 1-RTT packet). Once a client receives the TP, it might send a UDP datagram that is 2x of `max_packet_size` (consisting of full-sized Handshake and 1-RTT packet). Are we fine with that? Shouldn't we better change the TP to `max_datagram_size`? -- You are receiving this because you are subscribed to this thread. Reply to this email directly or view it on GitHub: https://github.com/quicwg/base-drafts/issues/3447#issuecomment-588714349 ----==_mimepart_5e4e3bf7df414_2b3f3fe38a6cd95c30555b Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: 7bit

@martinduke

I would like someone to articulate what harm is done if the server were to accept 0-RTT when the max_packet_size has decreased.

Consider the case where the original value of max_packet_size was 9000, and client sending 0-RTT packets of 9000 bytes. If the server's max_packet_size goes down to 1280 and the server accepts 0-RTT, the client would consider the 0-RTT packets it has sent to be lost. I think that would halve CWND (to 5 MTU) and we'd exit slow start. This negative impact is likely to be greater than the benefit we'd get from 0-RTT.

That said, I am not sure if I like the framing of the discussion, or the current definition of max_packet_size.

I think we might be conflating the maximum size of QUIC packets and the maximum size of UDP datagrams, and I might argue that what matters in reality is the size of UDP datagrams.

As max_packet_size is a limit at the QUIC packet level, the transport draft allows a sender to send (and therefore requires a receiver to not discard) a UDP datagram that contains multiple QUIC packets being colesced, each of those QUIC packets being as large as max_packet_size. A server might send a UDP datagram that is 3x of max_packet_size (datagram consisting of full-sized Initial, Handshake, 1-RTT packet). Once a client receives the TP, it might send a UDP datagram that is 2x of max_packet_size (consisting of full-sized Handshake and 1-RTT packet).

Are we fine with that? Shouldn't we better change the TP to max_datagram_size?

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