From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-iy0-f171.google.com (mail-iy0-f171.google.com [209.85.210.171]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id 57A2B202207 for ; Sat, 3 Dec 2011 22:55:05 -0800 (PST) Received: by iaen33 with SMTP id n33so9662804iae.16 for ; Sat, 03 Dec 2011 22:55:04 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type:content-transfer-encoding; bh=S4yLYFcrZW1Q9xZ93835ua5ZwNA+SZpioLYuuco7ul8=; b=J30AUE1nd0QpO1KRzf5t8Reezzul6F5tTmrXmcOqiQejxgS9XX6kVlpBROSoyFH4hx gMf7msQTGnzqqGqtTJ0zbSyXd0/jDmy2U/swNmgYbVFq0gFcTEuek8IW7FZXehjBlg+Y /uCkKxgg1o2M6/zMri+njudxHc5kpkziO/spk= MIME-Version: 1.0 Received: by 10.42.163.202 with SMTP id d10mr5035635icy.47.1322981703672; Sat, 03 Dec 2011 22:55:03 -0800 (PST) Received: by 10.231.204.83 with HTTP; Sat, 3 Dec 2011 22:55:03 -0800 (PST) In-Reply-To: <1322974639.3347.72.camel@denise.theartistscloset.com> References: <1322974639.3347.72.camel@denise.theartistscloset.com> Date: Sun, 4 Dec 2011 07:55:03 +0100 Message-ID: From: Dave Taht To: bloat Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Subject: [Bloat] Fwd: Understanding HFSC X-BeenThere: bloat@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: General list for discussing Bufferbloat List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 04 Dec 2011 06:55:05 -0000 As an example of how I'd like AQMs to be more deeply understood, and perhaps the lartc list ressurected... ---------- Forwarded message ---------- From: John A. Sullivan III Date: Sun, Dec 4, 2011 at 5:57 AM Subject: Understanding HFSC To: netdev@vger.kernel.org Hello, all. =A0I hope I am in the right place as this seems to be the place to ask questions formerly asked on lartc. =A0For the last three days, I've been banging my head against the wall trying to understand HFSC and it's finally starting to crack (the wall, not my head although that's close, too!). =A0It seems to be wonderful, powerful, mysterious, and poorly understood. I'm not sure I understand it either but it also seems much of what is written about it is written by people who don't fully grasp it, e.g., mostly focusing on guaranteed bandwidth and hierarchical sharing but not spending much time explaining the important concept of decoupling latency requirements and bandwidth - the part most interesting to us. So I'm hoping you'll indulge my questions and my attempt to articulate my understanding to see if I get it or if I've completely missed the plot! One of the most confusing bits to me is, does the m1 rate apply to each flow handled by the class or only to the entire class once it becomes active? In other words, if I want to ensure that my VoIP packets jump in front of my FTP bulk transfers as so fascinatingly illustrated on page 4 of http://trash.net/~kaber/hfsc/SIGCOM97.pdf and so specify a steeper m1 slope for the first 10 ms and I have a dozen RTP sessions running, does that mean that as many sessions as snuck a packet into the first 10 ms received that prioritized treatment and all the rest are treated at the m2 rate or is the 10ms acceleration in deadline time applied to every new RTP flow? I'm hoping the latter but it didn't appear to be explicitly stated. Perhaps it is even better illustrated by an example posted on https://calomel.org/pf_hfsc.html where they describe a web server serving its 10KB of text and then some large data files. =A0So if I set umax=3D80kbits and dmax=3D200ms so that I deliver the first 10KB text of th= e web page with no more than 200ms delay and then send the rest of the images, videos, etc., at the m2 rate, what happens with multiple users? The first user goes to the site, pulls down the 10KB text and then starts on the 10MB video (assuming they are not pipelining). =A0This puts the hfsc class firmly into m2. =A0A new user comes in while the first user is still downloading the video. =A0Is the first 10KB for the second user scheduled at the m2 rate or does m1 kick in to determine deadline and jump those text packets in front of both the http video download and any bulk file transfers that might be happening at the same time? Second, what must go into the umax size? Let's assume we want umax to be a single maximum sized packet on a non-jumbo frame Ethernet network. Should umax be: 1500 1514 (add Ethernet) 1518 (add CRC) 1526 (add preamble) 1538 (add interframe gap)? To keep this email from growing any longer, I'll put the rest in a separate email? Thanks - John -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at =A0http://vger.kernel.org/majordomo-info.html --=20 Dave T=E4ht SKYPE: davetaht US Tel: 1-239-829-5608 FR Tel: 0638645374 http://www.bufferbloat.net