From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-vn0-x233.google.com (mail-vn0-x233.google.com [IPv6:2607:f8b0:400c:c0f::233]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id E23F221F247 for ; Thu, 7 May 2015 00:18:25 -0700 (PDT) Received: by vnbg7 with SMTP id g7so2488302vnb.11 for ; Thu, 07 May 2015 00:18:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=NhgKGXCKWEliUhEn+B7VyHc2p+wN8C7wQQMKhKE0ixs=; b=WM0DcKgXa/FjmFYV3UPgAXn45XbeSOIhwJrXONF3COGq6VyqKkeS0Tb932p1NsPRtT OKB8JmmgSmtmfWoJafAlDh2XLf011IVpMBG4rUxv6rdNymENrKXWUiNYYXIhkiQFCVbT tBWCOl732dsrxuhPmtVb7WCyJ9d6YY8oLEVfxkuFPSsiLBXPKUBSHie0EBoEfavOoC90 bI1Q4lPqXRjfKxIlAsiFxbdx9JjpzxQ0nzdCnktcmIb2wOK8Sy3OJUdZ4JGq/RVnPs/8 gLJAGaCBlnvY/TXkjdd+kWc50f7j3r+bZKzPdm4PzzDtAHPetkfPep3aZsx3UYND5adG lmdw== MIME-Version: 1.0 X-Received: by 10.52.33.180 with SMTP id s20mr2037810vdi.35.1430983103944; Thu, 07 May 2015 00:18:23 -0700 (PDT) Received: by 10.52.12.167 with HTTP; Thu, 7 May 2015 00:18:23 -0700 (PDT) Received: by 10.52.12.167 with HTTP; Thu, 7 May 2015 00:18:23 -0700 (PDT) In-Reply-To: References: <1429722979.18561.112.camel@edumazet-glaptop2.roam.corp.google.com> <5537DA20.1090008@orange.com> <5537DE4D.8090100@orange.com> <553882D7.4020301@orange.com> <1429771718.22254.32.camel@edumazet-glaptop2.roam.corp.google.com> <6C0D04CF-53AA-4D18-A4E4-B746AF6487C7@gmx.de> <87wq123p5r.fsf@toke.dk> <2288B614-B415-4017-A842-76E8F5DFDE4C@gmx.de> <553B06CE.1050209@superduper.net> <14ceed3c818.27f7.e972a4f4d859b00521b2b659602cb2f9@superduper.net> <0C930D43-A05B-48E2-BC01-792CAA72CAD1@gmx.de> <5549A1B8.50005@superduper.net> Date: Thu, 7 May 2015 10:18:23 +0300 Message-ID: From: Jonathan Morton To: jb Content-Type: multipart/alternative; boundary=20cf3079baae9720ee051578b7e3 Cc: bloat Subject: Re: [Bloat] DSLReports Speed Test has latency measurement built-in 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: Thu, 07 May 2015 07:18:54 -0000 --20cf3079baae9720ee051578b7e3 Content-Type: text/plain; charset=UTF-8 It may depend on the application's tolerance to packet loss. A packet delayed further than the jitter buffer's tolerance counts as lost, so *IF* jitter is randomly distributed, jitter can be traded off against loss. For those purposes, standard deviation may be a valid metric. However the more common characteristic is that delay is sometimes low (link idle) and sometimes high (buffer full) and rarely in between. In other words, delay samples are not statistically independent; loss due to jitter is bursty, and real-time applications like VoIP can't cope with that. For that reason, and due to your low temporal sampling rate, you should take the peak delay observed under load and compare it to the average during idle. - Jonathan Morton --20cf3079baae9720ee051578b7e3 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable

It may depend on the application's tolerance to packet l= oss. A packet delayed further than the jitter buffer's tolerance counts= as lost, so *IF* jitter is randomly distributed, jitter can be traded off = against loss. For those purposes, standard deviation may be a valid metric.=

However the more common characteristic is that delay is some= times low (link idle) and sometimes high (buffer full) and rarely in betwee= n. In other words, delay samples are not statistically independent; loss du= e to jitter is bursty, and real-time applications like VoIP can't cope = with that. For that reason, and due to your low temporal sampling rate, you= should take the peak delay observed under load and compare it to the avera= ge during idle.

- Jonathan Morton

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