From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp1.sms.unimo.it (smtp1.sms.unimo.it [155.185.44.147]) (using TLSv1 with cipher DHE-RSA-AES128-SHA (128/128 bits)) (Client did not present a certificate) by huchra.bufferbloat.net (Postfix) with ESMTPS id 544F421F201 for ; Mon, 27 Apr 2015 03:19:36 -0700 (PDT) Received: from [212.84.39.131] (port=52183 helo=[192.168.15.101]) by smtp1.sms.unimo.it with esmtpsa (TLS1.0:RSA_AES_128_CBC_SHA1:128) (Exim 4.80) (envelope-from ) id 1Ymg8P-0000WZ-Eg; Mon, 27 Apr 2015 12:19:35 +0200 Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) Content-Type: text/plain; charset=iso-8859-1 From: Paolo Valente In-Reply-To: <04A0C729-6E87-49C6-84F7-3428F236CA15@unimore.it> Date: Mon, 27 Apr 2015 12:19:26 +0200 Content-Transfer-Encoding: quoted-printable Message-Id: <3DC1A2EA-6DDD-4FF9-AD12-BB509EFB96B8@unimore.it> References: <87r3r53ncb.fsf@toke.dk> <04A0C729-6E87-49C6-84F7-3428F236CA15@unimore.it> To: =?iso-8859-1?Q?Toke_H=F8iland-J=F8rgensen?= X-Mailer: Apple Mail (2.1878.6) UNIMORE-X-SA-Score: -2.9 Cc: bloat Subject: Re: [Bloat] Detecting bufferbloat from outside a node 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: Mon, 27 Apr 2015 10:20:05 -0000 Il giorno 27/apr/2015, alle ore 12:10, Paolo Valente = ha scritto: >=20 > Il giorno 27/apr/2015, alle ore 11:57, Toke H=F8iland-J=F8rgensen = ha scritto: >=20 >> Paolo Valente writes: >>=20 >>> a network-monitoring company got curious about bufferbloat issues = and >>> asked me to investigate a little bit the following issue (quite >>> interesting in my opinion). Is it possible to detect, from outside a >>> node, if the node is bufferbloated? In particular, the only action >>> allowed would be to observe the packets entering and leaving the = node >>> (plus, of course, their timing). >>=20 >> Sure. Just measure the timing when the network is unloaded and = compare >> it to when it is loaded to capacity. We do that all the time. >>=20 >> The details of course depend on what you define by a 'node', what = role >> it plays in the network (does it forward or originate packets?), and >> what control you have over the traffic flowing through it. :) >>=20 >=20 > Let us consider, for example, a host with a VoIP call and a large-file = transfer in progress. My concern is: from inside the host, we can = measure the delays experienced by the VoIP application, but, form = outside, how can we detect that the application is experiencing a high = latency, or, indirectly, that there is bufferbloat and hence that the = application is likely to be experiencing a high latency? (Of course, I = am also about to read the documents suggested by Neil.) >=20 I am sorry, but I realized that what I said was incomplete. The main = cause of my concern is that, from outside the node, we do not know = whether a VoIP packet departs ad a given time because the application = wants it to be sent at that time or because it has waited in the buffer = for a lot of time. Similarly, we do not know how long the VoIP = application will wait before getting its incoming packets delivered. Of course, if a bufferbloated state can be measured by other external = measurements, then we can infer the problem indirectly. Are there flaws in my above considerations? Thanks, Paolo > Thanks, > Paolo >=20 >> -Toke >=20 >=20 > -- > Paolo Valente =20 > Algogroup > Dipartimento di Fisica, Informatica e Matematica =09 > Via Campi, 213/B > 41125 Modena - Italy =20 > homepage: http://algogroup.unimore.it/people/paolo/ -- Paolo Valente =20 Algogroup Dipartimento di Fisica, Informatica e Matematica =09 Via Campi, 213/B 41125 Modena - Italy =20 homepage: http://algogroup.unimore.it/people/paolo/