From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ob0-x22f.google.com (mail-ob0-x22f.google.com [IPv6:2607:f8b0:4003:c01::22f]) (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 6CCD821F280 for ; Sun, 29 Mar 2015 09:34:27 -0700 (PDT) Received: by obvd1 with SMTP id d1so39705905obv.0 for ; Sun, 29 Mar 2015 09:34:27 -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=mwF/1oJg/B221/KVTxcbZ/rVPMYZCV+7J1OrT2PWS9Y=; b=t8JfgJoorBt7zkuHXy7aajEXINsPQGE8z5hkoJHFfL0ZvLmK/X4KlW/si8pLrtIGzP 6UDZ4DiKIPReCRvBDFFNutT/Die3B7fbtxVLEzehGbFR2S/30ARvK/QThzyvdwSeScHw czP2ZC8z6NWjWu+uoKSLANXEt8Ph7bIY9/wwnWWp5bK6gEC0SFFEvaWzDlx1kth0uCTx 8QMBLZAkAhS/nSwCB5tjFUYg3i9GPdR59eV0UKth7cbqez7Jgn/R+IkZsUGN4gEJnzon KVd99tTSlG6JrHB4oLK/QbcTns3aEy0utRJzTdtyz4k4y4kBI90a4SwvR093gKr2DFjh BY0g== MIME-Version: 1.0 X-Received: by 10.60.158.202 with SMTP id ww10mr23871829oeb.18.1427646867131; Sun, 29 Mar 2015 09:34:27 -0700 (PDT) Received: by 10.202.216.69 with HTTP; Sun, 29 Mar 2015 09:34:27 -0700 (PDT) In-Reply-To: <5BD9D41C-9631-4BD0-9C18-7909E9D6E9C0@gmail.com> References: <5BD9D41C-9631-4BD0-9C18-7909E9D6E9C0@gmail.com> Date: Sun, 29 Mar 2015 09:34:27 -0700 Message-ID: From: sahil grover To: Jonathan Morton Content-Type: multipart/alternative; boundary=047d7bd6aaf261525705126ff0ff Cc: bloat@lists.bufferbloat.net Subject: Re: [Bloat] Requirements for bufferbloat to occur 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, 29 Mar 2015 16:34:56 -0000 --047d7bd6aaf261525705126ff0ff Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Thanks a lot for replying. can you please explain me the concept of delay-bandwidth product,window size and buffer size(or something related with pipe size and packets in flight). because i am unable to understand it from papers/articles etc. And the way you explained to me everytime, was very effective. So please help in making me understand this(BDP,window size) concept too . On Sun, Mar 29, 2015 at 2:09 AM, Jonathan Morton wrote: > > > On 29 Mar, 2015, at 11:04, sahil grover > wrote: > > > > (1) All say bufferSize should be set very large for bufferbloat to occu= r. > > > > But how much large?? is there any condition? > > There=E2=80=99s a clue in the name: if the buffer is significantly larger= than it > needs to be (and is unmanaged), we call that bufferbloat. > > If the buffer is too small to absorb a typical burst of packets, the > resulting increase in packet loss will cause a reduction in throughput. > The correct size for an unmanaged buffer is typically the delay-bandwidth > product, which enables it to absorb a transitory burst from a single TCP > flow. > > However, determining the delay is difficult a priori, and frequently > differs substantially between different flows on the same connection. So > we usually make some reasonable assumption about the delay component of > that formula: 100ms is typical for a broadband connection to the public > Internet, and VoIP can just-about cope with that in practice. > > Or, to put it another way - if the buffer *induces* significantly more > than 100ms delay under load, that is bufferbloat. > > > (2) even after setting buffersize very very large, if packets get > dropped due to buffer > > overflow when heavy traffic is there. > > > > is it bufferbloat? > > Yes. Packet loss has nothing to do with it - it=E2=80=99s the induced de= lay that > matters. > > > sholud we take care that maximum limit of buffersize is never reached > and no > > packet drop is there due to queue overlow for bufferbloat condition? > > Extremely large buffers are usually the result of hardware engineers > naively attempting to achieve zero packet loss, by providing buffers larg= er > than the TCP receive window size. (That is a futile goal - rwnd is > unlimited in modern operating systems which support window scaling.) > However, zero packet loss is not a necessary condition. > > AQMs often deliberately drop packets in order to signal congestion to the > endpoints. Under some circumstances, this can actually result in less > overall packet loss than on an unmanaged buffer. Even without ECN, the A= QM > rarely causes burst losses, whereas overflowing an unmanaged queue often > does. With ECN, an AQM can often signal congestion sufficiently well > without dropping any packets at all. > > - Jonathan Morton > > --047d7bd6aaf261525705126ff0ff Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Thanks a lot for replying.

can you plea= se explain me =C2=A0the concept of=C2=A0=C2=A0delay-b= andwidth product,window size and buffer size(or something related with pipe size and packets in fl= ight).

=C2=A0because = i am unable to understand it from papers/articles etc.

And the way you explained to me everytime= , was very effective.

So please help in making me understand this(BDP,window size) concept too .=





On Sun, Mar 29, 2015 at 2:09 AM, Jonathan Morton <chr= omatix99@gmail.com> wrote:
=
> On 29 Mar, 2015, at 11:04, sahil grover <sahilgrover013@gmail.com> wrote:
>
> (1) All say bufferSize should be set very large for bufferbloat to occ= ur.
>
> But how much large?? is there any condition?

There=E2=80=99s a clue in the name: if the buffer is significantly l= arger than it needs to be (and is unmanaged), we call that bufferbloat.

If the buffer is too small to absorb a typical burst of packets, the result= ing increase in packet loss will cause a reduction in throughput.=C2=A0 The= correct size for an unmanaged buffer is typically the delay-bandwidth prod= uct, which enables it to absorb a transitory burst from a single TCP flow.<= br>
However, determining the delay is difficult a priori, and frequently differ= s substantially between different flows on the same connection.=C2=A0 So we= usually make some reasonable assumption about the delay component of that = formula: 100ms is typical for a broadband connection to the public Internet= , and VoIP can just-about cope with that in practice.

Or, to put it another way - if the buffer *induces* significantly more than= 100ms delay under load, that is bufferbloat.

> (2) even after setting buffersize very=C2=A0 very large,=C2=A0 if pack= ets get dropped due to buffer
> overflow=C2=A0 when heavy traffic is there.
>
> is it bufferbloat?

Yes.=C2=A0 Packet loss has nothing to do with it - it=E2=80=99s the = induced delay that matters.

> sholud we take care that maximum limit of buffersize is never reached = and no
> packet=C2=A0 drop is there due to queue overlow for bufferbloat condit= ion?

Extremely large buffers are usually the result of hardware engineers= naively attempting to achieve zero packet loss, by providing buffers large= r than the TCP receive window size.=C2=A0 (That is a futile goal - rwnd is = unlimited in modern operating systems which support window scaling.)=C2=A0 = However, zero packet loss is not a necessary condition.

AQMs often deliberately drop packets in order to signal congestion to the e= ndpoints.=C2=A0 Under some circumstances, this can actually result in less = overall packet loss than on an unmanaged buffer.=C2=A0 Even without ECN, th= e AQM rarely causes burst losses, whereas overflowing an unmanaged queue of= ten does.=C2=A0 With ECN, an AQM can often signal congestion sufficiently w= ell without dropping any packets at all.

=C2=A0- Jonathan Morton


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