From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ie0-f176.google.com (mail-ie0-f176.google.com [209.85.223.176]) (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 E14DF21F17F for ; Thu, 3 Jan 2013 01:18:28 -0800 (PST) Received: by mail-ie0-f176.google.com with SMTP id 13so17855274iea.21 for ; Thu, 03 Jan 2013 01:18:28 -0800 (PST) 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=dIkwWCcOVyvpxbNT9ohEUkSwoT++6G0vQXMnNa+m7Ew=; b=sQKZ5g7s1Xhjpx0+q94mt+hynygDXaN1DlUvvBsDp7g0L6438RPS3pDxOOscYaQ9at EdkcVm1RrFX7TdCHPHkxmXCGqtsNDeajQE8oDswvtky5FHZRaRKRyq/lSnY5KeTNAFJy WwcFffuR4xOOhrEA5ytYY58XGAwiiOsDtreUHa47abdH6UqHx11LhGVr5LPdBsSZBFNT 3VVJ6DSh7xVUzrvxnKRvI8Ilq7B2dZ37cois3ZWtLUFywP3dkg2HSFgIcxFXvVTag5ny xUy6hhrsB54fM5tgztIvR4v3Xoq55FnVfyxdO+VaBLJDi7mWPUnKojWeQJ4bSQEtBy7i tx7Q== MIME-Version: 1.0 Received: by 10.42.180.65 with SMTP id bt1mr36760687icb.41.1357204708038; Thu, 03 Jan 2013 01:18:28 -0800 (PST) Received: by 10.50.176.233 with HTTP; Thu, 3 Jan 2013 01:18:26 -0800 (PST) Received: by 10.50.176.233 with HTTP; Thu, 3 Jan 2013 01:18:26 -0800 (PST) In-Reply-To: <6584.1357062566@sandelman.ca> References: <6584.1357062566@sandelman.ca> Date: Thu, 3 Jan 2013 10:18:26 +0100 Message-ID: From: Pedro Tumusok To: Michael Richardson Content-Type: multipart/alternative; boundary=90e6ba6e81d882988a04d25ed8d8 Cc: bloat@bufferbloat.net Subject: Re: [Bloat] wifi AP switching time 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, 03 Jan 2013 09:18:29 -0000 --90e6ba6e81d882988a04d25ed8d8 Content-Type: text/plain; charset=ISO-8859-1 On Jan 1, 2013 6:50 PM, "Michael Richardson" wrote: > > > A comment was made a month ago or so about how long it takes wifi APs > to switch from transmitting (unicast) to one station to another. That > there was quite a large latency here, and that this was one reason that > the AP designers wanted large buffers to accmulate, so that the > switching time could be amortized over a larger number of packets. > > I'm looking for a definitive reference to this problem. > Will this be in the 802.11 specification, or is this an inherent problem > in the chipsets, not the physics? > I might be way of here, but to me this sounds like a-mpdu which is used to aggregate frames to get higher throughput. Thats in the specification, its in 802.11ac and I believe that it go introduced with 802.11n. It is there to mitigate the overhead of aquiring the channel. --90e6ba6e81d882988a04d25ed8d8 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable


On Jan 1, 2013 6:50 PM, "Michael Richardson" <mcr@sandelman.ca> wrote:
>
>
> A comment was made a month ago or so about how long it takes wifi APs<= br> > to switch from transmitting (unicast) to one station to another. =A0Th= at
> there was quite a large latency here, and that this was one reason tha= t
> the AP designers wanted large buffers to accmulate, so that the
> switching time could be amortized over a larger number of packets.
>
> I'm looking for a definitive reference to this problem.
> Will this be in the 802.11 specification, or is this an inherent probl= em
> in the chipsets, not the physics?
>

I might be way of here, but to me this sounds like a-mpdu which is used = to aggregate frames to get higher throughput. Thats in the specification, i= ts in 802.11ac and I believe that it go introduced with 802.11n.

It is there to mitigate the overhead of aquiring the channel.

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