From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ia0-f169.google.com (mail-ia0-f169.google.com [209.85.210.169]) (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 2913521F16D for ; Sun, 6 Jan 2013 19:43:23 -0800 (PST) Received: by mail-ia0-f169.google.com with SMTP id u20so9299311iag.14 for ; Sun, 06 Jan 2013 19:43:22 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:x-received:in-reply-to:references:date:message-id :subject:from:to:cc:content-type; bh=tKKQf+0pb81gxm2oNK2IQWbfcM0dUImMM62EgD+vowU=; b=I47ooZ2P/01uGkn09WdowSzl7zq+EPXooqnbgbvu13LAtilL25KnTC9Pzzth+pZMtQ WV28OzTcWCLwQKo1OM+Xn2T39gbJsKy2bnhq7EetMVJt2rHDLtruEXQMqbtsqAU/pyNf AxpPmJ2m7zHXU8SOJRfnqh+oyx+MeoRbnfQOWwDh+vTCq24VNnLM+vzHCq2pEw2BsZEF +YdoUW3bBQdgcNumDLOddgysqRvhmfnWqR6w0QPWYGeX3xdmjbgPy4tZsXt3HHED5mqq B1PdR4DlnP3wpz0wE3pJxTLHaiEu0H9xqnqr3jBoia0LsmWASa8gbvl+pnt2YTC6dsqs IW8A== MIME-Version: 1.0 X-Received: by 10.50.13.138 with SMTP id h10mr4652083igc.55.1357530202364; Sun, 06 Jan 2013 19:43:22 -0800 (PST) Received: by 10.50.176.233 with HTTP; Sun, 6 Jan 2013 19:43:21 -0800 (PST) Received: by 10.50.176.233 with HTTP; Sun, 6 Jan 2013 19:43:21 -0800 (PST) In-Reply-To: <17132.1357522471@sandelman.ca> References: <50E6F076.4070403@rogers.com> <17132.1357522471@sandelman.ca> Date: Mon, 7 Jan 2013 04:43:21 +0100 Message-ID: From: Pedro Tumusok To: Michael Richardson Content-Type: multipart/alternative; boundary=f46d044468e37bd9af04d2aaa132 Cc: davecb@spamcop.net, bloat 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: Mon, 07 Jan 2013 03:43:23 -0000 --f46d044468e37bd9af04d2aaa132 Content-Type: text/plain; charset=ISO-8859-1 On 7 Jan 2013 09:35, "Michael Richardson" wrote: > > > I asked > > 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. > > Pedro Tumusok replied > > 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. > > Does this mean that 802.11a,b do not suffer from this problem? > They do not have that feature, but I assume they would still be bloated in other places for other reasons. The a-mpdu got tweaked a bit in ac, to always use it. Even for single frames. Not only for aggregate as in n. --f46d044468e37bd9af04d2aaa132 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable


On 7 Jan 2013 09:35, "Michael Richardson" <mcr@sandelman.ca> wrote:
>
>
> I asked
> =A0 =A0 > A comment was made a month ago or so about how long it ta= kes wifi APs
> =A0 =A0 > to switch from transmitting (unicast) to one station to a= nother. =A0That
> =A0 =A0 > there was quite a large latency here, and that this was o= ne reason that
> =A0 =A0 > the AP designers wanted large buffers to accmulate, so th= at the
> =A0 =A0 > switching time could be amortized over a larger number of= packets.
>
> Pedro Tumusok <pedro.tum= usok@gmail.com> replied
> =A0 =A0 > I might be way of here, but to me this sounds like a-mpdu= which is
> =A0 =A0 > used to aggregate frames to get higher throughput. Thats = in the
> =A0 =A0 > specification, its
> =A0 =A0 > in 802.11ac and I believe that it go introduced with 802.= 11n.
> =A0 =A0 >
> =A0 =A0 > It is there to mitigate the overhead of aquiring the chan= nel.
>
> Does this mean that 802.11a,b do not suffer from this problem?
>

They do not have that feature, but I assume they would still be bloated in = other places for other reasons.

The a-mpdu got tweaked a bit in ac, to always use it. Even f= or single frames. Not only for aggregate as in n.

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