From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bifrost.lang.hm (mail.lang.hm [64.81.33.126]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by huchra.bufferbloat.net (Postfix) with ESMTPS id D8D2021F801 for ; Mon, 10 Aug 2015 11:44:46 -0700 (PDT) Received: from asgard.lang.hm (asgard.lang.hm [10.0.0.100]) by bifrost.lang.hm (8.13.4/8.13.4/Debian-3) with ESMTP id t7AIiidH026419; Mon, 10 Aug 2015 11:44:44 -0700 Date: Mon, 10 Aug 2015 11:44:44 -0700 (PDT) From: David Lang X-X-Sender: dlang@asgard.lang.hm To: Simon Barber In-Reply-To: <55C8AE88.9080202@superduper.net> Message-ID: References: <356F5FEE-9FBD-4FF9-AC17-86A642D918A4@gmail.com> <5CC1DC90-DFAF-4A4D-8204-16CD4E20D6E3@gmx.de> <4D24A497-5784-493D-B409-F704804326A7@gmx.de> <1438361254.45977158@apps.rackspace.com> <6E08E48D-5D53-48E5-B088-2D1DB5E566AD@gmail.com> <1438983998.16576420@apps.rackspace.com> <1439066765.7348311@apps.rackspace.com> <55C7B7A9.4070708@superduper.net> <55C8AE88.9080202@superduper.net> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; format=flowed; charset=US-ASCII Cc: make-wifi-fast@lists.bufferbloat.net Subject: Re: [Make-wifi-fast] [Cerowrt-devel] [tsvwg] Comments on draft-szigeti-tsvwg-ieee-802-11e X-BeenThere: make-wifi-fast@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 10 Aug 2015 18:45:15 -0000 On Mon, 10 Aug 2015, Simon Barber wrote: > On 8/9/2015 2:43 PM, David Lang wrote: >> On Sun, 9 Aug 2015, Simon Barber wrote: >> >>> 11ac with it's always on RTS/CTS and mandatory A-MPDUs really performs >>> much better than many 11n implementations. It's finally a fairly sane MAC. >>> The 64 bit limit in the compressed block ack is a limiter though. The >>> really wide channels are another complex area for busy networks. >>> >>> The aggregation overhead for 11ac is about 222uS, counting EDCA backoff, >>> RTS, CTS, PLCP header and the Block-ACK and all the inter frame spaces. >>> One full size ethernet frame at 1Gb/s = ~12us. Large aggregates are >>> critical to good efficiency and performance, and a certain amount of >>> queuing is required to form them. They have to be completely formed before >>> transmission starts. >> >> do you know the per-transmission overhead for different modes (n and a/g >> specifically)? Also, what parts of the overhead get extended when the data >> rate slows? It's all well and good to talk about a full size packet being >> 12us at 1GHz, but that requires a good signal an 3x3 radios. If instead you >> are on a 1x1 radio with not as good a signal, you can easily drop your data >> rate by an order of magnatude or so. At ~100Mb your data packet is now >> 120us, what is the overhead? if you drop to 10Mb your packet is now 1200us, >> what is the overhead. > > If you're using VHT modulation then the overhead stays the same at lower > rates (assuming the same no. of antennas). 11n is lower due to no RTS, only > CTS, and 11a is lower still due to no CTS, and no training symbols for MIMO. > Not quite half though. Just to clarify and make sure I'm understanding this properly A full size packet takes ~234us (222 + 12) at 1Gb/s bitrate and ~1422us (222 +1200) at 10Mb bitrate, correct? I would have expected that some of the overhead/framing would be bitrate dependent, while some is wall-clock time of waiting to make sure the channel is clear. David Lang