From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-x22f.google.com (mail-wm0-x22f.google.com [IPv6:2a00:1450:400c:c09::22f]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id D497B3B2A0 for ; Mon, 27 Jun 2016 16:34:03 -0400 (EDT) Received: by mail-wm0-x22f.google.com with SMTP id a66so131274312wme.0 for ; Mon, 27 Jun 2016 13:34:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=broadcom.com; s=google; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc; bh=U5lAwwMvFWQ1PNB6+bRLymQs3gjv9o3VfwzWpwYYJfA=; b=Rcsmj/oUdm9nUhive0Xw7GPyrrCtDky0LCoML0wOS2Orq6yQGD5nHiVpTFDmswrt07 bfOPMl7jJL2v439PX8cerK7UdnURpucaVg28+UCWs9lPjJA7fdYYbIltfJr/vGW3uADl sYyOf0eLo4hv22yf5kB/XRuG7Hb+vaIdrdOpo= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc; bh=U5lAwwMvFWQ1PNB6+bRLymQs3gjv9o3VfwzWpwYYJfA=; b=Mgy5FdpbXh0Z+jje8FPK/IGecUQVCCppv24udiEkOGiDYryazqDseI0YZVRFKQPHlG mbb1jrrh2+Gj6+ryK1zi6g85A+CLzgciP4y1Zn3z6Zg8sPfb8DdGdLJWp6LKrApoQyQD v0BzJus/QVRTmrOErTCyGrVdte3Fccrxsxgd8uVaTjAhObGsKT/BjvVwTbJvb7wUxxGa DN+rvcjITW7MgFZOylF1p1xERNQUBwcLDPiHeLE+th+wJTLN7+N1nHgelQGuMNJHWO++ 6nQio9omVsFPDgoMxzh5cjwDU8u7XDsUkSkaibbcCMWt80xDwCH5yPl+DsJBnsCrpSdi v9sQ== X-Gm-Message-State: ALyK8tJD1nPzG+Wf//fqNmWc69CzvjjBHEDf9JGSjxYQnW1FgQIxxbbZer6HiLyDqbWcYAINBQHPrKEuer6hUpB6 X-Received: by 10.194.113.104 with SMTP id ix8mr2845529wjb.2.1467059642406; Mon, 27 Jun 2016 13:34:02 -0700 (PDT) MIME-Version: 1.0 Received: by 10.194.239.202 with HTTP; Mon, 27 Jun 2016 13:34:00 -0700 (PDT) In-Reply-To: References: <1466803464.927322699@mobile.rackspace.com> From: Bob McMahon Message-ID: To: David Lang Cc: Dave Taht , make-wifi-fast@lists.bufferbloat.net, "cerowrt-devel@lists.bufferbloat.net" Content-Type: multipart/alternative; boundary=001a1130d182da4c9405364870db X-Mailman-Approved-At: Mon, 30 Mar 2020 07:21:14 -0400 Subject: Re: [Cerowrt-devel] [Make-wifi-fast] more well funded attempts showing market demandfor better wifi X-BeenThere: cerowrt-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: Development issues regarding the cerowrt test router project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Date: Mon, 27 Jun 2016 20:34:04 -0000 X-Original-Date: Mon, 27 Jun 2016 13:34:00 -0700 X-List-Received-Date: Mon, 27 Jun 2016 20:34:04 -0000 --001a1130d182da4c9405364870db Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable packet size is smallest udp payload per a socket write() which in turn drives the smallest packet supported by "the wire." Here is a back of the envelope calculation giving ~100 microseconds per BE access. # Overhead estimates (slot time is 9 us): # o DIFS 50 us or *AIFS (3 * 9 us) =3D 27 us # o *Backoff Slot * CWmin, 9 us * rand[0,xf] (avg) =3D 7 * 9=3D63 us # o 5G 20 us # o Multimode header 20 us # o PLCP (symbols) 2 * 4 us =3D 8 us # o *SIFS 16 us # o ACK 40 us # # Even if there is no collision and the CW stays at the aCWmin, the average # backoff time incurred by CSMA/CA is aDIFS + aCWmin/2 * aSlotTime =3D 16 = =C2=B5s # +(2+7.5)*9 =C2=B5s =3D 101.5 =C2=B5s for OFDM PHY, while the data rate wi= th OFDM PHY # can reach 600 Mbps in 802.11n, leading to a transmission time of 20 =C2= =B5s # for a 1500 byte packet. All devices in a BSSID would have to agree that the second radio is to be used for BSSID "carrier state" information and all energy will be sourced by the AP serving that BSSID. (A guess is doing this wouldn't improve the 100 us by enough to justify the cost and that a new MAC protocol is required. Just curious to what such a protocol and phy subsystem would look like assuming collision avoidance could be replaced with collision detect.) Bob On Mon, Jun 27, 2016 at 1:09 PM, David Lang wrote: > On Mon, 27 Jun 2016, Bob McMahon wrote: > > The ~10K is coming from empirical measurements where all aggregation >> technologies are disabled, i.e. only one small IP packet per medium >> arbitration/access and where there is only one transmitter and one >> receiver. 900Mb/sec is typically a peak-average throughput measurement >> where max (or near max) aggregation occurs, amortizing the access overhe= ad >> across multiple packets. >> > > so 10K is minimum size packets being transmitted?or around 200 > transmissions/sec (plus 200 ack transmissions/sec)? > > Yes, devices can be hidden from each other but not from the AP (hence the >> use of RTS/CTS per hidden node mitigation.) Isn't it the AP's view of th= e >> "carrier state" that matters (at least in infrastructure mode?) If that= 's >> the case, what about a different band (and different radio) such that th= e >> strong signal carrying the data could be separated from the the BSSID's >> "carrier/energy state" signal? >> > > how do you solve the interference problem on this other band/radio? When > you have other APs in the area operating, you will have the same problem > there. > > David Lang > > > Bob >> >> On Mon, Jun 27, 2016 at 12:40 PM, David Lang wrote: >> >> On Mon, 27 Jun 2016, Bob McMahon wrote: >>> >>> Hi All, >>> >>>> >>>> This is a very interesting thread - thanks to all for taking the time = to >>>> respond. (Personally, I now have better understanding of the >>>> difficulties >>>> associated with a PHY subsystem that supports a wide 1GHz.) >>>> >>>> Not to derail the current discussion, but I am curious to ideas on >>>> addressing the overhead associated with media access per collision >>>> avoidance. This overhead seems to be limiting transmits to about 10K >>>> per >>>> second (even when a link has no competition for access.) >>>> >>>> >>> I'm not sure where you're getting 10K/second from. We do need to limit >>> the >>> amount of data transmitted in one session to give other stations a chan= ce >>> to talk, but if the AP replies immediatly to ack the traffic, and the >>> airwaves are idle, you can transmit again pretty quickly. >>> >>> people using -ac equipment with a single station are getting 900Mb/sec >>> today. >>> >>> Is there a way, >>> >>>> maybe using another dedicated radio, to achieve near instantaneous >>>> collision detect (where the CD is driven by the receiver state) such >>>> that >>>> mobile devices can sample RF energy to get theses states and state >>>> changes >>>> much more quickly? >>>> >>>> >>> This gets back to the same problems (hidden transmitter , and the >>> simultanious reception of wildly different signal strengths) >>> >>> When you are sending, you will hear yourself as a VERY strong signal, >>> trying to hear if someone else is transmitting at the same time is almo= st >>> impossible (100 ft to 1 ft is 4 orders of magnatude, 1 ft to 1 inch is >>> another 2 orders of magnatude) >>> >>> And it's very possible that the station that you are colliding with isn= 't >>> one you can hear at all. >>> >>> Any AP is going to have a better antenna than any phone. (sometimes >>> several orders of magnatude better), so even if you were located at the >>> same place as the AP, the AP is going to hear signals that you don't. >>> >>> Then consider the case where you and the other station are on opposite >>> sides of the AP at max range. >>> >>> and then add cases where there is a wall between you and the other >>> station, but the AP can hear both of you. >>> >>> David Lang >>> >>> >> --001a1130d182da4c9405364870db Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
packet size is smallest udp payload per a socket write() w= hich in turn drives the smallest packet supported by "the wire." = =C2=A0

Here is a back of the envelope calculation giving= ~100 microseconds per BE access.

# Overhead estima= tes (slot time is 9 us):
# o DIFS 50 us or *AIFS (3 * 9 us) =3D 2= 7 us
# o *Backoff Slot * CWmin, =C2=A09 us * rand[0,xf] (avg) =3D= 7 * 9=3D63 us
# o 5G 20 us
# o Multimode header 20 us<= /div>
# o PLCP (symbols) 2 * 4 us =3D 8 us
# o *SIFS 16 us
# o ACK 40 us
#
# Even if there is no collision= and the CW stays at the aCWmin, the average
# backoff time incur= red by CSMA/CA is aDIFS + aCWmin/2 * aSlotTime =3D 16 =C2=B5s
# += (2+7.5)*9 =C2=B5s =3D 101.5 =C2=B5s for OFDM PHY, while the data rate with = OFDM PHY
# can reach 600 Mbps in 802.11n, leading to a transmissi= on time of 20 =C2=B5s
# for a 1500 byte packet.

All devices in a BSSID would have to agree that the second radio is= to be used for BSSID "carrier state" information and all energy = will be sourced by the AP serving that BSSID. =C2=A0(A guess is doing this = wouldn't improve the 100 us by enough to justify the cost and that a ne= w MAC protocol is required.=C2=A0 Just curious to what such a protocol and = phy subsystem would look like assuming collision avoidance could be replace= d with collision detect.)

Bob



On= Mon, Jun 27, 2016 at 1:09 PM, David Lang <david@lang.hm> wrote:=
On Mon, 27 Jun 2016, Bo= b McMahon wrote:

The ~10K is coming from empirical measurements where all aggregation
technologies are disabled, i.e. only one small IP packet per medium
arbitration/access and where there is only one transmitter and one
receiver.=C2=A0 900Mb/sec is typically a peak-average throughput measuremen= t
where max (or near max) aggregation occurs, amortizing the access overhead<= br> across multiple packets.

 so 10K is minimum size packets being transmitted?or around 200 transmission= s/sec (plus 200 ack transmissions/sec)?

Yes, devices can be hidden from each other but not from the AP (hence the use of RTS/CTS per hidden node mitigation.) Isn't it the AP's view = of the
"carrier state" that matters (at least in infrastructure mode?)= =C2=A0 If that's
the case, what about a different band (and different radio) such that the strong signal carrying the data could be separated from the the BSSID's=
"carrier/energy state" signal?

 how do you solve the interference problem on this other band/radio? When yo= u have other APs in the area operating, you will have the same problem ther= e.

David Lang


Bob

On Mon, Jun 27, 2016 at 12:40 PM, David Lang <david@lang.hm> wrote:

On Mon, 27 Jun 2016, Bob McMahon wrote:

Hi All,

This is a very interesting thread - thanks to all for taking the time to respond.=C2=A0 =C2=A0(Personally, I now have better understanding of the difficulties
associated with a PHY subsystem that supports a wide 1GHz.)

Not to derail the current discussion, but I am curious to ideas on
addressing the overhead associated with media access per collision
avoidance.=C2=A0 This overhead seems to be limiting transmits to about 10K = per
second (even when a link has no competition for access.)


I'm not sure where you're getting 10K/second from. We do need to li= mit the
amount of data transmitted in one session to give other stations a chance to talk, but if the AP replies immediatly to ack the traffic, and the
airwaves are idle, you can transmit again pretty quickly.

people using -ac equipment with a single station are getting 900Mb/sec
today.

=C2=A0 Is there a way,
maybe using another dedicated radio, to achieve near instantaneous
collision detect (where the CD is driven by the receiver state) such that mobile devices can sample RF energy to get theses states and state changes<= br> much more quickly?


This gets back to the same problems (hidden transmitter , and the
simultanious reception of wildly different signal strengths)

When you are sending, you will hear yourself as a VERY strong signal,
trying to hear if someone else is transmitting at the same time is almost impossible (100 ft to 1 ft is 4 orders of magnatude, 1 ft to 1 inch is
another 2 orders of magnatude)

And it's very possible that the station that you are colliding with isn= 't
one you can hear at all.

Any AP is going to have a better antenna than any phone. (sometimes
several orders of magnatude better), so even if you were located at the
same place as the AP, the AP is going to hear signals that you don't.
Then consider the case where you and the other station are on opposite
sides of the AP at max range.

and then add cases where there is a wall between you and the other
station, but the AP can hear both of you.

David Lang



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