From owner-freebsd-questions@freebsd.org Mon Apr 5 13:29:35 2021 Return-Path: Delivered-To: freebsd-questions@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 0C4465B91F5 for ; Mon, 5 Apr 2021 13:29:35 +0000 (UTC) (envelope-from galtsev@kicp.uchicago.edu) Received: from kicp.uchicago.edu (kicp.uchicago.edu [128.135.20.70]) by mx1.freebsd.org (Postfix) with ESMTP id 4FDWjB1t9dz4Yht for ; Mon, 5 Apr 2021 13:29:34 +0000 (UTC) (envelope-from galtsev@kicp.uchicago.edu) Received: from [IPv6:2607:fb90:a22f:8c88:38f2:bda3:2f12:8721] (unknown [172.58.136.25]) (Authenticated sender: galtsev) by kicp.uchicago.edu (Postfix) with ESMTPSA id 8210A4E66A; Mon, 5 Apr 2021 08:29:33 -0500 (CDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 13.4 \(3608.120.23.2.4\)) Subject: Re: Wifi scanner for FreeBSD From: Valeri Galtsev X-Priority: 5 In-Reply-To: Date: Mon, 5 Apr 2021 08:29:30 -0500 Cc: freebsd-questions@freebsd.org Content-Transfer-Encoding: quoted-printable Message-Id: <91D8B6CF-753A-4A10-A505-1673059EDB64@kicp.uchicago.edu> References: <20210404185713.4d19ea73@ws1.wobblyboot.net> <20210404204512.3ba04756@ws1.wobblyboot.net> <20210404133536.4fedf1e0@archlinux> To: Peter Cornelius X-Mailer: Apple Mail (2.3608.120.23.2.4) X-Rspamd-Queue-Id: 4FDWjB1t9dz4Yht X-Spamd-Bar: -- Authentication-Results: mx1.freebsd.org; dkim=none; dmarc=fail reason="No valid SPF, No valid DKIM" header.from=uchicago.edu (policy=none); spf=none (mx1.freebsd.org: domain of galtsev@kicp.uchicago.edu has no SPF policy when checking 128.135.20.70) smtp.mailfrom=galtsev@kicp.uchicago.edu X-Spamd-Result: default: False [-2.40 / 15.00]; RCVD_VIA_SMTP_AUTH(0.00)[]; TO_DN_SOME(0.00)[]; MV_CASE(0.50)[]; NEURAL_HAM_SHORT(-1.00)[-1.000]; RCPT_COUNT_TWO(0.00)[2]; FREEMAIL_TO(0.00)[gmx.net]; RCVD_NO_TLS_LAST(0.10)[]; RECEIVED_SPAMHAUS_PBL(0.00)[172.58.136.25:received]; FROM_EQ_ENVFROM(0.00)[]; R_DKIM_NA(0.00)[]; RBL_DBL_DONT_QUERY_IPS(0.00)[128.135.20.70:from]; MID_RHS_MATCH_FROM(0.00)[]; ASN(0.00)[asn:160, ipnet:128.135.0.0/16, country:US]; ARC_NA(0.00)[]; NEURAL_HAM_MEDIUM(-1.00)[-1.000]; FROM_HAS_DN(0.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MIME_TRACE(0.00)[0:+]; SPAMHAUS_ZRD(0.00)[128.135.20.70:from:127.0.2.255]; TO_MATCH_ENVRCPT_SOME(0.00)[]; R_SPF_NA(0.00)[no SPF record]; RCVD_COUNT_TWO(0.00)[2]; HAS_X_PRIO_FIVE(0.00)[5]; MAILMAN_DEST(0.00)[freebsd-questions]; DMARC_POLICY_SOFTFAIL(0.10)[uchicago.edu : No valid SPF, No valid DKIM,none] X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 05 Apr 2021 13:29:35 -0000 > On Apr 5, 2021, at 2:12 AM, Peter Cornelius wrote: >=20 > G'day, folks, > =20 > Regarding the first post, I would not mind to see such application in = ports myself though I think that the mobile apps suggest more than they = hold. > =20 > Regarding 2.4 GHz WiFi, I have come to the conclusion that I will = avoid that band with WiFi wherever I can. I have the experience from my = earlier place in town where I was able to see the beacons of the order = of 50 wlans, that a single station not on one of the non-overlapping = bands [1] causes so much interference to all on one of the = non-overlapping ones that there is no throughput at all for anyone. I = don't know what kind of pot people had when they invented that standard, = but that's how it is.=20 There is one more rationale to avoid 2.4 GHz band: there are commodity = devices that create strong interference in this band: microwave ovens, = cordless phones. However, if you are in the building with =E2=80=9Cwet=E2=80=9D wall (any = construction material that may host water: most notably brick, = concrete), then 5 GHz will work on much closer range than 2.4 GHz: = higher rf frequencies are more efficiently absorbed by construction = materials. I hope, this helps. Valeri > When you use such 'free' channel (as in the image at the mail starting = this thread), all that happens is that you can't decode the others, and = the others can't decode your emissions but you very effectively = interfere with each other, making the entire spectrum unusable. And all = the blue teeth and other emissions on that band just add to that. > =20 > In short, if all stick to the non-overlapping channels (and do not = bundle), one may get some throughput as the protocol can control the = channel. If one deviates, forget it. > =20 > Just my 2 cents. > =20 > Cheers, > =20 > Peter. > =20 > [1] https://en.wikipedia.org/wiki/List_of_WLAN_channels > =20 >=20 >=20 > =20 >=20 > Gesendet: Sonntag, 04. April 2021 um 13:35 Uhr > Von: "Ralf Mardorf" > An: freebsd-questions@freebsd.org > Betreff: Re: Wifi scanner for FreeBSD > On Sun, 4 Apr 2021 20:45:12 +1000, matti k wrote: >> https://imgur.com/a/J6HIGpZ >=20 > It does show "available" networks, but not transmitting > capacity. Due to digitalisation of elementary schools in Germany, > enforced by the coronavirus pandemic, as somebody working for after > school childcare, a teacher and I set up LTE wifi routers and iPads. > That a network is displayed, doesn't mean that you get a reliable > connection. The school has got 5 routers and IIRC 25 iPads + > several other receivers (a digital board, smartphones and a TV). >=20 > I described my private network and mentioned that "I would be = surprised > to see it in about a 9 meter distance". Actually it most likely is > recognized by devices >=3D 9 meters away, but it's unlikely usable at > this distance. >=20 > The forums link provided by Matthias, see > = https://lists.freebsd.org/pipermail/freebsd-questions/2021-April/293682.ht= ml[https://lists.freebsd.org/pipermail/freebsd-questions/2021-April/293682= .html] > mentions why it's a tricky subject. >=20 > In school those iPads show powerful access to the LTE wifi routers, = but > often the closest routers isn't usable, while a less close router can > be used, at least with a single iPad, dunno if it stands the traffic = of > all the iPads. >=20 > The graphic provided by Matthias' Ubuntu based cellphone shows an > amazing transmitting capacity spike. It could be important to actually > get such information, not only for wifi. Depending on atmospheric > condition, there could be e.g. interferences between DVB-T > transmitters. Too powerful signals could become a PITA for somebody = who > wants to watch television, OTOH amateur radio operators might welcome > such atmospheric conditions ;). >=20 > Getting a list without reliable information about the power is quite > useless. iPads for example provide a graphic showing 3 lines. Usually = 3 > and 2 lines are for a good connection and even 1 line still could be > reliable. At home 2 lines are ok for me, in school those lines mean > absolutely nothing. You could get those lines, but the connection = still > could be fishy. > _______________________________________________ > freebsd-questions@freebsd.org mailing list > = https://lists.freebsd.org/mailman/listinfo/freebsd-questions[https://lists= .freebsd.org/mailman/listinfo/freebsd-questions] > To unsubscribe, send any mail to = "freebsd-questions-unsubscribe@freebsd.org" > _______________________________________________ > freebsd-questions@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-questions > To unsubscribe, send any mail to = "freebsd-questions-unsubscribe@freebsd.org"