From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp66.iad3a.emailsrvr.com (smtp66.iad3a.emailsrvr.com [173.203.187.66]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 486973CB41 for ; Mon, 20 Sep 2021 17:30:30 -0400 (EDT) Received: from app56.wa-webapps.iad3a (relay-webapps.rsapps.net [172.27.255.140]) by smtp25.relay.iad3a.emailsrvr.com (SMTP Server) with ESMTP id A57222398A; Mon, 20 Sep 2021 17:30:29 -0400 (EDT) Received: from deepplum.com (localhost.localdomain [127.0.0.1]) by app56.wa-webapps.iad3a (Postfix) with ESMTP id 90CD4E1A81; Mon, 20 Sep 2021 17:30:29 -0400 (EDT) Received: by apps.rackspace.com (Authenticated sender: dpreed@deepplum.com, from: dpreed@deepplum.com) with HTTP; Mon, 20 Sep 2021 17:30:29 -0400 (EDT) X-Auth-ID: dpreed@deepplum.com Date: Mon, 20 Sep 2021 17:30:29 -0400 (EDT) From: "David P. Reed" To: "David Lang" Cc: "=?utf-8?Q?Valdis_Kl=C4=93tnieks?=" , "Dave Taht" , "Cake List" , "Make-Wifi-fast" , "Leonard Kleinrock" , "Bob McMahon" , starlink@lists.bufferbloat.net, codel@lists.bufferbloat.net, "cerowrt-devel" , "bloat" , "Ben Greear" MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_20210920173029000000_95626" Importance: Normal X-Priority: 3 (Normal) X-Type: html In-Reply-To: <2760o61s-408q-4613-r840-3sq96s8q1s1@ynat.uz> References: <1625188609.32718319@apps.rackspace.com> <989de0c1-e06c-cda9-ebe6-1f33df8a4c24@candelatech.com> <1625773080.94974089@apps.rackspace.com> <1625859083.09751240@apps.rackspace.com> <257851.1632110422@turing-police> <2760o61s-408q-4613-r840-3sq96s8q1s1@ynat.uz> X-Client-IP: 209.6.168.128 Message-ID: <1632173429.589822691@apps.rackspace.com> X-Mailer: webmail/19.0.12-RC X-Classification-ID: a50b29a7-6ccb-4351-afce-c9ac2ae9acad-1-1 Subject: Re: [Cerowrt-devel] [Bloat] Little's Law mea culpa, but not invalidating my main point 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: , X-List-Received-Date: Mon, 20 Sep 2021 21:30:30 -0000 ------=_20210920173029000000_95626 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable =0AI use the example all the time, but not for interviewing. What's sad is = that the answers seem to be quoting from some set of textbooks or popular e= xplanations of the Internet that really have got it all wrong, but which ma= ny professionals seem to believe is true.=0A =0AThe same phenomenon appears= in the various subfields of the design of radio communications at the phys= ical and front end electronics level. The examples of mental models that ar= e truly broken that are repeated by "experts" are truly incredible, and cov= er all fields. Two or three:=0A =0A1. why do the AM commercial broadcast ba= nd (540-1600 kHz) signals you receive in your home travel farther than VHF = band TV signals and UHF band TV signals? How does this explanation relate = to the fact that we can see stars a million light-years away using receiver= s that respond to 500 Terahertz radio (visible light antennas)?=0A =0A2. Wh= at is the "aperture" of an antenna system? Does it depend on frequency of t= he radiation? How does this relate to the idea of the size of an RF photon,= and the mass of an RF photon? How big must a cellphone be to contain the a= ntenna needed to receive and transmit signals in the 3G phone frequencies?= =0A =0A3. We can digitize the entire FM broadcast frequency band into a seq= uence of 14-bit digital samples at the Nyquist sampling rate of about 40 Me= ga-samples per second, which covers the 20 Mhz bandwidth of the FM band. Do= es this allow a receiver to use a digital receiver to tune into any FM stat= ion that can be received with an "analog FM radio" using the same antenna? = Why or why not?=0A =0AI'm sure Dick Roy understands all three of these ques= tions, and what is going on. But I'm equally sure that the designers of WiF= i radios or broadcast radios or even the base stations of cellular data sys= tems include few who understand.=0A =0AAnd literally no one at the FCC or C= TIA understand how to answer these questions. But the problem is that they= are *confident* that they know the answers, and that they are right.=0A = =0AThe same is true about the packet layers and routing layers of the Inter= net. Very few engineers, much less lay people realize that what they have b= een told by "experts" is like how Einstein explained how radio works to a t= eenaged kid:=0A =0A "Imagine a cat whose tail is in New York and his head = is in Los Angeles. If you pinch his tail in NY, he howls in Los Angeles. Ex= cept there is no cat."=0A =0AThough others have missed it, Einstein was not= making a joke. The non-cat is the laws of quantum electrodynamics (or clas= sically, the laws of Maxwell's Equations). The "cat" would be all the stori= es people talk about how radio works - beams of energy (or puffs of energy)= , modulated by some analog waveform, bouncing off of hard materials, going = through less dense materials, "hugging the ground", "far field" and "near f= ield" effects, etc.=0A =0AEinstein's point was that there is no cat - that = is, all the metaphors and models aren't accurate or equivalent to how radio= actually works. But the underlying physical phenomenon supporting radio is= real, and scientists do understand it pretty deeply.=0A =0ASame with how p= acket networks work. There are no "streams" that behave like water in pipes= , the connection you have to a shared network has no "speed" in megabits pe= r second built in to it, A "website" isn't coming from one place in the wor= ld, and bits don't have inherent meaning.=0A =0AThere is NO CAT (not even a= metaphorical one that behaves like the Internet actually works).=0A =0ABut= in the case of the Internet, unlike radio communications, there is no deep= mystery that requires new discoveries to understand it, because it's been = built by humans. We don't need metaphors like "streams of water" or "sites = in a place". We do it a disservice by making up these metaphors, which are = only apt in a narrow context.=0A =0AFor example, congestion in a shared net= work is just unnecessary queuing delay caused by multiplexing the capacity = of a particular link among different users. It can be cured by slowing down= all the different packet sources in some more or less fair way. The simple= st approach is just to discard from the queue excess packets that make that= queue longer than can fit through the link Then there can't be any congest= ion. However, telling the sources to slow down somehow would be an improvem= ent, hopefully before any discards are needed.=0A =0AThere is no "back pres= sure", because there is no "pressure" at all in a packet network. There are= just queues and links that empty queues of packets at a certain rate. Thin= king about back pressure comes from thinking about sessions and pipes. But = 90% of the Internet has no sessions and no pipes. Just as there is "no cat"= in real radio systems.=0A =0AOn Monday, September 20, 2021 12:09am, "David= Lang" said:=0A=0A=0A=0A> On Mon, 20 Sep 2021, Valdis Kl=C4= =93tnieks wrote:=0A> =0A> > On Sun, 19 Sep 2021 18:21:56 -0700, Dave Taht s= aid:=0A> >> what actually happens during a web page load,=0A> >=0A> > I'm p= retty sure that nobody actually understands that anymore, in any=0A> > more= than handwaving levels.=0A> =0A> This is my favorite interview question, i= t's amazing and saddning at the answers=0A> that I get, even from supposedl= y senior security and networking people.=0A> =0A> David Lang_______________= ________________________________=0A> Bloat mailing list=0A> Bloat@lists.buf= ferbloat.net=0A> https://lists.bufferbloat.net/listinfo/bloat=0A> ------=_20210920173029000000_95626 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable

I use the example all = the time, but not for interviewing. What's sad is that the answers seem to = be quoting from some set of textbooks or popular explanations of the Intern= et that really have got it all wrong, but which many professionals seem to = believe is true.

=0A

 

=0A

The same phenomenon appears in the various subfields of the design of ra= dio communications at the physical and front end electronics level. The exa= mples of mental models that are truly broken that are repeated by "experts"= are truly incredible, and cover all fields. Two or three:

=0A

 

=0A

1. why do the AM commercial = broadcast band (540-1600 kHz) signals you receive in your home travel farth= er than VHF band TV signals and UHF band TV signals?  How does this ex= planation relate to the fact that we can see stars a million light-years aw= ay using receivers that respond to 500 Terahertz radio (visible light anten= nas)?

=0A

 

=0A

2. What = is the "aperture" of an antenna system? Does it depend on frequency of the = radiation? How does this relate to the idea of the size of an RF photon, an= d the mass of an RF photon? How big must a cellphone be to contain the ante= nna needed to receive and transmit signals in the 3G phone frequencies?

= =0A

 

=0A

3. We can digitiz= e the entire FM broadcast frequency band into a sequence of 14-bit digital = samples at the Nyquist sampling rate of about 40 Mega-samples per second, w= hich covers the 20 Mhz bandwidth of the FM band. Does this allow a receiver= to use a digital receiver to tune into any FM station that can be received= with an "analog FM radio" using the same antenna? Why or why not?

=0A 

=0A

I'm sure Dick Roy unde= rstands all three of these questions, and what is going on. But I'm equally= sure that the designers of WiFi radios or broadcast radios or even the bas= e stations of cellular data systems include few who understand.

=0A

 

=0A

And literally no one at t= he FCC or CTIA understand how to answer these questions.  But the prob= lem is that they are *confident* that they know the answers, and that they = are right.

=0A

 

=0A

The= same is true about the packet layers and routing layers of the Internet. V= ery few engineers, much less lay people realize that what they have been to= ld by "experts" is like how Einstein explained how radio works to a teenage= d kid:

=0A

 

=0A

  = "Imagine a cat whose tail is in New York and his head is in Los Angeles. If= you pinch his tail in NY, he howls in Los Angeles. Except there is no cat.= "

=0A

 

=0A

Though other= s have missed it, Einstein was not making a joke. The non-cat is the laws o= f quantum electrodynamics (or classically, the laws of Maxwell's Equations)= . The "cat" would be all the stories people talk about how radio works - be= ams of energy (or puffs of energy), modulated by some analog waveform, boun= cing off of hard materials, going through less dense materials, "hugging th= e ground", "far field" and "near field" effects, etc.

=0A

 

=0A

Einstein's point was that there is = no cat - that is, all the metaphors and models aren't accurate or equivalen= t to how radio actually works. But the underlying physical phenomenon suppo= rting radio is real, and scientists do understand it pretty deeply.

=0A<= p style=3D"margin:0;padding:0;font-family: arial; font-size: 10pt; overflow= -wrap: break-word;"> 

=0A

Same with how packet = networks work. There are no "streams" that behave like water in pipes, the = connection you have to a shared network has no "speed" in megabits per seco= nd built in to it, A "website" isn't coming from one place in the world, an= d bits don't have inherent meaning.

=0A

 

= =0A

There is NO CAT (not even a metaphorical one that b= ehaves like the Internet actually works).

=0A

 =

=0A

But in the case of the Internet, unlike radio c= ommunications, there is no deep mystery that requires new discoveries to un= derstand it, because it's been built by humans. We don't need metaphors lik= e "streams of water" or "sites in a place". We do it a disservice by making= up these metaphors, which are only apt in a narrow context.

=0A

 

=0A

For example, congestion in a= shared network is just unnecessary queuing delay caused by multiplexing th= e capacity of a particular link among different users. It can be cured by s= lowing down all the different packet sources in some more or less fair way.= The simplest approach is just to discard from the queue excess packets tha= t make that queue longer than can fit through the link Then there can't be = any congestion. However, telling the sources to slow down somehow would be = an improvement, hopefully before any discards are needed.

=0A

 

=0A

There is no "back pressure", be= cause there is no "pressure" at all in a packet network. There are just que= ues and links that empty queues of packets at a certain rate. Thinking abou= t back pressure comes from thinking about sessions and pipes. But 90% of th= e Internet has no sessions and no pipes. Just as there is "no cat" in real = radio systems.

=0A

 

=0A

On Monday, September 20, 2021 12:09am, "David Lang" <david@lang.hm> = said:

=0A
=0A

> On Mon, 20 Sep 2021, Valdis Kl=C4=93tnieks wrote:
>
> > On Sun, 19 Sep 2021 18:21:56 -0700, Dave Taht said:
> &= gt;> what actually happens during a web page load,
> >
&= gt; > I'm pretty sure that nobody actually understands that anymore, in = any
> > more than handwaving levels.
>
> This i= s my favorite interview question, it's amazing and saddning at the answers<= br />> that I get, even from supposedly senior security and networking p= eople.
>
> David Lang_____________________________________= __________
> Bloat mailing list
> Bloat@lists.bufferbloat.n= et
> https://lists.bufferbloat.net/listinfo/bloat
>

=0A=
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