redecentralization 2.0

It has been a core thee of a lot of my work & interests. decentralized systems are just more interesting than centralized ones. they may be inherently more resilient (but not always), and they may be more complex (but not always).

the internet is largely decentralized in its lower layers (the tubes - the routers and links, and routing algorithms). that was always intended, from baran's report for rand onwards.
society and eco-systems are often decentralized (sure there are governments (but more than 1) and bee hives (but more than one) - but coordination happens peer-to-peer (a term which first arose in magna carta, but an idea which predates that by a billion years).

decentralized, infrastructureless networks are an interesting point in the design space - hence community mesh wireless networks, and opportunistic, delay and disruption tolerant networks work merely using users' devices and construct communication out of thin air. in this extreme environment, we are challenged to think of how we provide information about identity or trustworthiness, but in fact, on close examination, a central provision of those properties has many problems too - DNS certificates can be bogus or expired, source IP addresses do not have to refer to where the packet came from, an application layer user identifier (email address, facebook identity etc) is no more a true name than the Prince of Serendip.

so really, everything should be decentralized, as it forces us to confront the true problems and come up with decent solutions, instead of using the prop of underserved respectability of a centre.

That's why we founding the centre for redecentralization. :-)

future of work & AI

so techno-optimists paint a rosy future image with AI freeing us up from toil to have a life of infinite leisure.

lets go back to the victorian times and the industrial revolution - what happened? machines (steam engines etc) meant that food (and transport) no longer required most people to grow what they eat, or feed the horses - so most people should have been able to get free food or travel to the seaside for a dip. what happened? most people moved from fairly pleasant rural existence farming to working in the dark satanic mills - i.e. became urban factory workers with longer hours and shorter, less pleasant lives.

lets go back to when people stopped being hunter-gatherers and settled down to farming. could have been nice to stop worrying about the days when you stop being predator and become prey from time to time. but what happened? people built nation states and priesthoods and aristocracies and invented serfs/slavery.

so techno-pessimists paint a dystopic future picture with AIs enslaving us (or just disposing of us).
That's nonsense too.

So how will things play out? what of all this "makework" that mot of us in the developed world engage in that is trivially automatable (actually, doesn't need doing)?

I have no idea, but we better figure it out soon.

[1] homework

Rashomon sets as a metaphor for why interpretability is hard

So this  arxiv paper by  cynthia rudin  about why we should stop explaining black box AIs contains a beautiful metaphor, the idea of a Rashomon Set. For people who don't know, Rashomon is a classic film made by the Japanese director, Akira Kurosawa. Its plot is about an incident in the woods, told from multiple viewpoints, and as each one unfurls, you realize the previous one was not "true" for a different reason, until the "end" when you cease to be sure of what actually happened. Kurosawa made quite a few films that are not only classic, but slightly influential - for example, his series of lone samurai hero movies (sanjuro, Yojimbo) were remade by Sergio Leone into great spaghetti westerns that made Clint Eastwood's early career (a fist full of dollars and for a few dollars more) as well as the Seven Samurai (the magnificent Seven etc) . Kurosawa also made fine japanese versions of european classic plays (Throne of Blood == Macbeth, and Ran == King Lear). Of course, one of his slightly lesser (but still wonderful) films, The Hidden Fortress got a thinly disguised makeover by one George Lucas as the first (and pretty much all the successor) Star Wars films. Kurosawa often cast Toshiro Mifune, who had some success in Hollywood movies - usually as a tough soldier, but rarely capturing the humorous element that was part of his subtle signature in his home country films. The only thing where I think the japan<>western translations of film didn't work was a US remake of Rashomon (sadly, as it should be possible to do) - many of the others are great (in my personal opinion) in either take, whether shakespeare, or sci fi, samurai or gunslinger. If you see and like Kurosawa films, you will likely also enjoy books by Haruki Murakami, although don't blame me if you don't. Rashomon Sets - what a totally super idea! almost as good as explaining algorithms through Hungarian folk dance....

counterfactual reasoning example

spent a while yesterday trying to get additional car insurance on a 20+yr old subaru for member of family who has very recently passed driving test.

so go online on compare market and on several insurance company specific web sites and provide following info as input to their decision system:

1. car registration

2. existing insurance info

3. new driver license info

from the above, most (not all) the companies used the DVLA to verify car model/miles per year (via MOT at DVLA) and status of insurance and correct info about new driver...

so all ok (can obviously try making up other cars, but hard to fake driver:)

so outputs were mostly no - including existing insurance company, who said would add new driver after 6 months, but due to car's engine size (leaking quite a lot of info) they couldn't add a recently passed driver this is slightly weird as the car we got was bought because it ranked as safest car n class by AA and others:) - they and two other outfits said no problem if we got a smaller car (suggesting less safe vehicles:(

tried various other types of insurance - e.g. car-sharing (borrow) allegedly targetted at students coming home in vacation borrowing parents car - and pay-as-you-drive - all said no

so then ran a compare market on new driver insurance from sratch and got a couple of genuine offers- in fact, not completely mad prices either, if we're prepared to do a whole year  (we are) ...(still with fact insured party isn't car owner or keeper, but is in the family)

so the range of prices is probably a proxy for the risk level the insurance companies will tolerate (I assume they all have pretty much the same actuarial data on accident/theft rate with age, gender, car model/age, location, use of car,and other stuff they obviously gather....

privacy tech/statements from most of the website/forms/companies was pretty decent...

Putting the n in Ethics - i.e. where's the ethnic diversity in our discussions of this import topic?

There's been a trend in recent years to suggest that when you're asked to be on a panel (as a bloke), you should decline unless there is a plausible gender balance policy.

There's been another trend in recent years to talk a lot about ethics and AI.
Both of these trends seem like a good idea.

It is my observation that the trends should be combined in  another way -

The vast majority of people I see talking about ethics and AI are weird, in a technical sense. while there is a better gender balance in ethics panel discussions than pure tech, but I think they fail in general terms to represent diversity. As I wrote this, I did see one discussion of a new direction from an interesting part of the world, namely China.  I am sure there are discussions in many other places, but I don't think they are showing up in the 

the hype of incomprehensibility

I've been looking at various techs for a few years now and watch the lifecycle  - it doesn't always involve hype - sometimes, things just seep into everyday life (the internet kind of did this over a couple of decades - even mobile phones kind of did) - so looking at things that don't make it, or have to go through some massive transformation to stand any kind of chance, one of the tells is that the tech is very badly explained, often hidden behind some simplistic banner-phrases like "blockchain" or "quantum computing" or "deep learning" - when you look at the swathes and tranches of literature, what is striking is a lack of straightforward examples.

Sometimes, this can be simply because the tech is actually rather subtle and also might involve understanding several other things first (quantum computing seems to fit in this category, Bayes methods like MCMC might be another) - other times, it is that smart people that make it their business to explain important new stuff in really straight-speaking ways (e.g. The Morning Paper ) stick to stuff that is worth explaining.

So if you see a huge pile of gray-publications about something, and there isn't anything on one of the classier blogs or oped in a leading place, be suspicious (e.g. cold fusion, brexit, DLT, etc).

data is the new snake oil

we hear a lot hot air about data is the new oil - implying there's a rush of innovation and profits as with a gold rush (there's money in them there data hills etc)-

this is so baly broken a metaphor, we need to unpick (deconstruct) it further

1. data is free to copy (nearly), i.e. data is in some sense renewable, while oil gets used up (its nearly 50% gone now).
2. using oil does as much harm (or possibly more) as good
3. using data can do harm or good
4. AI/ML is compute intensive- deep learning in particular is massively inefficient, and data centers (like power stations, in close proximity to which they are sometimes built) burn %ages of globally generated electricity - not always renewable energy
5. data can increase in value as you have more of it, up to some point (sampling more about a population of people or things)
6. privacy could be modelled as efficiency (what's relevant/pertinent and what is none-of-your-business) in space and time (why do you still want to know that out-of-date thing about me or about that?).
7. much personal data collected by cloud providers is treated as if free, though some lawyers now are starting to point out that if you have a business model based on this, it is possibly a form of payment - so while facebook/zuckerberg might claim we are the product, if this legal position is true, we are customers, and he's working for us....
8. this mission creep really implies data could be the new fur (or indeed as john naughton has said, the new tobacco)
9. the models (e.g. face recognition, recommender networks etc) are often surprisingly bad - occasional successes of GANs&deep learning are relatively rare compared with a plethora of rather shoddy systems&applications.
10. perhaps data is the new oil after all, but its rapeseed or snake oil that would be a more precise metaphor.

Winnie the Who & other short short stories

Winnie the Who travels around in her Time&Relative Dimensions in Pooh potty, having potty adventures with all and sundry, frequently combatting her nemesis, the Young Master Robin.

In the not too distant future, it is discovered that privacy is actually a fluid, called efluvium, that can be secreted by a genetically engineered gland. It turns out that the efluvium blockchain wasn't immutable at all, after all.

Meanwhile, AIs with untaxed imagination will from now on be clamped.

As the story wore on, he realized that time was running out, and soon, so was he

life cycle

this great talk at the Royal Society by Professor Mark Jackson riffed on the Fall and Rise of Reginald Perrin, as exemplifying the speaker's hypothesis, that the mid-life crisis is more socially determined, than biological - the midlife of course refers to the period between adolescence and senescence, which are also, to some extent, movable feasts.

I asked him afterwards how valid it was to apply the same notions to institutions (is the Royal Society middle aged?, is democracy senile? etc etc)...but also, whether he could look at the 3 Rises of Leonard Rossiter, the genius actor who played Perrin so perfectly  - and was previously in RIsing Damp, perhaps an adolescent drama, and the very mature Resistible Rise of Arturo Ui, a Brecht piece which could very well be re-run as a riff on Nigel Farage, right now.

digital twinge

there's a trending meme concerning the use of digital twins, which is reminiscent of the old DARPA Total Information Awareness fantasy - in that world, every physical thing (and being) is fully instrumented and telemetry is sent/gathered by the cyber-panopticon (quite likely in the sky, like some early James Bond villain).

The problem with the vision is that it gains you nothing and costs you the earth (almost literally in terms of resource use, e.g. energy in communications, storage and computation).

The digital twin metaphor substitutes (or clones) the physical world with a digital replica.
Aside from the basic resource costs, there are also interesting challenges such as making sure the digital replica actually is a clone, and hasn't drifted out-of-synch with the physical sister - much as Hari Seldon did in second foundation recorded holograph appearances in Asimov's great original trilogy, when his much vaunted psychohistory prediction of the future had diverged  from reality due to the Mule's random mutation's intervention. And exactly as the Dr Who DVD blipverts (easter eggs) don't diverge at all in the fabulous Blink episode.

Aside from that, the reason it is pointless (as well as infeasible) is that it doesn't do what anyone wants - so you have a digital copy of everything - it doesn't abstract one whit - it doesn't let you introspect, it isn't interpretable or intelligable. One could subject it to some massive scale bayesian model inference, I suppose - but why? we have science - we have models of how physical (and social and biological) stuff works - we need only record instances and divergence from the model.

ethics theatre, but what kind of theatre?

so the internet abounds with people talking about ethics of ai. some organisations are accused of ethics washing, and others of ethics theatre. so what kind of theatre? is it soap opera (consistent with washing) or is it theatre of the absurd? is it tragic or comedic? is it a niche genre (science fiction ethics is quite a common trope) or is it a broadly popular form (romance, fantasy) or a deep, foundational literary form (tolstoyesque or janite, perhaps)?

perhaps its a fan-contributed-literature (like those popular Dr Who and Star Trek Episodes, or the posthumous novels stating James Bond or Philip Marlowe)?

I think we need a TV series to examine this meta-question.

redecentralized data centers

what makes us think a data center at the center is more efficient than a fully decentralized cloud of personal clouds?

partly its just google, amazon, microsoft et al selling us services because their initial requirement (a place to run pagerank, or a place to run billing and fulfilment for warehouses/delivery or a place to run xbox arena stuff - having spent a lot of money building a big place to (e.g.) pull all the web pages to and build an index so that search could run fast, and then had to deal with node/link failures in the data center, replicating and adding redundancy and consensus algorithms and so on, you end up with a fairly expensive resource, which is idle a lot of the time, so you start to think about leasing off time on it for other stuff (services and customers/tenants etc) - hence cloud stuff emerges - really the only cost saving is that you have a bunch of smart sys-admin dev-ops lying around idle 23/24 of the day. so ammortize their cost over some other customers :-)

given yo ucan't just greedily walk the web at max speed, and in any case, web sites change rarely, pagerank spider/robot can adjust its rate to match expected next change - but this means you have plenty of spare cycles in any data center scanning sites where no-one is awake  - or where no-one is still up playing games, or ordering stuff - so what do you do? you virtualize your compute, and net, and elastic (statistically) multiplex it (initially prioritizing your primary business, search, games, sales, but later dedicating new resources for these uses, and then priority pricing some to give them a "premium experience" etc etc)

start from a different starting place, and why bother? all that tech for availability would work fine in the wide area, and leave the data where it was and just run your algorithms (as they run on multiple nodes in the data) on all the home machines - no data center, no wate of energy and bandwidth moving all that stuff to and fro all the time.

so could you then do search etc? of course you could. you'd gossip the index instead of the pages, you'd run p2p games, and you'd have virtual high street shops everywhere

this is not a new idea: xenoservers 20 years ago, were partly at least envisaged as enrolling home machine spare cycles for this very reason, not for virtualising nodes in an expensive, energy hungry, data center built for profit...

machines like me? not really...

Literary writers trying their hand science fiction often causes problems. for SF aficionados, it annoys, as often the literary writer is unaware of the tropes of the genre, or that a particular topic may have been extremely well explored in a novel of ideas, that was published in the genre and not recognised in the classical literary world. for the non-SF aficionado reader, the sudden importation of tics and tells of the SF world may also rankle, although this has become much less so in recent years as so many of the "great and good" of the aforesaid classic world of letters have decided to write books which at least tackle the world's recent challenges by first reading a batch of the appropriate science (whether the dismal science of economics, to write about the crash of 2008, or the warm science of anthropology, to write about gender in alternative histories of the future (you know who I'm talking about, right? not Ursula Le Guin:), or else the science of computers, to create stories about the impact of apparently intelligent machines on robots - oops, sorry, got that the wrong way round - we humans aren't apparently intelligent machines, that's the robots, that is :-)

Hence to Ian McEwan's latest, Machines Like Me, an everyday tale of rape, suicide, and possibly, murder. Fairly everyday stuff from this author you might think....however, in this case, he's decided to write a book set in an alternative present, with an alternative recent past, which, crucially, allows him the luxury of having Alan Turing as a living character who has pursued many of the directions hinted at in his work, so that lifelike robots are now (almost) an every day, if somewhat expensive reality in the world. McEwan acknowledges Hodges fabulous biography of Turing as a source for background, rightly, as the character is pretty much what you'd get from that work, or else from the play, Breaking the Code (though less so from the film, Imitation Game). Turing is also supported by a cadre of interesting loosely fictionalised people, to render the progress on AI tech more plausible - most notably, the real-life Demis Hassabis (DeepMind, also acknowledged as a source at the end of the book) is relocated about 25 years earlier in time than his real self, to help Turing create the more important foreground character of (would you believe it, as the Cockney's have it, would you Adam and Eve) Adam, an apparently functional synthetic human (don't get me started on why McEwan seems unaware of the fabulous exploration of this topic in the wonderful Swedish, then Brit TV series, Humans). The key "real" humans in this fictional work are Charlie, a mid-30s man of somewhat relative moral virtue, and his friend, Miranda, a student of very dull eras of history. I assume she's called Miranda as a sly reference to Shakespeare's character from the Tempest, who uttered the words "Oh Brave New World, that has such people in it", on first seeing men. And of course, the source of the title of Aldous Huxley's classic literary SF dystopic vision.

Here, much of the dystopic vision is of the political/economic kind, and is set in a kind of mash up between 1970s/1980s Britain, with a few (c.f. Man in the High Castle, Philip K. Dick's alt.history) with some amusing takes on Thatcher, if we'd (spoiler alert)... or what if Tony Benn..... or what about that IRA bomb in Brighton... oh, ok , I won't spoil those bits, as they make up some of the novel's interesting bits, in the sense that, for this reader at least, they created a very interesting alternative exploration of why the UK is where it is today, 3 years after the Brexit referendum.

As for the foreground tale of two humans and a machine like them, I thought that Charlie and Miranda were underwritten, and Adam was overwritten. i thought that the exploration of ideas like "what is consciousness" was about ok, but did not bring anything new to the table - the tension between Phenomenology and the Turing test (for what it is worth) for intelligence, and notions of EQ, was covered far more effectively 5 decades ago in "Do Androids Dream" by the aforesaid Philip K DIck (who had actually studied philosophy and could write character and plot). I wanted to know more about Miranda's cranky dad (another non spoiler - there's a funny reflection on dementia and human mis-judgement that involves him and Charlie and Adam).

The ending did not bring a sense of an ending for me, rather left various plot-line, moral questions, and unknown unknowns, still unknown.

Still, McEwan sure can write, so I'd recommend this book as a decent read, though below his best. He really should get out more, and so should I.

TL;XR

we need a program of work like the internet (web) and like rasperry pi, for a sustainable future - some core building block (not sure what, but I'd call it a Perpetual Notion Machine), that doesn't over specify what we do  but leads to a plethora of new ideas from the grass roots/maker communities that would create cheap (free) energy and clean (safe) water and so on

one example tech I like is solar powered stirling engines (you can get toy ones e.g., or ones that actually generate quite a bit of electricity) as they can be build from junk (i.e. don't require solar cells) - we need a set of recipies for things like that so kids (climate strikers and extinction rebellion folks) everywhere can start to save us, as we sure and capable of saving ourselves and its more their future than ours anyhow...

another thing you could do with disaggregated identity/credential systems

table 1. online harms in scope in the government report just released is a good summary of the problems....but it would be possible to do better - for me, it would be nice to pull out the applicable law (to the left most column) and discuss its adequacy e.g. in extending laws about publishing lies during elections (making sure law that appies to print and broadcast media applies to internet channels in the same way, etc etc)...

so on the technical side, we then have the problem of provenance/attribution. compliance with takedown requests (whether content is illegal, offensive or just wrong) can be driven by social pressure - so we need to know also if the content creator/distributor, and the compainers are legit - this needs accountable id - so it could be possible to use the same tech we might develop (and has been around in some research outputs 15+ years ago) to have a low cost mechanism for online channels to carry out "Know Your Customer" as much as banks do - but to use 3rd party credential providers (in the same way a bar can check "are you over 18" without having to know anything else about you...). this would then mean that we can verify things - and in the event of actually illegal content, with appropriate checks and balances, map the online pseudonym to an actual person....

advantage is also that it can be used for alibis too:-)

of course, some people still require genuine anonymity - e.g. whistleblowers or folks working under dangerous regimes - and that requires enough cover traffic from apparently non anonymous or just pseudonymous users, to work effectively.....

that also probably means we need to think about rate limiting the creation of new accounts and figuring out what tolerable rates are (they won't be zero)

all of this would need another report - which maybe the Turing Institute could offer to advise on:-)

reclaim the internet

at the scloss dagstuhl seminar (on programmable network data planes) we have had a couple of key speeches, one from nick mckeown (kind of on why we are where we are with P4 and switches that implement it) and one from dave tennenhouse on the big picture of where we are in programmable networks as a result of 4 decades of software (internet, atm, active nets and so on).

What I find increasingly weird is that the desperate need for speed is driven more and more by machine-to-machine communication (including the inevitable analytics/ML/AI) or just software updates or media pushing to caches.

but the net doesn't have to be fast for humans - humans could be supported by around 2 Mbps per person 24*7 for 10 billion people, that is no big deal. but humans are dsitributed for many good reasons (food, land/water contstraints) and moving humans is expensive (and not sustainable)

but it is possible to put the machines in the right place (near the data) instead of moving all the data to the machines.

so we not only need re-dencentralization for latency, energy, privacy, we also need to get all the machine data out of the way so humans can go back to talking to each other instead of being talked to by adertisement/recommender bots who steal all our data and use it to sell us stuff we don't want so
humans are replacing the old adage (you can trade time for money, or money for time) to paying bots in both time and money.

open innovation

Yesterday, Allison Randal gave a great lecture on open innovation and open source and collaboration for the Turing Institute - the audience asked some really interesting questions (e.g. on open data; and on applying the model of open source to medicine - e.g. drugs - and on how much open source works across north/south divide in the world)....

I didn't want to take time, so i'll add my questions here:

1/ as well as open source software, we're seeing open hardware - not just processors (risc V) but peripherals, but also affordable 3D printing means even things like electric guitars - so the maker community that does a lot of this stuff (c.f. Cory Doctorow's books:) maybe exemplify the open collaborative ecosystems even more than coders, no? and they get to have a really good story about sustainability (repairing stuff is so much better than replacement.

2/ Sustainability - so machine learning (particularly deep learning) appears to be badly unsustainable in terms of compute resource training takes - this argues strongly for sharing trained classifiers - perhaps a carbon tax on neural networks could be turned into an incentive (carbon trading for AIs)

3/ some open ideas have horrible consequences - simple things like pagerank (which made google's search very hard to game compared to predecessors like Altavista) led to clickthrough which led to two-sided markets which led to surveillance capitalism. H-Index, which is supposed to replace publish-or-perish with citation count weight as a measure of quality, just leads to citation gaming. And so on - can we encourage replacements from the open source community, please, asap.

4/ Open source also depends somewhat on freedom of movement of people between different organisations - indeed, California mandated this right in law, stopping "golden handcuff" employment contracts.  In the Cambridge ecosystem, i know people that have moved from microsoft to oracle to amazon (and even back) to work on the next thing. In the US, famously, people went from Cisco to Juniper to Cisco, as innovation moved around - this is clearly a Good Thing - perhaps folks who are working on Brexit could learn something from this (although they seem impervious to learning anything based on evidence).

5/ Most of the talk was on details of uptake of the culture and forms by industry - of course, the Turing Institute (and its member universities) are not-for-profit - so the culture is probably adopted in a slightly different light - what are the appropriate incentive forms for academia to adopt openness (aside from just being told to by our funding agencies:-) ?

rumours of his death are accurately predictions...

Back in the day, legend has it, a newspaper published an obituary of Mark Twain, while he was travelling in England, and he famously quipped "The rumours of my death have been greatly exaggerated".

What if someone built an AI (ok, ok, machine learning algorithm), that could precisely predict the day of your death; for everyone; to the day. with only the occasional false positive or false negative (for example, due to sudden accident, or sudden unexpected advance in treatment techniques)?

How fanciful is this? 

if you look at actuarial tables, and the error margins, you'd be surprised how accurately they describe expected longevity already, and note that these are typically compiled for purposes like life insurance (i.e. to give risk&therefore  premium rates), and are not using all the detail that they might have (since the risk can be spread over broad groups, even if more precise predictions could be made). When looking after elderly relatives in recent years, these tables have been very useful for planning care costs and have proved (somewhat alarmingly) accurate. 

It is also well known that as you get older, especially in middle age, details of life style+health conditions start to provide ever more precise predictors of how long you will last. However, to date, these systems only make use of a relatively small fraction of personal health data about you. What if we use it all?

Recent work in the Turing looked at predicting when someone would have a subsequent hospital appointment after a visit to A&E (or respectively for elective). Other work looked at morality in certain wards and (more happily) at the predictors of who to release to go home and when with best chances of recovery. These systems have impressive performance (e.g. 98% to the day in some cases).

So imagine at some point (for the sake of argument, lets say if you make it to "majority"/adulthood), it is revealed what date you will live til? What would that do to society? Economics? What about ethics?

I can imagine people "cheating death" the wrong way.
No more health insurance (since there's certainty).
How might people plan funerals?
Many, many perverse incentives, unintended consequences and downright weird stuff.

Much harder than just having slightly better automatic language tools that might make better fake news, but also, much more likely to appear soon.

The Center for Mathematical Seances

The Center for Mathematical Seances (CMS), was not designed along the lines of Teletubby land, contrary to popular myth. In fact, it was flown here on Mistletoes by the Master of Duality College from the Miskatonic University in Arkham as a gift, when she realized that Cambridge could no longer afford architects, let alone builders. Of course, due to its unique Nomenklature, the Center (or Centre, which is of course near the edge of Cambridge) is able to operate at very reduced academic salaries, since many of its faculty have been, not to mince words, dead for some time. This hs caused no end of problems with the REF, since outputs cannot be returned through research fish or ORCID, for deceased, and much of the original work was done too many centuries earlier to be allowed for impact case studies, Fermat's first posthumous theorem being a standout example, and Turing's work on quantum ghosting with Paul Dirac and Paul Wittgenstein, which will haunt the UKRI policy makers for decades, since it has proved to have so many applications and saved the British economy from collapse after brexit, for example allowing true precognitive behavioural economic models of trade to be built with genuine precision.

clock synchronisation in data centers - why not just use GPS?

in a recent discussion about accurate one-way latency measurements in data centers, it was asked "why not use GPS?" (instead of PTP for example) - the rationale being every smart phone has GPS in so it must be cheap...

at first blush, this sounds plausible, given the pervasiveness of GPS (G=Global) and decent accuracy, so I started to come up with a (long) list of reasons why it isn't (plausible) - starting from

1. you're indoors.
no reception -
ok, so a) run an antennae from the roof of the building down to each rack, and re-dist across the systems in the rack
or b) have one receiver and re-broadcast the radio signal in the server rooms and have an antennae on every rack or system

2. distributed antennae
a) need to calibrate the latency of the signal over the roof to each system + significant wiring cost
b) re-broadcast could cause significant interference, plus the racks themselves would cause massive multi-path problems - since they're stationary could obviously calibrate for that....

note you need to have sight of enough satellites at any given time to get reliable signal, plus they are not actually 100% reliable anyhow....

3. What about re-distributing the GPS received data in packets (ideally as part of ethernet pre-amble)
So you still now have all the packet delay variance/jitter you had to solve with PTP (or NTP in the old days) and estimating that was the whole point of PTP - GPS is just one source - just have a local accurate master clock on some systems in the data center is fine and dandy

4. cost
phone GPS is actually Assisted GPS usually and not very accurate - indeed, even outdoors, mult-path (reflections off buildings) disrupts things sufficiently that most navigation systems resort to accelerometers, gyros and maps to validate (or rule out) received clock/location data. Also the signals need to be cross checked against Ephemeris data, which is 50k of info about where the satellites orbits take them. real precision GPS (satnav in planes/boats) is not cheap in fact.

that'll do for now