academia uber alles

i hope the eponymous taxi company hasn't got a "business process" Patent on it because there's prior art - the 100% hollowed out notion (gives a whole new life to the idea of shell company or the emperor's new clothes metaphor) has been alive and well in academia for many decades

you know the script, right - you get a missive saying
"here's a paper, we need reviewed - oh, and if you can't do it now, we'll out you on our books for later, and can you recommend someone who can?"

1. the paper was written by an academic, who type set it using software freely avaialble, designed by researchers, and is probably on a web site run by academics, running on software written by researchers, and maintained by academics, etc

2. when the paper is published, good chance some private company will make money by sending it to libraries curated by academics, and it will be read by researchers,

3. we can extend this to MOOCs

4. and graduate students (here's a student, wanna supervise them, then we'll hire them at Company X, having had them trained by you) etc

the "gift" economics is ok when everyone is (as we say in what Tom Lehrer used to call the Ed Biz,I think in that memorable song about Ivan Lobachevsky) collegiate.

but the reality is that there's a mix of behaviours (I'm sure its heavy tailed - like a fox, or whatever) where a few people do a zillion amounts of stuff, and most do doodly squat - after all, most papers are read by between 0 and 1 people (not even the reviewers in some cases) - its true - look at google scholar stats

I'm beginning to believe we are in the world described in Theodore Sturgeon's brilliant story "It Wasn't Syzygy" (see collection e pluribus unicorn) - a wonderful author who should be as well known as Ray Bradbury...

there really should only be 3 universities and 3 computers and 3 queens.

Principles of Communications -- Michaelmas Term 2016....weak ate (to Nov 30)

This week, wra up with Ad hoc Net capacity&coding tricks
+ systems structures
+ Course Overview - including 2 missing pieces
1/ didnt cover shared media (as was done in 1b)
2/ didn't cover traffic engineering&signaling (rsvp) as most the principles already covered in other lectures earlier in term (open & closed loop control, optimisation and fibbing).

Principles of Communications -- Michaelmas Term 2016....week 7 (to Nov 25)

scheduling & switching last week and this week - some associated info:

sorting queues

huis clos shows up in multicores, routers, and data centers:-)

will not cover shared media, friday, as was done in 1b physical & dala link layer really nicely already, so revise that - 

instead, will move on to ad hoc/mobile networking capacity *might talk about opportunistic networks and firechat too:-)

Principles of Communications -- Michaelmas Term 2016....week 5 (to Nov 11)

This week was feedback control, theory &
optimization (routing and congestion pricing)...a bit math/algebra/calculus heavy methinks (supervisions should work through one or two examples of a PID controller for different systems
and how you show stability&long term operating point) - next week, real world TCP, then scheduling.

Principles of Communications -- Michaelmas Term 2016....week 4 (to Nov 4)

Have  covered Sticky Random Routing (DAR material here) + Network Coding for TCP

see wikipedia for Gaussian Elimination, + Linear Network Coding articles - best source/explanation I can find

And Open Loop Flow Control (including leaky bucket regulators/policiers)

Next week, closed loop/feedback control, and underlying theory for controller design and stability/efficiency analysis.

Principles of Communications -- Michaelmas Term 2016....week 3 (to Oct 21)

Done centralised/hybrid routing/fibbing -- as someone pointed out, forwarding continues if a central controler caches - depends on timeout in openflow added state/fib entries - with fibbing, the timeout will be whatever OSPF Or equiv does - so a comparison is potentially a bit more subtle than as presented.
Also, SDN/Openflow lets you add entries based on 5-tuple, whereas fibbing lets you add by destination only.....so potentially more fine grain choices in SDN, even if at the cost of more state - so the "prefix hijack" in fibbing is neat, but not the last word in adding custom routes...(e.g. if you wanted by source, needs more state than can be added by fake Link State Advert - as far as I can see)

rest of week was on BGP - why, what, how, where, when, and why not!

Principles of Communications -- Michaelmas Term 2016....

Finishing up end of week 2 (lecture 4) with Compact routing
having done background graphs & reminder of routing basics.

See the  slides page for lecture material + links to papers with more detail if you want (where not covered in books -

I've also added some more pointers to background book like reading on the course materials page for people that want to read more around the area, as there's no specific single book that covers all the course materials.

ttfn

fairness, machine learning, versus optimal stopping and cognitive bias

There's a bunch of work in making sure that machine learning systems are, in some carefully defined sense, fair - see for example the MPI work by Krishna Gummadi, in removing biases in various ML use cases (e.g. gender as an explicit or implicit discriminator).

For me there's a really subtle problem here which links between this work and other problems of Optimal Stopping and Cognitive Biases, and how one choose to define fairness in ML and the feedback loop between this and human society and the views we take on each other.

So lets take two simple use cases:

1. Admissions to University and Gender

Imagine a Computer Science department has 100 applicants a month, over 3 months for 50 places and wants to pick the best 50 people. Naive use of Optimal stopping would say wait til you have 37% of the applicants (111 people), then pick. What if the population is drawn differently by gender - e.g. out of every 100 applicants, only 1 is female. Lets say this is because applicants are self selecting based on the position in the ability of their own sub-population.. You have about a 1/2 chance of having 0 women in the admissions. The feedback to the population in society is you have to be in the top 1% of female applicants, but in the top 18% of men. Assuming their isn't actually a gender basis for ability distribution. You've just built a system that re-enforces it. TO get out of this, you have to run a two-factor optimal stopping scheme. If you want to do this for other groups in society, it will get more complex too...

2. Stop&Search and Race

It may be the case that you stop and search people in safeguarding society by profiling individuals based on past cases of stopping and successfully apprehending miscreants. Lets say this leads to a higher probability of stopping people who "look middle eastern". Again there's a feedback loop between your "correct" but naive selection scheme, and how people behave - in this case, various cognitive biases in how society will regard the group you target, may lead to the group being marginalised, out of proportion to even your allegedly accurate statistical model. e.g. anchorism....or many others, will lead to over-weighting by society, especially since humans are risk averse.

sigcomm 2016 #2 - what worked well

a number of things about Sigcomm 2016 were really smooth, and i''d like to say what those were and why, for future reference

1/ a large number of volunteers did a meet/greet/arrange transport from the airport to the conference venue & hotels site - this was great - even delayed planes had a person with local knowledge 9of language/culture/taxi/etc) and so many panic moments were averted-  for example there were two flights from north america which were disrupted but people still got met - also
several people were severely mis-advised by airlines that their checked bags would go through from the international to the regional flight (this isn't the case in any country in the world that I know of, but united and tam managed to tell people this, despite that security demands passengers and bags are reconciled per flight) - nevertheless, with some local help, bags were retrieved within a day....

2/ the conference venue has a LOT of rooms and is very conveniently laid out so that almost instant access to coffee/lunch areas, and between rooms was very very easy. - the space is pleasant, acoustics are good, audio/visual (mikes/PA/speakers) worked well (including for remote speakers and for Q&A) - there are 6 main rooms next to the catering area, plus the large auditoriam area up one floor, with large bathroom area next to both, too - the groundfloor rooms can be reconfigured to 3 larger rooms - this is necessary as the 5 days of Sigcomm these days include
multiple tutorials and workshops on the monday & friday, plus multiple other events like the student research, the topic preview sessions, mentoriing meetings, and various committtee (sigcomm exec, next year handover)....all rooms were used most the time...

3/ many sponsors attended and several had desks for info for possible employment etc, out in the large catering area...

4/ the conference banquet (tue) and student dinners (wed) were both fantastic events - the former was 8 minutes walk from the conference venue, so people could get bak to hotels at their own leisure - the latter was a bus ride away - coaches whisked us there and back in about a half hour, and that was probably rhe best meal I have ever had at a sigcomm conference. The reception on monday (in the main conference auditorium) was good.

5/ there were a couple of pretty good local restaurants at the venue for people looking for socialising on the other days (including award winners dinner, N2women dinner +  for people arriving early, plus on the thursday nite)

6/ there was fairly seamless interaction between webmasters, and a/v team, so slides, papers, other access (e.g. to printers for boarding passes, for travel info/asking for taxis back to restaurants/airport etc) was all pretty painless

we had a day of wireless outage, which appeared to be on part of the internet not inside the conference venue site, but an engineer did come and fix it that day - this disrupted the live streaming (although we hope the recordings will still have worked and will soon be available via the ACM digital library links)

7/ the remote presentations were remarkably successful - this was because
a) the actual talk was a pre-recorded video, pre-shipped to us, so didn't depend on the net working well in realtime
b) most presenters had prepared lively talks with a super-imposed video of the full standing figure of the speaker, alongside the slide show
c) the talks all had a live Q&A (relying on skype/telephone call out as a backup of the internet was down) so there was little difference in terms of presentation between the remote presentation and local presentations in terms of human experience - indeed, several people commented that almost all the remote presentations were technically higher quality that most of the local ones....

8/ the size of the conference (approx 400 attendees) combined with the local relaxed culture was perhaps responsible for a very friendly atmosphere- I think this meant that it was a really fantastic experience for the (large number of) student attendees, giving many opportunities for mentoring moments and general exchange of ideas....a larger event might need slightly more formally organised mechanisms (certainly, last year's sigcomm in London with 700 attendees was a bit more of a "zoo").

9/ there was a lot of behind the scenes tech used to track all the organisation of things....this is available from the general chairs and other members of the organising committee (OC) on request

10/ the OC all carried out their tasks with incredible efficiency and timeliness. This matters as many of those tasks have dependencies  (e.g. travel grant, visa letters, or tutorial/registration/registration, or PC paper shepherding/web site program) - there are a couple of race conditions, but we had fixes....which requires everyone to be responsive (i.e. very day) and responsible....

thats all for now, folks...

sigcomm 2016 - so long & thanks for all the fishy behaviour

Sigcomm 2016 for me

As general chair, I felt I'd have to attend Sigcomm in Brazil, even though I 
had a co-chair who is local, in fact not least to give moral support for him.

However, for me, August involves my family holiday typically, and this year was no different.
So we'd booked a large villa in southwest france for 2 weeks for up to 20 people, so that the extended family (from
UK, Ireland, North America & Kenya and anyone else who wanted to drop in on their travels) could all be there.

So one week in, I had to head for the conference, taking a couple of the family with to get 1 to Berlin, 1 back to
london, (another couple were heading the other way from London to France at the same time...

Montpelier->Floreanopolis took about 30 hours (with a very good flight from LATAM for 830$ connecting in Sao Paolo
with only a 3 hour connection). I met a couple of people on the last 1 hour flight who had come from Beijing (one
poster & one paper author), who's journey was also about 30 hours, plus a couple of Europeans who had a journey of
about 15 hours - like mine would have been had I not been on annual vacation.


So while the conference, as a social event, and a technical piece of my day job, is really excellent (much
gratitude to the superb Brazilian hosts!), I missed a whole week of seeing my extended family, including some of them who 
I only see then, but won't til next year now.

So it is disappointing that a number of people who had papers to present (note, I didn't), did not attend. On papers
with an average of 5+ authors, they couldn't find one person to travel and present. The excuse was the Zika
outbreak. There is more Zika in some US locations than in the conference location, but hey, who expects everyone to
be rational. It seems also that many of these authors were connected with papers with Microsoft authors. Microsoft
were not a sponsor of the conference either (they have been in the past), despite having an author on 20% of papers
in the conference, and making a thing of this on social media. It seems that the conference has value as a place to 
get visibility for work of the company or student interns at the company, but not enough to have a presence (not 
even a recruiting desk at an event where there are around 200 junior researchers in networking, one assumes many 
of who are looking for interesting paces of employment next).

So for the first time we've allowed some remote presentations
at SIGCOMM - we had one live one in at the NetPL on day 1 because a 
speaker was held up by a plane failure and so managed to Skype in, 
but we had two on day 2 in the main conference paper sessions, which were
planned. Authors unable to attend ahead of time, sent in a canned video of 
their talk, then we skyped them in after for Q&A

The biggest problem with this is non-technical - its to do with the loss of community 
building opportunities based in hallway conversations triggered by the talk or other 
things th speaker/authors may have done that are of interest to attendees - this loss
is small for a small number of remote presentations, and in the case the remote
presenter is a student, probably worse for them than for conference physical attendees.
The loss is larger for the conference if the remote speaker is an experienced person
who might act as a mentor or offer useful feedback on other presentations,
live, in the other Q&A, or in hallways etc, if only they could have attended.
one simple example - the authors of the 2nd paper on the 1st main paper session day
differential provenance could interwork with authors of a paper on "light in the middle of the
tunnel" in hottmiddlebox on friday.

There's no advatnage to the primary author giving the remote presentation (rather than either anyone
else, or anyone else coming to present it in person) because no-one at the conference gets to
meet them anyhow, so they don't enhance theoir career any more than writing a Tech Report or putting a paper on 
ArXiv with a video.

There was some care taken (at extra cost to the conference organising committees) to get
decent videos and have them present (and esp. attention to audio both for speaker and for 
Q&A with the remote virtual attendee).

However, 3 semi-technical problems became obvious in the first 2 talks
1/ the speaker is canned - they can't adapt to audience attention, they can't re-pace
based on level of engagement, they can't change their presentation to account for other people's talks
or reference another talk where there's common ideas or differences - the speaker can't interact with the slides,
even pointing at axes to explain scales, or interesting features of a curve/anomalies, outliers etc....
2/ there's no obvious way in this model, to ask a speaker to "go back to slide 5" in the Q&A
3/ having a human figure in the projection who is larger than life (as would appear on stage) is an elementary
HCI fail.

On the 2nd&3rd day of the main conference we had quite a few more remote presentations. While they continued to be
well prepared, and the illusion of having the speaker in the room continued to be maintained by having a Skype
capability for Q&A at the end of each canned talk, the number was really stretching the credulity and patience of
many of us that out of 30+ distinct authors across that set of papers, 0 could get here. This continued on to
trying to have a handover meeting where the only people from 2017 able to be physically here on the lunchtime of
the last day of the main conference were people who were involved in the 2016 conference anyhow.

The event was no more difficult to get to than many past conferences, nor are there more real (rather than
perceived) risks about the location than many past locations.
[In fact, I attended last year in london to go to the handover meeting to learn the tasks required of us, so I
mssed vacation then too]

A lot of people went out of their way to make this a successful event, despite the lack of full engagement by many
people who obviously assume Sigcomm is worth submitting papers to for their career or their employers visibility,
but don't buy into the community idea. That's sadly shortsighted of them. They will be perceived as places less
interesting to go work for compared to those places that had a presence. Sad, because it has been incredible fun here and the local community showed up massively supportive, in huge numbers, and got a huge amount out of things. More loss for those who didn't make it here from north of the equator.

For those of us who took time out from valuable family life, took a lot of care about re-locating the conference to
deal with the public health issues with the original venue, it is doubly disappointing that there are people in our
profession who don't share our view of what the nature of the event should be. It is very unlikely that I shall 
bother attending again, or consider being on the PC if asked. I dont care to work for people who don't care.

unikernels & production

A recent blog called into question the fitness of unikernels for production. The title was a bit misleading as there are several unikernel  systems out there. some of which are actually in production - one of our faves is the NEC/Bucharest Uni work on ClickOS, for example, which is used for NFV on switches and is clearly a class act.

However, I think the article is also missing some of the main motives behind MirageOS (see e.g. Jitsu or the asplos paper) which was based in experiences with managing a lot of Xen based cloud systems - sure, Unikernels are specialised, and don't possess a lot of the micro-management/debugging tools (yet, although a lot are on the way) that you have for kernel debugging or system tracing of linux etc etc. But that's because OCaml real world experience in production was that you have faster system creation, and way faster debugging times. However, that's still not the whole story- the story is that the whole toolchain for managing source, building a unikernel, deploying it and tracing it is much more homogeneous - so a whole system of unikernels is easier to manage (as per previous experience).

Crucially, we are also able to verify some components of the MirageOS (e.g. Peter Sewell's group in cambridge did this (for some definition of "this") a while back for the TCP/IP stack, plus confidence about David and Hannes TLS implementation can be quite a bit higher than the "industry standard" that had 65 vulnerabilities in one year alone.

But all this is missing yet another key factor - unikernels don't replace xen/linux or containers - they play side-by-side with them, so you can have flexibility and familiarity, while affording better protection - that's in the Jitsu paper btw, and I thought was fairly clear.

Sure there's some way to go - there always is -there was when Xen first shipped too. But the computer science behind this is not that bleeding edge (nor were VMs back in Xensource's day either:-), but the science is 15 years further on, and we should all benefit from that, in my opinion. Indeed, it took a day to add profiling


xkcd has us in there thrice

readings in computer science found in a time capsule

recently, I was re-reading the classic old article on Smashing the stack for fun and profit in phrack, and wondering where the positive alternative lesson might be. Quite a while ago, I did a port of the SR(Synchronized Resources) programming language out of Arizona, to the newly minted RS6000 system out of IBM. The language is an elegant system for teaching principles of concurrency in lots of nice ways - at the time we didnt have a single agreed way to do it (e.g. wrong like in C11, or possibly ok in Java), so there was a need for a pedagogic approach and SR together with a nice book was very cool. However, we'd just bought a bunch of new IBM AIX systems with the new POWER PC RISC processor, which had a whole new instruction set - lets leave aside the amising idea of a "reduced" or "regular" instruction set that includes "floating point multiple and add" in its portfolio. However, in terms of registers, its a pretty nice system.

So why is porting SR to the Power CPU reminiscent of stack smashing, I hear you cry?
Because, you need to implement the threads system it uses to emulate real multi-core, I hear myself answer. And what does it take to do that, you continue? well you need to save the current context (like all the registers and thread state (i.e. PC, stack) move to a different thread/stack by calling the scheduler with a pointer to that context. To do this involves becoming familiar with the stack format used for most programming languages.as well as all the important (i.e. all) registers etc. So basically, slightly more than the Phrack folks....basically, writing stuff that moves to another exection context, but can get back again correctly, is harder:-)
You can see some nice examples of the context switch stuff for a variety of processors in the (not supported) SR archive

Meanwhile, I was also reading about the integrity check used for DNSSEC caches. so that will be reported elsewhere, but the interesting thing is that its a weak version of the IP header (and TCP) checksum algorithm. Again this is something that excercises computer science #101 - you need to add up all the 16 bit fields in the buffer (imagine you have a n byte buffer, then if n is odd, add a zero value byte and sum it as a vector of 16 bit values using "end round carry" (or ones-complement) artithmentic - basically, you have a 32 bit accumulator, and loop over the buffer. when you are done, you do one more thing - in the checksum case: check any bits above the 16 least sig are set, and fold them in (add again) and then do one more add in case that overflows too. In the integrity check case, just 0 any bits in the more significant 16 bits (i.e. && accumulator with 0x0ffff). For the ARM IP cksum case, see this
code with inline asm - the crucial bit's lines 78&79 after the bne loop.

amusing, back in the early days, i remember someone loop unrolling asm code for hte M68000 (that's not a 68020 or 68010, but 68000 - that was sold as a "Codata" computer in the uk, but was a Sun-1, i think, never sold by Sun) - the code went slower as the loop was now to big to fit in the miniscule instruction cache of said CPU...

hum...........what could possibly go oddly wrong with the allegedly simpler (by 1 instruction) integrity check algorithm? I leave that as an exercise for the coder

counciling the UK research councils

The UK research councils are unique in the way proposals are reviewed in several ways (in my experience)

firstly, unlike almost any other research funding agency (unlike DARPA, NSF in USA, CNRS in france, DFG in germany, the Japanese, scandinavian, and just about any other national funding agency I have dine reviewing for, which is a lot), the officers are not seconded experts so the assignment of reviewers depends on the reviewers self description - notoriously inaccurate. Unlike a journal (where the editor is an expert) there's not really a _peer_ review assignment process

secondly, the reviews can be rebutted by the proposer, but since the reviewers don't see each others reviews, they can't be calibrated against each other (unlike a conference or journal)

thirdly, the panel are not the reviewers and are not allowed to re-review the proposal, even if they are experts and only in exceptional circumstances will they discount an obviously incompetent or inappropriate review.

As a recipient of significant funding from the research councils, I am not expressing this through some sour grapes emotion, but more on behalf of my bewildered junior colleagues, who frequently receive inexplicably odd reviews and panel decisions. This is not good for community trust in the system - it may be ok at the obvious top 5-10% of proposals, but it results effectively in random decisions quite shortly after the very top (all 6s) ranked research. This is not good for confidence.

I can't give examples as that would be a breach of confidentiality, but everyone I know can tell a tale.

Maybe the new system after the recent review will involve people who have an answer to why the EPSRC and other councils should have a unique, and uniquely odd system. I have never heard an evidence based response to the comments above, which I have made several times to officials from the research councils. of course, since they themselves are not seconded from the community, how would they know, in any case. However, they could try talking to colleagues in other countries a bit more and see what works (or not) to persuade us that this is not just some random "we do it this way because we always have done"...

Part II Principles of Communications, 2015, to Dec 2

Wrapped up Traffic Management, including
idea of signaling protocols, and
space/time scales of different techniques;
and review of the course contents.

Planning to do revision classes next term.
Supervision notes will be linked to course web page after end of term.

[systems structures lecture moved to background]

some notes/problems from supervisions added
now

Part II Principles of Communications, 2015, to Nov 27

This week is

• Shared Media
• Mesh Network Capacity
• Coding and Multihop Radio (Cope)

Two useful network coding primer and coded storage articles...
and just what is a shim?

Part II Principles of Communications, 2015, to Nov 20

this week, covered scheduling, work conservation, max/min fairness, and PGPS approximations + queue jump!

Part II Principles of Communications, 2015, to Nov 13

Optimization (Nov 9) - background paper:-

from Princeton group

TCP in the wild - Optical Carrier Speed
table + Reminder about R-squared

Schedulers&Rounds....up to WFQ.

Part II Principles of Communications, 2015, to Nov 6

Flow Control, Congestion Control,
open and closed loop systems

Control Theory -
time domain model
transform to frequency domain
recipies for laplace transforms
stability & efficiency
proportional, integral and differential (and PID) controllers.

Online slides (PPT and PDF) are ok -
apologies for symbol/font problem in some of the printed pages!

Part II Principles of Communications, 2015, to Oct 30

Previously, Compact routing, Central routing (fibbing to link state),&path vector

This week covered
interdomain routing, including AS paths and deadlocks,
for which see interdomain revision notes/slides
+
multicast,
+
random routing

Just started on error and flow control.
[As usual, wikipedia is great on gaussian elimination ]

Pretty much as per schedule

Part II Principles of Communications, 2015, to Oct 23

This week has been about inter-domain routing, and BGP.
Covered background business relationships (peering, customer/provider etc), the protocol, the attributes/selection, SPP, and discussed scaling, convergence, and problems (like bad gadgets, wedgies) - as always, data is out of date, but Geoff Huston to the rescue...

Part II Principles of Communications, 2015

This week (to Dec 16) I should have covered the graph material (random graphs + alpha&beta models of small world/clustered graphs), and
Compact and Centralised routing - viz
http://www.cl.cam.ac.uk/teaching/1516/PrincComm/slides/schedule-2015.html

On graphs and networks there's a new really nice book by Jon Kleinberg


There's some lack of precision about the terms "small world" but basically, (wikipedia is your friend) a scale-free network refers to the power law degree distribution, and consequential small diameter (and some clustering), which leads to the small world property. Not all small world networks are scale free, but scale free networks are small world...

The Smell of Memory

scientists in cambridge have recently figured out how to code the smell of memory, not just a smell of one thing that evokes a particular memory, but the underlying phenomenon that is memory itself. It turns out that it is not so abstract, and that there are only really 7 key parameters (somewhat like taste, which is, of course, related to smell in any case). Working backwards from the examples of smells that evoke memories, using a statistical technique called PCA, scientists can now code the entire space that is memory - so not only evoking a particular memory, but replaying everything at once.

Of course, there are severe dangers of synaesthesia with this technique, so it will only be allowed in key, socially beneficial situations, such as court cases, or TV interviews with politicians.

And it must be noted that there will inevitably be people who have an innate fear of smell - loosely related to the smell of fear, but far more disabling in this context, except where you'd like the right to be forgotten - de-oderant amnesia.

Re-use ill-considered (twitter and hypothermia)

I've been reading a lot about ethics recently for a forthcoming workshop in Oxford on the topic.
It seems that a lot of the book keeping elements of ethics have been defined (I guess, perhaps, in reaction to the lamentably long list of unethical things that are done by all and sundry in online media commercial appropriation of the essence of you, and dodgy medical research re-owning folk knowledge on drugs from rainforest eco-systems, or testing stuff on people who have no political or economic choices...

So there's a long list of stuff we (as researchers) have to go through.....

but it seems to me that quite near the top of the list ought to be something about re-use

In computing (and in general in engineering), re-use of stuff (re-cycling harware, and re-cycling good ideas, or software) is regarded as a good thing - rep-purposing too - the internet came out of dual-use (re-purposing a survivable defense network, as a cheap extnesive global communications utility for the public)...

but the real elephant in the room for me is re-use of stuff in a new context without ethical consideration.

Let me give two examples (from the title of this post)

1/ someone (NOT ill-advisedly) tweets that, unless the snow in an airport is cleared soon, he will blow it up. This is a daft joke which maybe to his friends is funny coz he's that sort of a guy.
That's not the problem. THe problem is that it got re-tweeted or forward to the police - whoever did that, did they stop to consider the original intent. Or was this thoughtless? or possibly even malicious? why did the police not regard this as potentially a "crank call"? were they not wasting police time

2/ research on hypothermia received a boost from the Nazi doctors trying stuff out on people in concentration camps. The research actually turned out to be useful. Should we deny ourselves the benefit, despite the awful provenance of the results?

Some of this can be reduced (in a classic reductionist manner) by looking at cost-benefit tradeoffs. What are the risks the tweet really is a bad guy? what are the chances that if we use the nazi medical results, someone will start a land war with russia, to aid in their drug discovery programme?
How much extra work do we have to do to make deciding the right way about the incentives, or the re-use of results?

Why do I care?

Well, its clear that many open, public-minded people constrain themselves from doing potentially valuable research by setting barriers before working out the cost-benefit/incentive balance, whilst at the same time, a lot of industry just goes ahead and does it, and fixes things up after the event.
Is there a middle ground?

I'm suggesting that considering re-use and the safeguards one should put in place for that, might give a way to evaluate whether something is ethically acceptable or no.

It could also serve by offering "re-use cases" which might be easier to explain to people as part of the "informed consent" steps of any ethical experimental design.

As more pressure is put on us to do work with larger and larger data sets (whether the GCHQ surveillance data, or police crime/geo-loc data, or NHS care.data) we need to figure this out soonest.

Intellectual Property and Production - workshop in Law, 24.1.2015

at Wolfson College, 25 Jan 2015
Organised by Center for Intellectual Property and Information Law

Jennifer Davies introduced the workshop (6th in a series run by CIPIL ) and reminded attendees this was about production (and place!)

Session 1: Producing Output, led by Lionel Bently

Tanya Aplin: 'The Impact of Prosumers on Photojournalism' - this talk mapped out how the massive rise of amateur photography and the ubiquitous presence of cameras (especially in phones) had given rise to the de-skilling of the area of photojournalism, starting especially in disasters and emergencies (Katrina, Tsunami, Arab Spring etc), where classical photojournalists might not be on the scene for days in any case, but now supplanting every day coverage of events. The talk then went on to the new businesses that had arisen to "professionalise" the contributions by the public, and new agencies that would find takers for pictures and pay producers (albeit massively less than the famous photojournalists of yore).

Great talk - i think to be fair, the "professionals" always over-stated the skills you need to be a good journalist - many amateurs are massively better than many paparazzi - see my friend tim harris photos - he's a research leader at Oracle labs....this is also true of bloggers - for example my local kentish town blogger produces more timely and better job than the main traditional local newspaper (in my view:)

Alan Durant: ‘Kinds of Work in Copyright: a Semantic Perspective’

This was a foundational take on the triptych "Original Literary Works" unpicking the individual and combined meanings over history and showing how ambiguous the terms sepeaately and together were and still are. THis has important consequences for public and other stakeholders understanding of the relevant law!

Hye-Kyung Lee: ‘Media fans as new cultural intermediaries’

This was about fan contributed works with a new spin - the Manga translators - fandom who take japanese and korean comic art, and produce versions for other markets! Again (as with the first talk in this session) the emergent business models have first been squashed, but then embraced and extended by the original Manga production houses. Fans reactions vary (as you would expect) from approval to "uncool" - also, interestingly, cultural differences mean that Chinese reaction is quite different than other countries in this regards. I asked if anyone has tried personality profiling (c.f. psychometrics facebook app in cambridge) to see what sort of people enjoy these activities - is it mostly about fame, social capital, etc - inclusion - etc or do some really want to make it like their heroes in the original comics? or a mix (changing over time). Was reminded of two related stories. (Anecdotal) - 1/ The Dr Who fan contributed plots and characters were threatened with a lawsuit for copyright reasons, but then it emerged some of the writers of Dr Who had been reading the site, and may have inadvertently used material and fans suggested that they might countersue - so a quid pro quo was reached:) 2/ My cousin was teaching computer science in Brasil and translated US text books by reading then speaking aloud in portuguese, to a dictation/speech to text system (Dragon Dictate) - students bought the original book, so there's no loss to publishers or authors, but were given handouts of the text part in their own language.  Publishers became interested (low cost way to get foreign language editions of books....and discover markets).

This element of fan led A&R seems like an obvious way for producers of new work who live in the "long tail" of the popularity distribution to find their market, and for new fans to find content. Seems like a good thing - for a given area, it may not be a zero sum game  although over all content, I guess the population does have a finite disposable income. However, this new mode may lead to a wider breadth of availability, perhaps at the expense only of the few people at the very tip of the popularity (U2, Beyonce might lose a few percent of their gazillions) - maybe Thomas Pikety will approve!

Session 2: The Means of Production (I) led by: Ian Walden

Jon Crowcroft: ‘Software Tools and Die’
here's my talk which is mostly just about how we write software but also a plea not to do s/w patents (the clever bits are just math) and how copyright is ok, but there's lots of different uses (license models) which can all work (and co-exist)

Catherine Seville: “Controlling the Production of Literary Works: Hard
Then, Impossible Now?

This was a fascinating talk about the ways in which the technologies for production have always seen (mostly failed) attempts to control - from limited access to printing press, to control of rights to publish, through to DRM etc - really interesting...

Simon Eliot: ‘From 'Literary' to 'Commercial' in the Registry Books of
the Stationers' Company

Beautifully read and presented talk about this history and hilariously incompetent antics of rhe Stationers' company (registry for all things trademarkish) esp in the 19th century, which some fabulous graphic examples of Victorial graphic design for a wide range of useful, daft, and sentimental works. Sheer diversity of display is astonishing.

Session 3: The Means of Production (II) led by: Andrew Griffiths

Sean Bottomley: ‘Trade secrecy and production during the late
seventeenth and eighteenth centuries.’

Lovely talk about Worshipful socieiies and their control of their magic pixie dust techniques-  interestingly, the use of sanctions against people for revealing these tricks to "foreigners" (i.e. non guild members) was relatively rare in practice.  It makes you wonder why the Worshipful Company of Information Technologists was set up - What have they got to hide???

Dev Gangjee: ‘Why Wine is Not a Commodity: Geographic Indications,
Place and Process’

Great talk as with all the talks, really well presented and clear) on "terroir, and the way GIs are being used more and more, and yet have very little public recognition yet (outside of the original "Appelation Controle) - I asked the questions a) how "little britain" is all this and b) can you have a GI for "produced near here" for any definition of here (i.e. eco-didn't fly far food) - answer, yes...

Theresa Lopes: ‘Trademarks and Production of Consumer Goods from an
Historical Perspective’

Great econometric analysis of a large body of data from several places showing how IP protection trends track a) innovation b) the economic growth/shrinkage - a lot to take in - hopefully, we get some slides/paper post workshop!


Session 4: Geographical Delineation, led by Session leader: Graeme Dinwoodie

Sun Thathong: ‘A Marxian interpretation of the traditional knowledge
debate: the role of IP in the
coexistence of primitive and capitalist modes of production.’

Fun stuff -not quite as alarming as it sounds - basically, traditional knowledge is folk lore and crafts embedded in simple societies and held in common. It is being ram-raided by developed countries profit led companies (most obviously, plant medicines in rain forests being patented by big Pharma). This is about the moves to try and figure out a range of IP models that will appropriately recompense those "simple" societies (which, if course, are never so simple). Main bug is the hilariously naive Marxian description of primitive communism, which an anthropologist would have a field day with (literally and figuratively), but the model economically is good.

Here I had to leave to go to a memorial Mass for my brother in law, Declan McKeever
so I missed one of the organisers papers, which was a shame as it was

foundational to the main purpose of the workshop:

Jennifer Davis: ‘The End of Trade Marks as an Indicator of Place and

the Implications for Labour’

Graham Dutfield: ‘The compulsory working of patents and developing

countries.’

Henning Grosse Ruse-Khan: ‘From Local Manufacture Rules to Import

Barriers in Global Production Chains’

Science and Policy - Why should they pay attention to us?

Reading the latest CSAP (center for Science and Policy) report on "future Directions for Scientfic Advice in Whitehall" is quite frustrating if you are a geek.

Several behavioural weirdnesses define geeks, and these matter:

1. geeks tend to read about anything whatever their core training is, whether climate science, social media analytics, psychology, behavioural economics, and XKCD
2. notwithstanding Steve Hand's memorable pub rant[1], politics appears to be quite a lot simpler than a physics (Natural Sciences) or computer science or engineering degree, really.
3. they witness many people in political decision making roles who are actually less qualified even in terms of soft (social) sciences (lets not rehearse the PPE pub rant again just yet [2])

So what does this lead to?

1. incredulity when governments do not act on scientific advice (drugs, immigration, climate).
2. frustration when governments offer explanations as to why they cannot act on said advice.
3. strong inclination to walk away from bothering ever again to offer advice/evidence.

Far from this being something scientistcs should apoligise for, given the nature of the public's alienation with current western democratic policies (e.g. economics of austerity), it behoves politicians to rethnk how they react to public advice:

1. scientists have a methodology (atually lots, but lets stick with Popperian classical Object Knowledge for now).
2. Theories are falsifiable - the latest theory is "best of breed", that's all its merit is.
3. We dismiss theories when new ones come along that meet the criteria (better fit, simpler, more elegant -- pick any).
4. We change our minds. 

Indeed, there are honourable occasions (e.g. discovering that stomach ulcers were caused by bacteria, or the italians finding that their neutrinos did not go fast than the speed of light, or the cold fusion fail), when this is very public, but it happens every day on a finer granularity

I think the time has come for scientific method to be applied by politicians. Just as Jeanette Wing argued for computational thinking to be part of everyone's intellectual landscape, scientific method has already been embedded in everyone's subconscious for some time (e.g. since the Age of Enlightenment, aka Age of Reason)

Why not? As Oliver Cromwell said to one government (and remember what happened to them 

Think it possible you may be mistaken.

CLuDo

CLuDo

All bar one of the suspects was ruled out through a rigorous process of logic
and fermentation.  Suspect B was never identified, although her love of Citrus
flavoured chewing gum inclined Devonshire to discount her on the basis of the
lack of scent in any of the crime scenes. The fine detective had the measure
of Napier, and deemed his extremely asymmetric length arms to put him beyond
the reach of the law.  The recent Turkish immigrant who went by the moniker Moosh had an alibi (waylaid in a public loo by a nearly terminal bizarre
kebab accident). The Polis had no beef with Professor Baron, who was in any
case too absent minded to remember who could be next o nthe serial killer
list. Ms Bath was in the Ale House, where she tended to hang out with other
birds in hand. Dr Burleigh was too gentle a character, despite being a well
known Arms dealer.  The reverend Carlton was left handed, whilst the
Carpenters were both right handed, which saw them in the clear.
Thomas Champion was in london rowing, on the  Thames that day, and indeed,
had turned a corner since leaving the county seat for town, and given up his
unnatural addiction to Dobblers. (Dobblers is that well known breakfast dish
that looks like a classic grill, but in fact is made from dog & pheasant
and isn't as illegal as it is unpleasant).

The Earls of Beaconsfield and Derby were both out at a shoot, and so the
inspector was shot of them, even before five bells. Indeed, he thought to him
self with a wry ha-ha, pigs might fly and his golden hind come in, before
they'd commit any such gross moral turpentine. Henry was OK, since he'd made
peace with his Armenian girlfriend Ishca over the proper use of feathers in
millinery.

It was known that Milton was blind drunk, and waxing eloquent over some
jolly waterman about his time playing frag piano in old Orleans.
The chancellor was above suspicion, as were any of the occupant of the
Regent house. All five of the Irish brothers were known to react badly to the
men in blue, a red rag to a bull, but the inspector rose to the challenge, and
avoided a crowning.  Rupert Brooke was with Milton the whole day, according
to the sheep rustler known to everyone just as The Eagle, who had dropped in
after some wild spread betting.

Radegund's sainted aunt claimed he was down at Ally Pally, his Alma mater, and
the only anchor in his peripathetic life.
The inspector would give drink bakers dozen once the moon was over the yard
arm if that blackamoor's head was capable of such dark thoughts.
Devonshire asked his trusty sidekicks Argyle and Clarendon if they thought
there was anything in the rumour about the boats? Dr A saw on the
British Queen not, whilst det inspector C, smelling like a
brewery concurred. Devonshire looked at these two interchangeable chaps, like
peas in a pod - you couldn't tell if you swapped them, castle-to-castle like.
He hadn't graduated in the Jubilee year to waste time like this. He had other
buns in the shop to fry.

Back in  Cambridge feeling blue drinking a hog's head of big black cow and watching the
cricketers cut down another elm tree, failing to impress, as they fought
by George to keep the greyhounds and haymakers at bay, Inspector Devonshire
wondered if perhaps the evil genius artist, Geldart was behind it all.
Granted, he had the locomotive and was a man with a means, if not completely
in a pickerel. After all, he was known to have a predilection for chasing the
Green Dragon down King Street at quite a run. Many times, Dr Kingston had
tried to wean him off, but he would claim to be a master of the Marinade,
although everyone knew he was just driving them up the Maypole.

So summing up the first victim, Panton was found  bashed in by a
globe carved curiously with Fleur De Lys; the second, Portland,
rolled around a Fountain, pursued by a green manatee. The third,
Ms Parrot, crushed beneath a free press, like grapes, blood
spoiling all the nice mitred corners, pouring out like an old spring, only
attractive to the rats. The fourth, Salisbury trapped between the mill stone
and a rock, but curiously tied up with rope and twine. The fifth was drowned
regally when his ship ploughed into a dead end.

At six bells, listening to Bert Jansch playing
down by black Waterside on his iPod, the inspector suddenly remembers Arthur C Clark's story from Tales from the White Hart
(the one with all the violations of Sir Isaac Newton 3 laws of droog).
he lit a fine Unicorn cigar with a White Swan vesta matches, and decided to
see if the Wrestlers were still slugging it out over a bacon, lettuce and
tomato roll. As seven starts came out, the inspector took the last tram home
but fell asleep and landed up in the depot once again.

principles of communications, 2013/2014, end of week #7 to L22

This week, we covered shared media & ad hoc capacity, and started on traffic engineering.

A sharp question on proportional fairness in earlier material prompted me to notice that that isn't well contrasted with max-min fair sharing -- It turns out (as often with technical areas) Wikipedia has a nice explanation - see this article on
proportionally fair w.r.t weighted (max/min) fair queues

Next week will finish traffic engineering and wrap up with summary of course.

principles of communications, 2013/2014, end of week #6 to L19

This week have done scheduling, queue management and switching
and just about to start on shared media

One interesting point historically -the colossus computer at Bletcheley Park built for code breaking was not a von Neumann classical architecture computer but was a "switched programme" machine  - this made it incredibly fast (for a 1940s design) although incredibly inflexible -- and it took a very long time for people to catch up on a standard desktop (about 50 years) - amusingly, about as long as the Dr Who series has run on BBC TV:)

principles of communications, 2013/2014, end of week #5 to L16

This week, control theory and optimization...

Some minor inaccuracies in slides have been corrected in the online copies linked from the course materials page...[or will be as soon as I can get powerpoint with the right fonts:) - the key error is in the calculation of the steady state error of the proportional controller - for some reason, there's a subtraction of the two terms for U(s) where it should be +
(KUs + Rc) / (s(s+K)
I think {need to check this:) it kind of makes sense (if the completion rate increases, the admission rate should increase....)

then when we take the limit of s(U(s), as s->0, we'll get Us + Rc/K
so ess (error in steady state) is Us - (Us + Rc/K) which gives us -Rc/K
(i.e. the answer is right, but the system response wasn't...will check and correct soon...

again, to note, the chapter on control theory in Keshav's book is very clear if you want alternative source + some nice example problems.

principles of communications, 2013/2014, end of week #4 to L13

Error, Flow and Congestion Control done (99.9%)

further reading - maybe - on Network Coding (see Digital Fountains)
and on what's in Linux (CUBIC) and Windows (Compound) for congestion control, and what real traffic actually looks like - see CAIDA
http://www.caida.org/home/

next week: control theory...and optimzation:)

principles of communications, 2013/2014, end of week #3 to L10

This week we covered routing -

there's one egregious error on the slide explaining Dijkstra's algorithm in Link State where the sign on the comparison is the wrong way round (well spotted students!) - I leave it as an exercise for you to find, as it makes for careful reading:-)

In Sparse Mode, we use Rendezvous Points to coordinate a single RPF tree around a designated/configured router (maybe one for each of a different block or subset of multicast addresses) - there's no guarantee the RP is in a sensible place, although the switch from RP centric tree to source based tree after an traffic flows helps reduce latency -  automatic placement of an RP to be in the "centre" of the group would be a solution to the Steiner Tree (Min spanning tree) problem which is NP-Hard, although there are polynomial time approximation algorithms for it (but you probably wouldn't deploy them in routers, but in a network management system for e.g. a gamer or trader network, this might be sensible)

One other note - consistency, symmetry of routes, and so on - IP and IP routing make no guarantees about this at all! BGP (inter-AS routes) are often asymmetric...recent computer science work on building new protocols that provide global consistency during route update and computation does exist, but is still research, largely....although the techniques are promising!

Next week, errors, then flow and congestion control.

principles of communications, 2013/2014, end of week #2, to L7

To note for today- the slide on graphs, with Edge and Node list has a list of all edges, alongside o nthe right list of nodes  - the list of nodes isn't meant to line up with the list on the left - its just a list for node i=1-5, what other nodes, in the directed graph,  are adjacent (look at arrows on edges - note in 2 cases (1<->2 and 5<->4, they are bi-directional)....



fun references today:-
Ghost Maps

Collatz

Kirchoff

Erdos

Small Worlds...

DDOS visualised

Couple more corrigenda/errata
1. in the alpha/beta models of random graphs, there's k used for average degree of the net (e.g. pN in the alpha model), but also used for the toal number of edges (N*(N-1)/2) - so take care with k
2. there's an expression in the slides about max-flow in DAR (the "Sticky Random Routing" for the telephoen net) for using Erlang's call blocking probability for a given link, then work out what the toal capacity will be for 1 hop and 2-hop/tandem routes - this has n, which is number of calls you get through, then mentioned a technique called LP  to solve the maximisation problem given in terms of sum of calls that get through (or are blocked) over all direct and tandem routes- we are'nt covering that technique this year, but LP stands for Linear Programming, and is fairly straightforward if you want to look it up - it is commonly used in optimisation and shows up in Operations research/Logistics (freight etc) and so on all the time.

principles of communications, 2013/2014, end of week #1, to L4

We have now covered Systems, and Layers (lawyers)...

Next week, Graphs, and Routes!

principles of communications, 2013/2014, L1

Today this course starts: principles of communcations

This blog will be where I put errata, answers to questions, and just generally track progress of where we've got to for students and supervisors....

Today [11.10.13] got as far as 1/2 way through Systems lecture - Monday
intend to finish that and go about 1/2 way through Layers material:

slides

Publication Culture in Computing Research Design for impact: Rethinking academic institutions from the ground up

Why do we pretend that a publication is an event, rather than a part of an ongoing
process?
Computer Science is a Soft Subject. We create artificial systems/artefacts, and explore
their behaviours. We then report on this by talking about the behaviours at workshops
and conferences, and writing about the systems in papers for web pages, online
archives or even traditional print journals.
People assume that the artificial dichotomy between social events (workshops,
conferences) and archival repositories (journals and the like) is right. And some of the
debate about CS publication culture is oriented around trying to get people to use
these two modalities  more like other disciplines.
I think this is fundamentally wrong, and flies in the face of real scientific method.
Science does not deliver truth. It delivers things that work, and explanations that are
the best, current, simplest ones (c.f. Popper on Objective Knowledge, and of course
Occam’s Razor).
This means that a work is not the final word. It is just the current word. A goal of this
proposal is to reduce the “slice and dice” culture present today due to various perverse
incentives.
So the notion that an “archival paper” has been thoroughly checked and is infinitely
more “correct” than a “rapidly” reviewed conference submission is not tenable. There
is every chance that during the necessarily longer process to create an archival version
of a work, subsequent work has improved over the results. Hence much archived
material is actually less accurate because it is less timely.
The solution, for me, is to remove the notion of immutable publications, and admit
that we should update work continuously
This can apply to the entire process of socialising our work, hence a dialogue (or
multilogue) between authors, reviewers and readers, continually adds accuracy or
timeliness (or invalidates a work).  The same can apply to citations (which should, by
the way, have a “sign bit” to indicate whether the citation is building on fro ma work,
or citing it as the thing the new work invalidates).
Recognising this mutable publication model, would allow work to be presented at any
point along the “production line”, perhaps merely by “acclaim” - some work has
reached a point where it is mature enough and timely and interesting enough to merit
presentation at a social event (workshop or conference) - this could happen before or
after some notional point when it is recognized that an archival version is the current
best knowledge we have (a rare event).

Along side this continual process, I think one would have to abandon ideas of
anonymity in both authorship of work, and reviews/critiques (viz, the “dialogues”
mentioned above could only work in that open way). It goes without saying that code
and data associated with a systems’ behaviour should also be openly available as part
of this ongoing process (after all, since when did we declare code “bug free”
correctly? Why, therefore do we declare journal papers “correct”?).
Finally, this isn’t exclusive to Computer Science, but we built the tools that would
make the new approach viable, so we should use them first.
In fact we also have the next generation tools for this – we just need to combine Arxiv
with Github (versioning repositories)
1
.
Causes of paper count inflation.
CS is notable (in most branches at least) for submitted to conferences more than
journals. There are two pressures to do this
1. Urgency
2. Promotion
CS is a young disciple, and the young are noted for being impatient and impetuous -
our slogan might even be said to be “Publish Early and Publish Often”
2
.
Urgency
We live in a nanosecond world. More than other disciplines, partly because we built
it.
We supplied the tools and tool chains (the net, e-mail, the web, PDF, bibtex/latex,
databases, HotCRP/EDAS, etc)  that let us cooperate to develop ideas, systems,
results, and write papers faster, and deliver them for review, editing, and presentation
more quickly than any previous generation. Surely, other disciplines use the tools, but
we live and breath them.
As a result, there’s a feedback loop between publication of hot new work, This instant
gratification leads to an increase in the rate of submission.
Our profession has also a tendency (at least anecdotally) to attract a share of people
with OCD/Attention Deficit problems, who maybe (amateur psychologist’s hand
waving here) seek instant rather than deferred gratification.
                                             
1
 Github because we want distributed repositories to avoid re-concentrating power in
one place all over again.
2
 I could speculate here about whether these factors also contribute to the gender
imbalance in Computer Science as a profession and academic career (whether
directly, or simply as proxies for a root cause).


Promotion
Our academic research culture is funded largely by tax payers money (NSF, DARPA,
EU), and the tax payers seek metrics to see their money is well spent, and they seek
such feedback on an annual basis. Paper counts (and to a lesser extent, citation
counts) serve this. The same problem (inflation) has hit the industry research and
development world, where patents are a proxy for real work, and are rewarded.
The amount rather than significance of work is measured - hence, the aforesaid dice
and slice approach to work, producing minimal publishable units, and multiplying the
number of venues and publishable units year on year.
Because CS is young and vigorous, we have in the past been able to keep up with this
inflation. We are close to the limits though.
In the UK, we have a national Research Excellence Framework, for which researchers
in universities do not return all their work. Instead, every 5 years, up to 4 “outputs”
(e.g. papers) are returned. Secondly, and in addition, impact stories (pieces of work
10-20 years old, that have had a long term effect on the world, economically, socially,
or in terms of further developments in a discipline) are employed.
It will be interesting to see the outcome of this process, but for me, it is probably a
better basis for looking at some one person, or groups progress, so if we were to use
these sorts of indicators for tenure or similar, this would remove the aforesaid
perverse inventive to maximise the number of publications.
Acknowledgements
Thanks to Richard Clegg and Ioannis Avramopoulos for comments on this draft.

Principles of Communications 2012 up to L24 - week 8

Finished up with signalling, admission control, capacity planning today.

Comments on quantity of material and supervision q&a welcome 0- will work on this a lot for next year.

Was asked about reference (e.g. textbook) on WiFi  - not sure of good text (neither of Keshav's books cover this) but there's a nice tutorial online at Berkeley here

I'll see if I can find a better standard text on this, as it is quite interesting I feel!

Principles of Communications 2012 up to L21 - week 7

Have covered capacity of ad hoc wireless mesh, plus a bit on LP this week

As students pointed out, PR versus nPR is like comparing "reservation" and "staggered" forwarding in ad hoc mesh (i.e. pipelined forwarding is equiv to the first hop winner getting access to the whole path, whereas non pipelined case defers)

On SPT v. MST
http://www.me.utexas.edu/~jensen/exercises/mst_spt/mst_spt.html

xkcd has a (not so rare) educational cartoon on spectrum allocation which is useful:
http://xkcd.com/273/

LP - simplex solver - see
http://en.wikipedia.org/wiki/Simplex_algorithm

Principles of Communications - interim lesson

If someone wants to become a major hero, then fixing the Raspberry Pi linux USB/ethernet driver to remove "buffer boat" would be a very nice exercise - see here for references on what to do, and why - its an interesting lesson in
buffering, latency, and TCP/Queue Management interactions

http://www.teklibre.com/~d/bloat/Not_every_packet_is_sacred-Battling_Bufferbloat_on_wifi.pdf

Not every packet is sacred

Principles of Communications 2012 up to L18 - week 7

Scheduling

Randomness is your friend...see below too

Switching

should mention monsieur Clos!!
n.b. there may be an error in the slide on sorting/batcher switch - will check:)

Sharing

mention inventor of spread spectrum:
http://en.wikipedia.org/wiki/Hedy_Lamarr

A week full of s's...

Principles of Communications 2012 up to L15 - week 6

This week, Optimisation, and a start on Scheduling.

One question came up in optimisation - In the formulation of delay as
F/(C-F),  which I characterised as the load over the "headroom",
this is a dimensionless result - yes - its basically the average number of customers in an M/M/1 Queue (see Richard Gibbens slides from Computer Systems Modelling). However, in a work conserving router with a fixed speed output link, this translates into delay by multiplying by the
mean packet size/the output link line rate (which would have dimension time:)

Several people asked for more info about control theory - the chapter in Keshav's book (as per course web sight) is really quite clear (goes a bit past what I would ask, but knowledge is good, right?)...so recommend an hour reading that chapter - it also has exercises that are useful.
Keshav, S. (2011). Mathematical Foundations of Computer Networking. Addison-Wesley,
covers all but the graph theory bits of the maths I cover (and also covers some queueing and other performance things you might find useful as an alternative text, if you are attending Dr Gibbens' course too).

As per previous blog,
Keshav, S. (1997). An engineering approach to computer networking. Addison-Wesley
is also a useful text for the more protocol-oriented parts of this course.


Finally, if you are interested in the optimisation framework, then I recommend some of Frank Kelly's papers from the statslab - for example, this one briefly menions why we might take the sum of willing to pay times log of rates
w ln(x) 
as the  network view of the utility function..
.Fairness and stability of end-to-end congestion control

The two plots of functions of u_l (link utilisation of link l) are for
two different cost functions where the first one is exp(u_l)
and the second is n*(u_l^n) where n is a parameter (not the number of users - its just to generalise the function to a class of functions whose steepness/convexity can be varied by increasing n!

Principles of Communications 2012 up to L12 - week 5

Just made a hash of control theory....need to re-hash on monday to clarify- slides updated to show how G1 and G2 fit - see slide 23 on
control theory slides

Main point was to go through the decomposition of the control+gain+feedback
into separate boxes, to allow one to play with different controllers, and then re-compose to check the final transfer function for stability and for steady state error:- (slide update also fixes a couple of typos_

Hence, need to expand all the steps in the worked example with the video server and setpoint cpu load monitor

Will re-do on monday w/ additional steps for deriving the overall tranfer function in the s domain for the two different controllers of the CPU system whose basic (G0) behaviour is an integrator in time domain, so 1/s in Laplace transform/freq domain. this applies to the setpoint (Us) and the Mean Completion rate (Rc), so that when we look at these in the transform domain, we have the integral of them over time, which gives us a 1/s in the terms
for Us(s) -> Us/s and Rc(s) -> Rc/s


Looking at the slide where we first encounter G1 and G2, this is basically the design of a ne wsystem where G2 is what G0 was before (i.e. the video server modelled as an integrating service over time, but now with a new, regulated/controlled input), plus G2, which is the controller C, which has inputs which are the setpoint, and the demand, and outputs the new accepted/admitted flows which now go as inputs into our G2 (what was G0) who has an additional input, Rc(s) (or Rc/s).....

G0 = 1/s
Now add an (as yet unspecified) controller, C
and expand to the two stages, G1 and G2:

G1 = C.G0 / (1 + C.G0)
hence G1 = C/s (1+C/s) = C / (s + C)
G2 = G0 / (1 + C.G0)
hence G2 = 1/s / (1 + C/s) = 1 / (s + C)

Now our overall system is the composition of G1+G2, with
G1 handling the input decision, and G2 taking that plus the completion rate of work:
U(s) = G1.Uset/s + G2.Rc

so proportional controller just as C = K
and proportional-integral (PI) controller has C = K(1 + Ki/s)
where K and Ki are the constants to be chosen by designer:)


U(s) = C.Uset/s.(s+C)    + Rc / (s+C)       1.
which with C=K
 ( a proportional controller), gives
U(s) = K.Uset/s.(s+K) + Rc / (s+K)
Proportional controller:
stability: pole at s=-K, therefore ok.
error: lim of s.U(s)
= s . [K.Uset/s.(s+K) + Rc(s) / (s+K) ]
assume Rc(s) = Rc/s (i.e. Rc doesn't vary fast compared with feedback loop time)
= s.  [K.Uset/s.(s+K) + Rc /s.(s+K) ]
= [ K.Uset - R / (s+K) ]
which as s->0, goes to
Uset - Rc/K - so the error is Rc/K

For PI controller, put C = K(1 + Ki/s) in to 1 instead


G1=C G0 / (1 + C G0)
G2= G0 / (1 + C G0)

C = K(1+Ki/s)
G0 = 1/s

so G1 = K/s(1+Ki/s) / (1 +  K/s(1+Ki/s)) (* top and bottom by s^2)
 = (Ks + KKi) / (s^2 + Ks + KKi)

G2 = 1/s / (1 +  K/s(1+Ki/s)) (* top and bottom by s^2)
 = s / (s^2 + Ks + KKi)

response = Us G1 / s + Rc / s G2


....need to do this in tex:)

If people are interested in the stability of TCP's AIMD, then I have to say that its complex - to my knowledge, no-one has shown it for a network with FIFO "drop tail" queues, and heterogeneous RTTs - however, with an Active Queue Management system (like RED - see upcoming lectures on Scheduling and QUeue Management) there are some solutions - see
1. paganini's proof
and
2. INRIA work

Principles of Communications 2012 up to L10 - week 4

Made Errors:)

About to Start Flow Control. (Feedback welcome:)

Asked what books cover the non math component of PoC - answer is on the course web page - best reference is the other book by Keshav (An Engineering Approach to Computer Networking), which should be in most (college/lab) libraries.

Asked where to find proof of the bound on diameter of Erdos-Renyi graph - refer to this review/tutorial paper:
http://www.barabasilab.com/pubs/CCNR-ALB_Publications/200201-30_RevModernPhys-StatisticalMech/200201-30_RevModernPhys-StatisticalMech.pdf

Principles of Communications 2012 up to L7 - week 3

Couple of errata on graphs :

1.
s/walk/path/ in one slide (i.e. whether a vertex can appear more than once!)
2.
p<3 -="-" algorithm="algorithm" dar="dar" does="does" finding="finding" fraction="fraction" good="good" greedy="greedy" high="high" in="in" is="is" make="make" of="of" p="p" probability.="probability." property="property" succeed="succeed" sure="sure" that="that" to="to" triangles="triangles" with="with">
progress:
finished LS&DV Routing -
Coming Monday,  wil complete Multicast, Mobile
Wednesday, errors
Friday, Flow Control& Start on Control Theory

Principles of Communications 2012 up to L4 - week 2

Today, started Graph Theory (well, background at least)
Monday, will pick up on graph properties, random graphs, small world/clustering and searching. Then Next week, should cover most the Routing area.

For further edification and amusement,

Cambridge Networks Network

http://www.cnn.group.cam.ac.uk/

Erdos Bacon number
http://en.wikipedia.org/wiki/Erd%C5%91s%E2%80%93Bacon_number

Erdos zombies:
http://xkcd.com/599/

kirchoff geek traps
http://xkcd.com/356/

Principles of Communications 2012 L1 - week 1/2!

oops #1 - failed to spot 2nd box of lecture handouts - so they will be available on monday - apologies - mea culpa (not the admin fault)

oops #2 - 1kbps on the net is 1000 bps, because the k is from the sample rate (so a KHz refers to 1000 samples a second) but 1k bits (or bytes) in computer speak refers to 1024 bits (or bytes) coz its 2^10 memory locations or whatever

so being pedantic and wrong on slide 9 is a bit embarassing:)

Michaelmas Term 2012 - Start of Term & IET President's Inaugural Speech

Today (well this week) term kicks off and I'm teaching Principles of Communications to Part II, and Network Architecture to Part III and MPhil students.

Meanwhile, last night, I attended Andy Hopper's really excellent speech at the IET in London, where a host of stars turned out, including an MP who is an engineer (and female) and other luminaries to hear his very very good words on how to make things innovative - he used a lot of nice use cases, taken from his experience and others nearby (ARM, RealVNC, Xen and of course UbiSense) but he also made some very good high level points about UK industry (under investing in Research) and how to fix that, and about Universities (do LOTS of innnovation and let the market pick) and about government (stop the REF now - it served its purpose and is past its sell by date and actually probably damaging things now). All good stuff - I dn't want to stand up and ask a question but if I had, I'd have asked him about the new stuff we're doing with raspberry pi, Digital Life Foundation, OcamlLabs, and Computing at School, all of which have extreme "business model" approaches -
See IET TV of Andy Hopper's talk

might have been a good place to name check serial entrepreneurs like Ian Pratt and Keir Fraser (Bromium and Convergent.IO, post xen), too....next time:)

Two ideas
1. cheap opthalmoscope made out of toy microscope & android camera phone & some simple DSP code (on the phone
2. remote control for hearing aid using ultrasonic sound from the android phone (speaker can go to frequencies higher than you can hear, but hearing aid can hear them) so you can reset programmes for different environments
(both for me:)

3. Must talk to CCNx folks about Andrea lo Pumo's work on policy routes for content centric networking - ok, so we are ignoring "content value chain" but I think its more than just "cache flow" versus "packet flow" :)

Back to school.....

testbeds - its not what they are, its who they are

my experiences of testbeds (arpanet, satnet, dartnet, planetlab, onelab, umbrella, gini, etc etc) is that it isn't so much the technology and budget, but the cohort of people engaged that mark out a testbed for success or failure or damp squib.

but that's just my experience - what do other people say?

Principles of Communications - Week 7 - Nov 25

FInished COntention Networks, and Shared Media/Multihop Capacity, and just started Traffic Management.

Goal is to complete traffic management on Monday Nov 28th. And wrap there- LP is a step too far.

Will update on monday to describe which components are non-examinable. In general, see
the contents for the course,
here

Principles of Communications - Week 6 - Nov 18

Today, I wil finish the section on switching (covering routers as well as TDB and Space switch designs) - since we have "Silicon Valley comes to Cambridge" in the building today, its worth talking about the link between
Cisco, Sun Microsystems and Stanford University, then we can also mention the link with Granite and Google (Dave Cheriton) and Arista. Also, the early Sun 3 and CIscos were same M68000 multibus motherboard + ether*n + T1 serial line....alas, only sun ran BSD Unix, whereas Cisco wrote a low level executive called IOS (nowhere near as innovative as 3 years later when Apple wrote an Operating System for the iPhone and called it IOS...)....if routers had run BSD unix, the Internet might be a better place:-)

Next week, we;ll cover contention networks (shared media0 as well as capacity of multihop radio nets.

Principles of Communications - Week 5 - Nov 11

Finished Control Theory
and Optimzation Framework for IP/TCP networks

Next: Monday 14: Scheduling and possibly might get to Switching by next friday (18th).

Principles of Communications - Week 4 - Nov 4

Reached end of flow control

couple of very insightful questions about
1) reduce buffering in IP routers
ii) play with RTT by delaying acks in smart phones...to help redux negative impact of buffer bloat!

Monday - control theory
wed/fri optimization.

Principles of Communications - Week 3 - Oct 28

Got as far as channel model of errors after modulation/coding, and a basic intro to Shannon. [New copy of channel slides just posted that fixes a couple of errata pointed out by students - note, that specific material is non-examinable]

Starting Oct 31, Will finish errors, then move on to flow and congestion control.

Principles of Communications Week 2 2011

Today (21.10.2011), got as far as LS routing (having rather messed up explanation of DV).
Monday, will repair DV, and then cover
multicast and mobile.

I need to re-check the DV count to inf example isn't wrong....

Then wed/fri 26/28 cover errors...hopefully with less errors...

Principles of Communications Week 1 2011

I've just got up to the representation of graphs today (14.10.11) - see
lecture 4 including kirchoff - Monday, we'll do Erdos and Bacon.

SO we've covered Systems and Layers mainly, if you want to look at Supervision topics...

Escher Circuits and Perpetual Immotion

Followers of my blog will be aware of my discovery of circular wind patterns across Cambridge, that cyclists have suspected are always against them. For several years, I have taken advantage of this, and make my journeys out of phase with other cyclists
thus getting blown along in the right direction "for free".

Accidentally over the last couple of weeks I have discovered another phenomenon in Cambridge, which requires you to travel out of phase with the wind, but when there isn't any, and that is that there are certain routes which are down hill all the way there and back again. I refer to these routes as Escher Circuits after the great MC Escher's famous eternally descending waterfall (and the stairs in the library in the Name of the Rose of course, by the oft-copied inimitable Umberto Eco).

The existence of Escher Circuits has long been disputed since first suggested by the theoretical natural philosopher, H.King in his paper "Not enough string". The possible existence of Macro-circuits, measurable using crude mechanical devices was put forward in the seminal work by A. Hitchcock "Just enough Rope". But until now, these were mere hypotheses.

Of course, those of you who are students of natural philosophy will be aware that a naive analysis would dismiss such theories as contrary to the idea of conservation of energy, for surely, the cyclist pursing her cyclic route, would ever gain momentum.
However, my observations have shown that the real-world phenomenon is more subtle than the mind of man. While it is the case that the journey from A to B is downhill, as is the journey from B to A, nature, in her wisdom, has arranged the dimensions so that one arrives at A after a trip to B, at the same time that one started. Hence, time has flown backwards. And this is true no matter where you measure the progress of time - for any subset of the journey, for the return part, while you are on the 2D segment of the Escher circuit, time flows in the opposite direction, so you can take no advantage of the accumulated energy at all. A new branch of relativistic invariants must be supposed, not special, or general, but adversarial.

Thus Escher Circuits are rare, and exhibit adversarial relativistic time dilution.
Now, it is the case that one can make use of the properties, but only for a rather narrow application, and that is when one needs to use no energy to stand still in the face of a headwind. Of course, the hands of time and the wheels of the bike make the same amount of progress, which is to say, none at all. But you can get plenty of uninterrupted thinking done, which, after all, is the main reason we cycle everywhere in Cambridge anyhow, isn't it?

Week 7 - to Nov 26 - Got to Traffic Management.

Looks like we won't make it to the
Optimisation Theory and LP material this year -

I will wrap up on Monday 29th Nov
with last part of Traffic Management,
and an overview of what I've covered.

That will be the last lecture for Principles of Communications.

Students that are very keen can read the slide-ware on Optimisation and on LP - I am happy to answer questions on it too.

Students interested in the lower levels of physical/link layer may want to take the Digital SIgnal Processing course by Markus Kuhn next term (see here. Students interested in networking performance (and systems in general) may well want to go to Richard GIbbens' course on Computer Systems Modelling which covers a number of these topics in more theoretical depth. If really keen, please sign up for the new Part III, which will be running next year.

Note that next year, Information theory will be taught separately (again), which may make the amount of theory material in PrincComm slightly more tractable.

week 6 - to Nov 19 - Got to end of Switching

Next week, to cover
Shared Media
Capacity of Multihop net
Traffic Management

Then final week, will ust get to do optimisation and LP hopefully:)

n.b. to supervisors and students:- i've put a couple more links to some online information about
control theory, graph theory and some of the sources have worked problems...
see slides page for course
http://www.cl.cam.ac.uk/teaching/1011/PrincComm/ppt/

Week 5 - Nov 12 - end with Control Theory

Today, noticed that the wikipedia article on this is pretty good, but most especially nice is that it cites an 1868 Royal Society paper from the Royal Society by James Clerk Maxwell, which not only mentions Mr Watt's Steam Engine, but Mr J Thomson's experiments (noting that our building is between JJ Thomson Avenue and James Clerk Maxwell Road:)

Next week, we should cover
Scheduling
Switching
Shared Media Access


[The paper above also mentions a Mr Siemens!]

Week 4 Friday November 5th - Principles of Communications Progress

Today, we'll cover Queueing Theory. So that completes network layer stuff
(graphs, routing, errors, queueing)

Note in the printed (and old online pdf) queuing theory slides, there was a font error on some slides with \rho being rendered as ~n.
I've fixed it on the PDFs online (its ok in the ppt). apologies (again).

Next week we start on Flow Control, and hopefully get up to control theory.

Principles of Communications - End of Week 3

I have just about got to the end of routing
(having fixed, i think, some bugs in the distance vector worked example) -

next week
monday, wrap up multicast/mobile routing
then

error control
queueing
and maybe start flow control

Principles of Communications end of (full) week 2.

Today, I'll finish the graph theory lectures, covering social networks, small world nets, random graphs, alpha/beta and spreading/search.

So we'll have done:
# Introduction1
# Systems
# Layering
# Information Theory
On this topic, John Daugman's notes are great
# Channel Capacity
(not Modulation - this is on hold to end in case we have time)
# Graph Theory
# Social Networks+

On the last topic, this book on Small Worlds by Duncan Watts is a nice read. Another good book on the topic covers more about flows over such networks (information or diseases for example) is
Connected, by Nicholas A. Christakis and James H. Fowler

That means from monday (and most of next week, oct 25,27,29) we're doing Routing.
If things go to schedule, then subsequent week (nov 1,3,5) will be Error Contol, Queueing Theory and Flow Control.

Principles of Communications...end of first week (15.10.2010)

Should just have got up to first slide set on Information Theory (Entropy)
Monday 18th will start on Shannon - by 22.10.10 hope to get to Graph Theory.

Have just updated online slides (1up and 6up should all print ok now, fingers crossed:)

information theory - live example

powerpoint for lecture on information theory+colour printer -> slides without equations:(

powerpoint for lecture on information theory+mono printer -> slides with equations:)

ergo, colour printer driver is an erasure channel with memory and rather non random behaviour and information rate is massively reduced :-(

pushing this as an example for explaining shannon is a bit of a stretch...in the sense that the "physical channel" is the printer and the colour printer should have more capacity in some sense, although I suppose the point is that the "noise" process" is an erasure channel that removes (say) bytes that code yellow but not bits that code white/black...