Friday, November 25, 2011

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,

Friday, November 18, 2011

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.

Friday, November 11, 2011

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).

Friday, November 04, 2011

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 help redux negative impact of buffer bloat!

Monday - control theory
wed/fri optimization.

Sunday, October 30, 2011

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.

Friday, October 21, 2011

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...

Friday, October 14, 2011

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...

Wednesday, January 19, 2011

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?