Principles of Communications Week 1 8/10/2025

I'll be noting progress and also adding occasional related reading/ and corrections on this blog.

If you want to revise anything to warm up for the course, I suggest last year's Computer Networks course should be a quick re-read (e..g on routing ) A fun review of 40+ years of the Internet

This week we'll just make a start on routing. If you want to review just link-state (useful to understand fibbing (lecture 2), then video on link-state routing is very thorough.

Please do ask questions - two good ones today were

Q1 -so there's only one BGP for the whole world- yes, to have multiple Inter-domain routing protocols would mean every borader router might have to implement all of them (sort of "polyglot") which isn't impossible, but would be a nightmare of complexity to manage and operationally hard to understand - although these days, maybe we could use AI tools to manage it?

Q2 - isn't source routing a bit like virtual circuits - excellent question - yes&no - see later in MPLS where we see source routing is a way to manage VCs underlying IP potentially, but it can also be dynamic (well, more so than hard virtual circuit setup)

For fun, you might find this discussion on why LLMs aren't much use for networking, mostly interesting - video recording of panel session

Reference requested for Glossary of Terms: from ISOC

Some acronyms come from the 7 layer model of the communications stack including terms like PHY (short for physical, so not really an acronym).

tl;didn't red

Every year for the last 25 years, I've graded undergrad exam scripts in Cambridge. 

Every year, I reach for the same red ballpoint pen as the pile of scripts lands, wummppphh, on my desk. So this year, the ink pretty much ran out on that pen.

Is this a sign? Well, yes, it suggests biros are really quite well made, given how long they last, and whatever they use for ink has amazing longevity (as anyone knows who has had one leak in their white shirt pocket).

But it made me think - is there a lesson about the length and quality of an academic career that could be combined in this one metric: How long does that biro last?

The argument goes thus: the better you teach, the less red ink you have to use to give feedback (and grades) to students. so you are motivated to teach well (you can't game this by just setting easier questions, because there are second examiners and an exam board and all sorts of statistical checks across each student, each cohort, each paper etc etc). 

On arrival in cambridge, i suggest we give each university teaching officer a single red biro. and they get to retire (at least from teaching) when it runs out.

On a sample of one,  this roughly corresponds with my current expected retirement age (if you accept Cambridge's illegal EJRA arguments - but that's another story).

Fair?

(To note, I'm also attending an alumni dinner at Trinity College this year on the 50th anniversary of Matriculating (admission to Cambridge as a NatSci undergraduate). I also looked at my academic diary and note its 40 years since I formally started teaching (at UCL initially). I also recently met a 3rdyr PhD student whose advisor was advised by one of my past PhD students, so that's 4 generations of PhDs in one place - which kind of makes sense, if you think how long it takes from starting academic study to getting to the point you could advise others, then a generation is roughly a decade. so 4 decades of red ink.