An understanding of ISP-level filtering, by way of an analogy

I was once again taken aback by Professor Clive Hamilton’s inability to refrain from hypocrisy, or to construct a logical argument in his piece in Australian IT from 16 Feb. Perhaps even sadder was the number of people agreeing with Hamilton’s “argument”, without actually understanding the technology. Since I believe that education is a cure for ignorance (sadly, though there is no cure for stupidity, so Hamilton himself would appear to be beyond help) I thought it might be instructive for the laymen out there to get an understanding of what this filter would actually entail in an analogous situation. Remember, though, that analogies are used to illustrate, not to prove, so this is intended to provide an understandable overview of the technology involved, not to advocate for or against the filter (a topic which I have covered and will cover separately). Take note, Hamilton, this is the correct use of analogy.

Imagine, for a moment, that you are back in high school. There’s a new teacher around with some progressive views on how classes should be taught. Let’s make him a maths teacher, since, let’s face it, the internet is a lot like high school maths: everybody uses it, but only the nerds care about how it actually works. In deference to both Dead Poets Society and my actual high school maths teacher, let’s call our new friend Mr Williams.

Now, Mr Williams’ views on teaching differ greatly from the traditional methods employed by the history teacher Mr Bartlett down the hall. Mr Bartlett has always been old-school in his approach: he tells the students the information, and they write it down (or sleep through it). It’s very much a unidirectional approach: teacher imparts knowledge to students. Mr Williams, on the other hand, favours a more distributed approach: students work together on the problems, and Mr Williams will assist if and when it is needed. The students impart knowledge to each other, but there’s always a more definitive reference at hand. (As an aside, I intend no disrespect to History as a subject, nor to my history teacher, whose name was not Mr Bartlett.)

Imagine now that, in order to facilitate his new teaching method, Mr Williams allows students to pass notes to one another. All in all, this works pretty well and most of the students keep their notes on topic and only the occasional notes are passed which are, though not necessarily inappropriate, certainly more social in content. Mr Williams figures that this is a fair trade-off as long as the students are performing to the best of their abilities, so he doesn’t monitor the content of the notes.

Unfortunately, the headmaster of the school, Mr Conroy (but you can call him ‘Sir’), comes from the old school of teaching, like Mr Bartlett, and doesn’t really understand how Mr Williams’ methods work. To be honest, he is a little unsettled by Mr Williams’ methods since it seems largely uncontrolled — there is no indication that the notes being passed are relevant to the work at hand. He is willing to conceded, however, that Mr Williams has both a good rapport with the students, and also seems to have a good success rate.

Mr Conroy also dislikes Mr Williams’ methods because there is a lack of direct responsibility: if a student comes forth complaining that Mr Bartlett has said something inappropriate in history class, he can talk to Mr Bartlett directly to resolve the issue. In Mr Williams’ class, however, were a student to complain about the content of another student’s note, there would be no way to verify this with Mr Williams; indeed, it may not be possible to verify it even with the student(s) involved, as the notes are frequently destroyed after they have been read.

In an attempt to impose some level of control over the note-passing (so that nothing inappropriate or off-topic may be passed), Mr Conroy approaches Mr Williams with a possible solution: the students can continue to pass notes, but Mr Williams must personally inspect each note to ensure that it is neither inappropriate nor off-topic.

Mr Conroy’s system works reasonably well when only a handful of students is passing notes: each note takes a little longer to get to its intended recipient, but the notes are all on-topic, and it all seems very good. Mr Williams’ class is, however, very popular, so instead of just a handful of students passing notes, suddenly there is a significant number, more than Mr Williams can hope to monitor on his own. And the communication is not always back and forth between the same two people: students are often passing notes to five or six other students at a time. Mr Williams is hard-pressed to keep on top of all these notes, so he faces a dilemma: does he inspect every note carefully to ensure that no notes which are off-topic are passed around; or does he just glance at each note quickly to check for blatantly off-topic notes? Obviously, the most effective way to stop problematic notes (and note-passers) is to stop the whole note-passing structure in the first place, but this doesn’t sit well with Mr Williams’, who feels that the innovative structure teaches the students a lot more.

Mr Williams instead opts for the latter: a quick check of the notes as they come through, so that he has minimal impact on the system. Unfortunately, Katie, who is generally a good student, signs all her notes, regardless of the topic with ‘<3 Katie xox’, and since Mr Williams is only glancing at the notes rather than reading them, the note looks suspect, so her notes keep getting blocked whether or not there is a valid reason.

Other students have developed a system to get around the problem: they start passing all their notes in code, so that Mr Williams cannot tell if it is on- or off-topic. Mr Williams is a good teacher who trusts his students, so he assumes that the coded messages must be legitimate. (Mr Bartlett, on the other hand, insists that the fact that it is coded must mean that the note is suspect.) The system works, however, and quickly spreads, as more and more students develop code systems to pass notes. Mr Williams is unable to decipher what any of the notes says, since each student insists that any note sent to him must use his cypher so that he will be able to read it quickly. Naturally, when he passes a note back, he is polite enough to use the other student’s cypher to reply.

Still other students have bypassed the note system altogether, instead opting for a new method: talking. Since the students still look up to Mr Williams and do not blame him personally for the harsh regime forced upon all of them (they understand that Mr Conroy just doesn’t understand Mr Williams’ teaching methods), they only talk quietly, and do so in short bursts. That way, Mr Williams can only determine if their conversation is on- or off-topic after it is over.

Of course, Mr Conroy is not happy about the students talking in Mr Williams’ class, so he offers Mr Williams another choice: monitor the conversations more closely, or ban the students from talking altogether. Mr Williams, advocate for the students that he is, politely agrees to monitor the conversations more closely, albeit with a great deal of reservation. So what do the students do? They start talking in their respective codes, so Mr Williams cannot determine the content of the conversation.

So Mr Williams’ popular maths class (oxymoron?) has gone from an open and honest communication system to a system where everyone is paranoid about being caught talking off-topic or inappropriately, Mr Williams himself is powerless to actually enforce any of the rules laid down by Mr Conroy, and Mr Conroy has made himself the most hated headmaster in the history of the school.

Now, for those who could not follow the analogy too closely:

  • Mr Williams represents the ISPs.
  • Mr Bartlett represents traditional forms of media (print, television, etc.).

  • Passing notes represents HTTP (or XHR in Web 2.0), the means by which information is communicated to/from webpages.
  • Coded messages represent SSL encryption over HTTP (HTTPS).
  • Talking represents BitTorrent traffic.
  • Talking in code represent SSL encryption on BitTorrent traffic.
  • If you couldn’t figure out who or what Mr Conroy represents, you’re already lost.

Like any analogy, it’s not a perfect representation of the infrastructure. (For example, BitTorrent exists side-by-side with HTTP and is not necessarily used to get around the filter. I used it here because of Senator Conroy’s comments that the filter would now include BT traffic, and I wished to highlight the problems associated therewith.) It does, however, give some basic idea of how the filter works, and also how hard it is to implement effectively.


~ by MattR on February 19, 2009.

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