Posts by Matthew Newstead

Obviously....

This was a heddlu-copter !

GSM / Timing Advance 101

GSM uses a cyclical system whereby customers calls are all digitally sampled in turn. customer 1, then 2, then 3 etc... then back to customer 1 again. this all happens in a blink of an eye, so that customers can't detect the 'break' between each time their call is actually using a 'timeslot'.

GSM then gets clever... imagine you are standing by the BTS (phone mast) with your mate, talking to them on the phone (as you do), but then they dash off to Maccy D's 1km away.

You started off both covered by the same 'cell', and the BTS will use something called timing advance, whereby your mates signal is progressively broadcast fractions of a second sooner, to compensate far how far they are moving away from the BTS - this ensures that the above mentioned cyclical system remains intact, with customer 1 remaining as customer 1 within the cycle, and your mate say as customer 4... in a nutshell, timing advance tops your mates timeslot from running into customer 5's allocated timeslot.

As timing advance technology is based on the speed of radio waves through air, it can be used to find how far you are from the BTS. the frequency of this distance checking signal is such that GSM Timing advance maps you into one of several 500m 'distance zones' - so for your mate 1km away, their signal would have been broadcast one to two timing advance periods earlier than it would have been if they were still stood by you.

still awake?

So - you then get B-A listing where your phone maps out ALL it's surrounding BTS's, and figures out how far away it is from each. it's clever brain translates this into a trigonometric map showing roughly where you are.

HOWEVER the big no-no with this 'precision' shopping centre system is that the timeslot advance and B-A listing can only overlay several 500m zones over each other to build a probability map of which location you're actually in. You would need loads and loads of 'listening' equipment installed probably all the way out to 2km away from the shopping centre to get enough overlaid 500m zones to properly judge what individual phones are doing, This would require wayleaves and third party clauses with so many landlords etc for the install of 'black chopper kit' upon their rooftops that it would become unfeasible for a shopping centre to fund.

so - my conclusion? it's not using GSM timing to figure out where you are

Batfink

This actually reminds me of the star trek film in which captain kirk hacks the attack simulation to change the outcome.

makes me wonder, if this is an uber network, but the first interface layer (which actual human's use) is based on (say) DARPA buying up a few thousand dell laptops for it's staff, then isn't it like putting a Lambo engine into a 1970's trabant?

anyway, the physical layer is the weak spot - cyber terrorist teams would be hard pressed to do better than digging up the roads by each other's data centres to cut the fibre lines. remember the amount of financial damage done when a BT exchange in Manchester had a fire a few years ago?

My firewall is like a shield of steel :)

Crap my comms have gone off.......

mine's the hi-vis jacket, with hard hat and pneumatic drill ;)

Match of the Day!

Anti Competitive?

The iPlayer doesn't host 'Match of the Day' whatsoever!!

Why? because the BBC can only share the TV viewing rights of football matches for up to 24 hours before Sky etc claw them back. The BBC decided that the iPlayer would be in breach of this.

Plainly, the Beeb have done everything to be complicit with competition law, and in my mind, only Youtube is a direct 'competitor' for video delivery to your computer/mobile.

Would be nice to have a comment from the Youtube camp on what they make of the iPlayer