90,000,000,000
2009-02-25
A while ago there was an O2 (or is it O2; can't say I'd really paid attention) advert on, advertising some manner of 'friends and family' type scheme. It annoyed me at the time, enough to write the following post which has sat in my drafts ever since. Although it's not a shining example of information-age journalism, it's also no worse than most of the other junk I post, so I thought I'd let it out.
It may help if you realise that I was a systems manager in a telecoms company at the time.
It begins with the line:
Yes, well done, there are 90 billion eleven-digit numbers, and indeed ten billion more. (I'm assuming they mean short-form billions, i.e. 109).
I suppose that's the strangest part of the statement, although it's not the most misleading bit.
See, the number of eleven-digit numbers really isn't relevant to the UK dialling plan. First of all, all of the eleven-digit numbers begin with zero (in effect it's there simply to signify that this isn't a local number or an access code). Straight away we're down to ten billion.
The second digit of a national number is never zero. In the same way that a single zero at the beginning of a UK number marks it as belonging to the national dial plan, two zeroes indicates that it belongs to the international dial plan.
Next, although most ranges now include at least some allocation, there are very few assigned numbers in 03 and 04, and not all that many in 05. Some ranges that are in use haven't had all their subranges assigned yet. 070 is 'personal numbers' (until Ofcom gets rid of them [about time]) and 075 and up are assigned to mobiles and pagers, but the bits in between are empty. If memory serves 020 (which is certainly the most populous part of 02) only has allocations in 0200, 0203, 0207 and 0208.
There are still some ten-digit numbers in service, especially in the 05 and 08 ranges. Since the dialling plan is hierarchical (a number can't be a left substring of another) each ten-digit number still in service removes ten potential eleven-digit numbers.
Local numbers never begin with 1 or 0 (1 is reserved for the so-called 'access codes' - including alternative carriers, operators and things but now more commonly used for directory enquiries - and 0 signifies the start of a national number). Although the length of local numbers varies this takes a significant chunk out of the ones available in each range.
Most restrictive of all, ultimately, is that near the end the husky Northern man appears to say that your 'friends' must be O(2|2) numbers. Mobile numbers are normally assigned in blocks of one million (because mobile ranges don't support 'local' dialling, they can have zeroes wherever they like) and although I can't be bothered to check how many Otwo has, I doubt it's more than dozens.
A few dozen million is orders of magnitude less than ninety billion.
It may help if you realise that I was a systems manager in a telecoms company at the time.
It begins with the line:
There are 90 billion eleven-digit numbers
Yes, well done, there are 90 billion eleven-digit numbers, and indeed ten billion more. (I'm assuming they mean short-form billions, i.e. 109).
I suppose that's the strangest part of the statement, although it's not the most misleading bit.
See, the number of eleven-digit numbers really isn't relevant to the UK dialling plan. First of all, all of the eleven-digit numbers begin with zero (in effect it's there simply to signify that this isn't a local number or an access code). Straight away we're down to ten billion.
The second digit of a national number is never zero. In the same way that a single zero at the beginning of a UK number marks it as belonging to the national dial plan, two zeroes indicates that it belongs to the international dial plan.
Next, although most ranges now include at least some allocation, there are very few assigned numbers in 03 and 04, and not all that many in 05. Some ranges that are in use haven't had all their subranges assigned yet. 070 is 'personal numbers' (until Ofcom gets rid of them [about time]) and 075 and up are assigned to mobiles and pagers, but the bits in between are empty. If memory serves 020 (which is certainly the most populous part of 02) only has allocations in 0200, 0203, 0207 and 0208.
There are still some ten-digit numbers in service, especially in the 05 and 08 ranges. Since the dialling plan is hierarchical (a number can't be a left substring of another) each ten-digit number still in service removes ten potential eleven-digit numbers.
Local numbers never begin with 1 or 0 (1 is reserved for the so-called 'access codes' - including alternative carriers, operators and things but now more commonly used for directory enquiries - and 0 signifies the start of a national number). Although the length of local numbers varies this takes a significant chunk out of the ones available in each range.
Most restrictive of all, ultimately, is that near the end the husky Northern man appears to say that your 'friends' must be O(2|2) numbers. Mobile numbers are normally assigned in blocks of one million (because mobile ranges don't support 'local' dialling, they can have zeroes wherever they like) and although I can't be bothered to check how many Otwo has, I doubt it's more than dozens.
A few dozen million is orders of magnitude less than ninety billion.
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