ietf
[Top] [All Lists]

Re: IPv6: Past mistakes repeated?

2000-05-09 17:10:02
anthony(_at_)atkielski(_dot_)com (Anthony Atkielski)  wrote on 24.04.00 in 
<00db01bfae2b$eec52ef0$0a00000a(_at_)wanadoo(_dot_)fr>:

That is mostly because the telco(s) tried to impose a fixed address length
on a scheme that really should have remained variable.  Telephone numbers
overseas are truly variable.  When you dial 011+3, the remaining digits can
be anywhere from one to a thousand.  The local end just stores them all

Actually, no, it can't. I think the original limit was something like 12  
digits, and it's something like 20 now, especially with ISDN.

That's what ITU says, anyway, and what all the makers of telephone  
hardware use.

And enough places have switched to better than 12 digits so - guess what -  
all the telcos are still doing their best to keep numbers down to 12  
digits. Mine's 11 currently (49-251-xxxxxx). North America uses 11 (1-xxx- 
xxx-xxxx). Workplace - a newer assignment - theoretically has 12 (49-251- 
xxxxxx-x) but actually uses up to 14 (49-251-xxxxxx-xxx), because we need  
more than the 20 different numbers we'd otherwise get.

Oh, more than those 12 do get used. For example, if I want to dial a North  
American number with provider selection ...

010xx-001-xxx-xxx-xxxx

... and that doesn't count a possible 0 to escape the local PBX. Which  
makes it 19 digits. Dangerously close to the limit.

I do know a PBX that crashes when you send it numbers longer than 20  
digits. From a major PBX producer.

But if you use a truly variable scheme, you don't have to assign anything at
all.

No such scheme seems to exist. At least not in wide use.

Say Company X wants some addresses, and it is in an area where all addresses
start with 9482.  You just add some digits, tell them what they are, and
they can add as many addresses as they want behind those digits.  All you
have to care about is that 94825xxxxx gets routed to Company X.  The rest of
the address allocation is their business.  They might have just two digits
on the end, or they might have forty.

Except they cannot actually *use* forty. See above.

With fixed-length addresses, you're in trouble as soon as you make an
assignment.

And all addresses in actual practical use are either fixed length, or  
variable but limited length (which actually gives you less room than the  
same limit with fixed length).

You might assign 94820000 through 94829999 to Company X.  The
problem is that, if Company X needs only 200 addresses, you've wasted 9800
addresses, and you can't give them to anyone else.  Conversely, if Company X
ever needs more than 10000 addresses, you have to completely reallocate
everything, or fragment their address range.  Either way, you lose.

And that's exactly how the phone system works.


MfG Kai



<Prev in Thread] Current Thread [Next in Thread>