[asterisk-users] Matching *, + and # in the dialplan

[Karl Fife]

On Thu, 16 Oct 2008 11:47:15 -0500, "Tilghman Lesher"
<tilghman at mail.jeffandtilghman.com> said:
> 
> If you could explain what ISN is, that might help.

an ISN, stands for ITAD Subscriber Number, which in turn stands for
'Internet Telephony Administrative Domain Subscriber Number'. 
Essentially it is a very clever way of resolving numeric strings (easily
be entered on a twelve-key numeric keypad) to full SIP uri's. 

for example 1234 at sip.ucla.edu would be hard to enter on a telephone
keypad.  ISN (available through Freenum.org) offers a solution.  

sip.ucla.edu is assigned the resolvable numeric string '269'.  The
extension '1234' is already numeric.  The @ sign in the SIP uri is
replaced by *.  

1234*296 is dialed on the keypad, which resolves to 1234 at sip.ucla.edu. 
The call is completed bypassing the PSTN. 

Back to the main idea:

The ISN is unambiguous.  There are no other dial strings that have a
single * somewhere between position 2 and length-3

It seems silly and kludgey to have to use an ISN prefix to recognize the
ISN, so that it can be sent to the resolver, so that it can be routed,
but I suspect that there's no way to differentiate that format with the
parser as it currently functions.

-Karl