System information

Got ISN?
The heart of the freenum.org concept is the ITAD Subscriber Number (ISN). The ISN
is a numeric string that is composed of an extension number on your system, an asterisk
character separator (*),
‖
and a number that is unique to your organization called an IP
Telephony Administrative Domain (ITAD) number. The advantage of the ISN is that
it can be dialed from any telephone. An ISN would look something like this:
0*1273
which would represent extension zero at ITAD 1273
#
and would resolve to sip:0@
shifteight.org.
You control your extension numbers (everything to the left of the *). Your ITAD is
assigned by IANA (the same organization that controls IP and MAC addresses).
Once your ITAD is assigned, you will be able to publish ISNs on your website, or on
business cards, or wherever you would normally publish phone numbers. Any system
capable of dialing ISNs will allow its users to call you by dialing your ISN. Calls will be
routed directly between the two systems using the SIP URI that freenum.org returns.
ITAD Subscriber Numbers (ISNs)
The ISN does not replace a SIP URI, but rather complements it by allowing dialing of
VoIP numbers using only characters found on a standard telephone dialpad. In order
to resolve an ISN into a valid URI, the DNS system will query the ISN against the
freenum.org domain. Any DNS lookup against your ISN will return a URI that defines
how your system expects to receive calls to that ISN.
*
Management of Internet Numbering
The Internet Assigned Numbers Authority (IANA) is the body responsible for managing
any numbering system that exists as a result of an RFC that requires a numerical da-
tabase of some kind. The most well-known responsibility of IANA is the delegation of
IP addresses to the five Regional Internet Registries that control all of the public IP
addresses on the planet.
†
These organizations are responsible for the assignment of
IP addresses within their regions.
‖ This character has nothing to do with the software that is the subject of this book; it simply refers to the *
that is on the dialpad of every telephone. We wonder what might have been if, instead of Asterisk, Mark
Spencer had decided to call his creation Octothorpe.
#ITAD 1273 is assigned to shifteight.org.
* Although freenum.org can handle ITADs that resolve to non-SIP URIs, the handling of multiple protocols is
beyond the scope of this book. For now, we recommend you restrict your ISN to handling SIP URIs.
† AfriNIC, APNIC, ARIN, LACNIC, and RIPE NCC.
ISN, ITAD, and freenum.org | 251