Federation allows these islands of SIP communications to
grow and expand and interconnect. Businesses can maximize
the services and features from their SIP products and sys-
tems and participate in the growing SIP communication
ecosystem.
Mapping Phone Numbers
to URIs
When interconnecting islands of SIP, your network needs a
method of discovering a SIP URI from a telephone number.
The ENUM protocol has been developed to fulfill this purpose.
The ENUM protocol is the result of work of the Internet
Engineering Task Force (IETF) Telephone Number Mapping
working group. The charter of this working group was to
define a Domain Name System (DNS)–based architecture
and protocols for mapping a telephone number to a Uniform
Resource Identifier (URI), which can be used to contact a
resource associated with that number.
ENUM has a DNS-based architecture and protocol by which
standard telephone numbers can be expressed as a Fully
Qualified Domain Name (FQDN) in a specific Internet domain
defined for this purpose (e164.arpa). The result of the
ENUM query is a series of records (defined in RFC 3402) that
gateways, proxy servers, and even SIP endpoints can use to
contact one or more resources (for example, URIs) associ-
ated with that number.
ENUM and service providers
As SIP becomes increasingly popular with service providers,
ENUM will likely become part of the suite of services that
a service provider connecting to a SIP Enterprise Network
can deliver through the PSTN. On your SIP phone you’ll
be able to punch in a URI for your friend’s TDM landline
(or cellular) phone, and the carrier’s ENUM server will
magically connect you.
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