Countries are also identified by the right-most portion of the domain name. For example,
a domain in Canada would be identified by the .ca as the right-most portion of
the domain name. The next portion of the domain name would identify the next level
of the name. There can be 127 different levels, but it is rare to see more than four levels
used.
This next level is also referred to as registered domains, and they can be purchased
through companies acting as registrars for domain names. These registrars manage
various domain names for a fee, working with the master keeper of the main list,
Network Solutions.
Virtually anyone can own their own domain name for a small fee. The various domain
name administrators available through the Internet already offer personalized domain
names of individuals and small businesses. The master repository for all domain names
must then administer all domains globally.
In the IMS, domain name servers are an important entity just as they are within
the Internet. The address of the P-CSCF, I-CSCF, and S-CSCF must be resolved from a
SIP URI. The same is true of other IMS network entities such as the Home Subscriber
Server (HSS) and Application Servers (AS). Each of these entities is given public and
private user identities in the form of a SIP URI, along with an IP address. The domain
name server resolves these URIs to the actual IP addresses.
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