A connection between USA and Madras

The hosts of the Internet have names assigned to them in a structured way. The convention used is known as DNS, Domain Name System. A person with access to a machine or network, will have a user name in that system. The user name, together with the host/network name, forms the e-mail address of the person. For example, rahul@imsc.res.in is the e-mail address of a person with user name "rahul", in the domain "imsc.res.in" This last name contains quite some information: it is divided in several subdomains: "imsc", which is the domain that identifies all the machines in the Institute of Mathematical Sciences, and "ernet", the Educational and Research Network in India. Finally, the address ends with the domain that identifies the country, in this example "in" for India. So we can see that the structure of the e-mail address of the typical Internet user is
account@[subdomain].[subdomain]...domain
The domain is the right most label, and they are organized in a very well-specified and regulated system. The domains in the USA are gov, edu, arpa, com, mil, org and net. Outside the USA, each nation has a domain assigned to it, e.g. in=India, es=Spain, fr=France, etc. Within a nation there might be several subdomains, like "ac" for academic institutions in the uk (United Kingdom) domain. The following picture shows an example of domain structure.