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April 21, 2009

Internet Structure  

The structure of the Internet

The Internet is a tangled web of different machines in different networks with different users. A regular user does not need to understand all the complicated ways in which the Internet works. A general idea of its structure is enough to get the most out of it.

The participants in the Internet are a wide variety of machines, organizations and individuals (whose number keeps increasing steadily), all able to communicate and share information.

Each machine in the Internet is called a host. Hosts may be of many different types, as the following figure show:hosts

Variety of Internet hosts

The next diagram shows how a user in the USA send a mail to an user in the Theoretical Physics Department of the University of Madras. The user, from her home at USA, dials up (2400 bytes per second line) to a workstation in a university, writes and sends the message. The workstation send the mail, via a 2 Mbps line, to JVC net, a provider of Internet services. From there, a connection via satellite is made to the Software Technology Park, in Bangalore. There, the mail is forwarded to the Institute of Mathematical Sciences, via another satellite connection. Finally, the user in the Theoretical Physics Department of the University of Madras, dias up to IMSc, and collects his mail.example

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.




domain


Domain structure within India

The IP (Internet Protocol) address is the underlying identifier used by protocols that govern the Internet information exchange. Machines know each other by IP addresses, rather than names. For example, the host imsc1.imsc.res.in has IP address 202.41.95.2 When you send a message, or open an ftp connection, to another machine, your local host will try first to find the IP address of the host you are trying to connect. This is done via name servers, which are machines containing files with IP addresses. A way of finding an IP address corresponding to a given DNS name is by using the facility "nslookup" Details will be given in the practical demonstration. When you want to have an address for a new computer, you need to register it properly, so that it gets an IP address in an organized way, and the rest of the Internet knows about your machine. Registration is done usually by the "superuser" of your system. More information can be obtained from doe.ernet.in for hosts in academic institutions within India.

by Sareesh M Nair | 0 comments

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