LINK

structure of internet Introduction

STRUCTURE OF INTERNET

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 shows.

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.

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 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.

What is family

There are many interpretations of the term family. Definitions like 'nuclear family' and 'family household' tend to assume that families are only those groups consisting of parents and their children or living in the same household. For most New Zealanders, family means a kin-based group that extends beyond this to include other relatives and span more than one generation.
From a social development perspective, the importance of families and of culture specific groups such as whanau lies in the roles they play in development and wellbeing. As social institutions families:
provide wellbeing for their members;
nuture and protect children;
provide care for members who need it because of disabilities or age;
provide material and emotional support; and
pass on culture, knowledge, values, attitudes, property rights and obligations from one generation to the next.
Families need to be resilient to fulfil these roles successfully. Resiliency is associated with a number of attributes, including:
cohesion;
flexibility and adaptability;
effective communications;
good coping skills to deal with problems that arise;
positive parenting;
a well developed belief system; and
a sense of culture and heritage.
The resilience of families in contemporary New Zealand is under strain because of changes in their social and economic circumstances.
More parents are in paid work and they are faced with the pressures of balancing job demands with their responsibilities as caregivers.
Family structures are changing more often and they have to deal increasingly with issues like migration, separation, change of partners and split custodial arrangements.
Families are sometimes faced with the stress of job loss and inadequate income because of changes in the economy.
Changes in institutional care, education and training have increased demands on families to provide continuing care and support.
Most families cope with these changes. For some, the stress contributes to such things as family violence, abuse and neglect of children, and break-ups. Families need to be aware of and have access to support which is effective in helping them deal with these challenges.