MOTIVATION AND TOOLS

One of the reasons of motivation towards networking was resource sharing which
is discussed as follows.

RESOURCE SHARING:

Resource sharing means to share the resources available among many users.
In an office as it is very expensive to give a separate printer to each worker. So if
the printer is shared among the workers then a single printer will be accessible to each
worker. This leads to the motivation of resource sharing.

GOAL OF RESOURCE SHARING:

The goal of resource sharing is to make all programs, equipment and date
available to anyone in the network without regard to physical location of the resource and
the user.
For example: the sharing of a printer among the workers in an office and also the
sharing of information is a goal of resource sharing.

MAIN REASON FOR EARLY RESOURCE SHARING:

The main reason for early resource sharing was not to share the peripheral devices
rather to share the large-scale computational power because computer were extremely
expensive in those days and the government budgets were not sufficient to provide
computers for all scientist and engineers. By resource sharing a researcher could use
whichever computer was best suited to perform a given task.

EFFORTS OF ADVANCED RESEARCH PROJECT AGENCY (ARPA):

The efforts of ARPA was to enable all its research groups have access to latest
computers. For this purpose ARPA started investing in ways to do data networking
ARPA use a new approach consisting of packet switching and internet working to fulfill the purpose of resource sharing. As a result of ARPA research the first network was
established which was named ARPA NET.
In this way the internet was emerged in 1970’s and it has grown drastically since
then as shown in the figure below.

Figure. 2.1 Growth of the Internet

As shown in another figure below. In log scale the position on y-axis is proportional to
the log of the number being represented. So the values along y-axis represent the power

of 10.Fig. 2.2 Growth of the internet on Log Scale

We see that on log scale the growth appears almost linear it means that internet experienced an
exponential growth. We also observed that internet has been doubled every nine to twelve
months.

PROBING THE INTERNET:
Let us see how are the figures in above graphs obtained?
In the early days when there were some dozen computers on the network, it was done manually
but now as we have seen that there are millions of computers on the internet so how can we
calculate the number of computers connected to the internet. This is done through probing the
Internet.
Now an automated tool is required that tests to see whether the given computer is online or not.
For this purpose the first tool is the `PING program` which is shown in the figure below.

Figure 2.3 THE PING Command

We see that 5 packets of 64 bytes are sent to sears.com and 5 packets are received. We see that
ping has also given some additional information such the IP addresses of sears.com, the sequence
of packets and the times of transmission known as the round-trip time, as there is no packet loss
so it means that sears.com is connected to the internet

PROBLEM WITH ‘PING’:

Ping, as a tool seems to be simplistic. Now let’s see what are the problems attached with ping.
If ping does not review any responses from host computer it can not tell the reason of problem.
Because one of the following reasons occur but ping will not specify the reason.

• Remote computer might have a problem.
• Local computer might have a problem.
• Ping sometimes fails because of congestion.

Some networks or computers reject the ping packets. They do this to avoid denial of service of
flooding attack.
Inspite of these problems ping is still heavily used as a diagnostic tool.
Network administrators use ping as soon as they learn about the failure.

TRACING A ROUTE:

There is another probing tool i-e Trace Route. To get more detail it is used.

Figure 2.4

As shown in the figure about the route to DANDELION-PATCH.MIT.EDU was traced out and
the program showed all eight computers that were in the way. The additional information is also
shown in the figure.
Thus we see that tracing a route is more interesting tool than Ping as it tells about each computer
that falls in the way of source and destination computers.