1. Ping demonstration Skills: use ping
Concepts: network transit time, command-line user interface, prefixes for small quantities
We will use ping, a network utility program, to determine the time it takes to send a packet from one host to another across the Internet.
The global Internet works because, as we will see, data moves very fast.
We will also review prefixes for small quantities.
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2. Where does this topic fit?
Internet concepts
Applications
Technology (communication)
Implications
Internet skills
Application development
Content creation
User skills
This presentation deals with communication technology.

3. Local area network (LAN)
We saw earlier how packets are sent from a computer on one LAN across the Internet to a computer on another LAN.

4. How much time? How much time?
How long do you think it takes a packet to make it across the Internet and back?

5. Ping Client Server 1101101 Acknowledge
Ping is a simple client-server program that measures the amount of time it takes a packet to go from one host to another and back.
The client sends a data packet to a remote host.
When the packet arrives, the remote host sends back and acknowledgement.
When that arrives, the client records and displays the round trip time.
Let’s look at some Ping runs.

6. Ping demonstration Start > Run
Ping demonstration – check ping times to Google and the University of Chile.

7. Mind blowing speed
The round trip time averaged 181 milliseconds and the air distance is 5,600 miles.
That works out to about 1/3 the speed of light.
RT to Chile at around 62,000 miles per second – about 1/3 the speed of light.

8. Night = Day? Home = School? Same speed?
Why does the speed vary depending upon when and where you run the test?
Why is data not transmitted at the speed of light – what slows it down?

9. Prefixes for small quantities
Meaning
Fraction
Deci
One tenth
1/10
Centi
One hundredth
1/100
Milli
One thousandth
1/1,000
Micro
One millionth
1/1,000,000
Nano
One billionth
1/1,000,000,000
Pico
One trillionth
1/1,000,000,000,000
A final point.
Ping reports times in milliseconds.
A millisecond is 1/1,000 second.
Here are some other prefixes for small quantities.
It keeps going -- after these prefixes come femto, atto, zepto, and yocto, each 1,000 times smaller than the previous.
You don’t have to recall all of these, but you will often encounter the more common ones like centi, milli, micro and nano.
For example, the time it takes to do something inside a computer might be only a few nanoseconds and the wires etched inside an integrated circuit chip may be only a few nanometers apart.

10. For more on this topic, see this teaching module.