### Course overview

```Communication link speed
Skills: none
Concepts: link characteristics, unit of measure, rate,
amount of data, communication speed, asymmetrical
Where does this topic fit?
• Internet concepts
– Applications
– Technology (communication)
– Implications
• Internet skills
– Application development
– Content creation
– User skills
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Latency
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Latency
These are wireless– give an example of a short and a long wired link.
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Latency
Give some examples of wired
Give some examples of wireless
Wired media options – copper and fiber
Twisted copper pair
Coaxial copper cable
Multi-pair copper cable
Fiber optic cable
Which is generally fastest/slowest? What is each typically used for?
Wireless
List all the wireless communication examples you can think of.
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Cell phone call
Cell phone Internet access
Over the air television
WiFi
Bluetooth
Do you know what each of these is?
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Latency
What are some units of measure for …
Length?
Weight?
Amount
of data?
10101010101001011010
10101110010101010100
10110101000101010101
01101010100101010010
10110100100100100101
Some common units of measure
Inches
Feet
Meters
Ounces
Pounds
Grams
Bits
Bytes
Megabytes
10101010101001011010
10101110010101010100
10110101000101010101
01101010100101010010
10110100100100100101
How many bits are in the example shown here?
What are some units of measure for time?
Give a few examples before you go on.
Units of measure for time
hours, days, weeks, years, centuries, seconds,
microseconds, nanoseconds, and so forth
Rate = quantity per unit of time
What measure of speed does this speedometer show?
What is another measure of auto speed?
The rate water flows through a hose
The measure of water quantity is __.
The unit of time is ___.
The water flow rate is ___.
A second water flow rate is ___.
Units of measure for data transmission rate
Time
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Amount of data
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Transmission rate
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Transmission rate = amount of data per unit of time
Units of measure for data transmission rate
Time
Amount of data
Transmission rate
second
bit
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Transmission rate = amount of data per unit of time
Units of measure for data transmission rate
Time
Amount of data
Transmission rate
second
bit
bits per second
Transmission rate = amount of data per unit of time
Speedtest.net
Condo in Carpinteria:
Home:
Why are the results different?
Programs and data
Would you prefer your link at home to be faster up than down? Why?
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Latency
Ping: measures round trip packet time
1101101
Client
Acknowledge
Server
Latency
3 minutes
Mars
Earth
The latency time between Earth and Mars is about 3 minutes when they are at
their closest.
If I send 100 packets from Earth to Mars at 1 billion packets per second, how
long will the first packet take to get to mars? How long does it take the
second packet to get to Mars? The last packet?
If latency time between Earth and Mars is 3 minutes, what is the ping time?
Summary
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Self-study questions
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We mentioned several characteristics of a communication link. Without looking back, do you recall what they were?
Name two units of measure for each of the following: weight, length, rate at which you run, amount of data, rrate of data
transmission
The general form of a unit of measure for velocity is distance/time. What is the general form of a unit of measure for data
transmission speed?
What unit of measure would you use for a quantity of water?
What unit of measurement would you use for the rate at which water flows through a hose?
When you walk, you typically travel at rate of about 4 miles per hour. Convert that to miles per second.
When you walk, you typically travel at rate of about 4 miles per hour. Convert that to feet per second.
How many bits in a megabyte?
How long would it take to transmit a 100 megabit file over a 100 megabit/second link?
How long would it take to transmit a 100 megabit file over a 10 megabit/second link?
How long would it take to transmit a 100 megabit file over a one gigabit/second link?
How long would it take to transmit a 100 megabyte file over a 100 megabit/second link?
How long would it take to transmit a 100 megabit file over a 100 megabyte/second link?
How long would it take to transmit a 132 megabyte file over a 12 megabit/second link?
What are the speed and monthly cost of the link from your home to your Internet service provider?
We saw that Internet links are often asymmetric – faster in one direction than the other. Why is the transmission rate from your
ISP to your home usually faster than the other direction?
If it takes one second to send a 3 million bit file across the Internet from a server to a client, how long would it take to send a
300,000 bit file?
A file contains 1,000 bits of data -- how many bytes of storage would it require?
A file contains 1,000 bits of data -- how many bytes of memory would it require?
A file contains 1,000 bytes of data -- how many bits is that?
At 15 megabits per second, how long would it take to send a 3 megabit image across the Internet?
At 15 megabits per second, how long would it take to send a 3 megabyte image across the Internet?
If the round trip (ping) time for a packet going from two computers that are 1,000 miles apart is 200 milliseconds, how many miles
per hour did the packet travel?
Resources
Test data transmission rate: http://speedtest.net
Global Internet indicators:
http://www.itu.int/en/ITUD/Statistics/Documents/facts/ICTFactsFigures2013.pdf
A more detailed link speed test with hints to improve performance by