Link characteristics
Skills: none
Concepts: Link characteristics -- technology, length,
speed, latency, jitter and packet loss rate, units of
measure for amount of data and connection speed,
link trends and the gap between developed and
developing nations
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3.0 License.
Where does this topic fit?
• Internet concepts
– Applications
– Technology (communication)
– Implications
• Internet skills
– Application development
– Content creation
– User skills
Link characteristics
Computer 2
Computer 1
Link technology
Link length
Link speed
Latency, jitter and packet loss rate
Wireless connection technologies
Terrestrial radio
Satellite radio
Wire-line connection technologies
Copper, twisted pair
(electronic)
Copper, coaxial cable
(electronic)
Fiber (optical)
Only use wireless links when a wired
connection is not convenient or possible.
Link characteristics
Computer 1
Computer 2
Link technology
Link length
Link speed
Latency, jitter and packet loss rate
Link length
Link characteristics
Computer 1
Computer 2
Link technology
Link length
Link speed
Latency, jitter and packet loss rate
What are some unit of measure for …
Length?
Weight?
Data?
0101010101001011010
0101110010101010100
1010101000101010101
0101010100101010010
1010100100100100101
0101001000101010101
1101001010010101010
Units of measure for quantity
inches, meters,
millimeters, miles,
nanometers, light
years, etc.
bits, bytes, kilobytes,
kilobits, terabits,
megabits, gigabytes, etc.
pounds, ounces,
grams, kilograms,
tons, nanograms,
milligrams, etc.
0101010101001011010
0101110010101010100
1010101000101010101
0101010100101010010
1010100100100100101
0101001000101010101
1101001010010101010
What are some units of measure for time?
Units of measure for time
hours, days, weeks, years, centuries, seconds,
microseconds, nanoseconds, and so forth
Rate = quantity per unit of time
Distance traveled per unit of time
Units of measure for data transmission rate
Time
?
Amount of data
?
Transmission rate
?
Transmission rate = amount of data per unit of time
Units of measure for data transmission rate
Time
Amount of data
Transmission rate
second
bit
?
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
The Internet
Home
Link characteristics
Computer 1
Computer 2
Link technology
Link length
Link speed
Latency, jitter and packet loss rate
Latency – the time for the first packet to arrive
Jitter
Distance
(miles)
P1
(ms)
P2
(ms)
P3
(ms)
P4
(ms)
Avg.
(ms)
Jitter
(st dev)
Santiago
Chile
5,585
412
346
228
225
303
92.08
Oxford
England
5,408
195
194
195
193
194
.96
Which has the lowest jitter?
Packet loss rate
Service level agreement
Speed and ping tests
The link from your home to the Internet
?
Home LAN
The Internet
LAN router
ISP router
Typical speed examples
Link
Typical speed
residential DSL link
3 mb/s
residential cable link
10 mb/s
residential fiber link
25 mb/s
residential satellite
1 mb/s
Link from our campus to CSU net
1 gb/s
intercity fiber
10 gb/s
undersea fiber cable
1 tb/s
Global view
PingER at Stanford University
http://bit.ly/mnruYf
Steadily faster
International traffic
Intercontinental traffic flows
Summary
Computer 1
Computer 2
Self-study questions
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We discussed 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
•
Rate 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, technology, length 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 faster than the other direction?
Resources
Test ping times: http://pingtest.net
Test data transmission rate: http://speedtest.net
A more detailed link test with hints to improve performance by adjusting
TCP parameters: http://ndt.anl.gov
Current data on Verizon network performance:
http://www.verizonbusiness.com/about/network/latency/
The 2010 Stanford report on Internet performance:
http://www.slac.stanford.edu/xorg/icfa/icfa-net-paper-jan10/reportjan10.doc
Aladdin Nassar, Worldwide Inventory of Last-mile Bandwidths & Network
Latencies:
http://velocityconf.com/velocity2010/public/schedule/detail/14075
Project PingER: http://www-iepm.slac.stanford.edu/pinger/