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Skills: noneConcepts: 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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Link characteristics
Where does this topic fit?
• Internet concepts– Applications– Technology (communication)– Implications
• Internet skills– Application development– Content creation– User skills
Link technology
Link length
Link speed
Latency, jitter and packet loss rate
Link characteristics
Computer 1 Computer 2
Wireless connection technologies
Satellite radio
Terrestrial 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 technology
Link length
Link speed
Latency, jitter and packet loss rate
Link characteristics
Computer 1 Computer 2
Link length
Link technology
Link length
Link speed
Latency, jitter and packet loss rate
Link characteristics
Computer 1 Computer 2
0101010101001011010010111001010101010010101010001010101010101010100101010010101010010010010010101010010001010101011101001010010101010
What are some unit of measure for …
Length? Weight?
Data?
0101010101001011010010111001010101010010101010001010101010101010100101010010101010010010010010101010010001010101011101001010010101010
Units of measure for quantity
inches, meters, millimeters, miles, nanometers, light years, etc.
pounds, ounces, grams, kilograms, tons, nanograms, milligrams, etc.
bits, bytes, kilobytes, kilobits, terabits, megabits, gigabytes, etc.
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 second
Amount of data bit
Transmission rate ?
Transmission rate = amount of data per unit of time
Units of measure for data transmission rate
Time second
Amount of data bit
Transmission rate bits per second
Transmission rate = amount of data per unit of time
The Internet
Home
Link technology
Link length
Link speed
Latency, jitter and packet loss rate
Link characteristics
Computer 1 Computer 2
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)
SantiagoChile 5,585 412 346 228 225 303 92.08
OxfordEngland 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
LAN router
ISP router
Home LAN
The Internet
?
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
Typical speed examples
Steadily faster
International traffic
Intercontinental traffic flows
Summary
Computer 1 Computer 2
Self-study questions1. We discussed several characteristics of a communication link. Without looking back, do you recall what
they were?2. Name two units of measure for each of the following:
• Weight• Length• Rate at which you run• Amount of data• Rate of data transmission
3. 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?
4. What unit of measure would you use for a quantity of water?5. What unit of measurement would you use for the rate at which water flows through a hose?6. When you walk, you typically travel at rate of about 4 miles per hour. Convert that to miles per
second.7. When you walk, you typically travel at rate of about 4 miles per hour. Convert that to feet per second.8. How many bits in a megabyte?9. How long would it take to transmit a 100 megabit file over a 100 megabit/second link?10. How long would it take to transmit a 100 megabit file over a 10 megabit/second link?11. How long would it take to transmit a 100 megabit file over a one gigabit/second link?12. How long would it take to transmit a 100 megabyte file over a 100 megabit/second link?13. How long would it take to transmit a 100 megabit file over a 100 megabyte/second link?14. How long would it take to transmit a 132 megabyte file over a 12 megabit/second link?15. What are the speed, technology, length and monthly cost of the link from your home to your Internet
service provider?16. 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/report-jan10.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/
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