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 secondAmount of data bitTransmission rate ?

Transmission rate = amount of data per unit of time

Units of measure for data transmission rate

Time secondAmount of data bitTransmission 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 92.08OxfordEngland 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

http://bit.ly/mnruYf

PingER at Stanford University

Global view

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/