Communication link characteristics Skills none Concepts four link

Communication link characteristics Skills: none Concepts: four link characteristics, unit of measure, rate, amount of data, communication speed, asymmetrical link, ping time, synchronous versus asynchronous applications This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3. 0 License.

Where does this topic fit? • Internet concepts – Applications – Technology (communication) – Implications • Internet skills – Application development – Content creation – User skills

Communication link characteristics Device 1 Device 2 • • Link length Link technology Link speed Latency

Communication link characteristics Device 1 Device 2 • • Link length Link technology Link speed Latency

Long link Short link These are wireless– give an example of a short and a long wired link.

Communication link characteristics Device 1 Device 2 • • Link length Link technology Link speed Latency

Wired or wireless communication links Give some examples of wired communication links. Give some examples of wireless communication links.

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.

• • Cell phone call Cell phone Internet access Car radio Over the air television Wi. Fi Bluetooth High speed data links Do you know what each of these is?

Communication link characteristics Device 1 Device 2 • • Link length Link technology Link speed Latency

What are some units of measure for … Length? Weight? Amount of data? 10101001011010111001010100 1011010100010101 0110100101010010 10110100100101 Answer these questions before continuing.

Some common units of measure Ounces Pounds Grams Inches Feet Meters Bits Bytes Megabytes 10101001011010111001010100 1011010100010101 0110100101010010 10110100100101 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 ___. Another water flow rate is ___.

Units of measure for data transmission rate Time ? Amount of data ? 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 bits per second Transmission rate = amount of data per unit of time

Speedtest. net Condo in Carpinteria: Home: Why are the results different? What is the difference between upload and download speed? Why is download speed faster in these examples?

Asymmetric link speed Programs and data Would you prefer your link at home to be faster up than down? Why?

We have one more communication link characteristic to cover – do you recall what it is? If not, you are not thinking about the organization of this presentation.

Link characteristics Device 1 Device 2 • • Link length Link technology Link speed Latency

Latency – the time it takes a packet to move from one compute to another 1101101 Sending computer Receiving Computer

Ping: measures round trip packet time 1101101 Ping client Acknowledge Ping server

Latency to Mars 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 packet file from Earth to Mars at 100 million 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?

Is latency important in … • Synchronous applications like audio or video conversations? • Asynchronous applications like transferring files or email? • Interactive applications like browsing the Web or playing an online game? Explain your answers.

The problem with today’s satellite Internet service • Latency is high with today’s highaltitude satellite orbits. • Low-Earth orbit satellite networks may have lower latency than terrestrial fiber networks.

Summary Device 1 Device 2

Self-study questions 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 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/ICTFacts. Figures 2013. pdf A more detailed link speed test with hints to improve performance by adjusting TCP parameters: https: //www. measurementlab. net/tests/ndt/ To test ping times and data transfer rates (upload and download): http: //www. speedtest. net/