# Computing Network Performance Computation Activity

### Due Sept 15 by class time.

Each group will work together and collaborate on a solution for the following problems. It is NOT acceptable to break up the problem in to parts and have different students work on different parts. You must work together on ALL parts. You will then present a solution for each with complete notated equations, along with illustrations that show what is going on. Explain why the time differantials are SO large when the amount of data being sent is always the same.

### Groups

A B C D E
Joshua Aleshire
Benjamin Kindle
Nicholas Norckauer
Jared Phillips
Benjamin Camm
Cameron Davidson
Dean Wasil
Benjamin Yake
Micah Gentry
Eric Roby
Collin Shawler
Chandler Strouse
Jon Duke
Jasmine Lamb
Chase Tennant
Trevor Boardman
Kaitlin Roessner

1. Calculate the total time required to transfer a 5-MB file in the following cases, assuming an RTT of 80 ms, a packet size of 1 KB data, and an initial 2 × RTT of “handshaking” before data is sent:

1. The bandwidth is 100 Mbps, and data packets can be sent continuously.
2. The bandwidth is 100 Mbps, but after we finish sending each data packet we must wait one RTT before sending the next.
3. The link allows infinitely fast transmit, but limits bandwidth such that only 40 packets can be sent per RTT.
4. Redo #3 above, but consider the transmit rate at 100Mbps.
5. Zero transmit time as in (c), but during the first RTT we can send one packet, during the second RTT we can send two packets, during the third we can send four (23−1 ), etc. (A justification for such an exponential increase will be given in Chapter 6.)

2. Suppose a 1-Gbps point-to-point link is being set up between the Earth and a new lunar colony. The distance from the moon to the Earth is approximately 385,000 km, and data travels over the link at the speed of light—3×108 m/s.

1. Calculate the minimum RTT for the link.
2. Using the RTT as the delay, calculate the delay × bandwidth product for the link.3.
3. Assuming 1500 byte packets, how many packets have to be sent without acknowlegement in order to use the link with 100% efficiency? What is the significance of the delay × bandwidth product computed in (2)?
4. A camera on the lunar base takes pictures of the Earth and saves them in digital format to disk. Suppose Mission Control on Earth wishes to download the most current image, which is 25 MB. What is the minimum amount of time that will elapse between when the request for the data goes out and the transfer is finished?
3. Analysis Questions
1. What do these problems tell us about the effect of sending and acknowledging a single packet before sending the next? Sending out and acknowledging a multiple packets before sending the more?
2. What do these problem tell us about sending out expondentially growing numbers of packets?
Notes:

• 1Kbps = 1,000 bits/sec
• 1Mbps = 1,000,000 bits/sec
• 1Gbps = 1,000,000,000 bits/sec
• 1KB = 210 = 1024
• 1MB = 220 = 1,048,576
• 1GB = 230 = 1,073,741,824
Solution
Topic revision: r6 - 2015-09-15 - JimSkon

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