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20 Cards in this Set
- Front
- Back
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What would a plot of the AIMD Algorithm look like with rate compared to time? |
A sawtooth |
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What is a Phase Plot? |
c = network capacity x1 = allocation to user 1 x2 = allocation to user 2 AIMD: Additive Increase and Multiplicative Decrease push to the optimal point. |
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What is the sending rate giving the following values? Round Trip Time = 100 milliseconds Packet Size = 1 kB Window Size = 10 packets |
= 10 * 8000 bits / 100 milliseconds = 800 bits / milliseconds |
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How does TCP interpret packet loss? |
TCP assumes congestion. It increases window size to confirm congestion, then slows down. |
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What is the difference between TCP End-to-End and Network-Assisted Congestion Control? |
TCP End-to-End - No feedback from network - Congestion inferred from loss and delay Network-Assissted - Routers provide feedback - Sends explicit rate |
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What is the goal of Congestion Control? |
- Use network efficiently - Preserve fair allocation of resources - Avoid Congestion Collapse |
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What would cause Congestion Collapse? |
- Spurious re-transmissions of packets in flight - Undelivered packets |
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What could result in this situation? |
Congestion Collapse. Lost packets and delays could also occur. |
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What is Congestion Control? |
Fill the pipes without overflowing them. |
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How can VOIP and FTP applications compete for bandwidth fairly? |
Besides making the voice over internet protocol a higher priority, it can also be scheduled so the file transfer protocol can get capacity when the voip's buffer is filled. |
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What is the window based approach to adjusting rates? |
On success: one packet increase per round trip (additive increase). On failure: reduce window size by half (multiplicative decrease). |
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Does youtube use TCP or UDP and why? |
Youtube uses HTTP/TCP to convert uploaded videos to flash or HTML5 and apply compression. |
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Is TCP a good fit for audio/video and why? |
No, because it is slow upon loss and there is too much protocol overhead and places reliability needs too highly. UDP avoids these problems. |
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What is playout delay? |
Delay after a video has started playing, which is intolerable >:( Some delay at the start of video play or a small % of packet loss is tolerable. |
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How is video streamed? |
Video data is divided into segments and time stamped so clients can store data in a buffer to be played continuously. |
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How is video compressed? |
Differences between frames can be computed because many frames can be similar. |
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What is the TCP Incast Problem? |
Drastic reduction in throughput that results when TCP servers simultaneously request data. Occurs when RTT time is small, but retry time is large. |
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How do you fix barrier synchronization and idle time? |
- Fine tune retry times - Acknowledge every other packet. |
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How is audio digitized? |
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What are some challenges with multimedia streaming? |
- Large volume of data - Data volume varies over time - Low tolerance for delay variation |
