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Question 1: General What data rate is needed to transmit an uncompressed 4" x 6" photograph every second with a resolution of 1200 dots per inch and 24 bits per dot (pixel)? 691,200 kb/s 28.8 kb/s 8.29 Mb/s 829 Mb/s

Question 2: Layering "Layering" is commonly used in computer networks because (check all that apply): -It forces all network software to be written in C. -Encapsulation is the lowest overhead method to transmit data. -It provides a separation of concerns; each layer has well defined responsibilities. -It allows widespread re-use of code and functionality. -It keeps networks warm enabling them to run faster

Question 3: The Internet Protocol IP provides (check all that apply): -a connection-oriented service -unreliable delivery -best-effort delivery -in-sequence delivery

Question 4: The Transmission Control Protocol TCP provides (check all that apply): -a connection-oriented service -unreliable delivery -best-effort delivery -in-sequence delivery

Question 5: TCP and Flow Control You set up an experiment in which host A blasts a 26 Megabyte file to host B through a single TCP Tahoe connection over a 1 Gigabit/sec Ethernet. B transmits no data. Neither host uses any IP or TCP options. The maximum Ethernet payload size is 1500 bytes. With no options, the IP+TCP headers occupy exactly 40 bytes. This leaves a TCP maximum segment size (MSS) of 1,460 bytes, approximately 1/18,000 the size of the file. Which of the following statements are true (check all that apply):

-Host B can send TCP acknowledgements to host A, even though it has no data to send. -The size of the flow control window in segments B sends (the window field) cannot increase throughout the duration of the connection. -Suppose that the last RTT sample at host A is 10 msec. The current value of the RTT estimate must be greater than or equal to 10 msec. -If the user temporarily stops or suspends the process receiving the data on host B, host A will eventually stop sending new data until B's receiver process is resumed.

Question 6: TCP and Congestion Control a) So far, we have mostly discussed TCP's congestion control and AIMD in the context of single-packet losses. This question examines how very long-lived TCP flows sending large amounts of data respond to 2-packet bursts of losses. For sake of simplicity, you should assume only data packets are lost (no acknowledgements are lost), the RTT is constant, the packet loss rate is independent of the transmission rate, and the drop rate is low enough that the congestion window can grow to be at least 8 segments before a loss. Furthermore, packet losses are periodic rather than probabilistic. For example, with a 2% packet loss rate, single packet losses will cause 49 packets to be successfully delivered, followed by one loss, while 2-packet bursts will lead to 98 successful delivered packets followed by 2 losses. Under these constraints, which of the following is true? -TCP Tahoe will have lower throughput with 2-packet bursts of losses than evenly-spaced single losses. -TCP Tahoe will have higher throughput with 2-packet bursts of losses than evenly-spaced single losses.

b) Assume that 1 in 256 of packets are lost (1 every 256 for single losses, 2 in 512 for double losses). Which of the following most closely describes the difference in throughput? -They will be greatly different (the higher throughput one will be over twice as fast) -They will be significantly different (the higher throughput one will be over 10% faster but less than 100%) -They will be slightly different (the higher one will be over 1% faster but less than 10%)

Question 7: Queues While visiting Disneyland you watch the single queue of people waiting to go on one of the rides. You estimate an average of 12 new people arriving per minute, and an average of 240 people waiting in the queue. What is a reasonable estimate of the average time people wait in line before they board the ride? -20 seconds -240 seconds -20 minutes -0.5 minutes

For the next three questions: It has been predicted that the capacity of the public Internet will continue to grow significantly because of a continued growth in the amount of video traffic delivered to peoples homes. In the following questions, well make some crude assumptions to try and estimate how much total network capacity might be needed in the future.

Question 8 Assuming there are 100 million households in the US, and that each household has two HDTVs, and that each TV is used to watch 4 hours of video per day. Well assume that each (compressed) video streams at 2Mb/s. If all households are watching both TVs at the same time, and all are watching video on-demand (i.e. data is delivered unicast to every household), then which of the following is the closest approximation of the total peak aggregate data rate delivered to all homes? -100 Tb/s (100 10^12b/s) -400 Tb/s (400 x 10^12b/s) -1 Pb/s (1 x 10^15b/s) -100 Gb/s (100 x 10^9 b/s) -2 Tb/s (2 x 10^12b/s)

Question 9 Now lets compare our answer above with an estimate of the future capacity needed to carry web traffic. Well assume 100 million people download an average of 100 web pages per day (i.e. averaged over 24 hours), each containing 1Mbyte of data. If the peak traffic is five times the average, then which of the following is the closest estimate of the capacity needed by the network to deliver this traffic? -500 Gb/s -1 Tb/s -5 Tb/s -10 Tb/s

Question 10 We can think of the network as a spanning tree, with the video server at the root, and the one hundred million subscribers at the leaves. Assuming that the tree has degree eight (i.e. each router in the tree connects to eight other routers closer to the leaves), then roughly how many routers does a packet pass through from the root to each subscriber? -9 -10 -11 -12 -13

Question 11: Queues At the start of every second, a train of 100 bits arrive to a queue at rate 1000 bits/second. The departure rate from the queue is 500 bits/second. The queue is served bit-by-bit, and you can assume the buffer size is infinite.

a) What is the average queue occupancy? (in bits) Note: Enter an integer. Any other kind of answer will result in a 0 point grade for this question. 5

b) What is the average delay of a bit in the queue? (in milliseconds) Note: Enter an integer. Any other kind of answer will result in a 0 point grade for this question. 0.5

c) If the trains of 100 bits arrived at random intervals, one train per second on average, would the average queue occupancy be the same, lower or higher than in part (a)? -Higher -Same -Lower

d) If the departing bits from the queue are fed into a second, identical queue with the same departure rate, what is the average occupancy of the second queue? (in bits) Note: Enter an integer. Any other kind of answer will result in a 0 point grade for this question. -0

Question 12: Protocol Stack You plug a new laptop into a wired Ethernet jack for the first time. You have already told the network administrators your MAC address, and can join the network with no further action on your part.

Assume that: 1. your DHCP server is 171.64.7.77, 2. your Ethernet address is 00:11:22:33:44:55 3. the IP address you'll be given is 171.64.7.22 4. the gateway IP address is 171.64.7.1 5. the gateway Ethernet address is 00:66:77:88:99:00 6. the netmask is 255.255.255.0 Let's consider the series of packet exchanges that will occur on the link for your laptop to send a single IP packet to 128.30.2.1. We assume that no packets are lost or discarded, and that no other packets are exchanged on the link.

a) Which of the following protocols are involved in the series of packet exchanges (check all that apply)? -IP -ARP -UDP -ICMP -DHCP

b) How many packets will traverse the link ? -4

c) In which packet (sent or received) will your IP address be mentioned for the first time? -the 1st packet -the 2nd packet -the 3rd packet -the 4th packet -the 5th packet

d) How many packets (sent or received) contain the Ethernet address of the gateway? 2 e) How many packets (sent or received) contain the IP address of the DHCP server? 10