Please see the attached file

CIS527 Homework #1,

(Note, this is an individual homework assignment).

Note 1, we assume 1K = 1000, 1M = 1,000,000, 1G = 1,000,000,000, 1Byte = 8 bits

Note 2, 1s = 1,000 ms = 1,000,000µs

1. (20 points) We are sending a MP3 file of 1,000,000 bits from a source host to a destination host. All links in the path between source and destination have a bandwidth of 10 Mbps. Assume that the propagation speed is 2.0 * 108 meters/sec, and the distance between source and destination is 10,000 km.

1. Initially suppose there is only one link between source and destination. Suppose the MP3 file is sent as one message, what is the transmit time?

2. Referring to the above question, what is the total transfer time (transmit time plus propagation delay)?

3. Referring to the above question, how many bits will the source have transmitted when the first bit arrives at the destination?

4. Now suppose there are two links between source and destination, with one switch connecting the two links. Each link is 5,000 km long. Again suppose the MP3 file is sent as one message. Suppose there is no congestion, so that the message is transmitted onto the second link as soon as the router receives the entire message. What is the total transfer time?

5. Now suppose that the MP3 file is broken into 10 packets, each of 100,000 bits. Ignore headers that may be added to these packets. Also ignore switch processing delays. Assuming store and forward packet switching at the switch, what is the total transfer time?

1. (15 points) Suppose a 1Gbps point-to-point link is being set up between Earth and a new lunar colony. The distance from the moon to Earth is approximately 385,000 km, and data travels over the link at the speed of light – 3.0 * 108 m/s.

1. Calculate the minimum RTT for the link

2. Using the RTT as the delay, calculate the delay x bandwidth product for the link.

3. What is the significance of the delay x bandwidth product computed in (b)

4. A camera on the lunar base takes pictures of Earth and saves them in digital format to disk. Suppose Mission Control on Earth wishes to download the most current image, which is 10 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?

1. (10 points) For the following, assume that no data compression is done; this would in practice almost never be the case. Calculate the bandwidth necessary for transmitting in real time.

1. Video at a resolution of 640  480, 3 bytes/pixel, 60 frames/second

2. Video at a resolution of 320  240, 1 bytes/pixel, 5 frames/second

3. CD-ROM music, assuming one CD holds 60 minutes’ worth of and takes 650 MB.

4. POTS (plain old telephone service) voice audio of 8-bit samples at 8KHz

5. GSM mobile voice audio of 240-bit samples at 50Hz

1. (15 points) Calculate the transfer time (from the first bit sent to last bit received) for the following:

1. A 10 Mbps Ethernet with a single store-and-forward switch in the path, and a packet size of 5,000 bits. Assume that each link introduces a propagation delay of 50 s, and that the switch begins retransmitting immediately after it has finished receiving the packet.

2. Same as (a) but with three switches.

3. Same as (a) but assume the switch implements “cut-through” switching: it is able to begin retransmitting the packet after the first 200 bits have been received.

1. (15 points) Calculate the total time required to transfer a 1000-KB file in the following cases, assuming an RTT of 50 ms, a packet size of 1KB and an initial 2 x RTT of “handshaking” before data is sent

   1. The bandwidth is 1Mbps, and data packets can be sent continuously.

   2. The bandwidth is 1Mbps, but after we finish sending each data packet, we must wait for one RTT before sending the next.

   3. The bandwidth is “infinite,” meaning that we take transmit time to be zero, and up to 20 packets can be sent per RTT.

   4. The bandwidth is infinite, and during the first RTT we can send one packet (21-1), during the second RTT we can send two packets (22-1), during the third RTT we can send four packets (23-1), and so on.

1. (15 points) In this problem, we consider sending voice from Host A to Host B over a direct link network (for example, Internet phone). Host A converts analog voice to a digital 64Kbps bit stream on the fly. Host A then groups the bits into 128-byte packets. There is one link between Host A and Host B; its bandwidth is 10Mbps and its propagation delay is 50 msec. As soon as Host A gathers a packet, it sends it to Host B. As soon as Host B receives an entire packet, it converts the packet’s bits to analog signal. How much time elapses from the time a bit is created (from the original analog signal at Host A) until the bit is decoded (as part of the analog signal at Host B)? Disregard decoding time.

1. (10 points) Suppose that a 10Mbps Wireless LAN is transmitting 1000-byte frames back-to-back over a radio channel with a bit error rate of 10-5. How many frames per second will be damaged on average?