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computer science
computer networking
Computer Networking A Top-Down Approach 7th edition James Kurose, Keith Ross - Solutions
Suppose that Bob receives a POP message from Alice. How does Bob know for sure that Alice created the message (rather than, say, Trudy)? Does PGP use a MAC for message integrity?
Consider WEP for 802.11. Suppose that the data is 10101100 and the key-stream is 1111000. What is the resulting cipher text?
Streaming video systems can be classified into three categories. Name and briefly describe each of these categories.
In the VoIP example in Section 9.3, let h be the total number of header bytes added to each chunk including UDP and IP header. a. Assuming an IP datagram is emitted every 20 msecs, find the transmission rate in bits per second for the datagrams generated by one side of this
Consider the simple model for HTTP? Streaming. Suppose the server sends bits at a constant rate of 2 Mbps and playback begins when 8 million bits have been received. What is the initial buffering delay tp?
Section 9.3 describes two FEC schemes. Briefly summarize them. Both schemes increase the transmission rate of the stream by adding overhead. Does interleaving also increase the transmission rate?
Consider the hierarchical network in Figure 6.30 and suppose that the data center needs to support e-mail and video distribution among other applications. Suppose four racks of servers are reserved For c-mail and four racks are reserved for video. For each of the applications, all four racks must
Consider the sing-sender CDMA example in Figure 7.5. What would be the sender€™s output (for the 2 data bits shown) if the sender€™s CDMA code were (1, €”1, 1,€”1, 1, €”1€™1, €”1)?Figure 7.5 Sender Channel output Z;,m 1sibrtuk do
Consider sender 2 in Figure 7.6. What is the sender's output to the channel (before it is added to the signal from sender 1). Z2i,m? Figure 7.6 Senders T 3510g no 150 299R INRITOnini d=-1 Data bits Demic Code Data bits d=1 Bilibid men SHINE SU powoppling Bobb 1 1 1 1 htlg-1-1-1-1 461 Code 17 STID
Suppose that the receiver in Figure 7.6 wanted to receive the data being sent by sender 2. Show (by calculation) that the receiver is indeed able to recover sender 2€™s data from the aggregate channel signal by using sender 2€™s code.Figure 7.6 Senders suoresgusio hedis d = 1
Describe the role of the beacon frames in 802.11.
True or false; Before an 802.11 station transmits a data frame, it must first send an RTS frame and receive a corresponding CTS frame.
Suppose an 802.11 b station is configured to always reserve the channel with the RTS/CTS sequence. Suppose this station suddenly wants to transmit 1,000 bytes of data, and all other stations are idle at this time. As a function of SIFS and DIPS, and ignoring propagation delay and assuming no bit
Why are acknowledgments used in 802.11 but not in wired Ethernet.
True or false: Ethernet and 802.11 use the same frame structure.
Consider the following idealized LTE scenario. The downstream channel (see Figure 7.21) is slotted in time, across F frequencies. There are four nodes, A, B, C, and D, reachable from the base station at rates of 10 Mbps, 5 Mbps, 2.5 Mbps, and 1 Mbps, respectively, on the downstream channel. These
In Section 7.5, one proposed solution that allowed mobile users to maintain their IP addresses as they moved among foreign networks was to have a foreign network advertise a highly specific route to the mobile user and use the existing routing infrastructure to propagate this information throughout
Suppose the correspondent in Figure 7.23 were mobile. Sketch the additional network-layer infrastructure that would be needed to route the data-gram from the original mobile user to the (now mobile) correspondent. Show the structure of the data-gram(s) between the original mobile user and the (now
What are the differences between a master device in a Bluetooth network and a base station in an 802.11 network?
What is meant by a super frame in the 802.15.4 Zigbee standard?
Consider the chaining example discussed at the end of Section 7.7.2. Suppose a mobile user visits foreign networks A, B. and C, and that a correspondent begins a connection to the mobile user when it is resident in foreign network A. List the sequence of messages between foreign agents. and between
What is the role of the “core network” in the 3G cellular data architecture?
What is the role of the RNC in the 3G cellular data network architecture? What role does the RNC play in the cellular voice network?
What is the role of the eNodeB, MME. P-GW, and S-GW in 4G architecture?
What are three important differences between the 3G and 4G cellular architectures?
Consider a TCP connection going over Mobile IP. True or false: The TCP connection phase between the correspondent and the mobile host goes through the mobile’s home network, but the data transfer phase is directly between the correspondent and the mobile host, bypassing the home network.
What is the role of the anchor MSC in GSM networks?
Using the mono alphabetic cipher in Figure 8.3, encode the message "This is an easy problem." Decode the message "rmij'u uamu xyj."
Internet entities (routers, switches, DNS servers, Web servers, user end systems, and so on) often need to communicate securely. Give three specific example pairs of Internet entities that may want secure communication.
Suppose that an intruder has an encrypted message as well as the decrypted version of that message. Can the intruder mount a cipher text-only attack, a known-plain text attack, or a chosen-plain text attack?
Suppose you want to encrypt the message 10101111 by encrypting the decimal number that corresponds to the message. What is the decimal number?
Consider an 8-block cipher. How many possible input blocks does this cipher have? How many possible mappings are there? If we view each mapping as a key, then how many possible keys does this cipher have?
Suppose certifier.com creates a certificate for foo.com. Typically, the entire certificate would be encrypted with certificr.com's public key. True or false?
Consider our authentication protocol in Figure 8.18 in which Alice authenticates herself to Bob, which we saw works well (i.e., we found no flaws in hi. Now suppose that while Alice is authenticating herself to Bob, Bob must authenticate himself lo Alice. Give a scenario by which Tiudy, pretending
What is the purpose of Nonce in an end-point authentication protocol?
What does it mean to say that a nonce is a once-in-a-lifetime value? In whose lifetime?
Figure 8.19 shows tie operations that Alice must perform with POP to provide confidentiality, authentication, and integrity. Diagram the corresponding operations that Bob mat perform on the package received from Alice.Figure 8.19 Kşlm) Kg(m) K5() Ksl) Internet Kg () Ks Kg (Ks) Ka (KG) Bob receives
In the SSL record, there is a field for SSL sequence numbers. True or false?
In Section 8.6. 1, it is shown that without sequence numbers, Trudy (a woman- in-the middle) can wreak havoc in an SSL session by interchanging TCP segments. Can Trudy do something similar by deleting a TCP segment? What does she need to do to succeed at the deletion attack? What effect will it
What is the purpose of the random nonces in the SSL handshake?
Suppose Alice and Bob are communicating over an SSL session. Suppose an attacker, who does not have any of the shared keys. Inserts a bogus TCP segment into a packet stream with correct TCP checksum and sequence numbers (and correct IP addresses and port numbers). Will SSL at the receiving side
Suppose an SSL session employs a block cipher with CBC. True or false: The server sends to the client the IV in the clear.
The following true/false questions pertain to Figure 8.28.a. When a host in 172.16.1/24 sends a data-gram to an Amazon.con, server, the router Rl will encrypt the data-gram using IPsec.b. When a host in 172. 16. 1/24 sends a data-gram to a host in 172. 16.2/24, the rouler R I will change the source
Consider the example in Figure 8.28. Suppose Trudy is a woman-in-the middle. Who can insert data-grams into the stream of data-gram going from Rl and R2. As part of a reply attack, Trudy sends a duplicate copy of one of the data-grams sent from R I Lo R2. Will R2 decrypt the duplicate data-gram and
Consider sending a stream of packets from Host A to Host B using IPsec. Typically, a new SA will be established for each packet sent in the stream. True or false?
Suppose that TCP is being run over IPsec between headquarters and the branch office in Figure 8.28. If TCP re-transmits the same packet, then the two corresponding packets sent by R1 packets will have the same sequence number in the ESP header. True or false?
An IKE SA and an IPsec SA are the same thing. True or false?
In WEP, an IV is sent in the clear in every frame. True or false?
Stateful packet filters maintain two data structures. Name them and briefly describe what they do.
Consider a traditional (stateless) packet filter. This packet filter may filter packets based on TCP flag bits as well as other header fields. True or false?
In a traditional packet filter, each interface can have its own access control list. True or false?
Signature-based IDSs and IPSs inspect into the payloads of TCP and UDP segments. True or false?
Reconstruct Table 9.1 for when Victor Video is watching a 4 Mbps video, Facebook Frank is looking at a new 100 Kbyte image every 20 seconds, and Martha Music is listening to 200 kbps audio stream.Table 9.1 Bytes transferred in 67 min Bit rate 80 Mbytes 160 kbps 128 kbps Facebook Frank 64 Mbytes 1
Consider the figure below. Similar to our discussion of Figure 9.1. Suppose that video is encoded at a fixed bit rate, and thus each video block contains video frames that are to be played out over the same fixed amount of time, ˆ†. The server transmits the first video block at t0, the
Recall the simple model for HTTP streaming shown in Figure 9.3. Recall that B denotes the size of the client's application buffer, and Q denotes the number of bits that must be buffered before the client application begins play out. Also r denotes the video consumption rate. Assume that the server
There are two types of redundancy in video. Describe them, and discuss how they can be exploited for efficient compression.
Recall the simple model for HTTP streaming shown in Figure 9.3. Suppose the buffer size is infinite but the server sends bits at variable rate x(t). Specifically, suppose (t) has the following saw-tooth shape. The rate is initially zero at time t = 0 and linearly climbs to H at time t = T. It then
Suppose an analog audio signal is sampled 16,000 times per second, and each sample is quantized into one of 1024 levels. What would be the resulting bit rate of the PCM digital audio signal?
Recall the simple model for HTTP streaming shown in Figure 9.3. Suppose the client application buffer is infinite, the server sends at the constant rate x, and the video consumption rate is r with r < x. Also suppose playback begins immediately. Suppose that the user terminates the video early
Multimedia applications can be classified into three categories. Name and describe each category.
Consider a DASH system (as discussed in Section 2.6) for which there are N video versions (at N different rates and qualities) and N audio versions (at N different rates and qualities). Suppose we want to allow the player to choose at any time any of the A’ video versions and any of the N audio
List three disadvantages of UDP streaming.
Consider the procedure described in Section 9.3 for estimating average delay di. Suppose that u = 0.1. Let r1 – t1 be the most recent sample delay, let r2 – t2 be the next most recent sample delay, and so on. a. For a given audio application suppose four packets have arrived at the
With HTTP streaming, are the TCP receive buffer and the client’s application buffer the same thing? If not, how do they interact?
Repeat parts (a) and (b) in Question P7 for the estimate of average delay deviation.Data From Problem 7Consider the procedure described in Section 9.3 for estimating average delay di. Suppose that u = 0.1. Let r1 – t1 be the most recent sample delay, let r2 – t2 be the next most recent
For the VoIP example in Section 9.3, we introduced an online procedure (exponential moving average) for estimating delay. In this problem we will examine an alternative procedure. Let ti be the timestamp of the ith packet received; let ri be the time at which the ith packet is received. Let dn be
Compare the procedure described in Section 9.3 for estimating average delay with the procedure in Section 3.5 for estimating round-trip time. What do the procedures have in common? I-low are they different?
Why is a packet that is received after its scheduled play out time considered lost?
Consider the figure below (which is similar to Figure 9.3). A sender begins sending packetized audio periodically at t = 1. The first packet arrives at the receiver at t = 8.Figure 9.3a. What are the delays (from sender to receiver, ignoring any play out delays) of packets 2 through 8? Note that
How arc different RTP streams in different sessions identified by a receiver? How are different streams from within the same session identified?
Recall the two FEC schemes for VoIP described in Section 9.3. Suppose the first scheme generates a redundant chunk for every four original chunks. Suppose the second scheme uses a low-bit rate encoding whose transmission rate is 25 percent of the transmission rate of the nominal stream.a. How much
a. Consider an audio conference call in Skype with N > 2 participants. Suppose each participant generates a constant stream of rate r bps. How many bits per second will the call initiator need to send? How many bits per second will eh of the other N – 1 participants need to send? What is the
A packet flow is said to conform to a leaky bucket specification (r, b) with burst size b and average rate r if the number of packets that arrive to the leaky bucket is less than n + b packets in every interval of time of length at for all t. Will a packet flow that conforms to a leaky bucket
Visit the Go-sack-N Java applet at the companion Web site.a. Have the source send five packets, and then pause the animation before any of the five packets reach the destination. Then kill the first packet and resume the animation. Describe what happens.b. Repeat the experiment, bin now let the
Consider the rt2.2 receiver in Figure 3.14, and the creation of a new packet in the se1f-ansition (i.e., the transition from the state back to itself) in the Waifor-0-from-below arid the Wait-for-I-from-below states: sndpkt = make_pkt (ACK, 1, checksurn) and sndpkt = make_ pkt (ACK, 0, checkum).
In our rdt protocols, why did we need to introduce sequence numbers?
Is ¡t possible for an application to enjoy reliable data transfer even when the application runs over UDP If so, how?
Why is it that voice and video traffic is often sent over TCP rather than UDP in today’s Internet?
a. Suppose you have the following 2 bytes: 01011100 and 01100101 What is the is complement of the sum of these 2 bytes?b. Suppose you have the following 2 bytes: 11011010 and 01100101. What is the is complement of the sum of these 2 bytes’?c. For the bytes in part (a), give an example where one
UDP and TCP use Is complement for their check sums. Suppose you have the following three 8-bit bytes: 01010011, 01100110, 01110100. What is the Is complement of the sum of these 8-bit bytes? (That although UDP and TCP use 16-bit words in computing the checksum, for this problem you are being asked
What is the Apache Web server? How much does it cost? What functional ity does it currently have? You may want to look at Wikipedia to answer this question.
We have seen that Internet TCP sockets treat the data being sent as a byte stream but UDP sockets recognize message boundaries. What are one advantage arid one disadvantage of byte-oriented API versus having the API explicitly recognize and preserve application-defined message boundaries?
Can you configure your browser to open multiple simultaneous connections to a Web site? What are the advantages and disadvantages of having a large number of simultaneous TCP connections?
Suppose that in UDPClient.py, after we create the socket, we add the line: clientSocket.bind((‘‘, 5432)). Will it become necessary to change UDPServer.py? What are the port numbers for the sockets in UDP Client and UDPServer? What were they before making this change?
Install and compile the Python programs TCPClient and UDPClient on one host and TCPServer and UDPServer on another host.a. Suppose you run TCPClient before you run TCPServer. What happens’? Why?b. Suppose you run UDPClient before you run UDPServer, What happens? Why?c. What happens if you use
Consider a DASH system for which there are W video versions (at N different rates and qualities) and N audio versions (at N different rates and qualities). Suppose we want to allow the player to choose at any time any of the N video versions and any of the N audio versions.a. If we create files so
Besides network-related considerations such as delay, loss, and bandwidth performance, there are other important factors that go into designing a CON server selection strategy. What are they?
Consider an overlay network with N active peers, with each pair of peers haying an active TCP connection. Additionally, suppose that the TCP connection. pass through a total of M routers. How many nodes and edges are there in the corresponding overlay network?
CDNs typically adopt one of two different server placement philosophies. Name and briefly describe them.
In Bit Torrent, suppose Alice provides chunks to Bob throughout a 30-second interval. Will Bob necessarily return the favor and provide chunks to Alice in this same interval? Why or why not?
Look over your received e-mails, and examine the header of a message sent from a user with a .edu e-mail address. Is it possible to determine from the header the IP address of the host from which the message was sent? Do the same for a message sent from a Gmail account.
List several popular messaging apps. Do they use the same protocols as SMS?
Why do HTTP, SMTP, and POP3 run on top of TCP rather than on UDP?
What is meant by a handshaking protocol?
What information is used by a process running on one host to identify a process running on another host?
Consider an HTTP client that wants to retrieve a Web document at a given URL. The IP address of the HTTP server is initially unknown. What transport and application-layer protocols besides IITTP are needed in this scenario?
For a communication session between a pair of processes, which process is the client and which is the server?
List five non-proprietary Internet applications and the application-layer protocols that they use.
Skype offers a service that allows you to make a phone call from a PC to an ordinary phone. This means that the voice call must pass through both the Internet and through a telephone network. Discuss how this might be done.
Experiment with the Message Segmentation applet at the book’s Web site. Do the delays in the applet correspond to the delays in the previous problem? How do link propagation delays affect the overall end-to-end delay for packet switching (with message segmentation) and for message switching?
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