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Questions and Answers of Computer Networking

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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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.
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
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
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
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
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
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
Consider Figure 1.19(a). Assume that we know the bottleneck link along the path from the server to the client is the first link with rate Rsbits/sec. Suppose we send a pair of packets back to back
Consider Figure 1. 1 (b). Suppose that each link between the server and the client has a packet loss probability p, and the packet loss probabilities for these links are independent. What is the
Visit the Queuing and Loss applet at the companion Web site. What is the maximum emission rate and the minimum transmission rate? With those rates, what is the traffic intensity? Run the applet with
Consider Figure 1.19(b). Now suppose that there are M paths between the server and the client. Nu two paths share any link. Path k (k = 1,...,M) consists of N links with transmission rates Rk1, Rk2,
(a) Visit the site www.traceroute.org and perform traceroutes from two different cities in France to the same destination host in the United States.How many links are the same in the two traceroutes?
Consider sending a packet from a source host to a destination host over a fixed route. List the delay components in the end-to-end delay. Which of these delays are constant and which are variable?
Some content providers have created their own networks. Describe Google’s network. What motivates content providers to create these networks?
Why will two ISPs at the same level of the hierarchy often peer with each other? How does an TXP earn money?
(a) Suppose N packets arrive simultaneously to a link at which no packets are currently being transmitted or queued. Each packet is of length L and the link has transmission rate R. What is the
What are some of the physical media that Ethernet can run over?
List the available residential access technologies in your city. For each type of access, provide the advertised downstream rate, upstream rate, and monthly price.
Consider the circuit-switched network in Figure 1.13. Recall that there are 4 circuits on each link. Label the four switches A, B, C, and D, going in the clockwise direction.a. What is the maximum
List six access technologies. Classify each one as home access, enterprise access, or wide-area wireless access.
Why are standards important for protocols?
Equation 1.1 gives a formula for the end-to-end delay of sending one packet of length L over N links of transmission rate R. Generalize this formula for sending P such packets back-to-back over the N
The word protocol is often used to describe diplomatic relations. How does Wikipedia describe diplomatic protocol?
What is the difference between a host and an end system? List several different types of end systems. Is a Web server an end system?
Assume we need to create codewords that can automatically correct a one-bit error. What should the number of redundant bits (r) be, given the number of bits in the dataword (k)? Remember that the
How does a single-bit error differ from a burst error?
What is the maximum effect of a 2-ms burst of noise on data transmitted at the following rates?a. 1500 bpsb. 12 kbpsc. 100 kbpsd. 100 Mbps
What is the definition of a linear block code?
Assume that the probability that a bit in a data unit is corrupted during transmission is p. Find the probability that x number of bits are corrupted in an n-bit data unit for each of the following
In a block code, a dataword is 20 bits and the corresponding codeword is 25 bits. What are the values of k, r, and n according to the definitions in the text? How many redundant bits are added to
Exclusive-OR (XOR) is one of the most used operations in the calculation of codewords. Apply the exclusive-OR operation on the following pairs of patterns. Interpret the results.a. (10001) ⊕

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