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computer science
computer networking
Data Communications and Networking 5th edition Behrouz A. Forouzan - Solutions
What is the difference between a session and a connection in SSL?
Assume Alice needs to send an e-mail to Bob. Explain how the integrity of the e-mail is achieved using PGP.
How does SSL create a set of security parameters?
Assume Alice needs to send an e-mail to Bob. Explain how the confidentiality of the e-mail is achieved using PGP.
What are the names of the protocols, discussed in this chapter, that provide security for e-mail?
Assume Alice needs to send an e-mail to Bob. Explain how the integrity of the e-mail is achieved using S/MIME.
How does PGP create a set of security parameters?
Assume Alice needs to send an e-mail to Bob. Explain how the authentication of the e-mail is achieved using S/MIME.
What is the purpose of the Handshake Protocol in SSL?
Assume Alice needs to send an e-mail to Bob. Explain how the confidentiality of the e-mail is achieved using S/MIME.
What is the purpose of the Record Protocol in SSL?
When we talk about authentication in SSL, do we mean message authentication or entity authentication? Explain.
What is the purpose of a firewall?
When we talk about authentication in PGP (or S/MIME), do we mean message authentication or entity authentication? Explain.
What are the two types of firewalls?
If cryptography algorithms in PGP or S/MIME cannot be negotiated, how can the receiver of the e-mail determine which algorithm has been used by the sender?
What is a VPN and why is it needed?
How do LANs on a fully private internet communicate?
In a Chord network with m = 4, node N2 has the following finger-table values: N4, N7, N10, and N12. For each of the following keys, first find if N2 is the predecessor of the key. If the answer is no, find which node (the closest predecessor) should be contacted to help N2 find the predecessor.a.
Distinguish between structured and unstructured decentralized P2P networks.
In a Chord network using DHT with m = 4, draw the identifier space and place 4 peers with node ID addresses N3, N8, N11, and N13 and three keys with addresses k5, k9, and k14. Determine which node is responsible for each key. Create a finger table for each node.
What are the advantages and disadvantages of a decentralized P2P network?
In Chord, assume that the successor of node N12 is N17. Find whether node N12 is the predecessor of any of the following keys.a. K12b. K15c. K17d. K22
What are the advantages and disadvantages of a centralized P2P network?
In Chord, assume the size of the identifier space is 16. The active nodes are N3, N6, N8, and N12. Show the finger table (only the target-key and the successor column) for node N6.
Distinguish between centralized and decentralized P2P networks.
Can H.323 also be used for video?
Do some research and find out if SIP can provide the following services provided by modern telephone sets.a. Caller-IDb. Call-waitingc. Multiparty calling
Can the combination of RTP/RTCP and SIP operate in a wireless environment? Explain.
In which situation, a unicast session or a multicast session, can feedback received from an RTCP packet about the session be handled more easily by the sender?
Assume two parties need to establish IP telephony using the service of RTP. How can they define the two ephemeral port numbers to be used by RTP, one for each direction?
We discuss the use of SIP in this chapter for audio. Is there any drawback to prevent using it for video?
We mentioned that SIP is an application-layer program used to provide a signalling mechanism between the caller and the callee. Which party in this communication is the server and which one is the client?
Does SIP need to use the service of RTP? Explain.
Why does RTP need the service of another protocol, RTCP, but TCP does not?
Can we say UDP plus RTP is the same as TCP?
Assume an application program uses separate audio and video streams during an RTP session. How many SSRCs and CSRCs are used in each RTP packet?
UDP does not create a connection. How are different chunks of data, carried in different RTP packets, glued together?
Assume an image is sent from the source to the destination using 10 RTP packets. Can the first five packets define the encoding as JPEG and the last five packets define it as GIF?
Are encoding and decoding of the multimedia data done by RTP? Explain.
If we capture RTP packets, most of the time we see the total size of the RTP header as 12 bytes. Can you explain this?
Can UDP without RTP provide an appropriate service for real-time interactive multimedia applications?
Both TCP and RTP use sequence numbers. Do sequence numbers in these two protocols play the same role? Explain.
Explain why RTP cannot be used as a transport-layer protocol without being run on the top of another transport-layer protocol such as UDP
In a real-time multimedia communication, assume we have one sender and ten receivers. If the sender is sending multimedia data at 1 Mbps, how many RTCP packets can be sent by the sender and each receiver in a second? Assume the system allocates 80 percent of the RTCP bandwidth to the receivers and
When we use audio/video on demand, which of these three types of multimedia communication takes place: streaming stored audio/video, streaming live audio/video, or real-time interactive audio/video?
Given an RTP packet with the first 8 hexadecimal digits as (86032132)16, answer the following questions:a. What is the version of the RTP protocol?b. Is there any padding for security?c. Is there any extension header?d. How many contributors are defined in the packet?e. What is the type of payload
Figure 28.43 shows the generated and the arrival time for ten audio packets. Answer the following questions:Figure 28.43a. If we start our player at t8, which packets cannot be played?b. If we start our player at t9, which packets cannot be played? Packets generated Packets arrived Packets 10 9. 7
In the fourth approach to streaming audio/video (Figure 28.27), what is the role of RTSP?Figure 28.27 Server machine Client machine GET: metafile Web Browser RESPONSE server 3 Metafile SETUP RESPONSE PLAY Media RESPONSE Media player server Audio/video Stream TEARDOWN RESPONSE
When we stream stored audio/video, what is the difference between the second approach (Figure 28.25) and the third approach (Figure 28.26)?Figure 28.25Figure 28.26 Server machine Client machine GET: metafile Browser RESPONSE Web server Metafile GET: audio/video file Media 4 player RESPONSE
In Figure 28.31, what is the amount of data in the playback buffer at each of the following times?Figure 28.31a. 00:00:17b. 00:00:20c. 00:00:25d. 00:00:30 At time 00:00:08 Arrival Playback 7 At time 00:00:18 Arrival Playback 3 At time 00:00:28 Arrival Playback
In the first approach to streaming stored audio/video (Figure 28.24), assume that we need to listen to a compressed song of 4 megabytes (a typical situation). If our connection to the Internet is via a 56-kbps modem, how long will we need to wait before the song can be started (downloading
When we stream stored audio/video, what is the difference between the first approach (Figure 28.24) and the second approach (Figure 28.25)?Figure 28.24Figure 28.25 Server machine Client machine GET: audio/video file Web Browser RESPONSE server (3 Audio/video file Media player
Assume an image uses a palette of size 8 out of the table used by JPEG (GIF uses the same strategy, but the size of the palette is 256), with the combination of the following colors with the indicated level of intensities.Red: 0 and 7 Blue: 0 and 5 Green: 0 and 4Show the
In multimedia communication, assume a sender can encode an image using only JPEG encoding, but the potential receiver can only decode an image if it is encoded in GIF. Can these two entities exchange multimedia data?
Using one-dimensional DCT encoding, calculate the M matrix from the following three p matrices (which are given as row matrices but need to be considered as column matrices). Interpret the result.p1 = [1 2 3 4 5 6 7 8] p2 = [1 3 5 7 9 11 13 15] p3 = [1 6 11 16 21 26 31 36]
Explain why the combination of quantization/dequantization steps in JPEG is a lossy process even though we divide each element of the matrix M by the corresponding value in matrix Q when quantizing and multiply it by the same value when dequantizing.
Calculate the T matrix for DCT when N = 1, N = 2, N = 4, and N = 8.
In JPEG, explain why we need to round the result of division in the quantization step.
Explain why using Q10 gives a better compression ratio but a poorer image quality than using Q90 (see Figure 28.18).Figure 28.18 Figure 28.18 Three different quantization matrices 80 60 50 80 120 200 255 255 55 60 70 95 130 255 255 255 70 65 80 120 200 255 255 255 70 85 110 145 255 255 255 255 16
In JPEG, explain why the values of the Q(m, n) in the quantization matrix are not the same. In other words, why is each element in M(m, n) not divided by one fixed value instead of a different value?
In one-dimensional DCT, if N = 1, the matrix transformation is changed to simple multiplication. In other words, M = T × p, in which T, p, and M are numbers (scalar value) instead of matrices. What is the value of T in this case?
In JPEG, do we need less than 24 bits for each pixel if our image is using one or two primary colors? Explain.
Assume we have the following code. Show how we can calculate the reconstructed value (yn) for each sample if we use ADM. Let y0 = 20, Δ1 = 4, M1 = 1. Also assume that Mn = 1.5 × Mn–1 if qn = qn–1 (no change in qn) and Mn = 0.5 × Mn–1 otherwise. 1 3 4 5 6 8 9 10 11 1 1 2.
In transform coding, when a sender transmits the M matrix to a receiver, does the sender need to send the T matrix used in calculation? Explain.
What is the problem with a speech signal that is compressed using the LPC method?
In predictive coding, we have the following code. Show how we can calculate the reconstructed value (yn) for each sample if we use delta modulation (DM). We know that y0 = 8 and Δ = 6. 1 2 3 4 5 7 8 9. 10 11 1 1 1
What is the difference between DM and DPCM?
In predictive coding, assume we have the following sample (xn).a. Show the encoded message sent if we use delta modulation (DM). Let y0 = 10 and Δ = 8.b. From the calculated qn values, what can you say about the given Δ? 1 3 4 5 6 7 8 10 11 X 13 24 46 60 45 32 30 40 30 27 20
Answer the following questions about predictive coding:a. What are slope overload distortion and granular noise distortion in DM coding?b. Explain how ADM coding solves the above errors.
In arithmetic coding, assume we have received the code 100110011. If we know that the alphabet is made of four symbols with the probabilities of P(A) = 0.4, P(B) = 0.3, P(C) = 0.2, and P(*) = 0.1, find the original message.
Compare the number of bits transmitted for each PCM and DM sample if the maximum quantized value isa. 12b. 30c. 50
Given the message “ACCBCAAB*”, in which the probabilities of symbols are P(A) = 0.4, P(B) = 0.3, P(C) = 0.2, and P(*) = 0.1,a. find the compressed data using arithmetic coding with a precision of 10 binary digits.b. find the compression ratio if we use 8 bits to represent a character in the
In predictive coding, differentiate between DPCM and ADPCM.
In SCTP, a packet is carrying a COOKIE ACK message and a DATA chunk. If the user data is 20 bytes, what is the size of the packet?
Write a method in Java to find the first address (network address) in the block when one of the addresses in the block is given as a string representing a CIDR notation.
Show the encoding for the INTEGER 1456 using BER.
Given the code 02040000C738, decode it using BER.
Can an SNMP message reference a leaf node in the MIB tree? Explain.
Assume a manageable object has only three simple variables. How many leaves can be found in the MIB tree for this object?
Assume a manageable object has a table with three columns. How many leaves are there in the MIB tree for this table?
Distinguish between a GetRequest PDU and a SetRequest PDU.
In SNMP, which of the following PDUs are sent from a client SNMP to a server SNMP?a. GetRequestb. Responsec. Trap
What are the source and destination port numbers when an SNMP message carries one of the following PDUs?a. GetRequestb. Responsec. Trapd. Report
In dictionary coding, if there are 60 characters in the message, how many times is the loop in the compression algorithm iterated? Explain.
A program for coding and decoding the first version of the run-length compression method.A program for coding and decoding the second version of the run-length compression method.
Given the following message, find the compressed data using run-length coding.AAACCCCCCBCCCCDDDDDAAAABBB
In dictionary coding, should all dictionary entries that are created in the process be used for encoding or decoding?
A program for coding and decoding the second version of the run-length compression method.
Given the following message, find the compressed data using the second version of run-length coding with the count expressed as a four-bit binary number.10000001000001000000000000010000001
In an alphabet with 20 symbols, what is the number of leaves in a Huffman tree?
In dictionary coding, can you easily find the code if the message is each of the following (the message alphabet has only one character)?a. “A”b. “AA”c. “AAA”d. “AAAA”e. “AAAAA”f. “AAAAAA”
Is the following code an instantaneous one? Explain. 11 001 011 111 00 01 10
A program for encoding and decoding arithmetic compression.
In LZW coding, the message “AACCCBCCDDAB” is given.a. Encode the message. (See Figure 28.2.)Figure 28.2b. Find the compression ratio if we use 8 bits to represent a character and four bits to represent a digit (hexadecimal). Message| BAАВАВВBAABBВВА Notes: LZW Encoding Dictionary In
Assume a message is made of four characters (A, B, C, and D) with equal probability of occurrence. Guess what the encoding Huffman table for this message would be. Does encoding here really decrease the number of bits to be sent?
A program that reads a two-dimensional matrix of size N × N and writes the values using zigzag ordering described in the chapter.
In LZW coding, the code “0026163301” is given. Assuming that the alphabet is made of four characters: “A”, “B”, “C”, and “D”, decode the message. (See Figure 28.3.)Figure 28.3 Code 1002163670 LZW Decoding Notes: Dictionary In each iteration, we show A Output B whether an
In arithmetic coding, could two different messages be encoded in the same interval? Explain.
A program that finds the DCT transform of a one-dimensional matrix. Use matrix multiplication.
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