CS 742 Computer Communication Networks Final Exam - Name ...

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( B ) 17. Which device operates in the data link layer? (A) repeater (B) bridge (C) router (D) gateway ( D ) 18. Which is not a routing algorithm or protocol? (A) Distance Vector (B) BGP (C) OSPF (D) none of the above ( D ) 19. Which type is set to query the domain name server in nslookup? (A) MX (B) HINFO (C) CNAME (D) NS ( B ) 20. In Java socket programming, which class represents a socket for sending and receiving datagram packets on the server side? (A) DatagramPacket (B) DatagramSocket (C) ServerSocket (D) DatagramServerSocket ( D ) 21. The assigned port for the SMTP server is: (A) 21 (B) 22 (C) 23 (D) 25 ( C ) 22. Which server interprets name to IP address and vice versa? (A) SMTP (B) FTP (C) DNS (D) DHCP ( B ) 23. IPv6 represents local loopback address as (A) ::127.0.0.0 (B) ::1 (C) ::0 (D) none of the above ( A ) 24. Which can be used to encrypt and decrypt email? (A) PGP (B) TLS (C) RTP (D) SSH ( A ) 25. Which command prints network connections, routing tables, and interface statistics? (A) netstat (B) ping (C) traceroute (D) dig Part 2: (125 points) 1. (15 pts.) Briefly explain these terminologies. If they are acronyms, also write what they stand for. (a) BGP Border Gateway Protocol (BGP) is a protocol for exchanging routing information between autonomous systems. (b) NAT Network Address Translation (NAT) is the translation of an IP address used within one network to a different IP address known within another network. (c) CSMA/CA Carrier Sensing Multiple Access with Collision Avoidance (CSMA/CA) is a protocol used in wireless networking. (d) AODV Ad hoc On-demand Distance Vector (AODV) is a routing algorithm used to solve the problem of mobile routers. (e) HTTPS The HyperText Transport Protocol Secure (HTTPS), is standard encrypted communication mechanism on the World Wide Web. It is just HTTP over SSL. 2. (10 pts.) Complete the following table listing the seven layers in the OSI 7-Layer Reference Model. Then, identify three of the four layers used in the TCP/IP protocol suite (write TCP/IP beside them). Finally, identify where the following protocols belong: TCP, UDP, IP, ICMP, PPP, RARP, IMAP. • Layer 7: Application Layer - IMAP (TCP/IP) • Layer 6: Presentation Layer • Layer 5: Session Layer • Layer 4: Transport Layer - TCP, UDP (TCP/IP) • Layer 3: Network Layer - IP, ICMP (TCP/IP) • Layer 2: Data Link Layer - PPP, RARP (TCP/IP) • Layer 1: Physical Layer
3. (9 pts.) Recall the Nyquist’s theorem: A filtered signal, run through a filter of bandwidth H Hz, can be completely reconstructed by taking 2H exact samples per second. If the signal has V discrete levels: max. data rate = 2Hlog 2 (V ) bits/sec. Now, answer the following questions: (a) A media server is transmitting a video of 2 x 2 inch at a resolution 60 pixels per inch, 2 bytes/pixel color encoding and 30 frames/second. Calculate the bandwidth necessary for transmitting in real times. (b) A noiseless channel is 2-MHz wide. How many bits per second can be sent on this noiseless channel if four-level digital signals are used? (c) Without loss of the resolution and color, how many frames per second can this media server transfer on this noiseless channel? Ans: (a) A frame size is 2 × 2 × 60 2 × 2 × 8 = 0.2304 Mbps. The bandwidth is 0.2304 × 30 = 6.912 Mbps. (b) The noiseless channel provide 2 × 2 log 2 (4) = 8 Mbps transfer rate. (c) It can transfer 8/0.2304 = 34 frames/s 4. (12 pts.) Suppose that a code consists of the following valid codewords: {00000000, 00001111, 11110000, 11111111}. (a) What is the Hamming distance of the code? (b) Can a single bit error be corrected? Explain. (c) If a codeword 00000011 is received, it must contain errors. Assuming that only two errors have occurred, can these two errors be corrected? Briefly explain how it would corrected, or why it cannot be corrected. Ans: (a) The Hamming distance of the code is 4 because the number of bit positions in which two codewords differ is 4. (b) Yes, to correct a single bit error the Hamming distance 2 × 1 + 1 = 3 is required. The Hamming distance of the code is 4 > 3. So one bit error can be corrected. (c) No, there is no way to tell 00000000 or 00001111 will be the correct codeword. To correct 2 bit error, 2d + 1 = 2 × 2 + 1 = 5 Hamming distance is required.
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Page 5 and 6: 9. (12 pts.) An organization has a

CS 742 Computer Communication Networks Final Exam - Name ...

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