Mid Sweden University Exam in Computer Networks A (Datornätverk A) Course code: Time: Permitted tools Preliminary requirement for approval:

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1 Mid Sweden University Dept. of IT and Media (ITM) Magnus Eriksson Tel , Apr 20 Page of 7 Exam in Computer Networks A (Datornätverk A) Course code: DT024G Time: 8:00-2:00 Permitted tools: Arbitrary pocket calculator. A language dictionary, e.g. English-Swedish. Preliminary requirement for approval: 30 of 60 points. Only write on one side of each sheet. You may answer in Swedish or English. Your score will be presented at via the LADOK service in about three weeks, provided that you have concluded the course quizzes. Distance students: If you would like us to post you a copy of the marked exam, please contact our course expedition, itmexp.svl@miun.se. Good luck! THEORY PART. State what description (letter) that that corresponds to what illustration (number) below. Answer in alphabetical order. There is a one-to-one relationship. (2 p) a) TCP segment b) UDP datagram c) WDM d) UTP cable e) TDM f) Coaxial cable g) Ipv6 address h) IPv4 datagram i) STP cable j) FDM k) Ethernet frame l) Ethernet broadcast address.

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3 Exam in Computer Networks A 27 April 20 Page At which protocol layer in the five layer TCP/IP model are the following standards and protocols situated? (Only one layer for each sub-question) (6 p) a) RFC 2373; Ip version 6 addressing architecture. b) RFC 768; User Datagram Protocol. c) RFC 266; Hypertext Transfer Protocol HTTP/. d) The IEEE 802.3ab standard, also known as 000BASE-T, which defines gigabit Ethernet transmission over unshielded twisted pair (UTP) category 5, 5e, or 6 cabling. This standard does not specify the frame format. e) The IEEE 802.3x MAC sublayer frame format, common for all Ethernet II and IEEE networks independent of physical media. f) The V.42 error control standard used in dialup modems. It is based on automatic repeat request (ARQ) of data packets, and the ITU-T standard CRC32 polynomial x 32 +x 26 +x 23 +x 22 +x 6 +x 2 +x +x 0 +x 8 +x 7 +x 5 +x 4 +x 2 +x+.

4 Exam in Computer Networks A 27 April 20 Page 4 3. Explain the concept of Internet sockets. (Use the terms process, operational system, interface, port number, socket address, socket identifier, netstat command, IP address, server, client, TCP, UDP, listening state, uniquely identified by.) (6 p) 4. You are planning to deploy an Ethernet network in a new office building, and are considering three options for cabling:. Thinnet coaxial cable (Supports the 0Base-2 Ethernet physical layer standard, with BNC connector) 2. Unshielded twisted pair (category 5 cabling, which can support 0Base-T, 00Base-Tx and 000Base-Tx with RJ-45 connector) 3. Single mode fiber optics (supporting for example 00Base-Lx, 000Base-Lx or 0GBase-Lx4, the latter achieving 0 Gbit/s). What is the advantages and disadvantages of these three options in comparison to each other? Comment on at least eight of the following points. From your answer it should be clear which of the three cabling options: that is cheapest, that is standard in Network Interface Cards in today s computers, that may allow highest maximum bit rate, that facilitates longest maximum segment length, that is/is not sensitive to crosstalk (överhörning) and other electro-magnetic interference, that supports star, hub and bus network, and the advantages and disadvantages of these topologies, that provides full/half duplex that provides shared/dedicated bandwidth, that requires terminating resistors, where a cable breakdown typically affects many computers, that can be installed in the same cable channelization (tubes) as the telephone infrastructure, etc. (0 p)

5 Exam in Computer Networks A 27 April 20 Page 5 PROBLEM PART Show all calculcations. 5. A router has the following routing table. Destination Netmask Next-hop Interface Metric a. Where will a packet destined to address be forwarded? b. Where will a packet destined to address be forwarded? c. What is the broadcasting address of the subnet with subnet address ? d. How many subnets of the same size as subnet / can network / be divided into? (4 p) 6. A 50 mw signal is sent over a km long cable, which attenuates the signal 0.02 db/meter. What is the signal strength in mw in the other end of the cable? (2 p) 7. A TDM multiplexer combines four 8-Mbps channels using time slots of 4 bits. An overhead consisting of a frame header of 8 bit is added. What is the frame rate? What is the frame duration? What is the total bit rate of the multiplexed signal? What is the bit duration? (3 p) 8. You are assigned to design a system that should transfer data between an earth station and the international space station (ISCC), which is at about 400 km height over the earth station. You choose to use a full duplex radio link with the data rate of 00 Mbit/s, which transmits a sequence of data packets consisting of 4000 Bytes of data in each direction. a) What is the transmission time for one packet? (The time from the first until the last bit left the transmitter)? See also the equations in the end of the exam. b) What is the propagation delay (sw. utbrednings/överföringstiden), i.e the time from the packet left the transmitter until it reaches the receiver? c) What is the average throughput rate (genomsttrömningshastigheten) in bit/s if we use Stop-And-Wait ARQ? Piggy-backing is assumed, meaning that the ACK packets also include payload data, and that the packets have the same transmission time in both directions. d) If we use a sliding window protocol, what size of the buffer memory (the window) is required if we want to use the full data rate capacity of the radio link? (6 p)

6 Exam in Computer Networks A 27 April 20 Page 6 9. Below you find the constellation diagram for a modem. The bit rate is 3 Mbit/s. (5 p) a) What modululation method is used? PSK, ASK, QAM or FSK? How many symbols? b) Vhat is the symbol rate f sym in baud or symbols/second? c) Draw the time diagram for the message The carrier frequency (sw. bärfrekvensen) is 2 MHz. The time axis should be correctly graded. The horizental axis of the diagram (the I axis or inphase axis) corresponds to a sine wave amplitude, and the vertical axis (the Q axis, quadrature phase) shows the amplitude of the cosine component. 0. An error detecting code is added to the message What is the message inclusive of error detecting code, in case the following is used? (6 p) a. Odd parity (word length of 8 bit + parity bit). b. Two dimensional even parity, with row length of 4 bit. c. Check-sum, with row length of 4 bit. d. CRC with polynomial representation x 4 + x 3 + x + of the division. What is the binary representation of the divisor?

7 Exam in Computer Networks A 27 April 20 Page 7 Formelblad Datornätverk A Här följer ett urval av de formler som behandlas under kursens gång. Prefix kilo (k)= 0 3. Mega (M) = 0 6. Giga (G) = 0 9. Tera (T) = 0 2. milli (m)= 0-3. Micro (µ) = 0 6. Nano (n) = 0-9. Pico (p) = 0-2. Frekvens (Hertz) av periodisk signal: f =, T T = f där T är signalens periodtid i sekunder. Övertonsspektra: Grundfrekvens (first harmonic) f, första överton (second harmonic) 2f, andra överton (third harmonic) 3f, osv. DC-komponent (likspänning) 0 Hz. Datatakt (bit rate i bit/s): T b R =, Informationsmängd (bit): L bitar kan representera M = 2 N T b = där T är transmissionstiden för en bit R b olika koder. log M L = log2 M = (Oftast räcker huvudräkning.) log 2 Put Decibelmått: Effektförstärkning (power gain) GdB = 0log0 (ofta räcker P Analog bandbredd (Hertz): huvudräkning) Put P Dämpning (attenuation) AdB = GdB = 0log0 = 0log0 P P S Signal-brusförhållande SNRdB = 0log0 N Kaskadkopplade förstärkare: G = G + G2 + G TotaltdB db db db Bandbredd = Övre gränsfrekvens minus undre gränsfrevens. Basbandsbandbredd = Övre gränsfrekvens. Nyquists formel för samplingsfrekvens (samples/s): f > 2B krävs för att undvika vikningsdistorision Sampel (aliasing). Här är B den samplade signalens basbandsbandbredd. Nyquists formel för symboltakt: fs < 2B där fs är symboltakt i baud eller symboler/s, och B är kanalens bandbredd. Gäller främst linjekoder. I praktiken är fs < B vid många digitala modulationsmetoder, t.ex. QAM, PSK och ASK. Hartley s formel för digital modulation: R = fs log2 M S Shannon-Heartley s formel: I = B log 2 + N Transmissionstid: där R är datatakt, fs är symboltakt i baud eller symboler/s, och M är antal symboler, t.ex. vid M-QAM eller M-PSK-modulation där I är kanalkapaciteteten (max informationstakten eller net bit rate, inkl. ev. felrättande kod, i bit/s), B är bandbredden i Hertz och S/N är signalbrusförhållandet i gånger (inte decibel). Tx L R T = där L är meddelandets längd i bit, och R är datatakt i bit/s. Överföringstid (propagation time): T = där d är avståndet, och v är utbredningshastigheten. Ljusets och radiovågors utbredningshastighet: p d v 8 c = 3 0 m/s in in in ut