For your reference, the following formulae are listed: 1) Transmission rate = (Baud rate) (bits per baud) 2) Nyquist’s Theorem: C = 2 W log2(M) Where W is the bandwidth in Hz, M # of detectable events (a.k.a. signal elements) C is the channel capacity in bits per second 3) Shannon’s Law: C = W log2(1 + S/N) Where W is the bandwidth in Hz, S/N is the signal power to noise power ratio, C is the channel capacity in bits per second 4) The ratio P2/P1 expressed in decibel is: 10 log10(P2/P1)
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1. Given the following communication diagram, identify each of the blocks appropriately as DTE, or DCE, or CC (communication channel)

Personal Modem Telephone Modem Personal Computer System Computer

2. A channel has a signal to noise ratio of 2047.Shannon’s capacity for the channel is 11 kbps. What is the bandwidth of the channel?

C = W log2(1 + S/N)

11000 = W log2(2048) 11000 = W * 11 W=1000 Hz
3. Which of the following is a form of software flow control? a) XON/XOFF b) RTS/CTS c) Selective ARQ d) Continuous ARQ

4. Given three channels A, B, and C with Bit Error Rates 10-6 , 10-5 , and 10-9 respectively. Which channel is better? And what is the number of errors that you will likely see on that channel when you transmit a one giga-bit file? A: 1 bit error in 10**6 bits; 1000 bit in error likely B: 1 bit error in 10**5 bits; 10000 bits in error likely

C: 1 bit error in 10**9 bits; 1 bit error likely

5. This modem standard supports speed of theoretically up to 56 Kbps over an analog telephone line. a) V.42 b) V.34 c) V.90 d) V.69

6. For the network shown below, indicate the Flow of information in terms of OSI layers in a connection from Host S to Host D.

Upto Appl Layer phy. Network Dlc Appl.

7. A signal passes through five channels, each with 2dB loss. How much is the signal attenuated? 10 dB loss

8. Longitudinal Redundancy Checks and Cyclic Redundancy Checks are forms of a) error correction b) error prevention c) error detection d) constellation points

9. A block of 200 ASCII characters (with 1-bit even parity) is to be transmitted over a serial link. Calculate the number of bits transmitted and the efficiency of the link if the Asynchronous link uses 2 stop bits. What is the efficiency of the link?
7(ASCII code)+1(Parity)+2(stop bits)+1(Start bit) = 11 bits; 2200 bits; 70%

10. Match items listed under a) with items listed under b): These pertain to reducing noise or interference on a line: a) 1. Line Conditioning --A------ 2. Repeater ---B------ 3. Amplifier ---C----- b) A) Is a service provided by a phone company. B) Retransmits a digital signal free of noise. C) Strengthens and repeats an analog signal.
11. Assume we are using Cyclic Redundancy Check with CRC-CCITT generator polynomial, x16 + x12 + x5 + 1 for detecting errors. How many bits will there be in the CRC? 16 bits----------
12. Given the following encoded signal form (The space between two vertical dashed lines indicates one bit-time):

What is the data represented by the signal if the waveform uses the following encoding rule:
“A 0 is represented with a low-to-high transition in the center of the bit, and a 1 is represented with a high-to-low transition in the center of the bit” 1 1 1 0 0 0 1 1 0

13. An asynchronous link transmits at 2400 bits per second. If the clock in the receiver is running 2% slow how many bits received correctly before an error occurs due to loss of synchronization? Assume that both transmitter and the receiver clocks start at the same time.

1/2400 sec is bit time. Clocks in the middle: 1/4800 sec. 0.02 is 1/4800 how much is 1--> 50/4800 sec. 50/4800 * 2400 --> 25 bits

14. The constellation diagram of a 2400 bits per second Modem signal is shown below.

What is the baud rate of the Modem?

Bits per baud = 3 2400 = 3 * buad rate ; baud rate = 800 baud

15. Assume we are using Cyclic Redundancy Check with the CRC-16 generator polynomial, x16 + x15 + x2 + 1, for detecting errors. What is the maximum burst error length that this CRC code can detect 100% of the time? ---15--------------

16. Match items listed under a) with items listed under b): These pertain to Modulation/Demodulation: a) Modulation method 1. Amplitude Modulation --A------- 2. Frequency Modulation ----B------ 3. Phase Modulation ----C------ b) Encoding of a binary digit 1 or zero with A) Increased decreased height B) Shorter or longer wavelength C) Departure from the “normal” continuous pattern

17. Match items listed under a) with items listed under b): a) Interface Types: 1. Hardware to Hardware Interface ---C------ 2. Hardware to software Interface ----B------ 3. Software to Software Interface ----A------ b) Examples of Interfaces: A) Oracle DBMS supplying data to Microsoft Office. B) Kernel issuing commands to CPU C) NIC card Plugged into a PCI bus Slot

18. Consider the network topology shown below.

a) Assume that the boxes labeled with “?” are “Ethernet Hubs” 1. Indicate the number of Ethernet “Collision Domains” in the network. Explain. Ethernet hubs are mere physical layer repeaters. Thus the whole network is one LAN segment and, thus, one collision domain

2. Does node A’s ARP table ever contain entries for node B ands node C network addresses? Explain. Node A’s ARP table contains entries for B and C since they are on the same LAN.

3. When node A is sending a packet to C, whose Ethernet address does node A use for the destination? Explain. Node A uses node C’s MAC address listed in its ARP table

4. Suppose there is a two-way communication between nodes A and B. Does node C get to see this traffic? Explain. Since, nodes A, B, C are on the same LAN, node C can see the communication between nodes A and B

b) Assume that the boxes labeled with “?” are “Ethernet Switches” Answer the same questions from a) above. 1. Indicate the number of Ethernet “Collision Domains” in the network. Explain. Ethernet switches forward packets depending on the MAC address of the packet. They segregate the LAN into segments. There are thus, three collision domains separated by switches.

2. Does node A’s ARP table ever contain entries for node B ands node C network addresses? Explain. Yes

3. When node A is sending a packet to C, whose Ethernet address does node A use for the destination? Explain. Same as in a) 3)

4. Suppose there is a two-way communication between nodes A and B. Does node C get to see this traffic? Explain. No, because the switch connecting node B and nde C’s LAN segments do not forward packets meant for middle LAN segment onto rightmost LAN segment.

c) Assume that the boxes labeled with “?” are “IP Routers” Answer the same questions from a) above. 1. Indicate the number of Ethernet “Collision Domains” in the network. Explain. The IP routers divide the network into three different LANs, each of which is a single collision domain.

2. Does node A’s ARP table ever contain entries for node B ands node C network addresses? Explain. No, because they are not on the same LAN.

3. When node A is sending a packet to C, whose Ethernet address does node A use for the destination? Explain. Node A uses the MAC address of the IP router that connects the left-most LAN with middle LAN. 4. Suppose there is a two-way communication between nodes A and B. Does node C get to see this traffic? Explain. NO

19. Consider an analog signal, which can range from –4V to +4V. The input signal is sampled at 20000 samples per second. The sample values are quantized using 16 equally spaced steps. At what data rate the resulting signal is sent? If 32 equally spaced steps are used instead of 16, what improvement do you expect in Signal to Noise ratio due to quantization?

4 bits per sample --> 80000 bits per second; 5 bits per sample--> 100000 bps; 6dB improvement

20. Consider two hosts H1 and H2, connected by a link with length of “m” meters, transmission rate of “R” bits per second, and propagation speed of “s” meters per second. Let “p” denote the propagation delay in seconds and “d” denote the transmission time in seconds. Host H1 is to send a packet of size “L” bits to Host H2. Suppose Host H1 begins to transmit the packet at time t=0. a) At time t=d, where is the last bit of the packet? b) Suppose p>d. At time t=d, where is the first bit of the packet? c) Suppose p