ELEC 5120/6120 - Telecommunication Networks

Fall 2009

Instructor: Dr. Shiwen Mao

Course website: http://www.eng.auburn.edu/~szm0001/ELEC5120-6120-F09/

Textbook:

• W. Stallings, Data and Computer Communications, 8th Ed., Prentice Hall, 2007.

Reference books:

• B. A. Forouzan, Data Communications and Networking, 4th Ed., McGraw Hill, 2006.
• S. Keshav, An Engineering Approach to Computer Networking: ATM Networks, the Internet, and Telephone Network, Addison Wesley, 1997.

Syllabus: PDF

Questions & answers:

• Click here (last updated: Oct. 14, 2009)
• Questions & answers from previous classes: click here.

Class room & hour: Broun 107, Tuesday and Thursday, 14:00-15:15.

Office hour: Thursday 15:30-16:30, drop by my office (Broun 301) any time, or email for appointment

Final exam hours: Friday, December 11, 16:00 - 18:30, according to AU Exam Schedules

Aug. 17, 2009, Monday

• Welcome!

Aug. 19, 2009, Wednesday

• The slides for lectures 1 and 2 have been sent to you via email. If you have not received the email, please let me know.
• Our first reading assignment: Chapter 1 "Data Communications, Data Networking, and the Internet" and Chapter 2 "Protocol Architecture, TCP/IP, and Internet-Based Applications."

Aug. 24, 2009, Monday

• More readings: Appendix H of Stalling’s book.
• Homework assignment 1: Problems 2.3, 2.5, 2.6, 2.8, and 10.4 in the textbook. It is due Tuesday Sept. 1, before the class. The problems are:
• Prob. 2.3:  List the major disadvantages with the layered approach to protocols.
• Prob. 2.6:  In Figure 2.2, exactly one protocol data unit (PDU) in layer N is encapsulated in a PDU at layer (N-1). It is also possible to break one N-level PDU into multiple (N-1)-level PDUs (segmentation) or to group multiple N-level PDUs into one (N-1)-level PDU (blocking).
  o In the case of segmentation, is it necessary that each (N-1)-level segment contain a copy of the N-level header?
  o In the case of blocking, is it necessary that each N-level PDU retain its own header, or can the data be consolidated into a single N-level PDU with a single N-level header?
• Prob. 2.5:  A broadcast network is one in which a transmission from any one attached station is received by all other attached stations over a shared medium. Examples area a bus-topology local area network, such as Ethernet, and a wireless radio network. Discuss the need or lack of need for a network layer (OSI layer 3) in a broadcast network.
• Prob. 2.8: Why is UDP needed? Why cannot a user program directly access IP?
• Prob. 10.4: Explain the flaw in the following reasoning: Packet switching requires control and address bits to be added to each packet. This introduces considerable overhead in packet switching. In circuit switching, a transparent circuit is established. No extra bits are needed. Therefore, there is no overhead in circuit switching. Because there is no overhead in circuit switching, line utilization must be more efficient than in packet switching.
• I also put some hard copies of the homework problems in an envelop outside my office. You can pick it up if necessary.

Sept. 1, 2009, Tuesday

• Homework assignment 2: Problems 3.13, 3.14, 3.15, 3.16, and 3.19 in the textbook. It is due Tuesday Sept. 8, before the class.

          The problems are:

• Prob. 3.13:  (a) Suppose that a digitized TV picture is to be transmitted from a source that uses a matrix of 480*500 picture elements (pixels), where each pixel can take on one of 32 intensive values. Assume that 30 pictures are sent per second. (This digital source is roughly equivalent to broadcast TV standards that have been adopted.) Find the source rate R (bps).
  (b) Assume that the TV picture is to be transmitted over a channel with 4.5-MHz bandwidth and a 35 dB signal-to-noise ratio. Find the capacity of the channel (bps).
  (c) Discuss how the parameters given in part (a) could be modified to allow transmission of color TV signal s without increasing the required value for R.
• Prob. 3.14: Given an amplifier with an effective noise temperature of 10,000 K and a 10-MHz bandwidth, what thermal noise level, in dBW, may we expect at its output?
• Prob. 3.15:  What is the channel capacity for a teleprint channel with a 300-Hz bandwidth and a signal-to-noise ratio of 3 dB, where the nose is white thermal noise?
• Prob. 3.16: A digital signaling system is required to operate at 9600 b/s.
  - If a signal element encodes a 4-bit word, what is the minimum required bandwidth of the channel?
  - Repeat part (a) for the case of 8-bit words.
• Prob. 3.19: Consider a channel with a 1-MHz capacity and an SNR of 63.
  - What is the upper limit to the data rate that the channel can carry?
  - The result of part (a) is the upper limit. However, as a practical matter, better error performance will be achieved at a lower data rate. Assume we choose a data rate of 2/3 the maximum theoretical limit. How many signal levels are needed to achieve this data rate.

I also put some hard copies of the homework problems in an envelop outside my office. You can pick it up if necessary.

Sept. 8, 2009, Tuesday

• This is the H1N1 contingency statement as required by the provost:

        If normal class and/or lab activities are disrupted due to a high number of students experiencing illness or an emergency or crisis situation (such as a widespread H1N1 flu outbreak), the syllabus and other course plans and assignments may be modified to allow completion of the course. If this occurs, an addendum to your syllabus and/or course assignments will replace the original materials.

• Homework 2 solution has been emailed to the class.
• Homework assignment 3: Problems 3.21, 3.23, 4.1, 4.2, 4.17 in the textbook. It is due Tuesday Sept. 15, before the class. The problems are:
  • Prob. 3.21:  Given a channel with an intended capacity of 20 Mbps, the bandwidth of the channel is 3 MHz. Assuming white thermal noise, what signal-to-noise ratio is required to achieve this capacity?
  • Prob. 3.23: If the received signal level for a particular digital system is -151 dBW and the receiver system effective noise temperature is 1500K, what is Eb/N0 for a link transmitting 2400 bps?
  • Prob. 4.1:  Suppose that data are stored on 1.4-Mbyte floppy diskettes that weigh 30 g each. Suppose that an airliner carries 10,000 kg of these floppies at a speed of 1000 km/h over a distance of 5000 km. What is the data transmission rate in bits per second of this system?
  • Prob. 4.2: A telephone line is known to have a loss of 20 dB. The input signal power is measured as 0.5W, and the output noise level is measured as 4.5 uW. Using this information, calculate the output signal-to-noise ratio in dB.
  • Prob. 4.17: Determine the height of an antenna for a TV station that must be able to reach customers up to 80 km away.

Sept. 15, 2009, Tuesday

• Reminder: our first midterm exam will be on Thursday Sept. 24, 2:00am~3:15pm, BR 107. Chapter 1, 2, 3, 4 and 5 will be covered. Feel free to see me if you need any help with the material.
• Homework 3 solution has been emailed to the class.
• Homework assignment 4: Problems 4.3, 4.14, 4.15, 5.4, 5.6, 5.20, and 5.21 in the textbook. It is due Tuesday Sept. 22 before the class. This is a hard deadline since I will discuss the solution in the class and distribute the solutions after the class. The problems are:
  • Prob. 4.3: Given a 100 W power source, what is the maximum allowed length for the following transmission media if a signal of 1 W is to be received? (a) 24-gauge (0.5 mm) twisted pair operating at 300 Hz. (b) 24-gauge (0.5 mm) twisted pair operating at 1MHz. (c) 0.375-in (9.5 mm) coaxial cable operating at 1 MHz. (d) 0.375-in (9.5 mm) coaxial cable operating at 25 MHz. (e) optical fiber operating at its optimal frequency.
  • Prob. 4.14: Suppose a transmitter produces 50 W of power. (a) Express the transmit power in units of dBm and dBW. (b) If the transmitter’s power is applied to a unity gain antenna with a 900-MHz carrier frequency, what is the received power in dBm at a free space distance of 100 m? (c) Repeat (b) for a distance of 10 km. (d) Repeat (c) but assume a receiver antenna gain of 2.
  • Prob. 4.15:  A microwave transmitter has an output of 0.1 W at 2GHz. Assume that this transmitter is used in a microwave communication system where the transmitting and receiving antennas are parabolas, each 1.2 m in diameter. (a) What is the gain of each antenna in decibels? (b) Taking into account antenna gain, what is the effective radiated power of the transmitted signal? (c) If the receiving antenna is located 24 km from the transmitting antenna over a free space path, find the available signal power out of the receiving antenna in dBm units.
  • Prob. 5.4: Develop a state diagram (finite state machine) representation of pseudoternary coding.
  • Prob. 5.6: For the bit stream 01001110, sketch the waveforms for each of the codes of Table 5.2. Assume that the signal level for the preceding bit for NRZI was high; the most recent proceeding 1 bit (AMI) has a negative voltage; and the most recent preceding 0 bit (pseudoternary) has a negative voltage. 
  • Prob. 5.20: A signal is quantized using 10-bit PCM. Find the signal-to-quantization noise ratio.
  • Prob. 5.21: Consider an audio signal with spectral components in the range 300 to 3000 Hz. Assume that a sampling rate of 7000 samples per second will be used to generate a PCM signal. (a) For SNR=30 dB, what is the number of uniform quantization levels needed? (b) What data rate is required?

Oct. 8, 2009, Thursday

• Homework assignment 5: Problems 6.2, 6.10, 6.13, 6.14(b)(c), and 6.17 in Chapter 6. It is due Thursday Oct. 15 before the class. The problems are:
  • Prob. 6.2: A data source produces 7-bit IRA characters. Derive an expression of the maximum effective data rate (rate of IRA data bits) over an x-bps line for the following: (a) Asynchronous transmission, with a 1.5-unit stop element and a parity bit. (b) Synchronous transmission, with a frame consisting of 48 control bits and 128 information bits. The information field contains 8-bit (parity included) IRA characters. (c) Same as part (b), except that the information field is 1024 bits. 
  • Prob. 6.10: Consider a frame consisting of two characters of four bits each. Assume that the probability of bit error is 10-3 and that it is independent for each bit. (a) What is the probability that the received frame contains at least one error? (b) Now add a parity bit to each character. What is the probability?
  • Prob. 6.13:  For P=110011 and M=11100011, find the CRC.
  • Prob. 6.14: A CRC is constructed to generate a 4-bit FCS for an 11-bit message. The generator polynomial is X^4+X^3+1. (b) Encode the data bit sequence 10011011100 (leftmost bit is the least significant -- LSB) using the generator polynomial and give the codeword. (c) Now assume that bit 7 (counting from the LSB) in the codeword is in error and show that the detection algorithm detects the error.
  • Prob. 6.17: Calculate the Hamming pairwise distances among the following codewords: (a) 00000, 10101, 01010. (b) 000000, 010101, 101010, 110110. 

Oct. 13, 2009, Thursday

• Homework assignment 6: Problems 7.3, 7.4, 7.5, 7.7, and 7.10 in Chapter 7. It is due Tuesday Oct. 20 before the class. The problems are:
  • Prob. 7.3: A channel has a data rate of 4 kbps and a propagation delay of 20 ms. For what range of frame sizes does stop-and-wait give an efficiency of at least 50%? 
  • Prob. 7.4: Considering the use of 1000-bit frames on a 1-Mbps satellite channel with a 270-ms delay. What is the maximum link utilization for (a) stop-and-wait flow control? (b) Continuous flow control with a window size of 7? (c) Continuous flow control with a window size of 127? (d) Continuous flow control with a window size of 255?
  • Prob. 7.5: In Figure 7.10, frames are generated at node A and sent to node C through node B. Determine the minimum data rate required between nodes B and C so that the buffers of node B are not flooded, based on the following: (a) the data rate between A and B is 100 kbps, (b) the propagation delay is 5 us/km for both links, (c) there are full-duplex lines between the nodes, (d) all data frames are 1000 bits long, ACK frames are separate frames of negligible length, (e) between A and B, a sliding-window protocol with a window size of 3 is used, (f) between B and C, stop-and-wait is used, (g) there are no erros. HINT: in order not to flood the buffers of B, the average number of frames entering and leaving B must be the same over a long interval.

               

  • Prob. 7.7: No mention was made of reject (REJ) frames in the stop-and-wait ARQ discussion. Why is it not necessary to have REJ0 and REJ1 for stop-and-wait ARQ?
  • Prob. 7.10: Two neighboring nodes (A and B) use a sliding-window protocol with a 3-bit sequence number. As the ARQ mechanism, go-back-N is used with a window size of 4. Assuming A is transmitting and B is receiving, show the window positions for the following SUCCESSION of events: (a) Before A sends any frames, (b) After A sends frames 0, 1, 2 and receives acknowledgment from B for frames 0 and 1, (c) After A sends frames 3, 4, and 5 and B acknowledgments frame 4 and the ACK is received by A. 

Oct. 20, 2009, Tuesday

• Homework assignment 7: Question 8.6, Problems 8,1, 8.2, 8.7, and 8.8 in Chapter 8. Due Oct. 27, before the Tuesday class. I will discuss the solution in that class. The problems are:
  • Question 8.6: Why is a statistical time division multiplexer more efficient than a synchronous time division multiplexer? 
  • Prob. 8.1: The information in four analog signals is to be multiplexed and transmitted over a telephone channel that has a 400- to 3100Hz bandpass. Each of the analog baseband signals is bandlimited to 500 Hz. Design a communication system (block diagram) that will allow the transmission of these four sources over the telephone channel using (a) Frequency division multiplexing with SSB (single sideband) subcarriers; and (b) Time division multiplexing using PCM, assuming 4-bit samples. Show the block diagrams of the complete system, including the transmission, channel, and reception portions. Include the bandwidths of the signals at the various points in the systems.
  • Prob. 8.2: To paraphrase Lincoln: … all of the channel some of the time, some of the channel all of the time. … Refer to Figure 8.2 and relate the preceding to the figure.
  • Prob. 8.7: One of the 193 bits in the DS-1 transmission format is used for frame synchronization. Explain its use.
  • Prob. 8.8: In the DS-1 format, what is the control signal data rate for each voice channel?
• The second midterm exam is on Oct. 29, Thursday, 2:00pm – 3:15pm in 107 Broun Hall. It is closed-book but a sheet of notes is allowed.

Nov. 5, 2009, Thursday

• Homework assignment 8: Problems 9.2, 9.4 in Chapter 9, and 4 additional problems from the reference book. Due Nov. 12, before the Thursday class. The problems are:
  • Prob. 9.2: An FHSS system employs a total bandwidth of Ws=400 MHz and an individual channel bandwidth of 100 Hz. What is the minimum number of PN bits required for each frequency hop? 
  • Prob. 9.4: The following table illustrates the operation of an FHSS system for one complete period of the PN sequence.

    Time	0	1	2	3	4	5	6	7	8	9	10	11
    Input data	0	1	1	1	1	1	1	0	0	0	1	0
    Frequency	f1		f3		f23		f22		f8		f10
    PN Sequence	001				110				011
    Time	12	13	14	15	16	17	18	19
    Input data	0	1	1	1	1	0	1	0
    Frequency	f1		f3		f2		f2
    PN Sequence	001				001

    • What is the period of the PN sequence, in terms of bits in the sequence?
    • The system makes use of a form of FSK. What form of FSK is it?
    • What is the number of bits per signal element?
    • What is the length of a PN sequence per hop?
    • Is this a slow or fast FH system?
    • What is the total number of possible carrier frequencies?
    • Show the variation of the base, or demodulated, frequency with time.
  • Additional Prob. 1: We have a pure ALOHA network with 100 stations. If T_fr=1 us, what is the number of frames/s each station can send to achieve the maximum efficiency?
  • Additional Prob. 2: Repeat Additional Prob. 1 for slotted ALOHA.
  • Additional Prob. 3: One hundred stations on a pure ALOHA network share a 1-Mbps channel. If frames are 1000 bits long, find the throughput if each station is sending 10 frames per second.
  • Additional Prob. 4: In a CDMA/CD network with a data rate of 10 Mbps, the minimum frame size is found to be 512 bits for the correct operation of the collision detection process. What should be the minimum frame size if we increase the data rate to 100 Mbps? To 1 Gbps? To 10 Gbps?
• The final exam is on Friday, December 11, 16:00 - 18:30 in 107 Broun Hall. It is closed-book but a sheet of notes is allowed.

• Our arrangement for the last two classes:
  • Dec. 1, Tuesday: guest lecture by Mr. Sperby Piner.  He is an Auburn graduate and an network engineer working for AdTran, a Huntsville-based telecommunication company. He will talk about a brief history of telecommunication, current industrial practice, and job opportunities.
  • Dec. 3, Thursday: a presentation by Mr. Hasin A. Gandhakwala about a wireless networking project he is working on, and a presentation by Dr. Yihan Li, about a wireless networking project for search and rescue.

Nov. 12, 2009, Thursday

• Homework assignment 9: Question 10.6, Problems 10.2 and 10.3 in Chapter 10, and Question 12.4, Problems 12.1 and 12.7 in Chapter 12. Due Nov. 19, before the Thursday class. The problems are:
  • Question 10.6: What is the significance of packet size in a packet-switching network? 
  • Prob. 10.2: (a) If a crossbar matrix has n input lines and m output lines, how many crosspoints are required. (b) How many crosspoints would be required if there were no distinction between input and output lines (i.e., if any line could be interconnected to any other line serviced by the crossbar)? (c) Show the minimum configuration for (b).
  • Prob. 10.3: Consider a three-stage switch such as Figure 10.6. Assume that there are a total of N input lines and N output lines for the overall three-stage switch. If n is the number of input lines to a stage 1 crossbar and the number of output lines to a stage 3 crossbar, then there are N/n stage 1 crossbars and N/n stage 3 crossbars. Assume each stage 1 crossbar has one output line going to each stage 2 crossbar, and each stage 2 crossbar has one output line going go each stage 3 crossbar. For such a configuration it can be shown that, for the switch to be nonblocking, the number of stage 2 crossbar matrices must equal 2n-1. (a) What is the total number of crosspoints among all the crossbar switches? (b) For a given value of N, the total number of crosspoints depends on the value of n. That is the value depends on how many crossbars are used in the first stage to handle the total number of input lines. Assuming a large number of input lines to each crossbar (large value of n), what is the minimum number of crosspoints for a nonblocking configuration as a function of n? (c) For a range of N from 100 to 1,000,000, plot the number of crosspoints for a single-stage N by N switch and an optimum three-stage crossbar switch.
  • Question 12.4: What are the advantages and disadvantages of adaptive routing?
  • Prob. 12.1: Consider a packet switching network of N nodes, connected by the following topologies: (i) Star: once central node with no attached station; all other nodes attach to the central node. (ii) Loop: each node connects to two other nodes to form a closed loop. (iii) Fully connected: each node is directly connected to all other nodes. For each case, give the average number of hops between stations.
  • Prob. 12.7: Using Dijkstra’s algorithm, generate a least-cost route to all other nodes for nodes 2 throughput 6 of Figure 12.1. Display the results as in Table 12.2a (see page 10 of the slides)?

    

Nov. 17, 2009, Tuesday

• We will discuss congestion control today. The congestion control for ATM part in the chapter is not required. Instead, we will discuss the AIMD algorithm and its stability property. We have the following reading assignment:
  • DM Chiu and R Jain, "Analysis of the Increase and Decrease Algorithms for Congestion Avoidance in Computer Networks," Computer Networks and ISDN Systems, vol.17, pp.1-14, 1989. 
  • Chapter 24: Congestion Control and Quality of Service, in the reference book: B. A. Forouzan, Data Communications and Networking, 4th Ed., McGraw Hill, 2006. You can borrow my copy for a couple of hours a day. There is also a copy in the library.

• Prob. 12.5: In the discussion of the Bellman-Ford algorithm, it is asserted that at the iteration for which h=K, if any path of length K+1 is defined, the first K hops of that path form a path defined in the previous iteration. Demonstrate that this is true.
• Prob. 12.6: In step 3 of Dijkstra's algorithm, the least-cost path values are only updated for nodes not yet in T. Is it possible that a lower-cost path could be found to a node already in T? If so, demonstrate by example. If not, provide reasoning as to why not.
• Prob. 12.8: Repeat Problem 12.7 using the Bellman-Ford algorithm.
• Question 13.1: When a node experiences saturation with respect to incoming packets, what general strategy may be used?
• Question 13.3: Give a brief explanation of each of the congestion control techniques illustrated in Figure 13.5.

Nov. 18, 2009, Wednesday

• Announcement for HW 9: For problem 12.7, it is OK if you just generate the shortest path routes to all other nodes for Node 2.