Comp 346 Midterm Study Guide Midterm is now MONDAY, MARCH 21. Here is a summary of the sections we have covered: Chapter 1: You should skim all of this; there are some important concepts summarized in section 1.3. Chapter 2: 2.1, 2.2: protocols generally, and what they cover 2.3, 2.4: OSI and TCP/IP protocols; the layer model generally Chapter 3: 3.1: Frequency, bandwidth, spectrum; intro to Fourier analysis You are not expected to follow all the math, but you should have some idea that any signal can be expressed as a combination of sine waves. 3.2: Bandwidth requirements, mostly, for voice and video; analog v digital 3.3: Transmission impairments: attenuation, distortion, noise 3.4: Channel capacity Nyquist: C = 2B log_2 M B=bandwidth, M=#levels Shannon: C = B log_2 (1+SNR) Appendix 3A: decibels: Chapter 4: 4.1: Twisted pair Coax Optical Fiber 4.2: microwaves, etc Chapter 5: 5.1: Digital data, digital signals: NRZ, NRZI, bipolar, Differential Manchester, B8ZS 5.2: Digital data, analog signals: ASK, FSK, PSK 5.3: Analog data, digital signals: digitization nonlinear encoding delta modulation 5.4: Analog data, analog signals AM, FM, PM Chapter 6: omit Chapter 7: 7.1: stop-and-wait, sliding windows 7.2: add go-back-N ARQ versus selective-reject ARQ 7.3: HLDC (as an example of sliding windows) Chapter 8: 8.1: Frequency division multiplexing (basics) 8.2: Synchronous Time-Division Multiplexing, T-carrier, SONET Chapter 10: 10.1: basics of switching 10.2: circuit switching, trunks, subscriber lines 10.3: switches: crossbar, 3-stage space-division switch, etc 10.4: control signaling, inband v out-of-band, SS7 10.6: switching principles: datagram routing versus virtual circuits Any purely arbitrary distinctions, such as whether 1=low or 1=high, will be provided to you on the exam. ============================================== Here are a few exercises. The first number is the problem number in the seventh edition; the second number is the problem number from the sixth edition. Chapter 2: 4/1 7/7 Chapter 3 12/10 16/14 Chapter 4 2/2 4/4 Chapter 5 7/7 8/8 Chapter 7 1/1 3/3 9/17 Chapter 8 7/7 10/10 Chapter 10 1/Chapter 9 #2 3/1 4/2 Here are a few sample questions, intended to complement the exercises above. 1. Give a possible explanation for transmission distortion that is based on Fourier analysis. 2. Why is digital data often encoded via an analog signal? 3. Give some advantages of microwaves versus land lines, for long-distance transmission. 4. List some disadvantages with NRZ encoding for long lines (>= 10 km). Which, if any, are addressed by NRZI? Which, if any, are not an issue for shorter lines? 5. Suppose we take a 4-kHz voice signal and digitize it to a 56kbps signal. (a). What frequency bandwidth is needed to transmit this using binary signaling, so the signaling rate is also 56kbps? (b). What bandwidth is needed if we use 16-level signaling? How many bits can be sent in a single signal element? 6. Consider the following sequence of virtual-circuit routers, and tables. D | link3 | [1] A------link1-------[0]-B-[1]------link2---------[0]-C-[2]-----link4------E vci vci port vci vci port in out out in out out 3 5 1 5 4 2 4 2 1 2 3 1 List the VCI used on each link as A sends to D List the VCI used on each link as A sends to E 7. Why are virtual circuits called that? That is, why are they like circuits, and why is the adjective "virtual" there?