Comp 346/446 Midterm Study Guide

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:  Good discussion of exponential attenuation of guided media 
  	versus inverse-square attenuation of wireless is in the
  	subsection beginning Terrestrial Microwave -- Transmission Characteristics.
  	(p 110 of 7th ed)


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
 	(Seventh ed only, not in 8th ed)
 10.5/10.4: Softswitch architecture
 10.6/10.5:  packet switching principles: 
 	datagram routing versus virtual circuits
 	Note: details of VCI tables are *not* in Stallings
 10.7/10.6: X.25 (skim)
 10.8/10.7: frame relay


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 numbering is 9th_edition/8th_edition/7th_edition. 

Chapter 2:
4/4/4
6/6/7

Chapter 3
Review homework 1

Chapter 4
4/4/4
6/6/6

Chapter 5
7/7/7
8/8/8
18/18/17

Chapter 7
1/1/1
4/4/?
5/5/4 (a good problem)
10/10/9

Chapter 8
7/7/7
10/10/10
This is a little "engineery", but better problems are hard to find.
Assume the analog signal is sampled at a rate twice the bandwidth,
ie 1000 Hz.  (Those samples are the 4-bit PCM.)
Also, assume that the digital signals *enter* the Pulse Stuffers at 300 Hz,
but exit to the right at 400 Hz. Most of the remaining work is just
relabeling the diagram with new rates.

17/17/17

Chapter 10
1/1/1
3/3// (a good problem, but not there before the 8th edition)
4/4/3
5/5/4

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?


8. Look at the three-stage space division switch in Fig 10.6 (all editions).
Modify it so the second stage has 3x3 crossbars instead of 2x2, and any 
three connections can be made. What other changes do you have to make?