Answers to Review Questions Ch 2, 3
2.3 The process that takes advantage of redundancy to reduce the number of bits sent for a given piece of data is called what?
2.6 Explain the basic principles of vector graphics and raster graphics. In vector graphics, an image is represented as a collection of straight and curved line segments. Simple objects, such as rectangles and ovals, and more complex objects are defined by the grouping of line segments. In raster graphics, an image is represented as a two-dimensional array of spots, called pixels, which may take on the values black or white, or may be gray scale 2.10 Define response time.
The time is takes for a system to respond to a given input.
2.11 What is considered an acceptable system response time for interactive applications and how does this response time relate to acceptable response times for Web sites? In order to increase productivity, system response times should be kept to 2 seconds or less. For the World Wide Web, site response time should be kept to 3 seconds or less to ensure user interest levels are kept high.
2.1 How many CD-quality music channels can be transmitted simultaneously over a 10-Mbps Ethernet, assuming that no other traffic is carried on the same network and ignoring overhead? The required bandwidth for each CD-quality music channel is 44100 Hz ×2 ×16 bits = 1,411,200 bps . Assuming that no other traffic is carried on the same network, seven CD-quality music channels can be transmitted simultaneously.
2.3 A company’s telephone exchange digitizes telephone channels at 8000 smp/s, using 8 bits for quantization. This telephone exchange must transmit simultaneously 24 of these telephone channels over a communications link.
a. What’s the required data rate?
The required bandwidth for transmitting the 24 telephone channels is 1.536 Mbps. b. In order to provide answering-machine service, the telephone exchange can store 3-minute audio messages of the same quality as that of the telephone channels. How many megabytes of data storage space are needed to store each of these audio messages?
For storing each of the 3-minute audio messages, 1.152 MB of data storage space are needed
2.4 How many bits will it take to represent the following sets of outcomes? a. The uppercase alphabet A, B,...,Z
5 bits (25 = 32)
b. The digits 0, 1,...,9
4 bits (24 = 16, this is one reason why hexadecimal is used) c. The seconds in a 24-hour day
17 bits (The size of the set is 60 × 60 × 24 = 86,400
217 = 2 × 65,536 = 131,072)
d. The people in the United States (about 300,000,000 of them)
29 bits (229 = 536,870,912)
e. Population of the world (about 6 billion)
33 bits 233 = 8,589,934,592
2.7 In a document, what standard ASCII characters might fall into the category of invisible?
Carriage return, space, tabulation, form feed, line feed, separators
2.10 The text of the Encyclopaedia Britannica is about 44 million words. For a sample of about 2000 words, the average word length was 5.1 characters per word. a. Approximately how many characters are there in the encyclopedia? (Be sure to allow for spaces and punctuation between words.)
We allow one extra character per word for spaces and punctuation. Thus, the total number of characters is about 6.1 44,000,000 = 268,400,000 bytes, or 2.147 Gb
b. How long would it take to transmit the text over a T-1 line at 1.544 Mbps? On a fiber optic link at 2.488 Gbps?
Transmission time at 1.544 Mbps is 2,147/1.544 = 1391 seconds or about 23 minutes. At 2.488 Gbps the transmission time is under a second. c. Could the text fit on a 600-MB CD?
The text (note we have not considered the pictures) would take less than onehalf of a CD (2.147/5 = 0.43).
2.11 A drawing in a 8.5-by-11-inch sheet is digitized by means of a 300 dpi (dots per inch) scanner. a. What is the visual resolution of the resulting image (number of dots in each dimension)?
The visual resolution of the...
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