Solucion capitulo 3 -redes de computadores- garcia y wijaja

Solutions to Chapter 3
1. Suppose the size of an uncompressed text file is 1 megabyte. Solutions follow questions: [4 marks – 1 mark each for a & b, 2 marks c] a. How long does it take to downloadthe file over a 32 kilobit/second modem? T32k = 8 (1024) (1024) / 32000 = 262.144 seconds b. How long does it take to take to download the file over a 1 megabit/second modem? T1M = 8 (1024) (1024) bits/ 1x106 bits/sec = 8.38 seconds c. Suppose data compression is applied to the text file. How much do the transmission times in parts (a) and (b) change? If we assume a maximum compression ratio of1:6, then we have the following times for the 32 kilobit and 1 megabit lines respectively: T32k = 8 (1024) (1024) / (32000 x 6) = 43.69 sec T1M = 8 (1024) (1024) / (1x106 x 6) = 1.4 sec 2. A scanner hasa resolution of 600 x 600 pixels/square inch. How many bits are produced by an 8-inch x 10-inch image if scanning uses 8 bits/pixel? 24 bits/pixel? [3 marks – 1 mark for pixels per picture, 1 markseach representation] Solution: The number of pixels is 600x600x8x10 = 28.8x106 pixels per picture. With 8 bits/pixel representation, we have: 28.8x106 x 8 = 230.4 Mbits per picture. With 24 bits/pixelrepresentation, we have: 28.8x106 x 24 = 691.2 Mbits per picture.

6. Suppose a storage device has a capacity of 1 gigabyte. How many 1-minute songs can the device hold using conventional CD format?using MP3 coding? [4 marks – 2 marks each] Solution: A stereo CD signal has a bit rate of 1.4 megabits per second, or 84 megabits per minute, which is approximately 10 megabytes per minute. Thereforea 1 gigabyte storage will hold 1 gigabyte/10 megabyte = 100 songs. An MP3 signal has a lower bit rate than a CD signal by about a factor of 14, so 1 gigabyte storage will hold about 1400 songs.8. How many HDTV channels can be transmitted simultaneously over the optical fiber transmission systems in Table 3.3? [2 marks] Solution: Suppose that an optical fiber carries 1600 x 109 bps, and an...