Information Technology Reference
In-Depth Information
This would take 40 bits to transmit the coding, whereas it would take 304 bits without coding
(i.e. 16 + 4 + 16 + 2 + 128 + 10 + 128). This results in a compression ratio of 7.6:1.
Table 15.6
Black run-length coding
Run
length
Coding
Run
length
Coding
Run
length
Coding
0
0000110111
1
010
2
11
3
10
4
011
5
0011
6
0010
7
00011
8
000101
9
000100
10
0000100
11
0000101
12
0000111
13
00000100
14
00000111
15
000011000
16
0000010111
17
0000011000
18
0000001000
19
00001100111
61
000001011010
62
0000001100110
63
000001100111
EOL
00000000001
15.12 Exercises
15.12.1
What is the bandwidth of a telephone line:
(a)
Almost infinite
(b)
400 Hz to 3.4 kHz
(c)
400 Hz to 20 kHz
(d)
400 Hz to 100 kHz
15.12.2
How does a modem transmit at 9600bps, when the symbol rate is 4800 sym-
bols/sec (baud):
(a)
It sends two bits for every symbol sent
(b)
Its impossible as the bit rate is always the same as the symbol rate
(c)
It hides data
(d)
It uses more than one data line
15.12.3
How long does it take to transmit a 1 MB file over a 9600 bps modem connection:
(a)
13.89 min
(b)
1.74 min
(c)
833.33 min
(d)
104.2 min
15.12.4
What modem command is used to tone dial the number 123-456-789:
(a)
AT 123456789
(b)
AT 987654321
(c)
ATDT 123456789
(d)
DIAL 123456789
15.12.5
What character sequence is used to put the modem in the command mode:
(a)
AT
(b)
+++
(c)
HELLO?
(d)
+
15.12.6
Which character must appear at the end of a command string:
