© 2008 Pearson Education, Inc. Prentice Hall Upper Saddle River, NJ Investigating High-Tech Crime By Michael Knetzger and Jeremy Muraski Connecting to the Internet (Early Days) During the Internet’s popular infancy, the general public had to connect to the Internet via a telephone line and a modem (“dial-up connection”) The word modem, which is made up of abbreviations for the words modulate and demodulate, describes the physical hardware that connects the computer to the telephone line. A modem takes binary data signals (0s and 1s) and modulates them into sounds. A companion modem on the other end demodulates the sounds back into data.

© 2008 Pearson Education, Inc. Prentice Hall Upper Saddle River, NJ Investigating High-Tech Crime By Michael Knetzger and Jeremy Muraski Connecting to the Internet, con’t. Anyone who has ever used a dial-up modem can remember the distinctive metallic screeching sound of the two modems connecting. When first introduced, modems were very slow, having very little bandwidth. A data transfer rate of 300 baud was not uncommon. Baud is an older measure of bandwidth used in the infancy of Internet connectivity, when data transfer speeds were very slow. Baud measured how many bits per second (bps) a modem could send or receive.

© 2008 Pearson Education, Inc. Prentice Hall Upper Saddle River, NJ Investigating High-Tech Crime By Michael Knetzger and Jeremy Muraski Modem Speeds / Bandwidth As technology evolved, we started to see modems of 1200, 2400, 4800, and 9600 baud. As modem bandwidth speeds increased, a new speed designation was used, called bits per second (bps), and for higher speeds, Kbps and Mbps. Kbps stands for kilobits per second, and Mbps for megabits. Remember, a bit is 1/8 of a byte. When dealing with Internet bandwidth we will generally see them in bits per second (bps), but in dealing with hard drive or other bandwidths, we generally talk about bytes per second (Bps), with the upper case B designating bytes.

© 2008 Pearson Education, Inc. Prentice Hall Upper Saddle River, NJ Investigating High-Tech Crime By Michael Knetzger and Jeremy Muraski Bandwidth Comparison 1 bit = 1/8 of a byte 8 bits = 1 byte = 1 alphanumeric character 1 kilobit (Kb) = 1,024 bits = 128 bytes = 128 alphanumeric characters 1 megabit (Mb) = 1,024 kilobits = 1,048,576 bits = 131,072 bytes = 131,072 characters

© 2008 Pearson Education, Inc. Prentice Hall Upper Saddle River, NJ Investigating High-Tech Crime By Michael Knetzger and Jeremy Muraski The 56-Kilobit Frontier 56K maximum for dial-up modems. The final evolution of the dial-up modem is known as 56K, which is shorthand for 56 Kbps or the equivalent of 7,168 characters (bytes) per second. The theoretical bandwidth limitation of a standard telephone wire using a standard dial-up, or analog, modem. In other words, under perfect conditions, no analog modem can transmit more than 7,168 bytes per second.

© 2008 Pearson Education, Inc. Prentice Hall Upper Saddle River, NJ Investigating High-Tech Crime By Michael Knetzger and Jeremy Muraski We Wanted to Go Faster As data became more complex, users wanted more efficient ways to transfer larger data files,such as sound and music files, high-resolution images, and even video files. These files can range from several megabytes to several gigabytes in size, so a much faster transport mode was needed. This was the dawn of the broadband age. Broadband Internet connections generally fall into one of three types — Digital Subscriber Line (DSL), cable modems, or dedicated lines. A 3-Megabit connection can download 393,216 bytes per second, roughly 1/3 of a megabyte. A 3-Megabyte song file, for example could conceivably be received in roughly 9 seconds under ideal conditions. That same song file on a dial-up 56K modem would take at least 7 minutes to download.

© 2008 Pearson Education, Inc. Prentice Hall Upper Saddle River, NJ Investigating High-Tech Crime By Michael Knetzger and Jeremy Muraski Higher Speeds Speed  File Size 56K Dial-Up768 Kbps1.5 Mbps3.0 Mbps 500 KB file71 seconds5.2 seconds2.6 seconds1.3 seconds 1 MB file146 seconds10.7 seconds5.3 seconds2.65 seconds 5 MB file12.2 minutes53.3 seconds26.7 seconds13.35 seconds 100 MB file243.8 minutes17.75 minutes8.9 minutes4.45 minutes