Syngress - Eleventh Hour Network+ Exam N10-004 Study Guide (11 ...

42 CHAPTER 3 Network Devices
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Internal modem performs the same functions as the external modem. The
difference is that it is located inside the computer chassis.
Multiline rack or shelf-mounted is a solution that is a single chassis containing
a certain number of modem cards that can be connected directly to
the network.
ANALOG MODEMS
An analog modem is a communications device that enables a computer to talk to
another computer through a standard telephone line. It does this by converting
digital data from the computer to analog data for transmission over the telephone
line and then back to digital data for the receiving computer. They use an RJ-11
connector.
DIGITAL SUBSCRIBER LINE AND CABLE MODEMS
Cable modems and digital subscriber line (DSL) modems access technology
that provides connection speeds in the megabit per second (Mbps) range.
Characteristics of cable modems are as follows:
■ They use the broadband technology of cable television lines.
■ They transmit data into a coaxial-based technology, which is used to split
Internet access from television signals.
■ The transmission speeds are typically around 1.544 Mbps, but broadband
Internet can provide greater speeds allowing a download path of up to
27 Mbps.
■ Cable modems communicate with a cable modem termination system
(CMTS) and provide a constant connection to the cable service provider
that also acts in the role of an Internet service provider (ISP).
Characteristics of DSL modems are as follows:
■ They allow simultaneous voice and data communications.
■ They transmit and receive data digitally across the phone line’s twisted-pair
cable providing Internet access using existing telephone wiring.
■ They provide transmission speeds of 1.544 Mbps and can go up to data
transfer rates of 6.1 Mbps.
■ The speed of DSL decreases the further you are from a telephone company’s
offices or a repeater that regenerates the signal. The closer you are to the
telephone company’s offices, the faster your DSL connection will be.
■ There are several different variations of DSL available (shown in Table 3.2),
which offer different data transfer rates and distance limitations.
Fast Facts
An Integrated Services Digital Network (ISDN) is a system of digital telephone
connections that enables data to be transmitted simultaneously end to end. It
consists of multiple components: