Page 15 - M. Abrahim Thesis

Computer Network 2021

analog signals for transmission over the PSTN and then convert analog signals back to digital data
on the receiving end. The term modem derives from the function of this device. The process of
converting digital signals to analog and back again is called modulation/demodulation (hence the
term modem). Modems can be installed internally or attached to the computer via a serial or
USB interface externally. Modems connect a computer to the network by dialing the telephone
number of another computer’s modem, typically that of the Internet service provider (ISP). The
NIC lets hosts connect to the network. The NIC is considered a key component. NICs are available
in different types, depending on the individual device configuration. Notebook computers can
have a built-in interface or use a PCMCIA card. Desktop systems can use a builtin or adapter card-
type NIC.
Situations that require NIC installation include the following:

• Adding a NIC to a PC that does not already have one

• Replacing a bad or damaged NIC
• Upgrading from a 10-megabits per second (Mbps) NIC to a 10/100-Mbps NIC To install a
NIC, as shown in Figure below, you need the following resources:

• Knowledge of how the adapter is configured, including jumpers and plug-and-play
software. Most modern NICs do not require jumpers and are plug-and-play, requiring
little or no configuration. They can be configured using software that comes with the NIC
if necessary.
• Use of network card diagnostics, including the vendor-supplied diagnostics and loopback
test (see the card’s documentation).

• The ability to resolve hardware resource conflicts, including IRQ, I/O base address, and
direct memory address (DMA), which is used to transfer data from RAM to a device
without going through the CPU.
• https://www.youtube.com/watch?v=Mad4kQ5835Y&t=33s

1.4 Overview of High-Speed and Dialup Connectivity

In the early 1960s, modems were introduced to provide data communications
connectivity for dumb terminals to a centrally based computer. Many companies rented
computer time because owning an onsite system was cost-prohibitive. The connection rate was
very slow— 300 bits per second (bps), which translates to about 30 characters per second. As
PCs became affordable in the 1970s, Bulletin Board Systems (BBSs) appeared, allowing users to
connect and post or read messages on a discussion board. Running at 300 bps was acceptable,
because this exceeds the speed at which most people can read or type. BBSs did not become
widely used until the early 1980s, and the transfer of files and graphics began to be desirable.
The 300-bps speed quickly became intolerable, and modem speeds started to increase. By the
1990s, modems were running at 9600 bps. They reached the current standard of 56 kbps
(56,000 bps) by 1998. Inevitably, the high-speed services used in the corporate environment,
such as digital subscriber line (DSL) and cable modem access, migrated to the consumer market.
These services no longer required expensive equipment or a second phone line. They are also

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