Technology Guide 4
is a collection of compatible
hardware and software arranged to communicate information from
one location to another. The major components include;
continuous waves that
“carry” information by
that convey information in
like the central
processing unit in
Telecommunications media can carry two basic types of signals;
refers to the conversion from digital to analog and
the reverse is
The device that performs these two processes is called a
Modems are always used in pairs.
The unit at the sending end converts digital information into analog
signals for transmission over analog lines;
At the receiving end, another modem converts the analog signal
back into digital signals for the receiving computer.
Two main alternatives to analog modems are:
Digital subscriber line (DSL)
is an electronic device that allows a single
communications channel (e.g, a telephone circuit) to carry data
transmissions simultaneously from many sources.
all routing communications with peripheral devices.
refer to the
physical pathway or medium
for which data is
communicated from one
location to another.
There are two categories:
Wireline vs. Wireless Media
Twisted pair wire
Fiber optic cable
Global positioning system
Radio & Infrared light
the use of portable computer
devices in multiple locations.
power, higher frequency
radio waves than cellular
technology. As a result, PCS
cells are smaller, more
numerous and closer
Personal digital assistants
are small, pen
held computers capable of
is a relatively new
technology that allows wireless
communication between mobile
phones, laptops, and other
refers to the range of frequencies that can be sent
over a communications channel.
is a detectable change in a signal (i.e., a change from a
positive to a negative voltage in a wire).
refers to the rate at which signals can be transmitted
through a communications channel.
is usually divided into three bandwidths:
(e.g., telegraph lines)
(e.g., microwave, cable, and fiber
Simplex data transmission
uses one circuit in one direction
similar to a doorbell, a public announcement system, or
broadcast television and radio.
also uses only one circuit, but it is
used in both directions
one direction at a time.
uses two circuits for
one for each direction simultaneously.
e.g, a common telephone
Transmission Mode & Accuracy
Data transmissions may be either asynchronous or synchronous;
only one character is transmitted or received at a
a group of characters is sent over a communications
link in a continuous bit stream while data transfer is controlled by a
timing signal initiated by the sending device.
Because the loss of even one bit could alter a character or
control code, data transmission requires
These controls consist of bits called
refers to the
set of rules and procedures governing
transmission across a network
The simplest protocol is
where a master device polls, or
contacts, each node.
token passing approach
, a small data packet, called a
, is sent around the network.
In another approach called
a device that wants to
send a message checks the communications medium to see if it
is in use.
Transmission Control Protocol/Internet Protocol
is a protocol for sending information across sometimes
The major types of standards are
One or more protocols define precisely how software programs on
different systems interact to accomplish the functions for each layer.
The Open Systems Interconnection (OSI)
model has seven layers,
each having its own well
: Session layer
Data link layer
A number of network bandwidth boosters address the need for
greater bandwidth on networks for advanced computing
FDDI (fiber distributed data interface)
ATM (asynchronous transfer mode)
ISDN (integrated services digital network)
Interface & Topology
is a physical
connection between two
Parallel data transfer
Serial data transfer
of a network is
the physical layout and
connectivity of a network.
Local area networks (LAN)
Gateway, bridge, router
Network Interface Cards
Private branch exchange
Wide area networks (WAN)
added Network (VAN)
Virtual private network
There are two general network sizes:
Centralized computer systems
are centered around a large
computer, known as the
, that provides computational power
and internal storage.
Several devices that lack self
contained computer processors,
terminals and printers, are connected to the
Although mainframes have represented the dominant centralized
form of computing for over 30 years,
are challenging that dominance.
architectures are decentralized or
breaks centralized computing into
functionally equivalent parts, with each part essentially a smaller,
breaks centralized computing into many
computers that may not be (and usually are not) functionally
The basic structure of
is a client
device(s) and a server device(s) that are distinguishable, but
interact with each other.
In a client/server approach, the components of an application are
distributed over the enterprise rather than being centrally
There are three application components that can be distributed:
the presentation component
the applications (or processing) logic
the data management component
There are five models of client/server implementation;
Remote data management
Distributed data management
Peer Network Architecture
peer network architecture
allows two or more
computers to pool their resources together.
There are several advantages of peer
There is no need for a network administrator.
The network is fast and inexpensive to set up and maintain.
Each computer can make backup copies of its files to other
computers for security.
It is the easiest network to build.
provide flexibility in implementing IT solutions,
optimization of computing effectiveness, and the ability to provide
new levels of integrated functionality to meet user demands.
is the ability of the various computer resources to
communicate with each other through network devices without
have enabled networks to
completely span organizations.
is the ability to move applications, data, and even
people from one system to another with minimal adjustments.
refers to the ability of systems to work together
by sharing applications, data, and computer resources.
refers to the ability to run applications unchanged on
any open system where the hardware can range from a laptop
PC to a super computer.