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Data
Communications
Introduction
- Data
communication is the exchange of data (in binary form)
between two devices via some form of transmission medium.
It is considered local if the communicating devices are in
the same building or a similarly restricted geographical area,
and is considered remote if the devices are farther apart.
- The
effectiveness of a data communication system depends on three
fundamental characteristics.
- Delivery.
The system must deliver data to the correct destination.
Data must be received by the intended device or user and
only by that device or user.
- Accuracy.
The system must deliver data accurately. Data that have
been altered in transmission and left uncorrected are
unusable.
- Timeliness.
The system must deliver data in a timely manner.
- A
data communication system is made up of five components.
- Message.
The message is the information (data) to be communicated.
- Sender.
The sender is the device that sends the data message.
- Receiver.
The receiver is the device that receives the message.
- Medium.
The transmission medium is the physical path by which
a message travels from sender to receiver. It can consist
of twiste pair wire, coaxial cable, fiber-optic cable,
laser, or radio waves.
- Protocol.
A protocol is a set of rules that govern data communication.
It represents an agreement between the communicating devices.
- A
network is a set of devices (often referred to as nodes)
connected by media links. A node can be a computer, printer,
or any other device capable of sending and/or receiving data
generated by other nodes on the network. The links connecting
the devices are often called communication channels.
- Networks
use distributed processing. This is where a task is
divided among multiple comuters. Advantages of distributed
processing include the following.
- Security/encapsulation
- Distributed
databases
- Faster
problem solving
- Security
through redundancy
- Collaborative
processing
- A
network must meet a number of criteria.
- Performance
- Number
of users
- Type
of transmission medium
- Hardware
- Software
- Reliability
- Frequency
of failure
- Recovery
time of a network after failure
- Catastrophe
- Security
- Unauthorized
access
- Viruses
- Applications
- Marketing
and sales
- Financial
services
- Manufacturing
- Electronic
messaging
- Directory
services
- Information
services
- Electronic
data interchange (EDI)
- Teleconferencing
- Cellular
telephone
- Cable
television
- Protocols
and Standards -- a protocol defines what is communicated,
how it is communicated, and when it is communicated.
- Syntax
refers to the structure or format of the data, meaning
the order in which they are presented.
- Semantics
refers to the meaning of each section of bits.
- Timing
refers to two characteristics, when data should be sent
and how fast they can be sent.
- A
standard provides a model for development that makes
it possible for a product to work regardless of the individual
manufacturer.
- De
jure standards are those that have been legislated
by an officially recognized body.
- De
facto standards are subdivided into two classes. Proprietary
standards are those originally invented by a commercial
organization as a basis for the operation of its products.
They are also called closed standards because they
close off communications between systems produced by different
vendors. Nonproprietary standards are those originally
developed by groups or committees that have passed them
into the public domain; they are also called open
standards because they open communications between different
systems.
- Standards
are developed by cooperation among standards creation committees,
forums, and government regulartory agencies.
- The
International Standards Organization (ISO) is a
multinational body whose membership is drawn mainly from
the standards creation committees of various governments
throughout the world. The United States is represented
in the ISO by ANSI.
- The
International Telecommunications Union-Telecommuncation
Standards Sector (ITU-T) was formed by the United
Nations (ITU) as a committee called the Consultative Committee
for International Telegraphy and Telephony (CCITT). This
committee was devoted to the research and establishment
of standards for telecommunications in general and phone
and data systems in particular.
- The
American National Standards Institute (ANSI) is
a completely private nonprofit corporation not affiliated
with the US federal government. ANSI's expressed aims
include serving as the national coordinating institution
for voluntary standardization in the United States, furthering
the adoption of standards as a way of advancing the US
economy, and ensuring the participation and protection
of the public interests.
- The
Institute of Electrical and Electronics Engineers (IEEE)
is the largest professional engineering society in the
world. International in scope, it aims to advance theory,
creativity, and product quality in the fields of electrical
engineering, electronics, and ratio as well as in all
related branches of engineering.
- Aligned
with ANSI, the Electronic Industries Association (EIA)
is a nonprofit organization devoted to the promotion of
electronics manufacturing concerns. Its activities include
public awareness education and lobbying efforts in addition
to standards development.
- Telcordia,
formerly called Bellcore, is an outgrowth of the Bell
Labs. Telcordia provides research and development resources
for the advancement of telecommunications technology.
It is an important source of draft standards to ANSI.
- Forums
work with universities and users to test, evaluate, and
standardize new technologies. Examples are the frame relay
forum, the ATM forum and ATM Consortium, and the Internet
Society (ISOC) and Internet Engineering Task Force (IETF).
- All
commmunications technology is subject to regulation by
government agencies such as the Federal Communications
Commission (FCC) in the United States. The FCC has
authority over interstate and international commerce as
it relates to communications.
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