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Introduction

Data Communication

Networks

Protocols and Standards

Standard Organizations

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

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Data Communication

Data communication is the exchange of data between two devices via some

transmisson medium.

It is considered localif communicating devices are in the same building and is

considered remoteif the devices are farther apart

The effectiveness of data communication system depends on four fundamental

characteristics:

Delivery

Accuracy

Timeliness

Jitter

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Figure 1-1

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

Data Communication System Components

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Data Communication System Components

Message: The message is the information (data) to be communicated. It can consist of text,

pictures, sound, or video- or any combination of these.

Sender: The sender is the device that sends the data message. It can be a computer,

workstation, telephone handset and so on.

Receiver: The receiver is the device that receives the message. It can be computer,

workstation, telephone handset, television and so on.

Medium: The transmission medium is the physical path by which a message travels from

sender to receiver. It could be a twisted-paired wire, coaxial cable, fiber-optic cable, or radiowaves.

Protocol: A protocol is a set of rules that governs data communications It represents an

agreement between the communicating devices. Without a protocol, two devices may be

connected but not communicating.

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Figure 1-2

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

NetworkCriteria

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NetworkCriteria

Performance

Performance is the rate of transference of error-free data. It is measured by the response

time. Response time is the elapsed time between the end of an inquiry and the beginning of a

response, e.g. requesting a file transfer and starting the file transfer. Factors that affect

performance of a network are:

Number of Users: The more users are on a network, the slower the network will run

Transmission Speed: The speed that the data will be transmitted is measured in bits per

second (bps)

Media Type: The type of physical connection used to connect nodes together

Hardware Type: Slow computers such as XT, or fast ones such as Pentiums

Software Program: How well is the network operating system (NOS) written

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NetworkCriteria

Reliabilityis the measure of how often a network is usable. MTBF(Mean Time Between Failures) is a measure of the average time a component

is expected to operate between failures, and is normally provided by the

manufacturer. A network failure can be caused by a problem with thehardware, the data carrying medium, or the Network Operating System.

Securityis the protection of hardware, software and data fromunauthorized access. Restricted physical access to computers, password

protection, limiting user privileges and data encryption are common security

methods. Anti-virus monitoring programs to defend against computer virusesare also a security measure.

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Applications

Marketing and sales

Financial Services

Manufacturing

Electronic messaging

Directory Services to speed worldwide search operations

Information services

Electronic data interchange

Teleconferencing Cellular telephone

Cable Television

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Figure 1-3

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

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StandardsStandards are necessary to ensure that products from different manufacturers can work

together as expected.

De Jure standards means by law & developed and approved by an official organisation. .

For example the IEEE (Institute of Electrical and Electronic Engineers) has the authority

to create electrical standards such as wireless communication.

On a global levelISO, the International Standards Organisation was set up to create

standards. They have produced over 18,500 formal standards.

The usual way for a de jure standard to be created is to:

First of all identify a need for the standard.For example people wanted to make

wireless enabled computer equipment but there was no standard in place to make sure

equipment would be compatible. There was no de-facto standard in place either.

Identify an organisation that has the expertiseto create a standard. In the case of

wireless the IEEE was chosen. Form an expert group. Usually experts from industry are invited to sit on the committee.

In the case of wireless the group was called '801'.

Create a draft standard. This is the ideas stage, the experts seek opinions from industry.

Refine the standard. This can take ages - many years - this is the main criticism of de

jure standards, they can be extremely slow to come out.

Publish the final standard.For example 801.11n is a wireless communication standard

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Standards

Examples of de jure standards

Wireless 801.11n

Internet TCP / IP protocol

ASCII character set Unicode international character encoding

De facto means "by fact".

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Standards

De facto means "by fact". created almost by default because of one dominant

player in that industry. There is no formal outside organization that approved

or signed off the standard. These are of two types:

Proprietary(Closed standards) originally invented by a commercial

organization as a basis for the operation of its products & wholly owned by

the company that invented them.

Nonproprietary(Open Standards) originally developed by groups that have

passed them into public domain.

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Standards Organizations

ISO ITU-T(International Telecommunication

Union-Telecommunication Standards

Sector) ANSI(American National Standard

Institute)

IEEE EIA(Electronic Industries Association)

Telecordia