Fundamentals of Data Communications Systems and Networking, Slides of Fundamentals of E-Commerce

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ECT 250: Survey of e-commerce technology

Networking

2

In a network, communications equipment is usedto connect two or more computers allowing thesharing of various hardware, software, and dataresources.The basic components of a data communicationssystems used to transmit information are:• A sending device• A communications link, consisting of both

communications hardware and software.

• A receiving device

Networking

3

Binary information is represented by the presenceor absence of an electronic pulse. This is referredto as

digital signaling

.

Some communications devices in place today weredesigned for voice data which uses analog signals.Data communications systems may use theseexisting lines.

Data transmission

4

If the wires in place for communication use analogsignals, digital data must be converted to an analogsignal in order to be transmitted.•The digital signal is transformed into an analog

wave in a process called

modulation

.

•The analog wave is transmitted.•The analog signal is converted back into a digital

signal during a process called

demodulation

.

Piggybacking technology

5

A

modem

is the hardware device that does these

conversions. (Short for

mo

dulate/

dem

odulate).

Modem speeds are referred to by the number ofbits per second (bps) at which they can transmitand receive data.• The earliest modems has speeds around 300 bps.• Later modems had speeds ranging from 9600

to 33,600 bps.

• Today modems have speeds of 56,000 bps (or

56 Kbps).

Modems

6

A communications link is the physical mediumused for transmission of data.There are several kinds:

• Wire pairs/twisted pairs• Coaxial cables• Fiber optics• Microwave transmission• Satellite transmission

Communication links

7

Sometimes called twisted pair, this media useswire pairs twisted together to form a cable. Thecable is then insulated.Wire pairs are popular since this form of cablingis already installed and available in most places(telephone cabling).It is, however, susceptible to electrical interference,called

noise

.

Wire pairs

8

A coaxial cable is a single conductor wire that isthickly shielded.• It sends a very powerful signal.• It is used for cable television.• These cables can transmit data at a very fast

rate. Bundles of these cables can be laid undergroundor under the sea.

Coaxial cables

9

Fiber optic cables use light instead of electricityto transmit data.• The cables are made of ultra thin glass wires.

Light beams can be transmitted for miles withlittle attenuation (reduction in signal strength).

• This media can handle many different types

of information including voice and data at thesame time.

Fiber optic cables

10

In microwave transmission the signals are wirelessand can travel through the atmosphere.Signals can, however, be blocked by the curvatureof the earth. (Line of sight transmission)To prevent this, relay stations are located in highareas and are used to retransmit data to other relaystations.

Microwave transmission