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Communication Devices
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Page 1: Communication System Devices

Communication Devices

Page 2: Communication System Devices

Communication History

• The Telegraph - Samuel Morse

• The Telephone - A. Bell• Teletypewriter• Networks

Page 3: Communication System Devices

Computers & Communication

• In the 1960’s people were allowed to connect their own equipment to the Public Telephone Network.

Page 4: Communication System Devices

RS-232C Interface

• High speed computer communications operate on the principle of switching voltage on and off.

• To enable devices to communicate a standard was developed to define the electrical signalling.

Page 5: Communication System Devices

RS-232C Interface

• The RS-232C standard defines the function of signals as well as the physical connection.

Page 6: Communication System Devices

RS-232C Interface

• The standard is for two categories of serial connection– one for terminals (DTE - Data

Terminal Equipment)– one for communications

equipment (DCE - Data Communications Equipment)

Page 7: Communication System Devices

RS-232C Interface

• A DTE device usually connects to a DTE device– a computer connected to a

modem• The RS-232C connection

uses a 25 pin connector.• Some manufacturers now

also supply 9 pin plugs

Page 8: Communication System Devices

The Modem

• The public telephone system was designed to transmit the human voice which is an analog signal.

• Computers exchange information using digital signals.

Page 9: Communication System Devices

The Modem

• To be able to use the telephone network the digital signal must be converted to an analog signal and then back again.

Page 10: Communication System Devices

The Modem

• Modem were designed to do this conversion– i.e they MODulate the

digital signal to analog and then DEModulate the analog signal back to digital.

• A modem is required on both DTE devices

Page 11: Communication System Devices

The Modem

• Transmission involves data compression techniques which increase the rates, error detection and error correction for more reliability.

• The computer is connected to the modem via an RS-232C connection.

Page 12: Communication System Devices

Types of Modems

• Voice/Data– some modems can switch

between voice and data modes. In voice mode it acts likes a normal telephone, while in data mode it operates like a modem.

Page 13: Communication System Devices

Types of Modems• Cable Modem– A cable modem is a device that

enables the connection of a computer to a local cable TV line and receive data at a much higher rate that a normal modem.

Page 14: Communication System Devices

Types of Modems

• Auto-Answer Modem– An auto-answer modem

enables your computer to receive calls in your absence.

• Fax/Modem– These types of modems can

both send and receive faxes

Page 15: Communication System Devices

Network Interface Card

• This device acts an interface between the computer and network cabling.

• Its function is to control data in and out of the network cabling and also moves data in and out of memory.

Page 16: Communication System Devices

Network Interface Card

• It also re-arranges and buffers the data.

• It is an expansion card that must inserted inside the computer.

Page 17: Communication System Devices

Multiplexer• This is a communication

device that combines several signals together for transmission over a high speed communication line.

MUX MUX

Page 18: Communication System Devices

Multiplexer

• At the receiving DTE, another multiplexer (MUX) is needed to separate the signal into multiple sub channels.

MUX MUX

Page 19: Communication System Devices

Types of Multiplexing

• Frequency Division– a single frequency channel is

sub-divided into two or more sub-channels

– used in TV broadcasting and FM radio transmission

Page 20: Communication System Devices

Types of Multiplexing

• Time Division– Each node is allocated a small

time frame for communication.– Each node is checked on a

round-robin basis.