Upload
jason-hando
View
4.086
Download
1
Tags:
Embed Size (px)
DESCRIPTION
Citation preview
Communication Devices
Communication History
• The Telegraph - Samuel Morse
• The Telephone - A. Bell• Teletypewriter• Networks
Computers & Communication
• In the 1960’s people were allowed to connect their own equipment to the Public Telephone Network.
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.
RS-232C Interface
• The RS-232C standard defines the function of signals as well as the physical connection.
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)
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
The Modem
• The public telephone system was designed to transmit the human voice which is an analog signal.
• Computers exchange information using digital signals.
The Modem
• To be able to use the telephone network the digital signal must be converted to an analog signal and then back again.
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
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.
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.
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.
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
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.
Network Interface Card
• It also re-arranges and buffers the data.
• It is an expansion card that must inserted inside the computer.
Multiplexer• This is a communication
device that combines several signals together for transmission over a high speed communication line.
MUX MUX
Multiplexer
• At the receiving DTE, another multiplexer (MUX) is needed to separate the signal into multiple sub channels.
MUX MUX
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
Types of Multiplexing
• Time Division– Each node is allocated a small
time frame for communication.– Each node is checked on a
round-robin basis.