Topic 2 Electrical Interface and Modem
description
Transcript of Topic 2 Electrical Interface and Modem
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Topic 2 Basic Concept Of Data Communication
Understand types of interfaces
Understand MODEM (Modulation-Demodulation).
DEPARTMENT OF
ELECTRICAL ENGINEERING
EP601 DATA
COMMUNICATION
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At the end of this learning session, student must be able to;
Explain the importance of interface.
List type of electrical interfaces and its application.
RS232C/V.24, RS422/V.11, RJ45, USB
Build straight through and cross over cable using RJ45.
Explain characteristic interface RS232C/V.24 and RS422/V.11:
Electrical , Mechanical , Functional
Explain the importance of MODEM.
List type of modulations:
Analogue , Digital
Point out the characteristic of MODEM:
Asynchronous , Synchronous
Illustrate the operation of synchronous MODEM.
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Interfaces
A set of wire that connect DTE and DCE.
Interface is required in order to DTE and
DCE communicate each other
Interface enable the data and control
information to be exchanged between DTE
and DCE
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Types of electrical interface
RS232C/V.24
RS422/V.11,
RJ45
USB
Differences in the standards
include :
Mode of transmission
(single vs. differential)
Data transmission rates
Type of transmission line
and its length.
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Characteristic of interface
Mechanical actual physical connection of the DTE to the DCE, terminator connector,
male or female.
Electrical voltage level and timing of voltage level, data rates, distances
Functional specify the function of each terminal (data, control, timing and electrical
ground)
Procedural specify the sequence of events for transmitting data based on the
functional characteristics
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RS232-C/V.24
RS232 is a serial interface by Electronic Industries
Alliance (EIA) or known as EIAs Recommended Standard (RS)
RS232-C is the latest version of RS232 (1969).
Used to connect DTE and DCE (i.e modems and
Personal Computers)
RS232-C is identical to CCITT V.24/V.28. CCITT has
split the interface into its electrical description (V.28)
and a mechanical part (V.24).
Specifies mechanical, electrical ,functional and
procedural aspects of the interface
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RS232-C/V.24 : Mechanical
Specifications
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Use standard 25-pin D-shell connector (DB25)
A male D-shell connector is used on DTE and a
female on DCE
This connector is the terminating plug or socket
on a cable running from a DTE or DCE.
Some use a 9-pin D-shell connector (DB9)
instead of the 25-pin connector.
This connector provides the means to transmit
and receive the necessary signals for modem
applications
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RS-232 DB-25 & DB-9 Connectors
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DB-25 Female
DB-25 Male
DB-9 Female
DB-9 Male
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RS232 Standards : Connectors
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RS232-C/V.24 : Electrical Specifications
Mode of
operation :
single-ended (unbalanced)
Cable length : 50 feet max.
Data rate : 20 kbps max.
Signal State:
Mark :
(logical 1)
Signal State:
Space :
(logical 0)
Transmitter Voltage Range: -15V to -5V
Receiver Voltage Range:-25V to -3V
Transmitter Voltage Range: +5V to
+15V
Receiver Voltage Range:+3V to +25V
signals are represented by
a voltage with reference
to a common signal
ground.
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RS232-C/V.24 :Functional
Specifications
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Specifies the role of the individual circuits
Data circuits in both directions allow full-duplex
communication
The circuit can be group into the categories of
data, control, timing and ground.
Timing signals allow for synchronous
transmission
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Pin Name Function
2 Transmitted
Data (TD) This signal is generated by the DTE and received
by the DCE.
3 Received
Data (RD) This signals is generated by the DCE and
received by the DTE.
4 Request to
Send (RTS) When the host system (DTE) is ready to transmit
data to the peripheral system (DCE), RTS is turned
ON. After RTS is asserted, the DCE must assert CTS before communication can commence.
RS232-C/V.24 :Functional Specifications cont
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5
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Clear to
Send (CTS)
Data Set
Ready
(DSR)
CTS is used along with RTS to provide handshaking between the DTE and the DCE.
After the DCE sees an asserted RTS, it turns CTS
ON when it is ready to begin communication.
This signal is turned on by the DCE to indicate
that it is connected to the telecommunications
line
8 Data
Carrier
Detect
(DCD)
This signal is turned ON when the DCE is
receiving a signal from a remote DCE which
meets its suitable signal criteria. This signal
remains ON as long as the a suitable carrier signal can be detected.
RS232-C/V.24 :Functional Specifications
cont
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20 Data
Terminal
Ready
(DTR)
DTR indicates the readiness of the DTE. This
signal is turned ON by the DTE when it is ready
to transmit or receive data from the DCE. DTR
must be ON before the DCE can assert DSR.
22 Ring
Indicator
(RI):
RI, when asserted, indicates that a ringing
signal is being received on the communications
channel.
RS232-C/V.24 :Functional Specifications
cont
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Connection Establishment
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Dial Up Operation (1)
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Dial Up Operation (2)
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Dial Up Operation (3)
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RS-422/V.11
RS-422 also called EIA-422 is a technical standard that specifies electrical characteristics of a digital signaling circuit
The RS-422 standard defines a balanced (or differential) data communications interface using two separate wires for each signal (Transmit + and Transmit -, Receive + and Receive -)
Data transmission at higher speeds and longer distances than EIA-232.
Used in point-to-point communications.
Maximum distance and rate : a) 1200 meter/ 4000 feet @ max. 100 kbps b) 10 Mbps @ 12 meter/ 50 ft V.11 is the international equivalent ITU-T for RS-422.
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RS-422/V.11 cont.
Electrical - Voltage Level:
a) Transmitting
low logic 0 : + 2 V to + 6 V
high logic 1 : - 2 V to - 6 V
b) Receiving
low logic 0 : + 0.2 V to + 6 V
high logic 1 : - 0.2 V to - 6 V
c) Noise margin : ( 2 0.2 ) V = 1.8 V
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RS422 Voltage Transition Level
RS-422/V.11 cont.
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Comparison Item
RS232/ V.24 RS422/V.11
Signal Lines On lines which share a
common zero
Each signal line consists
of two wires, preferably twisted to reduce noise
Connection
to Receiver
Only designed to serve
one receiver
Line driver can serve up
to ten receivers in parallel.
Cable Length
Interface between
computers, printers and
terminals with modems
Direct connection of
intelligent devices, without the need of
modems
Comparison between RS232 and RS422
RS-422/V.11 cont.
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RJ45
RJ45 is a type of connector commonly used for
network cable.
The "RJ" in RJ45 stands for "registered jack" since it is
a standardized networking interface. The "45"
simply refers to the number of the interface
standard.
Each RJ45 connector has eight pins, which means
an RJ45 cable contains eight separate wires.
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Straight-through and cross-over wiring using RJ-45 cables
RJ-45 conductor data cable contains 4 pairs of wires ,
each consists of a solid colored wire and a stripe of the
same color.
There are two wiring standards for RJ-45 wiring: T-568A
and T-568B.
10BaseT/100BaseT Ethernet uses only 2 pairs: Orange
and Green.
The other two colors (blue and brown) may be used for
a second Ethernet line or for phone connections.
The unused pins are generally connected straight-
through in both straight-through and cross-over cables.
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T-568A and T-568B Standard.
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10BaseT/100BaseT Ethernet
The 10Base-T standard (also called Twisted Pair
Ethernet) uses a twisted pair cable with
maximum lengths of 100 meters.
The 10Base-T system operates at 10Mbps and
uses baseband transmission methods.
100BaseT Ethernet is a Fast Ethernet standard
that carry traffic at the nominal rate of
100 Mbit/s.
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Straight-through wiring using RJ45 cable
Used to connect DTE to DCE, such as computers to
modems or hubs.
Use either T-568A or T-568B on both ends of the
cable.
Uses only 2-pairs of wires:
Orange (pins 1 & 2)
Green (pins 3 & 6)
Connects pin 1 to pin 1, pin 2 to pin 2, pin 3 to pin 3,
and pin 6 to pin 6.
The unused pins are generally connected straight-
through in both straight-through and cross-over
cables.
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Straight
through
T-568A
T-568B
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Cross-over wiring using RJ45 cable
Used to connect DTE to DTE, or DCE to DCE
equipment; such as computer to computer,
computer to router; or gateway to hub.
To create a cross-over cable, you'll wire T-568A on
one end and T-568B on the other end of the cable.
Connects pin 1 to pin 3, pin 2 to pin 6, pin 3 to pin 1
and pin 6 to pin 2.
The unused pins are generally connected straight-
through in both straight-through and cross-over
cables.
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Cross-over
T-568B T-568A
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USB USB or Universal Serial Bus is a popular option for
external device communication.
USB was designed to standardize the connection of
computer peripherals (i.e keyboards, digital
cameras, printer)
USB 2.0 (High speed) is very fast, 480 Mb/s, USB 1
(Full Speed) is 12 Mb/s.
Its a 4-wire system, point-to-point system.
One advantage of USB is that it can provide power
for external hardware.
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Standard type A plug and receptacle
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USB to Other Devices
Connection
Cables
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USB to Serial
Adapter
USB to Internet
USB to Camera USB to Serial Adapter
USB to
Scanner
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Types
of USB
Cable
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USB Specification
USB 1.0: Specifies data rates of 1.5 Mbit/s (Low-
Bandwidth, is mostly used for Human Input Devices
(HID) such as keyboards, mouses, joysticks and
often the buttons on higher speed devices such as
printers or scanners) and 12 Mbit/s (Full-Bandwidth)
USB 2.0: In addition to USB 1.0 adds signaling rate of
480 Mbit/s (Hi-Speed).compatible with USB 1.0, but
some hardware designed for USB 2.0 may not work
with USB 1.0 host controllers.
USB 3.0: Added transmission rates up to 5 Gbit/s
(SuperSpeed)
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USB Version
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MODEM
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Modems
Modems are devices which allow digital data signals to be transmitted across an analogue link.
Modem stands for MOdulator/DEModulator.
A modem changes the digital signal to an analogue frequency : converts the signal to analog by varying the amplitude, frequency, or phase and sends this tone across the analogue link. At the other end, another modem receives the signal and converts it back to digital.
A modem may be an internal modem or it may be external.
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The importance of MODEM or , why is a
modem needed we need a converter so data can be transferred
to the analogue system of the telephone.
for giving higher quality and faster transfer of data. gives fast communication which is needed by many people.
giving good quality of graphics for bigger applications.
for creating the local area network for homes or offices.
for facilitating the fast growth of the economy of a country.
to reach/communicate remote places by computer
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MODEM
Structure of Modem
UART
Mod/ Demod Circuit
Transmitter Filter/ Receiver Filter
Buffer
Carrier Tracer
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COMPUTER
MOD / DEMOD
CIRCUIT
CARRIER
TRACER
UART
RECEIVER
FILTER
TRANSMITTER
FILTER
B
U
F
F
E
R
TO PSTN
Basic modem diagram
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MODEM cont
Block Diagram for Each Part
Transmitter: Computer, UART, MOD circuit,
transmitter filter, buffer, PSTN.
Receiver: PSTN, buffer, receiver filter and carrier
tracer, DEMOD circuit, UART, computer.
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UART
Transmitting: Parallel data from computer
change to serial data.
Receiving: Serial data from receiver change to
parallel data.
MOD/ DEMOD Circuit
Mod: change data from digital data to
telephone signal (analog signal).
Demod: change data from telephone signal
(analog signal) to digital data.
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Function for Each Block
MODEM cont
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Transmitter/ Receiver Filter
Filtering the signal before transmit / receive.
Buffer
Create a standard transmission signal level and impedance appropriate to telephone
Carrier Tracer
Trace the data input and inform to the computer.
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Function for Each Block cont..
MODEM cont
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Types of Modem External Internal
PC Card Wireless
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MODEM cont
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Types of Modem External
Digital Modem
1. Channel Service Unit (CSU)/ Digis Service Unit (DSU) modem:
Communication with digital modem technique as a Digital Transmission Service (DTS).
2. Digital Modems Converts the RS-232 digital signals to digital signals more suitable for transmission.
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MODEM cont
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Types of Modem External cont
3. Optical Modems:
Uses optical fiber cable instead of wire. The modem converts the digital signal to pulses of light to be transmitted over optical lines.
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MODEM cont
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Types of Modem External cont
4. Short Haul Modem:
Modems used to transmit over 20 miles or less.
Modems we use at home or to connect
computers together between different offices in
the same building.
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MODEM cont
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Types of Analog Modem
1. Acoustic Coupler Modem:
A modem that coupled to the telephone
handset with what looked like suction cups that
contained a speaker and microphone. Used for
connecting to hotel phones for travelling sales
people.
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MODEM cont
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Types of Analog Modem cont
2. Smart Modem
Modem with a CPU (microprocessor) on board
that uses the Hayes AT command set. This allows
auto-answer & dial capability rather than
manually dialing & answering.
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MODEM cont
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Modulation
modulation is the process of varying one or more
properties of a high-frequency waveform called the
carrier signal, with a modulating signal which
contains information to be transmitted
Types of modulation :
Analogue modulation
Pulse Modulation
Digital modulation
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Analog Modulation
Amplitude
Modulation (AM)
Frequency
Modulation (FM)
Phase
Modulation (PM)
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Amplitude Modulation (AM)
Amplitude modulation is the process of varying the
amplitude of the sinusoidal carrier wave by the
amplitude of the modulating signal.
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Frequency Modulation (FM) FM conveys information over a carrier wave
by varying its instantaneous frequency. This
contrasts with AM, in which the amplitude of
the carrier is varied while its frequency remains constant.
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Phase modulation (PM)
Phase Modulation changes the phase of the
carrier. The phase of the carrier is switch each time
that a one (1) bit is required, but does not change
for the duration of the zero (0) bit.
Phase modulation (PM) is a modulation that
represents information as variations in the
instantaneous phase of a carrier wave. OR A type
of electronic modulation in which the phase of a
carrier wave is varied in order to transmit the
information contained in the signal.
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The signal might has changed phase by +180 or -
180.
Phase modulation (PM) cont
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Digital Modulation
The parameters of the carrier that can be
modified are the amplitude, the frequency,
and the phase.
Amplitude Shift Keying (ASK)
Frequency Shift Keying (FSK)
Phase Shift Keying (PSK)
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Amplitude-shift keying (ASK)
Amplitude-shift keying (ASK) is a form of modulation
that represents digital data as variations in the
amplitude of a carrier wave.
In its simplest form, a burst of radio frequency is
transmitted only when a binary 1 appears and is
stopped when a 0 appears. In another variation,
the 0 and 1 are represented in the modulated
signal by a shift between two preselected
amplitudes.
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Frequency Shift Keying (FSK)
In the simplest form of FSK signaling, digital data is
transmitted using one of two frequencies, where by
one frequency is used to transmit a 1 and the other
frequency to transmit a 0.
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Phase Shift Keying (PSK)
In PSK, we change the phase of a sinusoidal carrier to indicate information. To transmit 0, we
shift the phase of the sinusoid by 180. Phase
shift represents the change in the state of the
information.
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Quadrature Amplitude Modulation (QAM)
(Quadrature Amplitude Modulation) A modulation
technique that employs both phase modulation
(PM) and amplitude modulation (AM).
In digital QAM, the input stream is divided into
groups of bits based on the number of modulation
states used. For example, in 8QAM, each three bits
of input, which provides eight values (0-7) alters
the phase and amplitude of the carrier to derive
eight unique modulation states (see example
below
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Quadrature Amplitude Modulation (QAM)
Sample of QAM waveform
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Concept of Asynchronous Modem
Random transmission No synchronization clock
The number of character bits are acknowledged
Every data transmission needs start bit, stop bit and parity bit
Asynchronous modems usually operate in FSK modulation
Operate in slow and moderate rates , up to 1800 bps
Less efficient due to the high number of control bits
Advantages : easy control of data errors
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Use of synchronization clock
More efficient due to the low number of control bits
The usual modulation methods are PSK modulation or QAM
In synchronous modems, equalizers are used, in order to offset the misfit of the telephone lines.
Operates at higher rates , between 2400 bps and 56000 bps over standard voice-grade telephone
Concept of Asynchronous Modem
cont
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Synchronous Modem
- block diagram -
Synchronous Modem Transmission/ Receiving
Block Diagram
Timing
Scramble/
Descramble
Phase Modulation
/ Demodulation
Equalizer
DAC/
ADC
Clock
Data
PSTN
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Function of each block for Transmitter/ Receiver
1. Clock (timing source): generate all the timing references require for all transmit or receive operation.
2. Scrambler/ Descrambler : change the data from random signal to the original signal / change the data from original signal to the random signal.
3. Phase Modulation/ Phase Demodulation : the data will be phase modulating / phase demodulating.
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Function of each block for Transmitter/ Receiver cont..
4. ADC/ DAC Analog to Digital Converter: change analog signal to digital signal/ Digital Analog Converter: change digital signal to analog signal
5. Equalizer: Increase and stabilize the signal to high frequency.
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Application of Synchronous Modem
and Asynchronous Modem
Connecting a host computer to remote
terminals that are polled using asynchronous
polling protocols
Connecting SCADA host computers to RTU's
Connecting host computers to terminals
using synchronous financial industry
protocols (HDLC, SDLC, etc)
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Application of Synchronous Modem
and Asynchronous Modem cont
Collecting data from multiple data
sources into a single remote port
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REFERENCES:
Main:
Forouzan, B.A. (2012). Data Communications
and Networking (5th edision). Mc Graw Hill.
(ISBN: 978-0-07-131586-9)
Additional:
William Stallings. (2011). Data And Computer
Communication (9th edition). Prentice Hall.
(ISBN-10: 0131392050)