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E5124 Data Communication

Chapter 1 / UNIT 2

Principles of Data Communication

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Chapter 1 / UNIT 2: Principles of Data Communication

Sender (source), transmission media, and receiver (destination)

DCE and DTEOne-way and two-way communicationSerial and parallel transmissionAsynchronous and synchronous

transmissionError CodingError Detection (parity and CRC)

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Sender (source), Transmission media, and Receiver (destination)

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Sender (Source) The Sender is the device that send the data Computer, workstation, telephone handset, video camera,

etc

Medium The transmission medium is the physical path by which a

message travels from sender to receiver. Twisted pair wire, coasial cable, fiber optic cable or radio

wave (terrestrial or satellite microwave)

Receiver (Destination) Device that receives the message. Computer, workstation, telephone handset, video camera,

etc

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Data Communication Block Diagram

Terminal Modem ComputerModem Telecommunication Network

DTE DCE DTEDCE

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DTE and DCE

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DTE

Data Terminal Equipment (DTE) is any equipment that is either a source or

destination for digital data DTE do not generally communicate with

each other to do so they need to use DCE to carry out the communication.

A typical example of DTE is a computer. Other common DTE examples include:

• Printers • Servers • PCs

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DCE

Data Terminal Circuit Equipment (DCE) / Data Communications Equipment / Data Circuit-Terminating Equipment Provide path for communication they make the

communication between you and your provider possible.

DCE performs functions such as signal conversion, coding, and line clocking and may be a part of the DTE or intermediate equipment.

Examples of DCE are:• Modem• NIC Card

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DTE (Data Terminal Equipment) DCE (Data Terminal Circuit Equipment)

peralatan pelanggan untuk komunikasi data, tanpa mengira kekompleksan.

Peralatan terdiri daripada punca

data atau penerima data atau kedua-duanya.

Peralatan yang biasa ialah seperti

unit-unit logik kawalan, buffer store, komputer-komputer, unit-unit paparan visual, stesen-stesen kerja berasaskan komputer dan peralatan yang terdapat dalam suatu automated office.

Peralatan ini boleh mengandungi

pengawalan ralat, penyegerakkan dan kebolehan pengenalan stesen.

Contoh : Komputer, Pencetak,

Server, Router

Disediakan oleh pihak berkuasa rangkaian komunikasi atau oleh pelanggan sendiri.

Fungsi-fungsi seperti melaksana,

mengendali dan memberhentikan suatu komunikasi data,

Melakukan pertukaran isyarat dan

melakukan pengkodan yang diperlukan untuk perhubungan antara DTE dan litar data.

DCE merupakan bahagian dalaman

suatu komputer

Contoh: Modem dan NIC Card

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Transmission Mode

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Transmission Mode

Data flow between two devices can occur in one of three ways:SimplexHalf-duplex, orFull-duplex

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Simplex

Data exchange in only one direction Simplex transmission are not often

used because it is not possible to send back error or control signals to the transmit end.

Example: Keyboard to computer monitor, radio and television broadcasting

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Half Duplex

A half-duplex transmission can send and receive in one direction, but not at the same time.

The stations take turns to transmit data. In addition, it is possible to perform error detection and

request the sender to retransmit information that arrived corrupted.

Example: Walkie talkie, internet browsing, telex

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DUPLEKS PENUH……

Data can travel in both directions simultaneously.

There is no need to switch from transmit to receive mode like in half duplex.

Example: Telephone

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Serial and Parallel Transmission

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PENGHANTARAN DATA…..

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Peng. Siri VS Peng. SelariSiri Selari

Sistem penghantaran bit satu persatu.

Hanya memerlukan satu talian sahaja.

Kos yang lebih murah dan sesuai untuk penghantaran jarak jauh.

Kadar penghantaran lambat.

Sistem penghantaran satu aksara pada satu masa.

Talian bergantung kepada bilangan bit.

Kos yang mahal dan sesuai untuk jarak dekat.

Kadar penghantaran lebih laju.

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Penghantaran Siri

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Parallel Transmission

8 wayar diperlukan

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Asynchronous and Synchronous Transmission

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Asynchronous Transmission

The ASYNCHRONOUS (ASYNC) format for data transmission is a procedure or protocol in which each information CHARACTER or BYTE is individually synchronized or FRAMED by the use of Start and Stop elements, also referred to as START BITS (0) and STOP BITS (1).

Data transmission in which each character contains its own start and stop pulses and there is no control over the time between characters.

Each character or byte is framed as a separate and independent unit of DATA that may be transmitted and received at irregular and independent time intervals.

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Synchronous Transmission

Block of data transmitted without start or stop bits Clocks must be synchronized (external clock) Need to indicate start and end of block Use preamble and postamble

e.g. series of SYN (hex 16) characters e.g. block of 11111111 patterns ending in 11111110

More efficient (lower overhead) than async

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Error Detection

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Types of Error

an error occurs when a bit is altered between transmission and reception

SINGLE BIT ERRORSonly one bit alteredcaused by white noiseAdjacent bits not affected

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Single Bit Errors

0 0 0 0 0 0 1 0

0 0 0 0 1 0 1 0

Error Bit

Transmitted Data

Received Data

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BURST ERRORScontiguous sequence of B bits in

which first last and any number of intermediate bits in error

caused by impulse noise or by fading in wireless

effect greater at higher data rates

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Burst Errors

Duration of error occurs = 5 bit

0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

0 1 0 1 1 1 0 1 0 1 0 0 0 0 1 1

Received Data

Transmitted Data

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Parity Checking

Also known as Vertical Redundancy Check (VRC), parity check is a method of adding a parity bit to a data stream to check that data for any errors. The EVEN method requires the number

of ‘1’s of a unit including the parity bit to be always even

Whereas the ODD parity technique checks for an odd number of bits.

This method is able to detect only one (bit) error with certainty.

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Pengesanan Lelebihan

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