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DATA COMMUNICATION AND NETWORKCHAPTER - 1Compile by Zafar Ayub

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WHAT IS DATA COMMUNICATION? Electronic transmission of information that has been

encoded digitally with some standard from one network (systems) to other network (systems) via certain medium, knows as Data Communication.

Elements of Data Communication; Information / Data Digital encoded Transfer of data / sender and receiver Specific medium

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WHAT IS NETWORK? A computer network often simply referred to as a

network, is a collection of hardware components, which are interconnected by communication channels that allow sharing of resources and information with respect to certain set of rules / protocols via OS / software.

Elements of Network; Hardware equipments Network OS / software Communication channel Information / Data / Recourse Protocols

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TERMINOLOGIES Data transmission process between sender and

receiver is refer to data communication, and deployed physical environment (hardware / software / protocols / channel ) is network.

Data: digital information over computer / network, which may define with certain type of file extension; like .doc, .ppt, .pdf, .exe, and etc. File extension dominate nature of data file

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Resource: all sharable / accessible items over network, which may physical / virtual, knows as resource.

physical resource - may be hard drive, printer, servers and etc.

virtual resource - may be data files, online application, web site, internet and etc.

Share Resource: a shared resource or network share is a device / piece of information means file / software or application, on a computer that can be remotely accessed from another computer.

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Channel: communication channel is a medium on which resource can be access over network and establish connectivity between sender and receiver. Channel speed / network speed is depends upon bandwidth.

bandwidth - channel capacity known as bandwidth.

There are two types of channels;

physical channel like; network cable, fiber optic, electrical wire, and etc.

logical or virtual channel like; wireless, radio frequency, Wi-Fi, Wi-Max, and Bluetooth

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Protocols: a communications protocol is a system of digital message formats and rules for exchanging those messages in or between computer systems and in network / telecommunications.

Protocols regulate the following characteristics of a network: access method, allowed physical topologies, types of cabling, and speed of data transfer.

Protocols may include signaling, authentication, error detection method, and network policies.

A protocol can be implement at hardware or software or both, and with respect to assignment these are implemented like; for web http, for security SSL, for email POP3 / SMTP, for LAN network Ethernet, for routing BGP / RIP, etc.

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Digital Encryption: in encryption is the process of transforming information / data using an algorithm to make it unreadable to anyone (except those possessing special knowledge, usually referred to as a key).

The result of the process is encrypted information and the reverse process, i.e. to make the encrypted information readable again is referred to as decryption.

algorithm – set of steps for assembling / reassembling of data with respect to define network technology.

Types of digital encryption;

Software Based Encryption – a software program to facilitate encryption process on data / file with respect to 256-bit AES / 448-bit Blowfish algorithms. Hardware is only responsible to deliver encrypted file to other end computer where again via software program file may be decrypt for original data / file.

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Drawbacks

all encryption perform on data / file during file transfer.

data / file size is also increase with addition of certain algorithms.

security risk for confidentiality documents.

Hardware Based Encryption – all data intensive encryption tasks are done onboard storage device, rather than on file, by this file size remain standard with maximum speed. Most important factor is hardware security protocols which are only configure same end device

Hardware encryption is also apply with specialize network equipment.

Drawbacks

higher cost of equipments

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Network Hardware: all equipments / devices which may used on network and facilitate for resource sharing and data connectivity like; router, switch, firewall, and servers etc.

Network Software: specialize software / OS which may establish logical connectivity, authentication, and management of network, commonly built-in with operating system. Some are like; teamviewer, skype, etc

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Sender: a computer / device from which data / files are send to specific destination.

Receiver a computer / device at which data / files are received by source.

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DATA TRANSMISSION Data transmission is the physical transfer of data over

a point-to-point or point-to-multipoint channel.

Data transmission is a subset of the field of data communications, which also includes computer networking or computer communication applications and networking protocols, for example routing and switching.

Point – to –point : In telecommunications a point-to-point connection refers to a communications connection between two nodes or endpoints.

Point – to –multipoint : refers to communication which is accomplished via a specific and distinct type of one-to-many connection

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DATA COMMUNICATION TECHNIQUESSerial Transmission - is the process of sending data one bit at a time, in sequentially, over a communication channel / computer bus. A data channel that transfers digital data in a serial mode, one bit after the other over one wire, with start and stop bit.

Serial interfaces may have multiple lines, but only one line is used for data. On earlier PCs, the serial port was a serial interface for attaching modems and data acquisition terminals, and sometimes mouse.

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Parallel Transmission - is a method of sending several data signals simultaneously over several parallel channels.

In parallel transmission, multiple bits (usually 8 bits or a byte/character) are sent simultaneously on different channels (wires, frequency channels) within the same cable, or radio path, and synchronized to a clock. Due to multi channels lines in parallel transmission, it may comparatively fast as serial transmission.

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Transmission Characteristic - The advantages, limitations and typical applications of parallel and serial transmissionmethodologies are summarized in chart;

TransmissionCharacteristic

Serial Parallel

Transmission description

One bit comes after another, one by one

All bits in a single character and transmit simultaneously

Comparative Speed Slower Faster

Distance Limitation Farther Shorter

Application Between two computer, from computer to external devices, and local and wide network

Within a computer the along computer buses, between drive controller to hard drive

Cable Description All bits travel down in single wire, one bit at one time

Each bit travel down its own wire simultaneously with other bits

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DATA COMMUNICATION CHANNELSThere are three data communication channels like;Simplex communication- refers to communication that occurs in one direction only. Examples radio broadcast, keyboard / mouse inputs to CPU, internet multicast, and one – lane and one side road only.

Half duplex communication - system provides communication in both directions, but only one direction at a time (not simultaneously). Typically, once a party begins receiving a signal, it must wait for the transmitter to stop transmitting, before replying. Examples walkie-talkie, one-lane road with traffic controllers at each end.

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Full duplex communication- sometimes called double-duplex system allows communication in both directions simultaneously. Virtually no collisions take place on a full-duplex transmission. Perhaps a bigger benefit is the increase in overall throughput- since we are sending and receiving on two different channels, we just theoretically doubled our data transfer rate. Examples landline / mobile phone, two way double side road.

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DATA COMMUNICATION MODESData communication modes define behavior of data flow during communication which is based on interval of time.

When devices are communicating, they must be know when ever data has to send or receive (in period of time). The two devices must establish and maintain some type of timing between them so that signals are produced, transmitted, and detected accurately.

There are two main alternatives to establishing and maintaining the timing for the sampling of the signals. These two timing alternatives are known as asynchronous and synchronous, also known as data communication modes.

Data Link Layer : all synchronization occurs on the data link layer (2nd layer of TCP/IP), where the data in form of frame.

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Asynchronous communication- The transmission of data in which each character is a self-contained unit with its own start and stop bits. Intervals between characters may be irregular.

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Start bit inform that transmission has to start with binary value of “0”. Stop bit inform to equipment that transmission has been stop with binary value of “1”. When no character is being transmitted, the line between transmitter and receiver is in an idle state (binary 1 level). A minimum length for the stop element is specified, and this is usually 1, 1.5, or 2 times the duration of an ordinary bit. Data contain may be 5 -8 character bits. Parity bit : Character bit may include parity bit, set by the transmitter such that the total number of ones in the character, including the parity bit, is even (even parity) or odd (odd parity). The receiver uses this bit for error detection.

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There are two types of parity biteven parity bitodd parity bit

Even parity bit - when using even parity, the parity bit is set to 1 if the number of ones in a given set of bits (not including the parity bit) is odd, making the number of ones in the entire set of bits (including the parity bit) even. If the number of ones in a given set of bits is already even, it is set to a 0.an even parity bit will be set to "1" if the number of 1s + 1 is

evenOdd parity bit - when using odd parity, the parity bit is set to 1 if the number of ones in a given set of bits (not including the parity bit) is even, keeping the number of ones in the entire set of bits (including the parity bit) odd. And when the number of set bits is already odd, the odd parity bit is set to 0.

an odd parity bit will be set to "1" if the number of 1s +1 is odd

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at end of transmission no maximum value is specified, because the stop element is the same as the idle state, the transmitter will continue to transmit the stop element until it is ready to send the next character.

Synchronous communication- The transmission of data in block set and time intervals between characters may be regular.

each block of data is formatted as a frame that includes a starting and an ending flag, and is transmitted in a steady stream without start and stop codes. Clock speed : time interval (clock speed) must be synchronized, to prevent timing drift between transmitter and receiver;

can use separate clock line

embed clock signal in data

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By adding clock line – add specific time of break between sender and receiver.By adding clock signal – add clock information in frame.

In synchronous transmission, there is another level of synchronization required, to allow the receiver to determine the beginning and end of a block of data.

each block begins with a preamble bit pattern (opening flag) and generally ends with a post-amble bit pattern (closing flag).

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preamble bit – The preamble is a 64-bit (8 byte) field that contains a synchronization pattern consisting of alternating ones and zeros and ending with two consecutive ones. After synchronization is established, the preamble is used to locate the first bit of the packet. The preamble is generated by the LAN interface card.

post-amble bit – commonly used end of synchronous transmission.

Control bit : start control bit contain destination MAC, source MAC, and protocol; and similar stop control bit contain CRC information.

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Comparison - some comparison between asynchronous communication and Synchronous communication as follow;

Characteristic Asynchronous Synchronous

Transmission techniques

Used serial communication Used parallel communication

Comparative capacity Data transmit one character at one time

Data transmit block (bunch of character) at one time

Distance limitation Farther (long) Shorter

Sync method Start and stop bit Clock speed

Comparative speed Low speed due to serial transmission

More efficient due to parallel transmission

Costing Simple and cheap Much cost due to mechanism

Bandwidth loss 20% to 30% over capacity 5% over capacity

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DATA COMMUNICATION PORTSFor interconnection with other device every data communication device have specific port / interface, by data communication mechanism two types of ports are available;

Serial port- a serial port is a serial communication physical interface through which information transfers in or out one bit at a time.Serial port available in DB-9, DB-25 and Mini Din-8 (apple format);DB-9 DB-25 Mini Din-8male male male

female female female

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DB- 9 – DB-9 also known as RS-422, pin configuration as follows;

DB- 25 – DB -25 also know as RS-232, pin configuration as follows;

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Mini Din -8 – Din-8 also known as RS-422, pin configuration as follows;

Note : serial port commonly used in old mouse port, game controller, modem port and some old printers.

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Parallel port- a parallel port is a parallel communication physical interface. It is also known as a printer port or centronics port.

Parallel port is standard of IBM known as (DB-25) 25-pin combinations. Some available speed of parallel ports;oBi-directional – 150 KbpsoEPP – 1.5 MbpsoECP – 2.5 MbpsoEPP PCI – 4.5 Mbps

Before the advent of USB, the parallel interface was adapted to access a number of peripheral devices other than printers. List are bellow here;Hardware dongles, Zip drives, Scanners, Webcam, External modem, Sound card, External HDD and CD Rom

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DB- 25 – DB-25 standard of IEEE 1284 as printer port;

Centronics – port with 36-pins interface;

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USB - Universal Serial Bus is also serial port with high speed data flow.

USB 1.0 with speed of 1.5 MbpsUSB 1.1 with speed of 12 MbpsUSB 2.0 with speed of 480 MbpsUSB 3.0 with speed of 5 Gbps (Super Speed)

USB 1 USB 2 USB 3

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USB - Data Transfer Rate Comparison

USB Revision USB1.0 USB2.0 USB3.0

Media (Data Size) Transfer Time

Song / Pic (4 MB) 5.3 sec 0.1 sec 0.01 sec

256 Flash (256 MB) 5.7 min 8.5 sec 0.8 sec

USB Flash (1 GB) 22 min 33 sec 3.3 sec

SD-Movie (6 GB) 2.2 hr 3.3 min 20 sec

USB Flash (16 GB) 5.9 hr 8.9 min 53.3 sec

HD-Movie (25GB) 9.3 hr 13.9 min 70 sec

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SIGNALS AND SYSTEMA signal is an electric current or electromagnetic field used to convey data from one place to another.

The simplest form of signal is a direct current (DC) that is switched on and off; this is the principle by which the early telegraph worked. More complex signals consist of an alternating-current (AC) or electromagnetic carrier that contains one or more data streams.

Data is superimposed on a carrier current or wave by means of a process called modulation. Signal modulation can be done in either of two main ways: analog and digital.

Note : In recent years, digital modulation has been getting more common, while analog modulation methods have been used less and less. There are still plenty of analog signals around, however, and they will probably never become totally extinct.

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There are three data transmissions core aspect;

Data – Actual information being sent / received, possibly Analog (continuous) or digital (discrete).Analog Data – Takes on continuous values. Ex. Voice or videoDigital Data – Takes on discrete values. Ex. Text and integers

Signal - Electronic or electromagnetic representation of data, possibly Analog or digital.Analog Signal – Continuously varying electromagnetic wave representing data carried over a variety of medium.Digital Signal – Sequence of voltage pulses representing data transmitted over a wire medium

Transmission – Communication of data by sending / receiving, and processing data.Analog Transmission – Communication of analog signalsDigital Transmission – Communication of digital signals

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Analog Signals - An analog signal is any continuous signals for which the time is variable of the signal.

Digital Signals - A digital signal is a physical signal that is a representation of a sequence of discrete values.

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Comparison - some comparison between analog and digital signals as follow;

Characteristic Analog Digital

Number of range Analog signals can have an infinite number of values in a range

Digital signals can have only a limited number of values (1 / 0)

Type of data Continuous Discrete

Value of data More exact values, but more difficult to work with

Not as exact as analog, but easier to work with

Wave types Sing waves Square waves

Type of value Negative / positive Positive

Medium Wire / un-wire Wire

Device Amplifier for signals boosting (noise also be amplify)

Repeater for signals regenerating (noise isn’t boost)

Security Non-encryption Encryption

Capacity / Bandwidth Low High

Examples Voice, video, file format on tape, Radio / TV transmission waves

Text, integers, images, computer format files (CD, HDD)

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Analog Signal Example - Telephones take sound vibrations and turn them into electrical vibrations of the same shape before they are transmitted over traditional telephone lines. Radio wave transmissions work in the same way. Computers, which handle data in digital form, require modems to turn signals from digital to analog before transmitting those signals over communication lines such as telephone lines that carry only analog signals. The signals are turned back into digital form (demodulated) at the receiving end so that the computer can process the data in its digital format.

Digital Signal Example - This is the principle behind compact discs (CDs). The music itself exists in an analog form, as waves in the air, but these sounds are then translated into a digital form that is encoded onto the disk. When you play a compact disc, the CD player reads the digital data, translates it back into its original analog form, and sends it to the amplifier and eventually the speakers.