Ata Ommunication And Etwork: Hapter

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DATA COMMUNICATION AND NETWORK CHAPTER - 1

WHAT IS DATA COMMUNICATION? 

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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? 

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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: 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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Data transmission process between sender and receiver is refer to data communication, and deployed physical environment (hardware / software / protocols / channel ) is network.

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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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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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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.

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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. Copyright revised for Zafar Ayub ([email protected])

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DATA TRANSMISSION 

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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 TECHNIQUES

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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Serial 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.

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

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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 transmission methodologies are summarized in chart; Serial

Parallel

Transmission description

One bit comes after another, one by All bits in a single character and one transmit simultaneously

Comparative Speed

Slower

Faster

Distance Limitation

Farther

Shorter

Application

Between two computer, from Within a computer the along computer to external devices, and computer buses, between drive local and wide network controller to hard drive

Cable Description

All bits travel down in single wire, Each bit travel down its own wire one bit at one time simultaneously with other bits

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Transmission Characteristic

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DATA COMMUNICATION CHANNELS

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, onelane road with traffic controllers at each end.

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There 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.

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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 fullduplex 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 MODES Data communication modes define behavior of data flow during communication which is based on interval of time.

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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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.

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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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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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 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.

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

Odd 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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 There are two types of parity bit even parity bit odd 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.

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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.

 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.

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

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.

 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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 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.

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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. –

commonly

used

end

of

synchronous

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

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post-amble bit transmission.

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

Characteristic

Synchronous

Transmission techniques Used serial communication

Used parallel communication

Comparative capacity Distance limitation

Data transmit one character at Data transmit block (bunch of one time character) at one time Farther (long) Shorter

Sync method

Start and stop bit

Comparative speed

Low speed transmission

Costing

Simple and cheap

Much cost due to mechanism

Bandwidth loss

20% to 30% over capacity

5% over capacity

due

Clock speed to

serial More efficient transmission

due

to

parallel

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Asynchronous

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

female

female

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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-8 male male male

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

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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;

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Note : serial port commonly used in old mouse port, game controller, modem port and some old printers. 28

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

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

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

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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

USB 2

USB 3

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

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USB -

Data Transfer Rate Comparison

USB Revision

USB1.0

Media (Data Size)

USB2.0

USB3.0

Transfer Time

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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Song / Pic (4 MB)

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

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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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.

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There are three data transmissions core aspect;

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 signals Digital Transmission – Communication of digital signals

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

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

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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 Number of range

Digital

Analog signals can have an Digital signals can have only a infinite number of values in a limited number of values (1 / 0) range Continuous Discrete

Wave types

More exact values, but more Not as exact as analog, but difficult to work with easier to work with Sing waves Square waves

Type of value

Negative / positive

Positive

Medium

Wire / un-wire

Wire

Device

Security

Amplifier for signals boosting Repeater for signals regenerating (noise also be amplify) (noise isn’t boost) Non-encryption Encryption

Capacity / Bandwidth

Low

Examples

Voice, video, file format on Text, integers, images, computer tape, Radio / TV transmission format files (CD, HDD) waves

Value of data

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Type of data

Analog

High

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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.

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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.

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