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DATA COMMUNICATIONSSYSTEM

TRANSMISSION MODES

A powerpoint presentation

ByEngr. Feirah Lovely Borbon

Faculty- College of Engineering andArchitecture

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Modes of Data rans!ission

Modes of Data Transmission is the "owof data between two points. hese can be

described as#

Simplex: data "ows in only one directionon the data co!!unication line $!ediu!%.

E&a!ples are radio and televisionbroadcasts. hey go fro! the ' station toyour ho!e television. $as in Figure (.)%

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Simplex

Data is trans!itted fro! the sender to receiveronly* eg# fro! a central co!puter to a du!bter!inal. he co!!unication can only ta+eplace in one direction and it is not possible forthe receiver to send data bac+. An e&a!ple of

si!ple& trans!ission would be data being sentto an electronic notice board such as thosefound in train stations and airports.

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Modes of Data rans!issionHalf-Dplex: data "ows in both

directions but only one direction at a

ti!e on the data co!!unication line.For e&a!ple* a conversation on wal+ie-tal+ies is a half-duple& data "ow. Eachperson ta+es turns tal+ing. ,f both tal+ at

once - nothing occurs Bi-directional but only direction at a

ti!e

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Half-Dplex

Data can travel in both directions but not at the sa!eti!e. Each end of the co!!unications lin+ acts assender and receiver* eg# two-way co!!unicationbetween co!puters and other co!puters that !ay beconnected to a hub. Controls will e&ist to ensure that

the devices do not send at the sa!e ti!e. /ne hu!ane&a!ple of this type of co!!unication is the use ofwal+ie-tal+ies* where each person co!!unicating!ust indicate when they have 0nished spea+ing.

E&. Citi1ens Band $CB% 2adio

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Modes of Data rans!ission

!ll-Dplex: data "ows in both directionssi!ultaneously. Mode!s are con0gured to

"ow data in both directions. Full 3 duple&$FD4% operation re5uires ) separateco!!unication channels* so thatsi!ultaneous ) way co!!unication can

occur. 6enerally* this is acco!plished by a( wire circuit.

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!ll-Dplex

Data can travel in both directions si!ultaneously*eg# two or !ore co!puters connected to a networ+device such as a switch that provides full duple&activity.

7ote# as well as the data that is sent betweensyste!s there is also control infor!ation* eg# readyto send and ready to receive. herefore* althoughthe data !ay be only one way in a passive si!ple&syste! there !ay be the need for controlinfor!ation to be collected and used by the sender.

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Modes of Data rans!ission T"o "ire #erss for-"ire:

 wo-wire over full duple&# signals propagatingin opposite directions !ust occupy di8erentbandwidth.

Four-wire over full duple&# signals propagatingin opposite directions are physically

separated. herefore* they can occupy thesa!e bandwidth without interfering with eachother.

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9erial co!!unicationSerial communication is the method of transferringone bit at a time through a medium.

,n serial data transfers* each bit of the word istrans!itted one after another. Due to the se5uential

nature of the serial data trans!ission* usually it ta+eslonger ti!e to send this way. 9erial trans!ission isused for long-distance co!!unications.

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Data TransmissionTe$%ni&es

:arallel co!!unication is the !ethod oftransferring bloc+s* eg# B;Es* of data at

the sa!e ti!e.

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:arallel co!!unication<owever* in parallel data transfer* all the bits

of a code word are transferred

si!ultaneously and as a result* it ise&tre!ely fast. his concept is illustrated in0gure (.=. ,n parallel data trans!ission* thereis one wire for each bit of infor!ation to betrans!itted. his !eans a !ulti wire cable

!ust be used. As a general rule* paralleltrans!ission is used for short-distanceco!!unications and within a co!puter.

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:arallel co!!unication As you can appreciate parallel co!!unication is

faster than serial. For this reason* the internal

connections in a co!puter* ie# the busses* arelin+ed together to allow parallel co!!unication.<owever* the use of parallel co!!unication forlonger distance data co!!unication isunfeasible for econo!ic and practical reasons*eg# a!ount of e&tra cable re5uired andsynchronisation di>culties. herefore* all longdistance data co!!unications ta+es place overserial connections.

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9E2,AL C/MM?7,CA,/7 ,n teleco!!unication and co!puter science*

Serial $ommni$ation is the process of sending data one bit at a ti!e*se5uentially* over a co!!unication channel or co!puter bus. his is in

contrast to parallel co!!unication* where several bits are sent as awhole* on a lin+ with several parallel channels.

9erial co!!unication is used for all long-haul co!!unication and!ost co!puter networ+s* where the costof cable and synchroni1ation di>culties !a+e parallel co!!unicationi!practical. 9erial co!puter buses are beco!ing !ore co!!on even atshorter distances* as i!proved signal integrity and trans!ission speeds

in newer serial technologies have begun to outweigh the parallel bussadvantage of si!plicity $no need for seriali1er and deseriali1er*or 9erDes% and to outstrip its disadvantages $cloc+ s+ew* interconnectdensity%. he !igration fro! :C, to :C, E&press is an e&a!ple.

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CABLE9 <A CA22; 9E2,AL DAA#

Many serial co!!unication syste!s were originally designed to transferdata over relatively large distances through so!e sort of data cable.

 he ter! serial !ost often refers to the 29)) port on the bac+ of theoriginal ,BM :C* often called the serial port* and the serial cable* designedto plug into it* and the !any devices designed to be co!patible with it.

:ractically all long-distance co!!unication trans!its data one bit at a ti!e*

rather than in parallel* because it reduces the cost of the cable. he cables

that carry this data $other than the serial cable% and the co!puterports they plug into are usually referred to with a !ore speci0c na!e* toreduce confusion.

eyboard and !ouse cables an Apple Des+top Bus and ?9B.

 he cables that carry digital video are al!ost invariably serial -- such as coa&

cable plugged into a <D-9D, port* a webca! plugged into a ?9B portor Firewire port* Ethernet cable connecting an ,: ca!era to a :ower overEthernet port* F:D-lin+* etc.

/ther such cables and ports* trans!itting data one bit at a ti!e*include 9erial AA* 9erial 9C9,* Ethernet cable plugged into Ethernet ports*the Displat Data Channel using previously reserved pins of the '6Aconnector or the D', port or the <DM, port.

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E4AM:LE9 /F 9E2,ALC/MM?7,CA,/7 92?C?2E#

Morse code telegraphy 29-)) $low-speed* i!ple!ented by serial ports% 29-()) 29-() 29-(IJ ,KC 9:, A2,7C II Avionics Digital 'ideo Bus Atari 9,/ $oe Decuir credits his wor+ on Atari 9,/ as the basis of ?9B% ?niversal 9erial Bus $!oderate-speed* for connecting peripherals to co!puters% Fireire Ethernet Fibre Channel $high-speed* for connecting co!puters to !ass storage devices% ,n0niBand $very high speed* broadly co!parable in scope to :C,%M,D, control of electronic !usical instru!ents DM4J) control of theatrical lighting 9D,-) industrial sensor protocol

Coa4:ress industrial ca!era protocol over Coa& 9erial Attached 9C9, 9erial AA

9paceire 9pacecraft co!!unication networ+ <yperransport :C, E&press 9/7E and 9D< $high speed teleco!!unication over optical 0bers% -* E- and variants $high speed teleco!!unication over copper pairs%M,L-9D-JJAB

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:A2ALLEL C/MM?7,CA,/7

,n teleco!!uication and co!puter science* parallel$ommni$ation is a !ethod of conveying !ultiple binary digits$bits% si!ultaneously. ,t contrasts with serial co!!unication* whichconveys only a single bit at a ti!eH this distinction is one way ofcharacteri1ing a co!!unications lin+.

 he basic di8erence between a parallel and a serial co!!unicationchannel is the nu!ber of electrical conductors used at the physicallayer to convey bits. :arallel co!!unication i!plies !ore than onesuch conductor. For e&a!ple* an I-bit parallel channel will conveyeight bits $or a byte% si!ultaneously* whereas a serial channelwould convey those sa!e bits se5uentially* one at a ti!e. ,f both

channels operated at the sa!e cloc+ speed* the parallel channelwould be eight ti!es faster. A parallel channel !ay have additionalconductors for other signals* such as a cloc+ signal to pace the "owof data* a signal to control the direction of data "ow*and handsha+ing signals.

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E4AM:LE9 /F :A2ALLELC/MM?7,CA,/7

,BM 9yste!= Direct Control

Feature $N=(%.OP#p.I. 9tandard 9yste!=

had an eight-bit wide port. he process-control variant Model (( had a )-bit width.

Co!puter peripheral buses# ,9A* AA* 9C9,*:C, and Front side bus* and the once-ubi5uitous ,EEE-)I(  Centronics printer port

Laboratory ,nstru!entation bus ,EEE-(II

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C/M:A2,9/7 ,< 9E2,ALL,79

Before the develop!ent of high-speed serial technologies* the choice ofparallel lin+s over serial lin+s was driven by these factors#

9peed# 9uper0cially* the speed of a parallel data lin+ is e5ual to the nu!berof bits sent at one ti!e ti!es the bit rate of each individual pathH doubling

the nu!ber of bits sent at once doubles the data rate. ,n practice* cloc+s+ew reduces the speed of every lin+ to the slowest of all of the lin+s.

Cable length# Crosstal+ creates interference between the parallel lines* andthe e8ect worsens with the length of the co!!unication lin+. his places anupper li!it on the length of a parallel data connection that is usually shorterthan a serial connection.

Co!ple&ity# :arallel data lin+s are easily i!ple!ented in hardware* !a+ing

the! a logical choice. Creating a parallel port in a co!puter syste! isrelatively si!ple* re5uiring only a latch to copy data onto a data bus. ,ncontrast* !ost serial co!!unication !ust 0rst be converted bac+ intoparallel for! by a universal asynchronous receivertrans!itter $?A2%before they !ay be directly connected to a data bus.

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 he decreasing cost of integrated circuits* co!binedwith greater consu!er de!and for speed and cable

length* has led to parallel co!!unication lin+sbeco!ing deprecated in favor of serial lin+sH fore&a!ple* ,EEE )I( printer ports vs. ?9B* :arallelAA vs. 9erial AA* and 9C9, vs. Fireire.

/n the other hand* there has been a resurgence ofparallel data lin+s in 2F co!!unication. 2ather thantrans!itting one bit at a ti!e $as in MoreCode and B:9%* well-+nown techni5ues suchas :9M* :AM* and Multiple-input !ultiple-output

co!!unication send a few bits in parallel. $Eachsuch group of bits is called a Qsy!bol%. 9uchtechni5ues can be e&tended to send an entire byteat once $)J=-RAM%.

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Serial and )arallel Comparison)arallel transmission re5uires a separate channel for each bit tobe trans!itted. herefore* to transfer a byte* eight channels will bere5uired between the sender and receiver. Added to these eightare additional channels that are needed for control infor!ation andif full duple& co!!unication is re5uired then even !ore channelswould be re5uired. :arallel trans!ission is rare* other than for very

short distances* eg# within a co!puter* eg# data bus* or between aco!puter and a printer* eg# Centronics printer interface.

Serial transmission is !uch !ore co!!on* particularly overlonger distances. ,t is generally !uch cheaper as only a singlechannel between sender and receiver is re5uired* eg# he sevenbits $plus one parity chec+ bit% !a+ing up an Ameri$an Standard

Code for Information Inter$%an*e +ASCII, character aretrans!itted serially in se5uence by the sender and arereasse!bled into the character by the receiver. A co!!one&a!ple of a serial interface standard is 2eco!!ended 9tandard)) $29))%.

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Serial Commni$ationsE&ipment

 hree things should be considered when discussingserial co!!unications and the e5uip!ent to carry

this out# Electrical standards associated with the interface

Mechanical standards associated with theinterface

9tandards organi1ations involved ,t is the organi1ations that govern the 0rst two

ite!s on the list.

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Standards Or*aniationsOr*anisation Responsi.ilities /e. Address

Ameri$an National Standards

Institte +ANSI,

A79, represents a nu!ber of ?9 standards

organi1ations. Me!bers sub!it their standards for

acceptance. An e&a!ple is the A79, standard for

representing A9C,, characters.

www.ansi.org

Ele$troni$s Indstries

Asso$iation +EIA,

E,A are !ade up by !anufacturers in the ?9A.

2esponsible for 29)) and si!ilar standards.www.eia.org

Institte of Ele$tri$al and

Ele$troni$ En*ineers +IEEE,

 he ,EEE $:ronounced Eye-triple-E% is a non- pro0t*

technical professional association of !ore than

SS* individual !e!bers in J countries.

www.ieee.org

International Or*aniation for

Standardiation +ISO,

A networ+ of national standards institutes fro! (

countries wor+ing in partnership with international

organi1ations* govern!ents* industry* business and

consu!er representatives. he ,9/ have standards

covering a wide range of co!puter related topics.

www.iso.org

International

Tele$ommni$ations Union +ITU,

+pre#iosl0 1no"n as t%e Comite

Consltatif International

Telep%oni&e et Tele*rap%i&e

+CCITT,

 he ,?* head5uartered in 6eneva* 9wit1erland is an

international organi1ation within the ?nited 7ations

9yste! where govern!ents and the private sector

coordinate global teleco! networ+s and services. hey

are also involved with the allocation of satellite

fre5uencies and orbits.

www.itu.int