Digital Transmission Handouts

8/10/2019 Digital Transmission Handouts

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Slide 1

Analog & Digital Transmission.

Signaling amounts to communicating information. The informationbeing communicated can take one of two forms analog or digital:

Analog information changes continuously and can take on manydifferent values. An analog clocks hands move constantly, displayingtime on a continuous scale.

Digital information is characterized by discrete states. A light bulb,for example, is on or off. A digital clock represents the time in one-minute intervals and doesnt change its numbers aga in until the nextminute. A digital clock can represent exact minutes but not theseconds that pass in between.

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Slide 2

ANALOG

ANALOG DATAFor example, telephones take sound vibrations and turn them intoelectrical vibrations of the same shape before they are transmitted overtraditional telephone lines. Radio wave transmissions work in the sameway. Computers, which handle data in digital form, require modems toturn signals from digital to analog before transmitting those signals overcommunication lines such as telephone lines that carry only analogsignals. The signals are turned back into digital form (demodulated) at thereceiving end so that the computer can process the data in its digitalformat.

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Slide 3

DIGITAL

DIGITAL DATAThis is the principle behind compact discs (CDs). The music itself exists in ananalog form, as waves in the air, but these sounds are then translated into adigital form that is encoded onto the disk. When you play a compact disc, the CDplayer reads the digital data, translates it back into its original analog form, andsends it to the amplifier and eventually the speakers.

Internally, computers are digital because they consist of discrete units called bitsthat are either on or off. But by combining many bits in complex ways,computers simulate analog events. In one sense, this is what computer science isall about.

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Slide 5

Bandwidth

bandwidth is the width, usually measured in hertz, of a frequency band f2 f1. It can alsobe used to describe a signal, in which case the meaning is the width of the smallestfrequency band within which the signal can fit.

It is usually notated B, W, or BW. The fact that real baseband systems have both negativeand positive frequencies can lead to confusion about bandwidth, since they aresometimes referred to only by the positive half, and one will occasionally see expressionssuch as B = 2W, where B is the total bandwidth, and W is the positive bandwidth. Forinstance, this signal would require a lowpass filter with cutoff frequency of at least W tostay intact.

The bandwidth of an electronic filter is the part of the filter's frequency response thatlies within 3 dB compared to the center frequency of its peak.

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Slide 6

Noise & Attenuation

Noise (Bunyi bising) can be considered data without meaning; that is,data that is not being used to transmit a signal, but is simply produced asan unwanted by-product of other activities.

Attenuation Attenuation (pengurangan) is a measure of how much a signal weakens asit travels through a medium.

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Slide 7

Categories of Noise.

1) Johnson-Nyquist noise (sometimes thermal noise , Johnson noise or Nyquist noise ) is thenoise generated by the equilibrium fluctuations of the electric current inside an electricalconductor, which happens without any applied voltage, due to the random thermalmotion of the charge carriers (the electrons).

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Slide 8

Categories of Noise.

2) Intermodulation or intermod is the result of two radio signals of differentfrequencies being mixed together, forming additional signals at frequencies thatare not at harmonic frequencies (integer multiples) of either.

3) Crosstalk (XT) has the following meanings:Undesired capacitive, inductive, or conductive coupling from one circuit, part of acircuit, or channel, to another.Any phenomenon by which a signal transmitted on one circuit or channel of atransmission system creates an undesired effect in another circuit or channel.

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Slide 9

TWISTED PAIR CABLE

Twisted-pair cable has become the dominant cable type for all new network designs thatemploy copper cable. Among the several reasons for the popularity of twisted-pair cable,the most significant is its low cost. Twisted-pair cable is inexpensive to install and offersthe lowest cost per foot of any cable type

Two types of twisted-pair cable are used in LANs: shielded (STP) andunshielded (UTP).

CATEGORIES OF CABLE

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Slide 10

STP

Shielded twisted-pair(STP)Shielded twisted-pair cabling consists of one ormore twisted pairs of cables enclosed in a foilwrap and woven copper shielding. first cabletype used with IBM Token Ring. Early LANdesigners used shielded twisted-pair cablebecause the shield further reduces thetendency of the cable to radiate EMI and thusreduces the cables sensitivity to outsideinterference.

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Slide 11

UTP

Unshielded Twisted-Pair (UTP) Cable .Unshielded twisted- pair cable doesnt incorporate a braided shield into its structure.However, the characteristics of UTP are similar in many ways to STP, differing primarily inattenuation and EMI. Telephone systems commonly use UTP cabling. Network engineerscan sometimes use existing UTP telephone cabling (if it is new enough and of a highenough quality to support network communications) for network cabling.

UTP cable is a latecomer to high-performance LANs because engineers only recentlysolved the problems of managing radiated noise and susceptibility to EMI. Now,however, a clear trend toward UTP is in operation, and all new copper-based cablingschemes are based on UTP.

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Slide 12

UTP

UTP cable is available in the following five grades, or categories: Categories 1 and 2. These voice-grade cables are suitable only for voice and for low data rates (below 4

Mbps). Cate-gory 1 was once the standard voice-grade cable for telephone systems. The growing needfor data-ready cabling systems, however, has caused Categories 1 and 2 cable to be supplanted byCategory 3 for new installations.

Category 3. As the lowest data-grade cable, this type of cable generally is suited for data rates up to 10Mbps. Some innovative schemes, however, enable the cable to support data rates up to 100 Mbps.Category 3, which uses four twisted-pairs with three twists per foot, is now the standard cable used formost telephone installations.

Category 4. This data-grade cable, which consists of four twisted-pairs, is suitable for data rates up to 16Mbps.

Category 5. This data-grade cable, which also consists of four twisted-pairs, is suitable for data rates upto 100 Mbps. Most new cabling systems for 100 Mbps data rates are designed around Category 5 cable.

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Slide 14

Coaxial cable

1) Thinnet is a light and flexible cabling medium that is inexpensive and easy to install.

2) Thicknet big surprise is thicker than Thinnet. Thicknet coaxial cable is approximately 0.5inches (13 mm) in diameter. Because it is thicker and does not bend as readily as Thinnet, Thicknetcable is harder to work with.A thicker center core, however, means that Thicknet can carry more signals a longer distance thanThinnet. Thicknet can transmit a signal approximately 500 meters (1650 feet). Thicknet cable issometimes called Standard Ethernet (although other cabling types described in this chapter areused for Ethernet also). Thicknet can be used to connect two or more small Thinnet LANs into alarger network.

Because of its greater size, Thicknet is also more expensive than Thinnet. Thicknet can be installedsafely outside, running from building to building.

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Slide 15

Fiber Optic cableFiber-Optic Cable.In almost every way, fiber-opticcable is the ideal cable for datatransmission. Not only does thistype of cable accommodateextremely high bandwidths, butit also presents no problems withEMI and supports durable cablesand cable runs as long as severalkilometers. The twodisadvantages of fiber-optic,however, are cost andinstallation difficulty.

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Slide 16

Fiber optic cable

A fiber-optic network cable consists of two strands separately enclosed in plastic sheaths one strand sends and the other receives.

Two types of cable configurations are available: loose and tight configurations.

a) Loose configurations incorporate a space between the fiber sheath and the outer plasticencasement; this space is filled with a gel or other material.

b) Tight configurations contain strength wires between the conductor and the outer plasticencasement. In both cases , the plastic encasement must supply the strength of thecable, while the gel layer or strength wires protect the delicate fiber from mechanicaldamage.

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Slide 17

DTE

DTEis an abbreviation for Data Terminal Equipment . An end instrument that converts user information into signals for transmission or reconverts

the received signals into user information. The functional unit of a data station that serves as a data source or a data sink and provides

for the data communication control function to be performed in accordance with linkprotocol.

The data terminal equipment (DTE) may be a single piece of equipment or an interconnectedsubsystem of multiple pieces of equipment that perform all the required functions necessaryto permit users to communicate.

A user interacts with the DTE, or the DTE may be the user. The DTE interacts with the datacircuit-terminating equipment (DCE).

Usually, the DTE device is the terminal (or computer), and the DCE is a modem.Insertcontents.

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Slide 18

DCE

DCE-Data Circuit-Terminating Equipment

DCEis an abbreviation for Data Circuit-Terminating Equipment and its synonyms are Data Communications Equipmentand Data Carrier Equipment .

In a data stat ion, the equipment that performs functions, such as signal conversion and coding, at t he network end ofthe line between the data t erminal equipment (DTE) and the line, and that may be a separate or an integral part of theDTE or of intermediate equipment.

The interfacing equipment that may be required to couple the data terminal equipment (DTE) into a transmissioncircuit or channel and from a transmission circuit or channel into the DTE.

Data Communications Equipment (DCE) is a device that communicates with a Data Terminal Equipment (DTE) device inRS-232C communications.

Usually, the DTE device is the terminal (or computer), and the DCE is a modem. When two devices that are both DTE or both DCE that must be connected together without a modem or a similar

media translater between them, a NULL modem must be used

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Slide 19

Methods of Synchronization

Synchronous TransmissionIn synchronous transmission, the stream of data to be transferred is encoded asfluctuating voltages on one wire, and a periodic pulse of voltage is put on another wirethat tells the receiver "here's where one bit/byte ends and the next one begins".

Asynchronous TransmissionIn asynchronous transmission, there is only one wire /signal carrying the transmission. thetransmitter sends a stream of data and periodically inserts a certain signal element intothe stream which can be "seen" and distinguished by the receiver as a synch signal.Obviously, the term "asynchronous" is misleading in its litera l interpretation and must beunderstood as a term which is dictated by conventional usage.

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Slide 20

Serial & Parallel Transmission

Serial transmission is :the sequential transmission of the signal elements of a group representing a character or other entity of data.Note: The characters are transmitted in a sequence over a sing le line, rather than simultaneously over two ormore lines, as in parallel transmission. The sequential elements may be transmitted with or withoutinterruption. Synonym sequential transmission.

Parallel transmission is:

The simultaneous transmission of the signal elements of a character or other data item.In digital communications, the simultaneous transmission of related signal elements over two or more separatepaths.

Note: Protocols for parallel transmission, such as those used for computer ports, have been standardized byANSI

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Slide 21

Half duplex and Full Duplex

Half-duplexAhalf-duplex system allows communications in both directions, but only one direction at a time (notsimultaneously). Any radio system where you must use "Over" to indicate the end of transmission, or anyother procedure to ensure that only one party broadcasts at a time would be a half-duplex system.

A good analogy for a half-duplex system would be a one lane road with traffic controllers at each end.Traffic can flow in both directions, but only one direction at a time with this being regulated by thecontrollers. Can be describe as a walkie-talkie system also.

Full-duplexAfull-duplex system allows communication in both directions, and unlike half-duplex allows this tohappen simultaneously. Most telephone networks are full duplex as they allow both callers to speak atthe same time.

A good analogy for a full-duplexsystem would be a two lane road with one lane for each direction.

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Digital Transmission Handouts