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lecture4 - transmission media 1 Komunikasi Data Interface – minggu 4 Media transmisi Beberapa macam tipe fisik media transmisi yang dipergunakan untuk data transmisi Karakteristik dan limitasi dari setiap tipe Tipe-tipe sinyal Beberapa tipe sinyal yang digunakan dalam komunikasi data Sumber sinyal Materi Kuliah
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transmission media.ppt

Jan 19, 2016

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Page 1: transmission media.ppt

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Komunikasi Data Interface – minggu 4

• Media transmisi

Beberapa macam tipe fisik media transmisi yang dipergunakan untuk data transmisi

Karakteristik dan limitasi dari setiap tipe

• Tipe-tipe sinyal

Beberapa tipe sinyal yang digunakan dalam komunikasi data

Sumber sinyal

Materi Kuliah

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The importance of type of transmission medium: It determines the maximum number of bits (binary digits) that can be transmitted per second or bps.Examples: a pair of conductors or wires, a beam of light guided by a glass fiber, electromagnetic waves propagating through free space

• Transmission media:

– Guided transmission media• Conductive Metal

– Two wire open lines; Twisted-pair lines; Coaxial cable

• Glass or Plastic– Optical fiber

– Unguided transmission• Satellites; Terrestrial microwave; Radio broadcast; Infra red

Transmission Media

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Transmission Media

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Two-wire open lines

• The simplest transmission medium

• Each wire is insulated from the other and both are open to free space

• This is sufficient for connecting equipment up to 50m apart using moderate bit rates (less than 19.2 kbps)

• Mainly used for connecting a DTE (Data Terminal Equipment) to local DCE (Data Circuit-terminating Equipment), i.e. modem

• DTE-DCE connection usually utilize multiple lines; where the most common arrangement is a separate insulated wire for each signal and a single wire for the common ground reference

Transmission Media

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Two-wire open lines

• The complete set of wires is either enclosed in a single protected multicore cable or shaped into a flat ribbon cable

• It must be avoided cross-coupling of electrical signals between adjacent wires in the same cable; known as crosstalk, caused by capacitive coupling between two wires

• Open structure is vulnerable to get a false noise signals from other electrical signal sources caused by electromagnetic radiation

Transmission Media

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Twisted-pair lines

• It is a pair of wires that twisted together

• Much better immunity to false signals

• Proximity of the signal and ground reference wires means that any interference signal is picked up by both wires reducing its effect on the difference signal; then if multiple twisted pairs are enclosed within the same cable, the twisting of each pair within the cable reduce crosstalk

• Suitable for bit rates in order of 1 Mbps over short distances (less than 100m) and lower bit rates over longer distances

Transmission Media

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Unshielded Twisted Pairs (UTPs)

• A more sophisticated circuits; able to achieved similar or higher bit rates over much longer distances

• Used extensively in telephone networks and with special integrated circuits in many data communication applications

Transmission Media

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Shielded Twisted Pairs (STPs)

• A protective screen or shield used to reduce further the effects of interference signals

Transmission Media

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Transmission Media

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Transmission Media

Coaxial cable

• The signal and ground reference wires as a solid center conductor running concentrically (coaxially) inside a solid (or braided) outer circular conductor

• Ideally, the space between the two conductors should be filled with a dielectric insulating material with a solid or honeycomb structure

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Coaxial cable

• The center conductor is effectively shielded from external interference signals by the outer conductor

• Minimal losses occur as a result of electromagnetic radiation and the skin effect because of the presence of the outer conductor

• Advantages:

– Minimize the effect of attenuation, since increasing the electrical resistance of the wires for high-frequency signal

– Suitable for bit rates higher than 1 Mbps

• Used typically for :

– Signal of 10 Mbps (or higher with modulation) over several hundred meters

– Applicable for point-to-point and multipoint topologies

Transmission Media

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Transmission MediaHardware Stuff

MAGNETIC MEDIA: Sometimes it's cheaper and faster to load a box of tapes in your car !!!

TWISTED PAIR: Simply two wires twisted together - the twisting cuts down on electrical

interference. Heavily used in the phone system - the typical office has four pairs for

phones, etc. Category 3 and 5 - with 5 having more twists and better insulation.

BASEBAND COAXIAL CABLE: Used for digital transmissions (called baseband.) Good noise immunity. Data rates as high as 1 Gbps for short distances. Now being replaced by fiber.

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Transmission MediaHardware Stuff

BROADBAND COAXIAL CABLE: Used for analog transmissions (called broadband.) Can run 300 MHz for long distances. Analog signaling has better S/N than digital signaling. Interfaces must convert digital signals to analog and vice versa. Designed for long distances - can use amplifiers.

FIBER OPTICS: Transmission of light through fiber - properties include total internal

reflection and attenuation of particular frequencies. Fiber Optic Networks - can be used for LANs and long-haul.

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Optical fiber

• It carriers the transmitted information in the form of fluctuating beam of light in a glass fiber, rather than as an electrical signal on a wire

• Advantages:

– Achieved transmission rates of hundreds Mbps since light waves have a much wider bandwidth than electrical waves

– Light waves are also immune to electromagnetic interference and crosstalk

– Useful for transmission of lower bit rate signals in electrically noisy environments, i.e. steel plants, which employ much high-voltage and current-switching equipments

– It is difficult to tap; used where security is important

Transmission Media

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Transmission Media

Optical fiber

• It consists of a single glass fiber for each signal to be transmitted, contained within the cable’s protective coating which also shields the fiber from any external light sources

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Optical fiber

• The light signal is generated by an optical transmitter, that performs the conversion from normal electric signal as used in a DTE

• Optical receiver used to perform the reverse function at the receiving end

• Typically, the transmitter uses a light-emitting diode (LED) or laser diode (LD) to perform the conversion operation, while the receiver uses a light-sensitive photodiode or photo transistor

• Light propagates along the optical fiber core in different ways, depending on the type and width of core material used:

– Multimode: stepped index fiber & graded index fiber

– Single mode

Transmission Media

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Transmission Media

Multimode stepped index fiber

• Each cladding and core material has a different but uniform refractive index

• All the light emitted by the diode at an angle less than the critical angle is reflected at the cladding interference and propagates along the core by means of multiple (internal) reflections

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Transmission Media

Multimode stepped index fiber

• Depending on the angle at which it is emitted by the diode, the light will take a variable amount of time to propagate along the cable

• Therefore the received signal has a wider pulse width than the input signal with a corresponding decrease in the maximum permissible bit rate

• Used primarily for modest bit rates with relatively inexpensive LEDs compare to laser diodes

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Transmission Media

Multimode graded index fiber

• Reducing dispersion by using a core material that has a variable refractive index

• Here, light is refracted by an increasing amount as it moves away from the core

• This has the effect on narrowing the pulse width of the received signal compared with stepped index fiber, allowing a corresponding increase in maximum bit rate

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Transmission Media

Single mode / monomode fiber

• Improvement of other optical fiber, by reducing the core diameter to that of a single wavelength (3-10 μm) so that all the emitted light propagates along a single (dispersionless) path

• Consequently, the received signal is of a comparable width to the input signal

• Used with Lased Diodes (LDs), that can operate at hundreds of Mbps

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Satellites systems

• Data is transmitted using electromagnetic (radio) waves through free space

• A microwave beam, onto which data is modulated, is transmitted to the satellite from the ground; which is received and retransmitted (relayed) to the predetermined destination(s) using on-board circuit known as a transponder

• Single satellite has many transponders, each covering a particular band of frequencies

• A typical satellite channel has an extremely high bandwidth (500 MHz) and can provide many hundreds of high bit rate data links using a technique known as multiplexing

• Essentially, the total capacity of the channel is divided into a number of subchannels, each of which can support a high bit rate link

Transmission Media

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Satellites systems

Transmission Media

Using microwave

Receive and retransmit usingtransponder

Upward transmission (uplink) 4 GHz

Downward transmission (downlink)6 GHz

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Satellites systems

• Satellites used for communication purposes are normally geostationary, means that the satellite orbits the earth once every 24 hours in synchronism with the earth’s rotation and hence appears stationary from the ground

• The orbit of the satellite is chosen so that it provides a line-of-sight communication path to the transmitting and receiving station(s)

• The degree of the collimation of the microwave beam retransmitted by the satellite can be coarse (signal can be picked up over a wide geographical area) or focused (signal can be picked up over only a limited area)

• In the second case the signal power is higher, so that smaller-diameter receivers antenna or dishes is used. It is also known as very small aperture terminals or VSATs

Transmission Media

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Satellites systems

Transmission Media

Remains in a fixed position relative toground station

Used for communication purposed

Used 3 satellites to cover all over theearth

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Terrestrial microwave links

• Used to provide communication links if it is impractical or too expensive to install physical transmission media, i.e. across a river of a swamp or desert

• As the collimated microwave beam travels through the earth’s atmosphere, it can be disturbed by such factors as manufactured structures and adverse weather conditions. In a satellite link, the beam travels mainly through free space, therefore less prone to such effects

• Line-of-sight microwave communication through the earth’s atmosphere can be used reliably over distances in excess of 50 km

Transmission Media

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Terrestrial microwave links

Transmission Media

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Radio waves

• Used to provide a cordless (wireless) link between a fixed-wire termination point and the distributed computers. A radio transmitter (known as base station) is placed at the fixed-wire termination point, providing a cordless link between each computer and the central site

• Multiple base stations must be used for applications that require a wider coverage area or a higher density of users

• The coverage area of each base station is restricted (limited by its power output) so that it provides only sufficient channels to support the total load in that area. Wider coverage is achieved by arranging multiple base stations in a cell structure

• The size of each cell varies and is determined by such factors as the terminal density and local terrain

Transmission Media

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Radio waves

• Each base station operates using different band of frequencies from its neighbors

• However, since the field of coverage of each base station is limited, it is possible to reuse its frequency band in other parts of the network

Transmission Media

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Radio waves

Transmission Media

Wireless link between fixed terminalpoint (base station) and terminal

F2

z

F1

z

z

F3

z

z

F2 F3

z

F1

z

F2

z

F1

z

F2

z

F3

z

F1

z

F3

z

F2

F1, F2, F3 = frequencies used in channel

(b) multiple cellsBS

BS = Base station

= user computer/terminal

(a) single cell Radio field of coverage of base station

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Factors to select media:

• Cost

• Data rate & bandwidth

• Distance

Transmission Media

Twisted pair Coaxial Optical fiber Microwave Satellite

Data rate 1-100 Mbps 10 Mbps 400-500 Mbps 200-300 Mbps 1-2 Mbps

Interference electrical electrical immune solid objectatmosphere

condition

Distance

up to 1 mile (1-2 Mbps for 1mile, 10 Mbps for 100m,

2.4 kbps for 10miles)

2-3 miles 20 - 30 miles 20 - 30 miles

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• Two DTE that are close to one another; use modest bit rates; can be transmitted using two-wire open lines and simple interface circuits, that change the signal level used within the equipment to a level compatible with the interconnecting cable

• When DTEs are in different parts of the world, it needed to use the lines provided by the authorities responsible for the provision of telecommunication services.

• For this type of communication medium, the electrical signal output of the DTE source has to convert into a form analogous to the signals used to convey spoken messages. On the reception, these signals has to convert back into a form suitable for the use by the destination DTE.

• Modem is used to perform these functions.

• Some of different signal types are:

Signal Types

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V.28

• Standard interface has been defined for use with all of the modem types which specifies both the number and function of the electrical signals, the physical size of the plug and socket, and the pin configurations within them. E.g. the EIA-232D interface or the V.24 interface.

• The electrical signal levels defined for use with above interfaces are defined in recommendation V.28.

• The voltage signals used on the lines are symmetric to the ground reference signals and at least 3V: +3V for binary 0 and –3V for a binary 1. In practice, the actual voltage levels used are determined by the supply voltages applied to the interface circuits, 12V or even 15V not being uncommon.

Signal Types

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V.28

• The transmit circuits convert the low-level signal voltages used within the equipment to the higher voltage levels used on the transmission lines. Similarly, the receive circuits perform the reverse function.

• Interface circuits, known as line drivers and line receivers perform the necessary voltage conversion functions.

• The interfaces here used in a maximum physical separation of less than 15m and bit rates lower than 20kbps, although larger values are often used when connecting a peripheral to a computer.

Signal Types

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20mA current loop

• It uses a current signal.

• It doesn’t extend the available bit rate, but increases the physical separation between two communicating devices.

• The noise immunity of this interface is better than a basic voltage-driven interface since it uses a pair of wires for each signal. This means that any external noise (common-mode noise) is picked up in both wires, which has a minimal effect on the basic current-sensitive receiver circuit.

• This interface is suitable for up to 1km lines, but at modest bit rate (because of the limited operational rate of the switches and current sensitive circuits)

Signal Types

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RS-422A/V.11

• They increase the physical separation and the bit rate

• They use a twisted-pair cable and a pair of differential (also referred as balanced or double-ended) transmitter and receiver circuits.

• Differential transmitter produces twin signals of equal and opposite polarity for every binary 1 or 0 signal to be transmitted.Differential receiver is sensitive only to difference between two signals on its two inputs; noise picked up by both wires will not affect receiver operation.

• Summary of the alternative cable lengths and transmission rates:

Signal Types

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RS-422A/V.11

Signal Types

Signal type Length (m)Maximum transmission rate

(kbps)

10 100,000100 10,000

1000 1,00010 1,000,000

100 100,0001000 10,000

10 10,000,000100 1,000,000

1000 100,000

RS-423A/V.10

RS-422A/V.11 (unterminated)

RS-422A/V.11 (terminated)

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Coaxial cable signals

• Two different mode:

– Baseband mode

The available bandwidth is used to derive a single high bit rate transmission path (channel). Each of 10Mbps or higher.

– Broadband mode

The available bandwidth is devided to derive a number of lower bandwidth subchannels (as transmission path) on one cable.

• Mostly used in point-to-point or multipoint/multidrop configuration (where the high bit rate transmission channel is time/frequency shared by a number of systems)

Signal Types

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Optical fiber signals

• Used mainly in a point-to-point mode, but the transmission capacity available may be utilized either for a single high bit rate channel or to derive multiple lower bit rate channels on a single link

Satellite and radio

• A number of different access control methods are used to control access to the available capacity:

– Random access; all stations compete for a transmission channel in a random (uncontrolled) way

– Fixed assignment; both the channel frequency and the channel time slot are preassigned to each ground or cordless station

– Demand assignment; when a station wishes to transmit data, it first requests channel capacity from a central site which assigns the required capacity (time slots) to the requesting station

Signal Types