1

Media Transmisi

• Guided transmission

– coaxial cable

– twisted pair cable

– untwisted pair, including serial cables and power lines

– fiber optic cable

• Unguided transmission

– infrared

– radio wave

– microwave: terrestrial and satellite links

2

Media Transmisi

3

Available Bandwidth and Range

Media Bandwidth Range

Voice quality twisted pair 0 to 1 MHz 5 km

with loading 0.3 - 3.4 kHz 10 km

Coax cable (broadband) 1k - 1GHz 1-100 km

Category 5 twisted pair 1k - 100 MHz 0.1-2 km

Fiber optic cable 180-370 THz 1-100 km

For short distances, higher rates may be possible. Cat-5 twisted pair has achieved > 200 MHz.

4

Coaxial Cable

Karakteristik

– Outer conductor berbentuk serabut (biasanya dihubungkan ke ground)

– Inner conductor (solid) digunakan untuk mengirimkan signal

– Kebal thd noise EMI (Electromagnetic Interference ) dan RFI (Radio Frequency Interference)

Coax digunakan pada LAN, termasuk ethernet:

Thick coax (0.4 in, RG8): tapped by coring

Thin coax (0.4cm, RG58): uses BNC connectors

Keduanya berimpedansi 50 ohm (menggunakan terminator 50 ohm)

Digunakan pada LANs (baseband) berkecepatan 10 Mbps

RG58 coax and BNC Connector

5

Coax Cable (cont.)baseband vs broadband

• Baseband transmission

• Broadband transmission

6

Cable T.V. Coax• Kabel Coax yang digunakan untuk cable T.V. adalah RG1

1 yang beriimpedansi 75 ohm, dengan bandwidth sampai 5

00 MHz. Transmisinya broadband dengan bandwidth 6 M

Hz per T.V. channel

• Cable T.V. bersifat simplex, broadcast, shared access netw

ork.

• Untuk data networks, dapat mengirimkan data 40Mbps

dalam satu kanal 6MHz menggunakan pengkodean (misal

QPSK/QAM).

7

Cable T.V. Network

8

Twisted Pair

• Balanced signaling (+V and -V on pair) reduces cross-talk and increases ability to filter out noise.

• Telephone cable has twist length 5-15 cm. Cat-3 UTP is thicker cable (24 gauge) with twist length 7.5-10cmCat-5 has twist length 2-4 cm.

• Office telephone cable usually contain 2 pairs; computer cable contains 4 pairs; also available in 20 - 100 pairs per cable (“trunk” cabling).

9

Twisted Pair

• Rapid attenuation and susceptibility to noise limit lengths to 5-6 km (analog) or 0.1-2 km (digital).

• Uses 100 ohm impedance cable.

• 10Mbps ethernet uses Manchester encoding, resulting in an actual signaling rate of 20Mbps!

Max Data Rate Attenuation NEXTCategory-3 UTP 16 Mbps 13.1 db/100m 23db @16MHz

9.8 db/100m 26db @10MHzCategory-4 UTP 20 Mbps 10.1 db/100m 36db @20MHzCategory-5 UTP 100 Mbps 22db/100m 44db @100MHzCategory-5e UTP 200 Mbps 32db/100m 40db @200MHz

10

Category 5 UTP

• Category 5 Unshielded Twisted Pair (UTP) is the standard for local area computer networks.

• Shielded Twisted Pair (STP) is also available, but not popular and performance not better than UTP.

• Can be used for 100MHz ethernet links up to 100m; ATM (155.5MHz) up to 90m.

• Gigabit ethernet (1000MHz) specs include 100m runs over Category 5 UTP using all 4 pair.

• Token ring and CDDI also use twisted pair cables.

11

Twisted Pair Connectors

• Computer cables use 8-pin RJ45 connectors.

• In 10baseT ethernet and 100baseTX fast ethernet, one pair (pins 1-2) is used to transmit and another pair (pins 3-6) is used to receive.

• 100baseT4 (used for fast ethernet over Cat-3 cable) and gigabit ethernet use all four pair for data transmission. Two pair alternate in direction.

12

Twisted Pair WiringANSI/EIA 568-A Wiring Method

Pin Color Code Signal1 White/Green Transmit+2 Green/White Transmit-3 White/Orange Receive+4 Blue/White none5 White/Blue none6 Orange/White Receive-7 White/Brown none8 Brown/White none

1: TX+

2: TX-

3: RX+

4:

5:

6: RX-

7:

8:

1: RX+

2: RX-

3: TX+

4:

5:

6: TX-

7:

8:

1: RX+

2: RX-

3: TX+

4:

5:

6: TX-

7:

8:

Computer Hub/Switch Hub/Switch

Alternate color code: exchange green pair (1,2) and orange pair (3,6).

Middle pair (pins 4-5) not used as a precaution against accidental connection of telephone equipment.

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Fiber Optic Cable

A core made of pure fused silica, glass, or plastic transmits light, surrounded by a glass or plastic cladding of a lower refractive index, which reflects light back into core. Opaque jacket absorbs light and protects the core/cladding.

14

Snell’s Law and Reflection

1

1

2

2

3

3

c = critical angle

4 4

n2

n1

For n1>n2

i

t

n1sini = n2sint

i = sin-1n2/n1

= c

n1

n2

Light striking the surface at greater than the critical angle is reflected. This is why light remains in fiber optic cable even though it may contain many loops and bends.

Media 2

Media 1

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Fiber Optic Cable Types

Step-index multimode. Used with 850nm, 1300 nm source.

Graded-index multimode. Used with 850nm, 1300 nm source.

Single mode. Used with 1300 nm, 1550 nm source.

16

Fiber Optic Cable Types

Multimode (or step-index multimode) reflects light off of cladding, permitting multiple transmission paths through fiber.

In graded-index multimode fiber the core has several concentric layers of different refractive index (and hence different light propagation speeds) to reduce reflected path lengths. Pulses taking different paths spread out less than in step-index multimode fiber.

17

Fiber Optic Cable Types

Single mode fiber has only one transmission path for transmitted light, so signal pulses do not spread out as much as in multimode fiber.

Fiber optic cable size is expressed as “core/cladding” size, e.g. “62.5/125”. Typical sizes:

Core diam.Cladding diam.

Single mode fiber 3 - 10 m 100 - 125 m

Multimode 50, 62.5 m 100 - 125 m

62.5/125 is the most common size for multimode fiber.

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Transmission in Fiber Optic Cable

Silica glass transmits light best in infrared bands centered at 1.30 m and 1.55 m. The 0.85 m band is used because cost-effective GaAlAs light sources and electronics can be made to transmit in this band.

19

Light SourcesLEDs and injection laser diodes (ILD) are used as f/o light sources. Lasers emit more directional, coherent light pulses than LEDs, suitable for longer distance transmission.

LED Injection Laser DiodeAvailable bandwidth ~1 GHz up to 1000 GHzWavelength (mm) 850 1300, 1550Lifetime long shortTemp. sensitivity minor highly sensitiveCost low cost high costUsed in multimode single or multimode

20

Fiber Optic Transmitters

Data transmission in fiber optic cable is analog using amplitude shift keying (ASK).

LED source: LED is on for “1”, off for “0”.

Laser source: Laser is on high power for “1”, low power for “0”. Turning laser off (as with LED) is not practical for high speed transmission.

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Light Receivers

The receiver in fiber optic systems is a photodiode, which emits a current when struck by light. The typical response time of a photodiode is 1 nanosecond, but faster photodiodes (down to around 0.1 ns) exist.

Fiber optic transmission in computer networks is limited by the speed of conversion to/from electrical signals. To fully utilize the capacity of fiber optics will require purely optical methods, e.g. wave division multiplexing.

Design of purely optical networks is a topic of intense research and product development efforts.

Fiber optic transmission in computer networks is limited by the speed of conversion to/from electrical signals. To fully utilize the capacity of fiber optics will require purely optical methods, e.g. wave division multiplexing.

Design of purely optical networks is a topic of intense research and product development efforts.

22

Fiber Optic Links

Computer network links always use a pair of fibers: one to transmit and one to receive.

The end of a fiber optic patch cable using SC connectors.

Indoor “8 core” fiber optic cable (enough for 4 pair).

23

Fiber Optic Cables

• Several fibers are bundled per cable: 8-12 fibers is common for LAN, several hundred for trunk lines.

• Riser cables contain extra strength members to bear the weight of the cable. Aerial cables (outdoor, strung on telephone poles) also contain a metal cable to bear weight and for attachments.

• Underground cables contain extra shielding and moisture resistant cover.

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Fiber Optic Advantages

Fiber optic has several advantages over electrical cable:

• Higher bandwidth and data transmission rates

• Low attenuation: greater distance between repeaters

• Immune to electromagnetic interference; no crosstalk

• Resistant to corrosive damage by water and chemicals

• More secure: difficult to tap cable and intercept signal

• Lighter: 1 kg of fiber can replace 500 kg of copper cable

• Uses less space (in many places, data conduits are full)

• Compared to equivalent capacity of copper cables, easier to install

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Other Cable Types

Serial cable: point-to-point connection at rates up to 39.2 kbps, 25 - 100 feet.

Parallel (printer) cable: point-to-point connection at rates up to 2 Mbps over 8 meters.

Telephone lines (WAN): currently 1.5 Mbps using ADSL at distances up to 5.5 km

Telephone lines (LAN): 10Mbps home LANs using IEEE home network (e.g. Intel AnyPoint)

Power Lines: possible use for WAN at rates up to several hundred Mbps ... many technical problems.

26

Unguided Transmission Media

27

Microwave

• 1 - 40 GHz frequency range

• transmission mostly in straight line (line of sight)

• uses a focused beam: transmitter and receiving dish antenna must be aligned

• license required for use of most frequencies

• not transmitted through solid objects (buildings)

• terrestrial (earth-to-earth) and satellite applications

28

Microwave

• Signal attenuation at a distance d: S

S d

d

d

0

2

2

4

10 4

FH IK

Attenuation dblog( )

• Multipath fading (for terrestrial systems): some waves bounce off the earth or sky and arrive out-of-phase with directly transmitted signal.

• above 8 GHz, absorbed by water particles– rain can block transmission

29

Satellite Microwave

1 - 10 GHz is the optimal frequency range: below 1 GHz there is interference from natural and man-made sources; above 10 GHz there is significant atmospheric absorption.

The C band is used for geosynchronous satellites (4-degree spacing) and already crowded. RTT is 250-300 msec.

The Ku band is used by geosynchronous satellites (3-degree spacing) but less crowded.

Band (GHz) Name Uplink Download Use

4/6 C 5.9 - 6.4 3.7 - 4.2 commercial

7/8 X 7.9 - 8.4 7.9 - 8.4 military

11/14 Ku 14.0 - 14.5 11.7 - 12.2 commercial

20/30 Ka 27.5 - 30.5 17.7 - 21.2 military

20/44 Q 43.4 - 45.5 20.2 - 21.3 military

Band (GHz) Name Uplink Download Use

4/6 C 5.9 - 6.4 3.7 - 4.2 commercial

7/8 X 7.9 - 8.4 7.9 - 8.4 military

11/14 Ku 14.0 - 14.5 11.7 - 12.2 commercial

20/30 Ka 27.5 - 30.5 17.7 - 21.2 military

20/44 Q 43.4 - 45.5 20.2 - 21.3 military

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Satellite Systems

Low and medium orbit systems have much lower delay. They offer 2Mbps data channels (channels can be combined for higher data rates).

Non-stationary satellites use a system similar to cellular telephones to pass connections from one satellite to the next.

System Orbit (km) No. satellites Freq. Band

Geosynchronous 35,784 90 4/6 (C)

Teledesic 1,350 288 Ka

Iridium 780 66 1.6 GHz

System Orbit (km) No. satellites Freq. Band

Geosynchronous 35,784 90 4/6 (C)

Teledesic 1,350 288 Ka

Iridium 780 66 1.6 GHz

31

Terrestrial Wireless• Microwave is used for commercial telecomm links, cellular

phones, and short-to-medium distance LANs.

• IEEE 802.11 is an 11 Mbps wireless network at the 2.4 GHz band. Lucent’s Orinoco (WaveLAN) products use this (see www.wavelan.com).

Freq. Band Use Range Data Rate

824 - 894 MHz Analog cell phones (AMPS) 20 km per cell 13 kbps/channel

902-928 MHz License free in North America

1.7 - 2.3 GHz PCS digital cell phones < 1 km per cell

1.8 GHz GSM digital cell phones 16 kbps/channel

2.400-2.484 GHz global license free band

2.4 GHz 802.11, Lucent WaveLAN 100 m - 25 km 2 - 11 Mbps

2.45 GHz Bluetooth about 10 m 1 Mbps

4 - 6 GHz commercial (telecomm.) 40 - 80 km 100 Mbps

Infrared short distance line of sight 5 - 100 m 1 Mbps

Freq. Band Use Range Data Rate

824 - 894 MHz Analog cell phones (AMPS) 20 km per cell 13 kbps/channel

902-928 MHz License free in North America

1.7 - 2.3 GHz PCS digital cell phones < 1 km per cell

1.8 GHz GSM digital cell phones 16 kbps/channel

2.400-2.484 GHz global license free band

2.4 GHz 802.11, Lucent WaveLAN 100 m - 25 km 2 - 11 Mbps

2.45 GHz Bluetooth about 10 m 1 Mbps

4 - 6 GHz commercial (telecomm.) 40 - 80 km 100 Mbps

Infrared short distance line of sight 5 - 100 m 1 Mbps