1 Kyung Hee University Prof. Choong Seon HONG Multiplexing

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Kyung Hee University

Prof. Choong Seon HONG

MultiplexingMultiplexing

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8 8 장 다중화장 다중화 (Multiplexing)(Multiplexing)

8.1 Many to One/One to Many

8.2 Type of Multiplexing

8.3 Multiplexing Application : Telephone system

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다중화다중화 (Multiplexing)(Multiplexing)

다중화 (Multiplexing)

is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link.

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다중화다중화 (Multiplexing)(Multiplexing)

Multiplexing vs. No Multiplexing

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8.1 Many to One/One to Many8.1 Many to One/One to Many

다중화기 (Multiplexer)

transmission streams combine into a single stream(many to one)

역다중화기 (Demultiplexer)

stream separates into its component transmission(one to many) and directs them to their intended receiving devices

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8.2 8.2 Many to One/One to ManyMany to One/One to Many

Categories of Multiplexing

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FDMFDM

FDM(Frequency-Division Multiplexing)

is an analog technique that can be applied when the bandwidth of a link is greater than the combined bandwidths of the signals to be transmitted

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FDM (cont’d)FDM (cont’d)

FDM process

each telephone generates a signal of a similar frequency range

these signals are modulated onto different carrier frequencies(f1, f2, f3)

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FDM (cont’d)FDM (cont’d)

FDM multiplexing process, time-domain

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FDM(cont’d)FDM(cont’d)

FDM multiplexing process, frequency-domain

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Demultiplexing

separates the individual signals from their carries and passes them to the waiting receivers.

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FDM demultiplexing process, time-domain

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FDM demultiplexing, frequency-domain

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Example : Cable Television

coaxial cable has a bandwidth of approximately 500Mhz

individual television channel require about 6Mhz of bandwidth for transmission

can carry 83 channels theoretically

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8.3 Wave Division Multiplexing (WDM)8.3 Wave Division Multiplexing (WDM)

WDM is conceptually same as FDM

except that the multiplexing and demultiplexing involve light signals transmitted through fiber-optic channels

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WDM (cont’d)WDM (cont’d)

Combining and splitting of light sources are easily han

dled by a prism

Prism bends a beam of light based on the angle of incidence and the frequency.

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TDM(cont’d)TDM(cont’d)

TDM(Time-Division Multiplexing)

is a digital process that can be applied when the data rate capacity of the transmission medium is greater than the data rate required by the sending and receiving device

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TDM

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TDM can be implemented in two ways

Synchronous TDM

Asynchronous TDM

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Synchronous TDM

the multiplexer allocates exactly the same time slot to each device at all times, whether or not a device has anything to transmit.

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Frame

Time slots are grouped into frames

A frame consists of one complete cycle of time slots, including one or more slots dedicated to each sending device, plus framing bits.

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Synchronous TDM

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TDM(cont’d)TDM(cont’d)Interleaving

synchronous TDM can be compared to a very fast rotating switch

switch moves from device to device at a constant rate and in a fixed order

6 empty slots out of 24 are being wasted

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Demultiplexer decomposes each frame by discarding th

e framing bits and extracting each character in turn

Synchronous TDM, demultiplexing process

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Framing bits

~ allows the demultiplexer to synchronize with the incoming stream so that it can separate the time slots accurately

(ex: 01010101 ….)

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Synchronous TDM Example4 characters + 1 framing bit

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Asynchronous TDM : statistical time-division multiplexing

Synchronous or Asynchronous : Not flexible or Flexible

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Examples of asynchronous TDM frames

a. Case 1: Only three lines sending data

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b. Case 2: Only four lines sending data

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c. Case 3: All five lines sending data

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Inverse Multiplexing

takes the data stream from one high-speed line and breaks it into portion that can be sent across several lower speed lines simultaneously, with no loss in the collective data rate

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Multiplexing and inverse multiplexing

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Why do we need inverse multiplexing ?

wants to send data, voice, and video each of which requires a different data rate.

[example]

voice - 64 Kbps link

data - 128 Kbps link

video - 1,544 Mbps link

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8.5 Multiplexing application : Telephone system8.5 Multiplexing application : Telephone system

Telephone Network

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Multiplexing application(cont’d)Multiplexing application(cont’d)

Common Carrier Services

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Analog Service

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Analog Switched Service

~ is the familiar dial-up service most often encountered when using a home telephone

(PSTN : Public Switched Telephone Network)

local loop : connection from the subscriber’s handset

to the network

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Analog Leased Service : dedicated line

~ offers customers the opportunity to lease line(dedicated line), that is permanently connected to another customer.

No dialing is needed

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Analog Hierarchy

To maximize the efficiency of their infrastructure, telephone companies have traditionally multiplexed signals from lower bandwidth lines onto higher bandwidth lines.

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Multiplexing application(cont’d)Multiplexing application(cont’d)Analog hierarchy

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Digital Services

advantage

- less sensitive than analog service to noise

- lower cost

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Categories of digital service

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Switched/56 service

~ is the digital version of an analog switched line

~ allows data rates of up to 56Kbps

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DDS(Digital Data Service)

~ is the digital version of an analog leased line (maximum speed : 56Kbps)

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DS(Digital Signal) Service

~ is a hierarchy of digital signal

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DS Service

DS-0 : single digital channel of 64Kbps

DS-1 : 1,544Mbps, 24 개의 64Kbps + 8Kbps 의 overhead

DS-2 : 6,312Mbps, 96 개의 64Kbps+168Kbps 의 overhead

DS-3 : 44,376Mbps, 672 개의 64Kbps+1.368Mbps 의

overhead

DS-4 : 274,176Mbps,4032 개의 64Kbps+16.128Mbps 의

overhead

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T Lines

Service Line Rate(Mbps) Voice Channels

DS-1

DS-2

DS-3

DS-4

T-1

T-2

T-3

T-4

1,544

6,312

44,736

274,176

24

96

672

4032

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T lines for Analog Transmission

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T-1 frame structure

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Fractional T Lines

DSU/CSU (Data Service Unit / Channel Service Unit)

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E Lines

Europeans use a version of T lines called E lines

Service Rate(Mbps) Voice Channels

E-1

E-2

E-3

E-4

2,048

8,448

34,368

139,264

30

120

480

1920

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Other Multiplexing Service

ISDN(Integrated Services Digital Network)

SONET(Synchronous Optical Network)

ATM(Asynchronous Transfer Mode)

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8.6 Digital Subscriber Line (DSL)8.6 Digital Subscriber Line (DSL) uses a newer technology that used the existing teleco

mmunications networks such as the local loop telephon

e line

Asymmetric Digital Subscriber Line (ADSL)

provides higher bit rates in the downstream direction (from the telephone central office to the subscriber’s site) than the upstream direction

divides the bandwidth of a twisted-pair cable (one megahertz) into three bands

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DSL (cont’d)DSL (cont’d)

Modulation Techniques

CAP (carrierless amplitude/phase)

similar to QAM carrier signal is eliminated

DMT (discrete multitone technique)

combines QAM and FDM the available bandwidth for each direction is divided into 4

Khz channels, each having its own carrier frequency

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The concept of DMT with N channels

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ANSI standard defines a rate of 60 Kbps for each 4-Khz channel, which means a QAM modulation with 15 bits per baud

The upstream channel usually occupies 25 channels (60kbps x 20 = 1.5 Mbps)

The downstream channel usually occupies 200 channels (200 x 60Kbps = 12 Mbps)

– But, the bit rate in this direction ranges from 500 Kbps to 8 Mbps due to noise

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DSL (cont’d)DSL (cont’d) ADSL and the bit rates in each direction

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RADSL (Rate Adaptive Digital Subscriber Line)

allows different data rates depending on the type of communication : voice, data, multimedia, and so on.

Differing rates may also be assigned to subscribers based on their demand of the bandwidth.

HDSL (High bit rate digital subscriber line)

was designed by Bellcore (now Telcordia) as an alternative to the T-1 (1.544 Mbps)

T1 line uses AMI encoding, but HDSL uses 2B1Q encoding, which is less susceptible to attenuation

A data rate of almost 2 Mbps can be achieved without repeaters up to a distance of 3.6 km

uses two twisted-pair wires to achieve full-duplex transmission

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SDSL (symmetric digital subscriber line)

is same as HDSL but uses one single twisted-pair cable

achieves the same data rate as HDSL

echo cancellation technique is employed to create a full-duplex transmission

VDSL (very high bit rate digital subscriber line)

an alternative approach that is similar to ADSL

uses coaxial, fiber-optic, or twisted-pair cable for short distances (300 to 1800 meters)

modulation technique is DMT with a bit rate of 50 to 55 Mbps downstream and 1.5 to 2.5 Mbps upstream

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8.7 FTTC8.7 FTTC

Optical fiber has noise resistance and high bandwidth

capacity, but every expensive

Fiber to the curb (FTTC)

Optical fiber is the medium from the central office of the telephone office or from the head office of a cable company

The medium from the curb to the subscriber premise is the less expensive twisted-pair or coaxial cable

Optical signals at the switching station are multiplexed, using WDM

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FTTC (cont’d)FTTC (cont’d)

FTTC in the telephone network

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FTTC (cont’d)FTTC (cont’d)

FTTC in the cable TV network

Documents

1 Kyung Hee University Prof. Choong Seon HONG Multiplexing