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Kyung Hee University
Prof. Choong Seon HONG
MultiplexingMultiplexing
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Kyung Hee University
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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FDM(cont’d)FDM(cont’d)
Demultiplexing
separates the individual signals from their carries and passes them to the waiting receivers.
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FDM(cont’d)FDM(cont’d)
FDM demultiplexing process, time-domain
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FDM(cont’d)FDM(cont’d)
FDM demultiplexing, frequency-domain
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FDM(cont’d)FDM(cont’d)
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(cont’d)TDM(cont’d)
TDM
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TDM(cont’d)TDM(cont’d)
TDM can be implemented in two ways
Synchronous TDM
Asynchronous TDM
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TDM(cont’d)TDM(cont’d)
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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TDM(cont’d)TDM(cont’d)
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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TDM(cont’d)TDM(cont’d)
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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TDM(cont’d)TDM(cont’d)
Demultiplexer decomposes each frame by discarding th
e framing bits and extracting each character in turn
Synchronous TDM, demultiplexing process
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TDM(cont’d)TDM(cont’d)
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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TDM(cont’d)TDM(cont’d)
Synchronous TDM Example4 characters + 1 framing bit
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TDM(cont’d)TDM(cont’d)
Asynchronous TDM : statistical time-division multiplexing
Synchronous or Asynchronous : Not flexible or Flexible
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TDM(cont’d)TDM(cont’d)
Examples of asynchronous TDM frames
a. Case 1: Only three lines sending data
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TDM(cont’d)TDM(cont’d)
b. Case 2: Only four lines sending data
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TDM(cont’d)TDM(cont’d)
c. Case 3: All five lines sending data
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TDM(cont’d)TDM(cont’d)
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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TDM(cont’d)TDM(cont’d)
Multiplexing and inverse multiplexing
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TDM(cont’d)TDM(cont’d)
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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Multiplexing application(cont’d)Multiplexing application(cont’d)
Analog Service
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Multiplexing application(cont’d)Multiplexing application(cont’d)
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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Multiplexing application(cont’d)Multiplexing application(cont’d)
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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Multiplexing application(cont’d)Multiplexing application(cont’d)
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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Multiplexing application(cont’d)Multiplexing application(cont’d)
Digital Services
advantage
- less sensitive than analog service to noise
- lower cost
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Multiplexing application(cont’d)Multiplexing application(cont’d)
Categories of digital service
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Multiplexing application(cont’d)Multiplexing application(cont’d)
Switched/56 service
~ is the digital version of an analog switched line
~ allows data rates of up to 56Kbps
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Multiplexing application(cont’d)Multiplexing application(cont’d)
DDS(Digital Data Service)
~ is the digital version of an analog leased line (maximum speed : 56Kbps)
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Multiplexing application(cont’d)Multiplexing application(cont’d)
DS(Digital Signal) Service
~ is a hierarchy of digital signal
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Multiplexing application(cont’d)Multiplexing application(cont’d)
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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Multiplexing application(cont’d)Multiplexing application(cont’d)
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
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Multiplexing application(cont’d)Multiplexing application(cont’d)
T lines for Analog Transmission
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Multiplexing application(cont’d)Multiplexing application(cont’d)
T-1 frame structure
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Multiplexing application(cont’d)Multiplexing application(cont’d)
Fractional T Lines
DSU/CSU (Data Service Unit / Channel Service Unit)
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Multiplexing application(cont’d)Multiplexing application(cont’d)
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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Multiplexing application(cont’d)Multiplexing application(cont’d)
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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DSL (cont’d)DSL (cont’d)
The concept of DMT with N channels
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DSL (cont’d)DSL (cont’d)
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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DSL (cont’d)DSL (cont’d)
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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DSL (cont’d)DSL (cont’d)
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