Transcript Multiplexing(DSL, FTTC

Multiplexing
Prof. Choong Seon HONG
Kyung Hee
University
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8 장 다중화(Multiplexing)
8.1 Many to One/One to Many
8.2 Type of Multiplexing
8.3 Multiplexing Application : Telephone system
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다중화(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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다중화(Multiplexing)
Multiplexing vs. No Multiplexing
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8.1 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 Many to One/One to Many
Categories of Multiplexing
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FDM
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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University
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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 multiplexing process, time-domain
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FDM(cont’d)
FDM multiplexing process, frequency-domain
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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 demultiplexing process, time-domain
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FDM(cont’d)
FDM demultiplexing, frequency-domain
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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)
 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)
 Combining and splitting of light sources are easily
handled 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(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
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TDM(cont’d)
TDM can be implemented in two ways
Synchronous TDM
Asynchronous TDM
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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)
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)
Synchronous TDM
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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)
Demultiplexer decomposes each frame by discarding
the framing bits and extracting each character in turn
Synchronous TDM, demultiplexing process
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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)
Synchronous TDM Example
4 characters + 1 framing bit
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TDM(cont’d)
Asynchronous TDM : statistical time-division multiplexing
Synchronous or Asynchronous : Not flexible or Flexible
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TDM(cont’d)
Examples of asynchronous TDM frames
a. Case 1: Only three lines sending data
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TDM(cont’d)
b. Case 2: Only four lines sending data
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TDM(cont’d)
c. Case 3: All five lines sending data
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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)
Multiplexing and inverse multiplexing
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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 system
Telephone Network
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Multiplexing application(cont’d)
Common Carrier Services
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Multiplexing application(cont’d)
Analog Service
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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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University
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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)
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)
Analog hierarchy
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Multiplexing application(cont’d)
Digital Services
advantage
- less sensitive than analog service to noise
- lower cost
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Multiplexing application(cont’d)
Categories of digital service
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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)
DDS(Digital Data Service)
~ is the digital version of an analog leased line (maximum
speed : 56Kbps)
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Multiplexing application(cont’d)
DS(Digital Signal) Service
~ is a hierarchy of digital signal
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Multiplexing application(cont’d)
DS Service
DS-0 : single digital channel of 64Kbps
DS-1 : 1,544Mbps, 24개의 64Kbps + 8Kbps의 overhead
DS-2 : 6,312Mbps, 96개의 64Kbps+168Kbps의 overhead
DS-3 : 44,376Mbps, 672개의 64Kbps+1.368Mbps의
overhead
DS-4 : 274,176Mbps,4032개의 64Kbps+16.128Mbps의
overhead
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University
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Multiplexing application(cont’d)
T Lines
Service
Line
DS-1
T-1
1,544
24
DS-2
T-2
6,312
96
DS-3
T-3
44,736
672
DS-4
T-4
274,176
4032
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University
Rate(Mbps)
Voice Channels
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Multiplexing application(cont’d)
T lines for Analog Transmission
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Multiplexing application(cont’d)
T-1 frame structure
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Multiplexing application(cont’d)
Fractional T Lines
DSU/CSU (Data Service Unit / Channel Service Unit)
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University
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Multiplexing application(cont’d)
E Lines
Europeans use a version of T lines called E lines
Service
Rate(Mbps)
Voice Channels
E-1
2,048
30
E-2
8,448
120
E-3
34,368
480
E-4
139,264
1920
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University
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Multiplexing application(cont’d)
Other Multiplexing Service
ISDN(Integrated Services Digital Network)
SONET(Synchronous Optical Network)
ATM(Asynchronous Transfer Mode)
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University
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8.6 Digital Subscriber Line (DSL)
 uses a newer technology that used the existing
telecommunications networks such as the local loop
telephone 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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University
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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
4Khz channels, each having its own carrier frequency
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DSL (cont’d)
 The concept of DMT with N channels
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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)
–
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But, the bit rate in this direction ranges from 500 Kbps to 8
Mbps due to noise
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DSL (cont’d)
 ADSL and the bit rates in each direction
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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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University
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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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University
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8.7 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 in the telephone network
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FTTC (cont’d)
 FTTC in the cable TV network
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