2 6 (Multiplexing) Dividing a link into channels Word link
refers to the physical path Channel refers to the portion of a link
that carries a transmission between a given pair of lines.
Slide 3
3 Kyung Hee University (Multiplexing) (Multiplexing) is the set
of techniques that allows the simultaneous transmission of multiple
signals across a single data link.
Slide 4
4 Kyung Hee University 6.1 FDM (Multiplexer) transmission
streams combine into a single stream(many to one) (Demultiplexer)
stream separates into its component transmission(one to many) and
directs them to their intended receiving devices
Slide 5
5 Kyung Hee University 8.2 Many to One/One to Many Categories
of Multiplexing
Slide 6
6 Kyung Hee University 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
Slide 7
7 Kyung Hee University FDM (contd) FDM process each telephone
generates a signal of a similar frequency range these signals are
modulated onto different carrier frequencies(f1, f2, f3)
Slide 8
8 Kyung Hee University FDM (contd) FDM multiplexing process,
time-domain
Slide 9
9 Kyung Hee University FDM(contd) FDM multiplexing process,
frequency-domain
Slide 10
10 Kyung Hee University FDM(contd) Demultiplexing separates the
individual signals from their carries and passes them to the
waiting receivers.
Slide 11
11 Kyung Hee University FDM(contd) FDM demultiplexing process,
time-domain
Slide 12
12 Kyung Hee University FDM(contd) FDM demultiplexing,
frequency-domain
Slide 13
13 Kyung Hee University Example 1 Assume that a voice channel
occupies a bandwidth of 4 KHz. We need to combine three voice
channels into a link with a bandwidth of 12 KHz, from 20 to 32 KHz.
Show the configuration using the frequency domain without the use
of guard bands. Solution Shift (modulate) each of the three voice
channels to a different bandwidth, as shown in Figure 6.6.
Slide 14
14 Kyung Hee University Example 1 (contd)
Slide 15
15 Kyung Hee University Example 2 Five channels, each with a
100-KHz bandwidth, are to be multiplexed together. What is the
minimum bandwidth of the link if there is a need for a guard band
of 10 KHz between the channels to prevent interference? Solution
For five channels, we need at least four guard bands. This means
that the required bandwidth is at least 5 x 100 + 4 x 10 = 540 KHz,
as shown in Figure 6.7.
Slide 16
16 Kyung Hee University Example 2 (contd)
Slide 17
17 Kyung Hee University Example 3 Four data channels (digital),
each transmitting at 1 Mbps, use a satellite channel of 1 MHz.
Design an appropriate configuration using FDM Solution The
satellite channel is analog. We divide it into four channels, each
channel having a 250-KHz bandwidth. Each digital channel of 1 Mbps
is modulated such that each 4 bits are modulated to 1 Hz. One
solution is 16- QAM modulation. Figure 6.8 shows one possible
configuration.
Slide 18
18 Kyung Hee University Example 3 (contd)
Slide 19
19 Kyung Hee University FDM(contd) 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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20 Kyung Hee University 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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21 Kyung Hee University Applications of FDM Example 4 The
Advanced Mobile Phone System (AMPS) uses two bands. The first band,
824 to 849 MHz, is used for sending; and 869 to 894 MHz is used for
receiving. Each user has a bandwidth of 30 KHz in each direction.
The 3- KHz voice is modulated using FM, creating 30 KHz of
modulated signal. How many people can use their cellular phones
simultaneously? Solution Each band is 25 MHz. If we divide 25 MHz
into 30 KHz, we get 833.33. In reality, the band is divided into
832 channels.
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22 Kyung Hee University 6.2 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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23 Kyung Hee University WDM (contd) WDM is an analog
multiplexing technique to combine optical signals. Very narrow
bands of light from different sources are combined to make a wider
band of light
Slide 24
24 Kyung Hee University WDM (contd) 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. One
application is the SONET.
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25 Kyung Hee University 6.3 TDM 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 TDM is a digital
multiplexing technique to combine data.
Slide 26
26 Kyung Hee University TDM(contd)
Slide 27
27 TDM (contd) In a TDM, the data rate of the link is n times
faster, and the unit duration is n times shorter.
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28 Kyung Hee University TDM (contd) Example 5 Four 1-Kbps
connections are multiplexed together. A unit is 1 bit. Find (1) the
duration of 1 bit before multiplexing, (2) the transmission rate of
the link, (3) the duration of a time slot, and (4) the duration of
a frame? Solution We can answer the questions as follows: 1. The
duration of 1 bit is 1/1 Kbps, or 0.001 s (1 ms). 2. The rate of
the link is 4 Kbps. 3. The duration of each time slot 1/4 ms or 250
s. 4. The duration of a frame 1 ms.
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29 Kyung Hee University TDM(contd) TDM can be implemented in
two ways Synchronous TDM Asynchronous TDM
Slide 30
30 Kyung Hee University TDM(contd) 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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31 Kyung Hee University TDM(contd) 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.
Slide 32
32 Kyung Hee University TDM(contd) Synchronous TDM
Slide 33
33 Kyung Hee University TDM(contd) 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
Slide 34
34 Kyung Hee University TDM(contd) Demultiplexer decomposes
each frame by discarding the framing bits and extracting each
character in turn Synchronous TDM, demultiplexing process
Slide 35
35 Kyung Hee University TDM(contd)
Slide 36
36 TDM(contd) Example 6 Four channels are multiplexed using
TDM. If each channel sends 100 bytes/s and we multiplex 1 byte per
channel, show the frame traveling on the link, the size of the
frame, the duration of a frame, the frame rate, and the bit rate
for the link. Solution
Slide 37
37 Kyung Hee University TDM(contd) Example 7 A multiplexer
combines four 100-Kbps channels using a time slot of 2 bits. Show
the output with four arbitrary inputs. What is the frame rate? What
is the frame duration? What is the bit rate? What is the bit
duration? Solution Figure 6.16 shows the output for four arbitrary
inputs.
Slide 38
38 Kyung Hee University TDM(contd)
Slide 39
39 TDM(contd) Framing bits ~ allows the demultiplexer to
synchronize with the incoming stream so that it can separate the
time slots accurately (ex: 01010101 .)
Slide 40
40 Kyung Hee University TDM(contd) Synchronous TDM Example 4
characters + 1 framing bit
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41 Kyung Hee University TDM(contd) Asynchronous TDM :
statistical time-division multiplexing Synchronous or Asynchronous
: Not flexible or Flexible
Slide 42
42 Kyung Hee University TDM(contd) Examples of asynchronous TDM
frames a. Case 1: Only three lines sending data
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43 Kyung Hee University TDM(contd) b. Case 2: Only four lines
sending data
Slide 44
44 Kyung Hee University TDM(contd) c. Case 3: All five lines
sending data
Slide 45
45 Kyung Hee University Multiplexing application(contd) Analog
Hierarchy To maximize the efficiency of their infrastructure,
telephone companies have traditionally multiplexed signals from
lower bandwidth lines onto higher bandwidth lines.
Slide 46
46 Kyung Hee University Multiplexing application(contd) Digital
Services advantage - less sensitive than analog service to noise -
lower cost
Slide 47
47 Kyung Hee University Multiplexing application(contd)
DS(Digital Signal) Service ~ is a hierarchy of digital signal
Slide 48
48 Kyung Hee University Multiplexing application(contd) DS
Service DS-0 : single digital channel of 64Kbps DS-1 : 1,544Mbps,
24 64Kbps + 8Kbps overhead DS-2 : 6,312Mbps, 96 64Kbps+168Kbps
overhead DS-3 : 44,376Mbps, 672 64Kbps+1.368Mbps overhead DS-4 :
274,176Mbps,4032 64Kbps+16.128Mbps overhead
50 Kyung Hee University T Lines for Analog Transmission T-1
line for multiplexing telephone lines
Slide 51
51 Kyung Hee University T-1 Frame 193 = 24 x 8 + 1(1 bit for
synchronization)
Slide 52
52 Kyung Hee University E Lines E line rates E Line Rate (Mbps)
Voice Channels E-1 2.048 2.048 30 30 E-2 8.448 8.448 120 120 E-3
34.368 34.368 480 480 E-4139.2641920
Slide 53
53 Kyung Hee University TDM(contd) 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
Slide 54
54 Kyung Hee University TDM(contd) Multiplexing and inverse
multiplexing
Slide 55
55 Kyung Hee University TDM(contd) 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