7.multiplexing upload

Agenda
Topics to be Discussed
1. Bit Rate and Baud Rate
2. Parallel and Serial Transmission
3. Multiplexing

Bit Rate vs. Baud Rate
Bit Rate and Baud Rate
•Bit rate is the number of bits transmitted across a
channel per second.
•Baud rate is the number of signal elements
transmitted across a channel per second.
•In the analog transmission of digital data, the baud
rate is less than or equal to the bit rate.

Bit Rate vs. Baud Rate

Problem

Serial and Parallel Transmission

Serial Transmission
• In Serial Transmission, the bits of a byte are serially
transmitted one after other.
• As an advantage only one wire is used in serial
transmission between the transmitter and the receiver.

Advantages and Disadvantages
Advantages Disadvantages
• Only one wire is required.
• Reduction in cost due to
less number of conductor
wires
• It is the most used method
for long distance data
transfers.
• Since there is only one
line of transmission
therefore the speed of
transmission is quite slow.
• If we have to increase the
speed of data transfer then
it is necessary to increase
the clock frequency. But
there is a limit of clock
frequency.

Applications
• Morse code telegraphy
• RS-232 (low-speed, implemented by serial ports)
• RS-422
• RS-423
• RS-485
• Ethernet
• T-1, E-1 Lines

Types of Serial Transmission
Serial Transmission
Asynchronous Synchronous

Asynchronous Serial Transmission
• It is called asynchronous because timing of the signal is not an
issue.
•The information can be sent & received as per mutual
agreement of the sender & receiver.
•In asynchronous transmission two extra bits are used. i.e. 0 is
used as start bit and 1 is used as stop bit.
•There is a time delay between communication of two bytes.
•The transmitter and receiver may function at different clock
frequencies.
• Asynchronous transmission is mostly used by asynchronous
modems.

Asynchronous Transmission

• Synchronization between the
transmitter and receiver is not
necessary.
• It is possible to transmit
signals from the sources having
different bit rates.
• The transmission can
commence as soon as the data
byte to be transmitted becomes
available.
• This mode of transmission is
easy to implement.
• It is an cost effective scheme.
•Additional bits called start
and stop bits are required to
be used.
• The timing error may take
place because it is difficult to
determine synchronicity.
• It has slower transmission
rate.

Synchronous Serial Transmission
• Synchronous transmission is carried out under the control of a
common master clock.
•The receivers operates at the same clock frequency as that of
transmitter.
• Here the bits which are being transmitted as synchronized to the
same reference clock.
• The stream of bits is combined into bigger frames which may
comprise more than one byte.
• Each byte is transmitted without gap between the next byte.
• No start and stop bits are used instead the bytes are
transmitted as a block in a continuous stream of bits.
• It is the duty of the receiver to separate the bits sent in group.

•The main advantage is
speed. The speed of
transmission is much higher
than that asynchronous
transmission.
• This is due to the absence
of gaps between the data
units and absence of start
stop bits.
• Timing errors are reduced
due to synchronization.
•The timing is very important.
The accuracy of the received
data is dependent entirely on
the ability of the receiver to
count the received bits
accurately.
• The transmitter and receiver
have to operate at the same
clock frequency. This
requires proper
synchronization which makes
the system complicated.

Problem
A channel is transmitting at an speed of 1m bits
per second in a serial synchronous mode.
Calculate how many extra bits will be receive if a
clock has become faster by .001%.

Parallel Transmission
• A group of bits is transmitted simultaneously on separate wires.
• Multiple circuits for connection.
• Devices close to each other.
E.g. Data transmission between computer and printer.

• Time required is only one
clock cycle.
• Clock frequency can be
kept low.
• Number of wires.
• Too many wires.

Multiplexing
Multiplexing
• Whenever the bandwidth of a medium linking two devices is
greater than the bandwidth needs of the devices, the link can
be shared.
• Multiplexing is the set of techniques that allows the
simultaneous transmission of multiple signals across a single
data link.

Types of Multiplexing
Multiplexing

FDM
Multiplexing
 Bandwidth of a channel is divided into smaller independent frequency
channels.
 Using modulation independent message signals are translated into
different frequency bands.
The carriers used to modulate the individual signals are called sub-
carriers.
 All the modulated signals are combined into a linear summing circuit to
form a composite signal for transmission.
 FDM is an analog multiplexing technique that combines analog signals.

De-multiplexing Process
Multiplexing

Problem
Multiplexing
Q. 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 × 100 + 4 × 10 = 540 kHz.

Problem
Multiplexing
Q. 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. Assume
there are no guard bands.

Analog Hierarchy of FDM
Multiplexing

Applications
Multiplexing
 FM radio broadcasting/AM radio
 TV broadcasting
 Cable TV
A Co-axial cable with 600mhz bandwidth can
accommodate 100 channels each with 6mhz bandwidth
requirement.
Now, all channels can be separated at receiver by the
tuner of the receiver.

WDM
Multiplexing
 It is similar to FDM, only the medium is optical fiber.
 Large number of light signals are multiplexed to overcome Opto-
electronic bandwidth mismatch (this is the case, where the bandwidth
requirement of each individual signal is much lesser than the available
bandwidth of the channel)
WDM optical fiber network comprises of optical wavelength
switches/routers inter connected by point to point fiber links.

WDM Multiplexing and De-multiplexing
with Prism
Multiplexing
 Filtering is done in the optical domain by the use of prisms.
 Here, the light coming out other side of the prism depends upon angle of
incidence and wavelength.
Therefore, light beams are incident to one side with different angles, so
that they come out at other side with same angle, which can be sent out
through optical fiber cable and at the receiver end, the signal then separate
out by the use of another prism.

TDM
Multiplexing
 TDM is a digital multiplexing technique for combining several low-
rate channels into one high-rate one.
 Here, a composite signal is formed, which is known as frame.
 In the frame, a signal element from each source is placed and
assigned a time slot.
 Here, the link bandwidth is utilized by each transmitted source by
interleaving their bits in the frame.

Types of TDM
Multiplexing
TDM
Synchronous Asynchronous

Synchronous TDM
Multiplexing
 Here, the frame/composite signal that is formed has as many number of
slots as the number of sources connected to the link.
 It means there is a time slot for each input source even though it is
transmitted or not.
 In the frame, a signal element from each source is placed and assigned a
time slot.
 Here, the link bandwidth is utilized by each transmitted source by
interleaving their bits in the frame.
“Syn” characters are added to each frame. These are required to identify
the starting of a frame.

Multiplexing
• Fixed time slot is given to
the data of each source,
which helps in ease of
separation of data at the
receiving end.
• Ineffective bandwidth
utilization as a time slot is
fixed for each source, so
when a source is not
transmitting, still its time slot
is reserved due to its
connectivity to the network,
which results in ineffective
bandwidth utilization.

Asynchronous/Statistical TDM
Multiplexing
 Here, time slots are allocated to the connecting sources on demand.
 There is no fixed number of slots in each frame.
 The number of slots in a frame is decided by the number of sources
interested in transmitting the data at that particular point of time.

Data Rate Management
Multiplexing
 In most cases, the data rates of input line connected to a
channel are same, if data rate of some of the inputs are not
same, then the following techniques are used.
1. Multi-level Multiplexing
2. Multiple Slot Allocation
3. Pulse Stuffing

Multi-level Multiplexing
Multiplexing
 It is a technique used when the data rate of an input
line is a multiple of others.
In the Example below, the first two input lines can be
multiplexed together to provide a data rate equal to the
last three.

Multiple Slot Allocation
Multiplexing
 Allocation of more than one slot in a frame for a single input line.
In the Example below, the input line with 50kbps data rate can be
given two slots in the output frame.
We insert a serial to parallel converter in the line to make two
inputs out of one.

Pulse Stuffing
Multiplexing
 Sometimes, bit rates of sources are not multiple integers of each
other.
So, in this case the highest input data rate is the considered as the
dominant data rate and then dummy bits are added to the input lines
with lower rates, this will increase their data rates, this technique is
called pulse stuffing.

Inverse Multiplexing
Multiplexing
 When the available bandwidth of a channel is quiet lesser than the
required bandwidth of a signal, then the signal is first de-multiplexed
into several similar type of signal passing through the available
channels.
 At the receiver end it will be multiplexed again to get the original
signal.

7.multiplexing upload

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