Multiplexing
#1

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Multiplexing
• Enable two or more transmission sources to share a common circuit
• Most common forms – FDM and TDM
• FDM – associated with analog signal, simultaneous transmission
• TDM – associated with digital signal (could also be analog, but single frequency) with time slices
Frequency Division Multiplexing
• FDM
• Each signal is modulated to a different carrier frequency
• Carrier frequencies separated so signals do not overlap (guard bands)
• e.g. broadcast radio
• Channel allocated even if no data
• Broadband
Frequency Division Multiplexing Diagram
• Wavelength Division Multiplexing
• Multiple beams of light at different frequency
• Carried by optical fiber
• A form of FDM
• Each color of light (wavelength) carries separate data channel
• 1997 Bell Labs
— 100 beams
— Each at 10 Gbps
— Giving 1 terabit per second (Tbps)
• Commercial systems of 160 channels of 10 Gbps now available
• Lab systems (Alcatel) 256 channels at 39.8 Gbps each
— 10.1 Tbps
— Over 100km
WDM Operation
• Same general architecture as other FDM
• Number of sources generating laser beams at different frequencies
• Multiplexer consolidates sources for transmission over single fiber
• Optical amplifiers amplify all wavelengths
— Typically tens of km apart
• Demux separates channels at the destination
• Was 200MHz per channel
• Now 50GHz
• Synchronous Time Division Multiplexing
Multiple digital signals interleaved in time
• May interleave bits, so not necessarily synchronous transmission
• Time slots pre-assigned to sources and fixed
• Time slots allocated even if no data
• Time slots do not have to be evenly distributed amongst sources
• Baseband
Time Division Multiplexing
• TDM Link Control
• No headers and trailers
• Data page link control protocols not needed
• Flow control
— Data rate of multiplexed line is fixed
— If one channel receiver can not receive data, the others must carry on
— The corresponding source must be quenched
— This leaves empty slots
• Error control
— Errors are detected and handled by individual channel systems
Optical TDM
• In early days of Fiber Optics, every telco had its own proprietary optical TDM
• After break up of AT&T, phone companies had to connect to multiple long distance carriers, all with different optical TDMs
• This created the need for standardized optical TDM – SONET – synchronized optical network
Design Goals of SONET
• Enable different carriers to interoperate – resulted in need of common signaling standard with respect to wavelength, timing, framing structure, etc.
• Needed to unify US, European, and Japanese signalling systems
• Had to provide a way to multiplex multiple digital signals
• Provide support for operations, administration, and maintenance
SONET/SDH
• Synchronous Optical Network (ANSI standard - USA)
• Synchronous Digital Hierarchy (ITU-T standard - Europe)
• Compatible
• Both are fiber optic standards for high speed data transmission
• Signal Hierarchy
— Synchronous Transport Signal level 1 (STS-1) or Optical Carrier level 1 (OC-1)
— 51.84Mbps
— ITU-T lowest rate is 155.52Mbps (STM-1)
Statistical TDM
• In Synchronous TDM many slots are wasted
• Statistical TDM allocates time slots dynamically based on demand
• Multiplexer scans input lines and collects data until frame full
• Statistical TDM Frame Formats
Performance
• Output data rate less than aggregate input rates
• May cause problems during peak periods
— Buffer inputs
— Keep buffer size to minimum to reduce delay
— Cable Modem Outline
• Two channels from cable TV provider dedicated to data transfer
— One in each direction
• Each channel shared by number of subscribers
— Scheme needed to allocate capacity
— Statistical TDM
Asymmetrical Digital Subscriber Line ADSL
• Link between subscriber and network
— Local loop
• Uses currently installed twisted pair cable
— Can carry broader spectrum
— 1 MHz or more
— ADSL Design
• Asymmetric
— Greater capacity downstream than upstream
• Frequency division multiplexing
— Lowest 25kHz for voice
• Plain old telephone service (POTS)
— Use echo cancellation or FDM to give two bands
— Use FDM within bands
• Range 5.5km
• Required Reading
• Stallings chapter 8
• Web sites on
— ADSL
— SONET
Chapter 8 Review Questions
• Explain the basics of multiplexing.Why is multiplexing so cost effective?
• How is interference avoided by using FDM?
• Explain how TDM works. Why is statistical time division multiplexing more efficient than TDM
• Compare and contrast TDM, STDM, and FDM
• (note: for purpose of this class, STDM = statistical, not synchronous)
What is SONET?
• Compare and contrast cable modems and DSL
• Define upstream and downstream with respect to subscriber lines? What is the greatest advantage of ADSL?
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#2
PRESENTED BY:
Mohatsim Billah
Moshsaka Akhter

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What is a multiplexer ?
A multiplexer(data selector) or mux is a digital logic circuit that selects one of several analog or digital input signals and forwards the selected input into a single line. A multiplexer of 2n inputs has n select lines, which are used to select which input line to send to the output.
Criterion based on input output
Digital Multiplexers are constructed from individual analogue switches. Generally, multiplexers have an even number of data inputs. Based this property different types of multiplexer has being constructed.
A two input line multiplexer.
A 4 to 1 input line multiplexer.
A 4 to 2 input line multiplexer.
A 8 to 1 input line multiplexer.
A quad two input line multiplexer.
Functional diagram of MUX
Logical Diagram of a 2-to-1 input multiplexer
The Four-Input Multiplexer
The same basic idea of 2 input mux can be used to form 4-INPUT multiplexer. A circuit diagram for a possible 4-LINE to 1-LINE data selector/multiplexer is shown in the figure. Here, the output y is equal to the input i0 , i1 , i2 , i 3 depending on whether the select lines s1 and s0 have values 00, 01, 10, 11 for s1 and s0 respectively. That is, the output y is selected to be equal to the input of the line given by the binary value of the select lines s1 s0
Example of a 4 line to 1 line MUX implementation according to the following the truth table (Y=A’*B’+A*B) & showing block diagram .
Eight-Input Multiplexer
74ALS151 eight input multiplexer is shown in figure 3.0 proximate
slide. This multiplexer has an enable input E’ and provide both the normal and inverted outputs. When E’=0 the select inputs S2 S1S0 will
select data input(from I0 to I7) for passage to the output Z. When E’=1
the multiplexer is disable so that Z=0 regardless of the select input
code.
The operation is summarized in the next slide with logic diagram and block diagram.
Block diagram of 74ALS151
Application of multiplexer
1.Data routing.
2.Parallel to Serial conversion
3.Operation sequencing
4.Logic function generation.
Application of multiplexer (con)
In telecommunication, a multiplexer is a device that combines several input information signals into one output signal, which carries several communication channel, by means of some multiplexing technique.
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#3

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