Bandwidth Utilization: Multiplexing

What is multiplexing?

the simultaneous transmission of multiple signals across a single data link

How is bandwidth shared in multiplexing?

by sharing the bandwidth of one link among multiple lines

What are the three basic multiplexing techniques?

Frequency-Division Multiplexing (FDM), Wavelength-Division Multiplexing (WDM), Time-Division Multiplexing (TDM)

Describe Frequency-Division Multiplexing (FDM).

analog technique that combines signals from different devices by modulating them onto different carrier frequencies

What is the purpose of Wavelength-Division Multiplexing (WDM)?

to combine different optical signals of different frequencies into one signal for fiber-optic cable transmission

Explain Time-Division Multiplexing (TDM).

a digital process that allows several connections to share the high bandwidth of a link by sharing time slots in the link

What is synchronous TDM?

TDM where each input connection has an allotment in the output even if it is not sending data

How does statistical TDM improve efficiency compared to synchronous TDM?

by dynamically allocating slots based on data availability, removing empty slots from the frame

What are three strategies for handling disparity in input data rates in TDM?

multilevel multiplexing, multiple-slot allocation, pulse stuffing

Why is frame synchronizing important in TDM?

to ensure accurate separation of time slots and synchronization between multiplexer and demultiplexer

What is DS service or digital hierarchy used for in TDM?

TDM implementation by telephone companies with various levels supporting different data rates and voice channels

Can T lines designed for digital transmission be used for analog transmission as well?

Yes, with sampling and TDM to combine multiple telephone lines into one line for efficiency

What is the T-1 frame?

The frame on a T-1 line consisting of 193 bits divided into 24 slots plus a synchronization bit

What are E lines?

European versions of T lines with different capacities

How do second-generation cellular telephone companies use synchronous TDM?

They divide available bandwidth into 30-kHz bands and allocate time slots for multiple users to share the band, increasing the number of telephone users.

How does statistical TDM differ from synchronous TDM in terms of slot allocation?

In synchronous TDM, each input has a reserved slot in the output frame, while in statistical TDM, slots are allocated only when an input line has data to send.

What is the difference between synchronous and statistical TDM regarding addressing?

Synchronous TDM does not require addressing as there are preassigned relationships between inputs and outputs. Statistical TDM requires addresses since there are no fixed relationships.

How can multiple stations share the same expanded bandwidth in FHSS?

By using an appropriate modulation technique like multiple FSK (MFSK)

How does DSSS provide privacy and immunity against interference?

By using different spreading codes for each station

What is spread spectrum used for in wireless applications?

To ensure secure communication without interception or jamming

Name two principles of spread spectrum.

Bandwidth allocation larger than needed and spreading process occurring after signal creation using a pseudorandom pattern.

What are the two techniques of spread spectrum?

Frequency hopping spread spectrum (FHSS) and direct sequence spread spectrum (DSSS)

Why is it important to have redundancy in spread spectrum systems?

To increase security by expanding the original bandwidth required for each station

How does FHSS provide privacy and anti-jamming effects?

It switches between multiple carrier frequencies in a pseudorandom pattern that an intruder cannot quickly adapt to.

How does DSSS expand bandwidth further compared to FHSS?

By replacing each data bit with multiple chips using a spreading code

What does the efficiency of statistical TDM depend on during peak times?

The statistics of load for each channel and the average fill rate of input slots

What is pulse stuffing in data rate management?

Adding dummy bits to lower-rate input lines to match the higher rate

Why are synchronization bits added at the beginning of each frame in TDM?

To ensure accurate separation of time slots and synchronization between multiplexer and demultiplexer

What is the main goal of multiplexing?

To maximize the utilization of a data link by transmitting multiple signals simultaneously

Name three basic multiplexing techniques.

Frequency-Division Multiplexing (FDM), Wavelength-Division Multiplexing (WDM), Time-Division Multiplexing (TDM)

How does frequency-division multiplexing combine signals from different devices?

By modulating them onto different carrier frequencies

What is the purpose of wavelength-division multiplexing in fiber-optic cable transmission?

To combine different optical signals of different frequencies into one signal

How does time-division multiplexing allow several connections to share high bandwidth?

By sharing time slots in the link, where each connection occupies a portion of time within a frame

What is synchronous TDM and why is it inefficient when sources have no data to send?

Synchronous TDM is where each input has an allotment in the output even if not sending data. It becomes inefficient because empty slots appear in output frames.

How can synchronous TDM efficiency be improved with statistical TDM?

Statistical TDM dynamically allocates slots based on data availability, removing empty slots from frames.

In TDM, what strategies are used to handle disparity in input data rates?

Multilevel multiplexing, multiple-slot allocation, pulse stuffing

Why are framing bits added to TDM frames?

For synchronization and accurate time slot separation between multiplexer and demultiplexer

What is DS service or digital hierarchy used for in TDM?

It is a hierarchy of digital signals used by telephone companies to support different data rates and voice channels.

Can T lines designed for digital transmission be used for analog transmission as well?

Yes, with sampling and time-division multiplexing (TDM) techniques

What are E lines and how do they differ from T lines?

E lines are European versions of T lines with different capacities for transmitting digital data, audio, or video.

How do second-generation cellular telephone companies use synchronous TDM to increase the number of users?

By dividing available bandwidth into 30-kHz bands and allocating time slots for multiple users to share the band.

What is statistical time-division multiplexing (TDM) and how does it improve efficiency compared to synchronous TDM?

Statistical TDM dynamically allocates slots based on data availability, removing empty slots from frames, thus improving bandwidth efficiency.

In synchronous Time Division Multiplexing (TDM), what does an output slot solely occupy?

Data only.

In statistical Time Division Multiplexing (TDM), what does a slot carry besides data?

Data and the address of the destination.

Does Synchronous TDM require addressing?

No, as inputs and outputs have preassigned relationships.

Why is addressing required in Statistical TDM? Because there are no fixed relationships between inputs and outputs.