BANDWIDTH
UTILIZATION
BY MALVIKA KAUSHIK
BANDWIDTH
– Bandwidth is measured as the amount of data that can be transferred from one
point to another within a network in a specific amount of time.
– bandwidth is expressed as a bitrate and measured in bits per second (bps).
– One byte is eight bits. Thus, 10 MB/s = 80 Mb/s.
– Bandwidth maximums: Some types of connections have a maximum defined
bandwidth. Actual bandwidth depends on many factors including environment,
cabling, and usage, and is usually less than the theoretical maximum.
BANDWIDTH UTILIZATION
“ THE WISE USE OF AVAILABLE BANDWIDTH TO
ACHIEVE SPECIFIC GOALS”
❖ MULTIPLEXING
❖ SPREADING
MULTIPLEXING
– Multiplexing is the process of combining multiple signals into one signal, over a
shared medium.
– If analog signals are multiplexed, it is Analog Multiplexing and if digital signals
are multiplexed, that process is Digital Multiplexing
TYPE OF MULTIPLEXER
FDM
– Frequency division multiplexing (FDM) is a technique of multiplexing which
means combining more than one signal over a shared medium.
– In FDM, signals of different frequencies are combined for concurrent
transmission.
Concept and Process
– In FDM, the total bandwidth is divided to a set of frequency bands that do not
overlap. Each of these bands is a carrier of a different signal that is generated
and modulated by one of the sending devices. The frequency bands are
separated from one another by strips of unused frequencies called the guard
bands, to prevent overlapping of signals.
– The modulated signals are combined together using a multiplexer (MUX) in the
sending end. The combined signal is transmitted over the communication
channel, thus allowing multiple independent data streams to be transmitted
simultaneously. At the receiving end, the individual signals are extracted from
the combined signal by the process of demultiplexing (DEMUX).
WDM
– Wavelength division multiplexing (WDM) is a technique of multiplexing multiple
optical carrier signals through a single optical fiber channel by varying the
wavelengths of laser lights. WDM allows communication in both the directions
in the fiber cable.
Concept and Process
– In WDM, the optical signals from different sources or (transponders) are
combined by a multiplexer, which is essentially an optical combiner. They are
combined so that their wavelengths are different.
– The combined signal is transmitted via a single optical fiber strand. At the
receiving end, a demultiplexer splits the incoming beam into its components
and each of the beams is send to the corresponding receivers
TDM
– Time division multiplexing (TDM) is a technique of multiplexing, where the users
are allowed the total available bandwidth on time sharing basis. Here the time
domain is divided into several recurrent slots of fixed length, and each signal is
allotted a time slot on a round-robin basis
Synchronous TDM
– The time slots are pre-assigned and fixed.
– This slot is even given if the source is not ready with data at this time. In this
case the slot is transmitted empty.
– It is used for multiplexing digitized voice stream.
Asynchronous (or statistical) TDM
-The slots are allocated dynamically depending on the speed of source or their
ready state.
-It dynamically allocates the time slots according to different input channel’s
needs, thus saving the channel capacity.
Spread Spectrum
– Spread spectrum is designed to be used in wireless applications
– In wireless applications, all stations use air (or a vacuum) as the medium for
communication. Stations must be able to share this medium without
interception by an eavesdropper and without being subject to jamming from a
malicious intruder
– To achieve these goals, spread spectrum techniques add redundancy; they
spread the original spectrum needed for each station
– Ifthe required bandwidth for each station is B, spread spectrum expands it to
Bss' such that Bss » B.
– Spread spectrum achieves its goals through two principles:
1. The bandwidth allocated to each station needs to be, by far, larger than what
is needed. This allows redundancy.
2. The expanding of the original bandwidth B to the bandwidth Bss must be done
by a process that is independent of the original signal. In other words, the
spreading process occurs after the signal is created by the source.
