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Optical
Burst Switching
Optical
burst switching is a promising solution for all optical WDM networks It combines
the benefits of optical packet switching and wavelength routing while taking into
account the limitations of current all optical technology In OBS the user data
is collected at the edge of the network, sorted based on destination address,and
grouped into variable sized bursts Prior to transmitting a burst, a control packet
is created and immediately send toward the destination in order to setup a buffer
less optical path for its corresponding burst After an offset delay time, the
data burst itself is transmitted without waiting for positive acknowledgement
from the destination node the OBS framework has been widely studied in the past
few years because it achieves high traffic throughput and high resource utilization
.
Introduction:
Optical communication
has been used for a long time and it very much popular with the invention of wavelength-division
multiplexing(WDM) Current WDM works over point-to-point links,where optical-to-electrical-to-optical(OEO)
conversion is required over each step The elimination of OEO conversion in all
optical networks(AON) allows for unprecedented transmission rates AON's can further
be categorized as wavelength-routed networks(WRNs).,optical burst switched networks(OBSNs),or
optical packet switched networks(OPSNs).Now we discuss here about optical burst
switching(OBS)
In optical burst switching(OBS)
data is transported in variable sized units called bursts Due to the great variability
in the duration of bursts the OBS network can be viewed as lying between OPSNs
and WRNS That is, when all burst durations are very short,equal to the duration
of an optical packet,OBSN can be seen as resembling an OPSN On the other hand,when
all the burst durations are extremely long the OBSN may seem resembling a WRN
In OBS there is strong separation between the data and control planes,which allows
for greater network manageability and flexibility In addition its dynamic nature
leads to high network adaptability and scalability,which makes it quite suitable
for transmission of bursty traffic .
In
general,the OBS network consists of interconnected core nodes that transport data
from various edge users The users consist of an electronic router and an OBS interface,
while the core OBS nodes require an optical switching matrix,a switch control;
unit and routing and signaling processors OBS has received considerable attention
in the past few years and various solutions have been proposed and analyzed in
an attempt to improve it's performance Here we describe the various OBS architectures
by grouping the material logically per OBS design parameter
Burst
aggregation:
OBS collects upper layer traffic and sort it based on
destination addresses and aggregate it into variable size bursts The exact algorithm
for creating the bursts can greatly impact the overall network operation because
it allows the network designers to control the burst characteristics and therefore
shape the burst arrival traffic The burst assembly algorithm has to consider a
preset timer and maximum and minimum burst lengths The burst aggregation algorithm
may use bit-padding ,the differentiation of class traffic , create classes of
service by varying the preset timers and maximum/minimum burst sizes
One of the most interesting benefit of burst aggregation is it shapes the traffic
by reducing the degree of self-similarity,making it less bursty in comparison
to the flow of the original higher-layer packets Traffic is considered bursty
if busy periods with a large of arrivals are followed by long idle periods The
term self-similar traffic refers to an arrival process that exhibits burstiness
when viewed at varying time scales:milliseconds,seconds,minutes,hours even days
and weeks Self-similar traffic is characterized by longer queuing delays therefore
degrades network performance Therefore reducing self-similarity is a desirable
feature of the burst assembly process and concluded that traffic is less self-similar
after the assembly.