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A
SEMINAR REPORT
ON
ANALYSIS OF QUEUING DELAY IN OPTICAL SPACE NETWORK ON LEO SATELLITE
CONSTELLATIONS
Under the guidance of:
Asso.prof(Dr.) NILAMANI BHOI
Submitted by:
Name: SAUMMIT KANOONGO
Roll no.:13040111
Branch : M.Tech , 2 nd
sem (CSE)
DEPARTMENT OF ELECTRONICS AND TELECOMMUNICATION ENGINEERING (VEER SURENDRA SAI UNIVERSITY OF TECHNOLOGY, ODISHA)
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ACKNOWLEDGEMENT
It is difficult to acknowledge the precious debt of knowledge and learning. But we
can only repay it through our gratitude. First and foremost I wish to express my
profound gratitude to the almighty. It is my privilege to express my sincere thanks
to Prof. Sanjay Agrawal, H.O.D. EL & TC who has always been a constant
source of inspiration. All the faculty members have helped me during the
preparation of report by spending their precious time.
I convey my sincere thanks to Dr. Nilamani Bhoi who has given his most valuable
time and effort in guiding me to complete this seminar in due time and in this
shape.
Last but not the least I would like to thank my parents, friends for their co-
operation and continuous support during the course of the assignment.
saummit kanoongo
Regd no: 13040111
2nd
Semester, M.Tech ( CSE)
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CERTIFICATE
This is to certify that saummit kanoongo Of 2 nd
semester M.Tech in Electronics
and Telecommunication Engineering dept, Communication System Engineering
specialization bearing Regd No.13040111 has given his seminar talk and prepared
seminar report on Analysis of queuing delay in optical space network on LEO satellite constellations Under our guidance and advice.
Dr. Sanjay Agrawal DrNilamani Bhoi
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A B S T R A C T ON
Analysis of queuing delay in optical space network on LEO satellite constellations
Low earth orbit (LEO) satellite constellations using laser inter-
satellite links (ISLs) are recognized as a promising technology
to provide global broadband network services. In this paper, the
queuing delay model of an optical space network built on LEO
satellite constellations is established. It is assumed that the
optical space network employs wavelength division
multiplexing ISLs with wavelength routing technology to
communication satellites and makes routing decisions. With
consideration of the network task characterizations such as
distribution of task arrival time and task holding duration,
simulation experiment results are analyzed and the expression of
optical space network queuing delay is given. Both theoretical
analysis and simulation results show that features of queuing
delay vary with distribution characterizations of the network
tasks. It is hoped that the study can be helpful to evaluate the
design of constellation networking.
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CONTENTS
1. Introduction..6
2. What Is New In This Paper.7
3. Model And Analysis Of The Network .......................................12
4. Theoretical Analysis Of Network Traffic Parameters..12
5. Numerical Results And Analysis ....13
6. Future Work ..17
7. Features Technology....18
8. Conclusion......19
9. References.20
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Introduction :-
Optical space network based on wavelength division multiplexing (WDM)
architecture and wavelength routing technology has emerged as the befitting
backbone for the dramatic increase in bandwidth demand of emerging applications
[1]. Several optical space network have been proposed such as Celestri
[2],Teledesic [3], and NeLS [4]. These satellite systems built on non-
geosynchronous orbits, use a single wavelength or WDM laser inter-satellite links
(ISLs) for broadband inter-satellite communications.
In contrast to single wavelength ISLs, WDM ISLs with onboard wavelength
routing equipment perform better by offering more routing selection and by
reducing processor delays in high band-width communications [5].The key factor
of optical space network transmission feasibility is the transmission delay, also
called network delay, which is the duration of the signal passage from the source
satellite transmission to the destination satellite. In optical space networks based on
WDM technology, network delay is mostly decided by the queuing delay. Queuing
delay indicates the duration from one signal transmission network task arrived at
the source satellite to the time when this signal was ready to be transmitted.
During queuing delay, the satellite system is expected to assign the light path for
communication and the wavelength for the corresponding network task, and
check the light path and wavelength till they are available. Due to the periodic
motion of the satellites, each network task has a waiting limitation until it can be
executed. Thus, the increase of the queuing delay will be a destructive defect to
the optical satellite network. For this reason, it is necessary to research the
generative mechanism and characterization of the queuing delay in the optical
space network in order to reduce it to an acceptable range. Previous study has
mainly focused on the network structure in LEO satellite communication system,
in order to optimize the orbit parameters to enhance the performance of
communication service [6].
In these feasibility studies on the LEO satellite networks, Walker constellations
with optical ISL are employed to form a global satellite network and the
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constellation parameters such as orbits altitudes, number of orbital planes,
number of satellites in the orbital plane and the orbital inclination were studied
for optimization [7]. However, to the best of our knowledge, no previous work
concerned the performance of queuing delay in random network tasks on the LEO
satellite networks. In this paper, on the assumption that WDM architectures with
wavelength routing were available for the ISLs, and in view of random network
tasks, queuing delay in the optical space network is analyzed for the Walker
constellation with optical ISLs.
The paper is organized as follows. Section 2 describes the system model and
theoretical analysis of the queuing delay in the optical space network. Section 3 is
devoted to the simulation and numerical analysis with discussion. Section 4 states
the conclusions of this work.
Model and analysis of the network :-
Logical connections of LEO space network :-
In optical space network employing low earth orbit (LEO) satellite constellations,
the geographic topology of the network changes periodically. This dynamic
network architecture is considered as a great challenge to the light path routing and
wavelength assignment of the WDM based optical network. Therefore, in order to
improve the effectiveness of routing and wavelength assignment, the topology of
the network has to be simplified.
Through the use of continuous ISL connections, a typical LEO optical space
network in the Walker constellation can be seen as a modified Manhattan network
[8], as is shown in Fig. 1, an example of a typical LEO satellite network with five
orbital planes and six satellites in each orbital plane is given. Each satellite in the
network is connected to four adjacent satellites by optical ISLs. However, in
addition to the model shown in Fig. 1, there are also several different logical
connection architectures studied by researchers, corresponding to different
schematics of the network.
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When a network task, also called connection request, arrives at the
LEO satellite network, a sequence of ISLs which starts from the source satellite
and ends in destination satellite is generated and assigned to this connection
request. Each generated sequence of the ISLs is a specific route to the
corresponding connection, and each specific route needs a customized
wavelength to meet the communication requirement.
A practical problem is that the amount of available wavelengths is finite in the
network, which means the number of connections simultaneously operating on
the network is limited. Some network tasks arriving at the network have to wait
for an accessible route along with an unoccupied wavelength in this route to
accomplish communication mission.
On this occasion, the time spent on the waiting is called queuing delay.
Obviously, queuing delay is associated with the network capacity, routing
principle, temporal distribution of network tasks and some other network
parameters.
Theoretical analysis of network traffic parameters :-
Since queuing delay in the optical space network is relevant to network
capacity, clearly are expression of network capacity should be given.
Considering a LEO satellite network with L orbital planes and M satellites in
each orbital plane, total number of ISLs in the network can be written as
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In number of ISLs, the average connection length count between network node
pairs can be expressed as
where pi is the connection length count in number of ISLs between the reference
satellite and ith satellite in the network. What should to be point out is that the
average connection length count Pav shown in Eq. (2) is computed with assigning
the shortest path to each node pair.
The network capacity can be measured by the number of connections operating
on the network simultaneously. With average connection length shown in Eq. (2)
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and total number of ISLs shown in Eq. (1), the theoretical network capacity NTL
can be depicted as
where n is the number of available wavelengths in the optical satellite network.
Practically, not all of the ISLs and their wave-lengths can be utilizing at the same
time, and then the practical network capacity can be written as
where P(t) stands for the number of occupied ISLs at time t in the network.
In general, in the care of identical temporal distribution of the network tasks,
increasing network capacity can decrease the number of queuing connections. On
the other hand, under the condition of certain network capacity, increasing
network task generation rate will lead to a boost of the queuing delay.
Distribution of the arrival time determines the amount of connection requests per
unit duration, while service time distribution affects the operating speed of
connection requests.
To build a reasonable temporal distribution model of network tasks, arrival time
and service time of connection requests generated on certain distributions should
be considered. Actually, plentiful approaches have been proposed in order to
model large network flows as well as their superposition properties [9].In this
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paper, arrival times with Poisson distribution [10] and service times with
lognormal distribution [11] were chosen both for their simplicity and because
they provide rather general and realistic representation of large network systems.
Under these assumptions, the mean arrival time can be define das _ and mean
service time is assumed as _. Since the expression of network capacity is depicted
and network model is built, queuing delay of the network in unit duration can be
written as
In order to estimate the average queuing delay for every connection requirement,
the total number of connection requirements should be considered and the
average queuing delay in unit duration can be expressed as
From Eqs. (6) and (7) it can be seen that the queuing delay of the entire network
must be a function related to the Dun or Dunav. To understand and quantify the
performance of queuing delay in an optical space network, a series of
experiments carried out.
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Numerical results and analysis
Simulation setup
To investigate the relation between temporal distribution of connection requires
and queuing delay on LEO optical satellite net-work, the parameters for the
simulation process are set as follows: the satellites orbital altitude is 1200 km, the
period of satellite is6565 s, the inclination of orbital plane is 55, the number of
orbits is 5 and every orbit have 6 satellites, the same logical connections as shown
in Fig. 1. Unless otherwise mentioned, these parameters are used for all the results.
At the beginning of optical space network process simulation, connection
requirements were generated randomly with Poisson distribution arrival time and
lognormal distribution service time. Following the arrival time schedule, the
connection requirements arrived at the network system in chronological order
and became activated. The satellite system will work out a specified light path
with a dedicated wavelength for every activated connection requirement.
The shortest path routing method and first fit wavelength assignment [12] are
employed through the network. All wave-lengths are numbered from 1 to n.
Subsequently the network with n wavelengths in each link is decomposed into n
layered networks. Each of which has the same topology but one wave-length
capacity in each link. For a connection requirement, when the light path was
worked out by the satellite system, check every numbered network layer if the
corresponding light path is free. The wavelength with the lowest number is
selected from the available wavelengths.
However, a connection requirement should wait if every wave-length of the
corresponding light path is occupied, and the waiting time will be added to the
network queuing delay. With network time going on, one connection requirement
will be performed immediately when its assigned light path and wave-length are
free. All the waiting time will be summed up at the end of the network time, and
ISL utilization ratio at every satellite time is also recorded .As is mentioned above,
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the light path for new connection requirements follows the shortest path routing
method, and the wavelength assignment for a new connection requirement is
deter-mined both by the required light path and first fit wavelength assignment
mechanism.
Results and analysis :-
The simulation result of ISLs utilization ratio for different arrival time and service
time distributions is shown in Fig. 2.
Fig. 2 plots the ISLs utilization ratio in various temporal distribution statuses of
connection requirements. A larger ratio, which is the key feature of the connection
requirements distribution, implies a heavier traffic on the network as the system is
going to deal with more connection requirements simultaneously. It is
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in Fig. 2 that ISL utilization ratio becomes larger with increasing of the ratio,
because more ISLs are occupied by increasing network traffic. Contrasting the Fig.
2(b) with (a), it can be seen that optical space network with more available
wavelengths is more capable in dealing with larger connection requirements at
the same time and the ISL utilization ratio is steadier than with fewer
wavelengths. Fig. 3 shows the average ISLs utilization ratio varying along with the
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ratio. When ratio less than theoretical network capacity NTL, average ISLs
utilization ratio is increasing linearly along with the ratio. However, the increasing
speed is lower when ratio above NTL. It has been demonstrated that raising ratio
is leading to increasing network traffic and a indicates the used ISL resources.
When the increasing is no match for corresponding ratio increasing, a
conspicuous rising of queuing delay will be generated in the network. The result
represented in Fig. 3 is helpful in designing an optical space network. On one
hand, if the number of satellites is previously settled by other reasons, in order to
improve the utilization ratio of network ISLs, a proper ratio should be considered.
On the other hand, if the network traffic demand is the core factor of the
designed network, the designer should assign reasonable satellites and ISLs to
meet the network requirements. The plot in Fig. 4 depicts the average waiting
time performance at different network traffic level, and the average waiting time
is the mean value of queuing delay for each network connection requirement.
Average waiting time, also called average queuing delay, is less than 200 s when
the ratio is below the value of theoretical
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Network capacity NTL. And the results in Figs. 3 and 4 indicate that the
performance of optical satellite network with different avail-able wavelengths is
similar. To investigate the similitude character of optical satellite network with
different available wavelengths, a normalized network traffic level should be
utilized.
As shown in Fig. 5, when the traffic level in different network (mainly
distinguished by number of available wavelengths n_) are normalized by the
transformation of , their performances of average queuing delay are nearly the
same.
This result implies that the analysis of network queuing delay can be unified by
the normalized network traffic level rather than dealing with many different
situations of n. On the other hand, that also suggests the normalized network
traffic level in optical space network depend on the temporal distribution of the
network tasks and theoretical network capacity.
Eq. (8) describes the relationship between the average waiting time and
normalized network traffic level under several given conditions. These conditions
include network logical topology, light path routing method, and the wavelength
assignment mechanism. And parameters describes in Eq. (8) vary along with the
above condition changes.
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A contrast of theoretical and experimental average waiting time is represented in
Fig. 6. Results show that the value obtained numerically from Eq. (8) and through
simulations match closely. Curves expressed in Figs. 5 and 6 prove that average
queuing delay in optical space network could be written as a function of
normalized network traffic level . If queuing delay in a designing network can be
modeled, the predesign of this network will benefit.
FUTURE WORK :-
In this paper, arrival times with Poisson distribution and service times with
lognormal distribution were chosen both for their simplicity.
So better model can be used because they can provide rather general realistic
representation of large network systems.
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Conclusion:-
In this paper, queuing delay in the optical space network on LEO satellite
constellations was analyzed with the consideration of the network logical
topology, routing and wavelength assignment method and temporal distribution
of the connection requires. To research the performance of queuing delay, a
model of the optical space network on LEO satellite constellations with shortest
path routing method and first fit wavelength assignment mechanism was built.
Distributions of connection requirement such as arrival time and service time
were chosen reasonable. Arrival time with Poisson distribution and service time
with lognormal distribution were chosen to simulate connection requirements in
large network systems. Under these preconditions, the experimental results
show that the performance of optical satellite networks with different available
wavelengths is similar, and the normalized network traffic level in optical space
networks depends on the temporal distribution of network tasks and theoretical
network capacity. Through all the theories and simulation results, the
performance of ISLs utilization ratio and the average queuing delay in a given
optical space network has been proved describable as function of normalized
network traffic level. The results of the study will help to improve optical space
net-work design and to advance the performance of networking in optical space
networks.
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