1

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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