Dropping based contention resolution for service differentiation to provide qo s

INTERNATIONALComputer EngineeringCOMPUTER ENGINEERING
International Journal of JOURNAL OF and Technology (IJCET), ISSN 0976-
6367(Print), ISSN 0976 – 6375(Online) Volume 4, Issue 1, January- February (2013), © IAEME
& TECHNOLOGY (IJCET)
ISSN 0976 – 6367(Print)
ISSN 0976 – 6375(Online)
Volume 4, Issue 1, January- February (2013), pp. 218-228
IJCET
© IAEME: www.iaeme.com/ijcet.asp
Journal Impact Factor (2012): 3.9580 (Calculated by GISI) ©IAEME
www.jifactor.com

DROPPING BASED CONTENTION RESOLUTION FOR SERVICE
DIFFERENTIATION TO PROVIDE QoS IN WDM OBS NETWORKS

Prof. J. R. Pathan1, Prof. A. R. Teke2, Prof. M. A. Parjane3, Prof. P.S. Togrikar4
1, 2
Department of Computer Engineering, S. B. Patil College of Engineering, Indapur, Pune
(MS), India
3, 4
Department of E & TC Engineering, S. B. Patil College of Engineering, Indapur, Pune
(MS), India
pathan.pathan@gmail.com1, aish_art@rediffmail.com2, mparjane@gmail.com3,
pradeep.togrikar@gmail.com4

ABSTRACT

In the recent years, the bandwidth demand on the Internet is increasing phenomenally,
due to rising of multimedia applications and real time applications. WDM technology enables
to respond to the explosive growth of Internet traffic by exploiting huge bandwidth of the
fiber. Optical burst switching (OBS) in WDM is a promising technology to use in the next
generation optical network. One of the challenges in OBS based network is wavelength
contention to provide quality of service (QoS). QoS helps to provide priorities to different
applications depending on their bandwidth requirement. In case of insufficient bandwidth,
QoS also helps to guarantee the burst dropping probability. In this paper, an effective
approach is proposed to provide QoS in OBS networks. The primary aim of the proposed
approach is to reduce loss of high delay sensitive data. High delay sensitive data is allowed to
lease the channels which are allocated to the data having low priority. We put counters at
each core node to measure number of low priority and high priority burst drop. If value
reaches to its threshold then respective burst is not allowed to drop. Simulations are
conducted to evaluate the performance of proposed algorithm in terms of burst dropping
probability. The performance of proposed algorithm is then compared with LAUC-VF
algorithm. The dropping probability behaviour of high priority and low priority data bursts
with increasing load of high delay sensitive data burst is studied.

Keywords: WDM, Optical burst switching (OBS), Quality of service (QoS), Service
differentiation, Burst dropping probability.

218

International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-

I. INTRODUCTION

In WDM system, each fiber carries multiple communication channels with each
channel operating on a different wavelength. Since, it is an attractive optical multiplexing
technique that allows better exploitation of the fiber capacity and reducing the cost of
core network. Hence, WDM has received much more attention as a promising approach
to building the next generation Internet. There are several optical network switching
paradigms, namely optical circuit switching (OCS), optical packet switching (OPS), and
optical burst switching (OBS). Of all these paradigms OBS combines the best of circuit
switching and packet switching while avoiding their shortcomings [5]. Due to the
statistical multiplexing in OBS, an improvement is observed in efficiency and scalability
as compared with OCS. In OBS, the bandwidth utilization is more efficient than OPS. In
an OBS based network, a burst consisting of multiple IP packets is switched through the
network all optically [7]. The control packet (header of a burst) is transmitted on a
separate wavelength ahead of the transmission of burst payload to ensure sufficient time
for header processing [5]. Due to the one-way reservation scheme, burst loss may occur in
an OBS network because the control may not succeed in reserving resources at some of
the intermediate OBS core nodes [9].
Although OBS provides better solution over OCS and OPS, several issues like
burst assembly, signalling schemes, contention resolution, burst scheduling, and quality
of service (QoS) need to be consider. Contention occurs when more than one burst
contends for the same resource at the same time. In an OBS based networks, contention
among bursts can be resolved using deflection, dropping, and pre-emption [7]. It is also
possible to break the incoming burst into multiple segments, and each segment can then
be deflected, dropped and pre-empted [7]. In this paper, we are using dropping based
approach for contention resolution.
Another challenging issue in OBS based networks is support to QoS. The
bandwidth requirement for the multimedia and real time applications is increasing
phenomenally. For such applications, there should be sufficient bandwidth available to
guarantee dropping probability. In case of insufficient bandwidth, QoS helps to guarantee
burst dropping probability. QoS also helps to provide different priorities to different
applications depending on their bandwidth requirement. So, recently QoS has gain much
attention and is becoming motivation for present research. In general, QoS can be
provided by introducing differentiation at some point in the network. Many algorithms
have been proposed to provide QoS in OBS based networks. In [2], a simple but cost
efficient priority scheme is proposed to support QoS at the WDM layer of the optical
Internet. More specifically, by assigning different offset times to different traffic classes,
it is possible for a higher priority class to be isolated from lower priority traffic class.
Though offset-time based QoS scheme does not mandate the use of Fiber Delay Lines
(FDLs), in [3,4] it is given that QoS performance can be significantly improved even with
limited FDLs to resolve contention for bandwidth among multiple bursts. The
proportional QoS model in [10] is proposed which introduces an intentional dropping
scheme to give a controllable burst loss probability for different service classes.
Rescheduling based QoS control algorithm using delayed pre-emption and controlled
deadlines has been proposed in [14].

219


II. SERVICE DIFFERENTIATION IN OBS

There is a great demand for Internet to be extended with service differentiation. As
we have said earlier, the QoS can be provided by introducing differentiation at some point
in the network. Various techniques of service differentiation are designed to provide QoS
including differentiated signalling, differentiated offset-time [1], differentiated offset-time
[2,3], differentiated contention resolution [8], differentiated burst assembly [6,7],
differentiated scheduling [6], differentiated path selection [13]. Recently, a new approach
is proposed in [12] which provide QoS based on differentiation scheme. This approach
uses pre-emption for contention resolution and guarantees zero burst loss of high delay
sensitive data by using independent wavelength assignment scheme for high delay
sensitive data and synchronizing all core nodes by a single clock to avoid wavelength
contention but it has some limitations. There is a need of synchronization of all core
nodes to set lightpath. The additional mechanism is required to calculate number of
wavelengths for high delay sensitive data at each core node. This algorithm uses the static
wavelength assignment scheme for high delay sensitive data bursts.
We are proposing a new approach which uses dropping technique for contention
resolution and also reduces the loss of high delay sensitive data. In the proposed approach
no lightpath is created for high delay sensitive data transmission. It means that proposed
algorithm does not need independent wavelength assignment for high delay sensitive data
and clock synchronization at each core node.The additional mechanism is not required to
calculate number of wavelengths for high delay sensitive data at each core node. So, the
complexity of proposed algorithm is reduced. The proposed algorithm uses packet level
differentiation in which packets from different service classes are assembled into different
bursts. In this paper, like [12] the Internet traffic at ingress node is classified into three
classes of service: Most high priority data, High priority data and Low priority data. This
classification isbased on the current and next generation demands ofthe users and real
time applications which is the reasonof classifying video further in to live videos and
streaming videos. The concept of service differentiation has been employed to reduce the
loss of MHP data bursts.

III. PROPOSED APPROACH

In order to describe the proposed dropping based contention resolution algorithm,
it is assumed that wavelength converters and FDLs are used at each core node. The
Internet traffic at ingress node is classified into three classes of service: Most high priority
data, High priority data and Low priority data. High delay sensitive data packets (e.g. live
video conference, voice etc) are assembled into a bursts of most high priority (MHP), the
data packets (e.g. streaming video etc) are assembled into high priority (HP) bursts, while
best effort data packets (e.g. FTP, email etc) are assembled into low priority (LP) bursts.
All available wavelengths are divided MHP data channels, HP data channels and
LP data channels. Proposed scheme uses dropping technique for wavelength contention
resolution. The idea is that if data burst having high priority is contending with burst with
low priority, then drop the low priority data to schedule data burst having high priority.

220


A. Algorithm

In proposed approach, bursts are generated by using threshold-based scheme of burst
aggregation. It is ensure that BHP is processed before data burst is transmitted. The time
complexity of proposed algorithm is O(n).

BEGIN
Check the class of incoming burst
IF MHP burst is at core
IF λ is available
Generate control packet and transmit burst after offset time
ELSE
Check the possibility to lease λ
IF Possible to lease LP data channel
Channel is reserved to transmit MHP burst after offset time
ELSE
IFPossible to lease HP data channel
Channel is reserved to transmit MHP burst after offset time
ELSE
MHP burst is dropped
END IF
END IF
END IF
ELSE IF HP burst is at core
IFλ is available
ELSE
Check possibility to lease λ
IFPossible to lease LP data channel
Channel is reserved to transmit HP burst after offset time
ELSE
HP burst is dropped
END IF
END IF
ELSELP burst is at core
IFλ is available
ELSE
LP burst is dropped
END IF
END IF
END IF
END

221


B. Operation Of Proposed Algorithm

When any burst arrives at core node then algorithm first checks service class of the burst.
If type of the burst is MHP then algorithm checks whether the wavelength is available to
schedule arriving data burst. If wavelength is available then it is assigned, control packet is
generated and MHP burst is scheduled on channel after offset time to transmit. If wavelength
is not available for MHP burst then algorithm first checks the possibility to lease LP data
channel. If it is possible then LP data channel is reserved to schedule MHP burst after offset
time. If it is not possible to lease LP data channel then again a check is made to lease HP data
channel. If it is possible to lease HP data channel then HP data channel is reserved to
schedule MHP burst and transmitted after offset time else MHP data burst is dropped as
shown in flowchart 1. It means that algorithm has given the full authority to MHP burst to
lease the wavelengths of LP and HP bursts so that it helps to minimize dropping probability
of MHP burst. So, proposed algorithm guarantees to reduce the loss of MHP burst.
If the service class of burst at core is HP, then algorithm checks whether wavelength is
available to schedule arriving burst. If wavelength is available then wavelength is assigned,
control packet is generated and HP burst is scheduled on channel to transmit after offset time.
If wavelength is not available for burst then algorithm checks the possibility to lease LP data
channel. If it is possible, then LP data channel is reserved to schedule HP burst after offset
time. If it is not possible to lease LP data channel, then HP burst is dropped shown in
flowchart 3.

Flowchart 1: Operation of Algorithm when MHP burst at core node

If the class of arriving burst at core is LP, then algorithm checks whether wavelength is
available to schedule arriving LP burst. If wavelength is available then wavelength is
assigned, control packet is generated and LP burst is scheduled on channel to transmit after
offset time. If wavelength is not available LP burst is dropped shown in flowchart 2.

222


Flowchart 2: Operation of Algorithm when LP Flowchart 3: Operation of Algorithm when HP burst at
burst at core node core node

The dropping probability of HP class data burst depends on the load of MHP data burst. As
number of MHP data burst increases, possibility of HP burst drop also increases. Similarly,
the dropping probability of LP class data burst depends on the percentage load of both MHP
and HP bursts. As number of MHP and HP data burst increases, possibility of dropping of LP
burst also increases.

C. Wavelength Allocation Scheme

The wavelength allocation scheme in the proposed algorithm is not static. The total
available wavelengths are grouped as MHP data channels, HP data channels, and LP data
channels. To make wavelength allocation dynamic, MHP data bursts are allowed to lease
wavelengths of HP and LP data channels, while HP data bursts are allowed to lease LP data
channels if wavelength is not available. But, this scheme may lead to total loss of LP data
burst. So, a count is placed at each core node to measure number of LP burst drop and is not
allowed if count reaches to a threshold value. Similarly, another count is placed at each core
node to measure HP burst drop and if count reaches to its threshold value, then dropping of
HP burst is not allowed. Figure 1 shows the dynamic nature of wavelength allocation scheme.

IV. SIMULATION AND RESULTS

Extensive simulations are carried out to study the performance of proposed dropping
based approach and to see how it fares in comparison with standard LAUC-VF algorithm. To
evaluate the performance of proposed algorithm NS-2.33 with OBS patch is used. In this
section, the method used for conducting simulations is described and the performance
parameter used to analyse the proposed approach is defined. Finally, the results obtained
from the simulation are presented.

223


Figure 1: Wavelength Allocation Scheme in Proposed Algorithm

A. Simulation Model

We have conducted simulations using NS-2.33 integrated with OBS patch and
NSFNET topology consisting of total 14 nodes. The simulation model consists of 10 core
nodes and 4 edge nodes with 21 bidirectional links. A bidirectional link is realized by two
unidirectional links in opposite direction. Each unidirectional link consists of 7 data
channels and 1 control channel as shown in figure 2. Burst arrivals to the network are
Self-similar. Bursts are generated by using Threshold-based scheme. Shortest path is
used for routing the burst from source to destination. The BHP processing time is 1 µs. It
is ensure that BHP is processed before data burst is transmitted.

B. Performance Metric

The burst dropping probability metric is selected to study the performance of proposed
algorithm. The burst dropping probability is defined as number of bursts dropped over
number bursts sent. The efficiency of scheduling algorithm depends on burst dropping
probability and it should be as minimum as possible. Because, burst dropping probability
is very important factor as it leads to very huge amount of data loss in optical network.
Load in the network depends on total bandwidth available and burst size. The maximum
load that can be handled by network is calculated by dividing total available wavelength
by burst size.

224


Figure 2: Simulation Model

C. Simulation Results

The performanceof proposedalgorithm in terms of dropping probability and compares it
with LAUC-VF algorithm is shown in figure 3. Proposed algorithm shows the reduction in
loss of MHP class data bursts. Even though data load is 100%, the burst loss recorded is
minimum than LAUC-VF, because MHP burst can lease channels which are allocated to LP
and HP data channels. It has been observed that using LAUC-VF when data load is 100%,
dropping probability reaches to 0.14 [12].
Similarly, figure 4 shows effect of data load on dropping probability of HP bursts. It
clearly shows that as data load increases, dropping probability of HP also increases.
Because, as data load increases MHP load also increases and MHP burst can lease channels
which are allocated to HP and those which can be leased by HP.

Figure 3: Comparison of LAUC-VF and Proposed Algorithm

225


Figure 4: Behaviour of Dropping Probability of HP Bursts with
Increasing Load of MHP Bursts

The effect of data load on dropping probability of LP bursts is shown in figure 5. It is
observed that as data load increases, dropping probability of LP data also increases. With
increasing load of MHP class data bursts, the availability of wavelengths decreases. In that
case, MHP burst is going to lease channels of LP to reduce dropping. As a result, there is
increase in dropping of LP.

Figure 5: Behaviour of Dropping Probability of LP Bursts with
Increasing Load of MHP Bursts

226


V. CONCLUSION

In this paper, a simple and effective dropping based scheme is proposed which uses
packet level service differentiation by dividing the IP traffic into three service classes. It has
been observed that proposed algorithm reduces the loss of high delay sensitive data. The idea
is that if wavelength is not available to schedule burst then wavelength of burst having low
priority can be can be dropped to lease that wavelength. MHP burst loss is reduced, because
MHP class data burst can lease the wavelengths of both LP and HP class data burst. To avoid
total loss of LP burst, some threshold value is placed at each core node to measure LP drop.
Simulations are carried out to study the performance of proposed approach and compared
with standard LAUC-VF algorithm. While implementing proposed algorithm, it is observed
that as MHP class data burst load increases, dropping probability of LP and HP data burst
also increases.

REFERENCES

[1] Jason P. Jue, Vinod M. Vokkarane. “Optical Burst Switched Networks”, Springer
Publication, 2005.
[2] MyungsikYoo and ChunmingQiao. ``Supporting Multiple Classes of Services In IP Over
WDM Networks'', IEEE CONFERENCE, Page(s) 1023 - 1027 vol. 1b, 1999.
[3] MyungsikYoo, ChunmingQiao and Sudhir Dixit. ``QoS Performance of Optical Burst
Switching in IP-Over-WDM Networks'', IEEE JOURNALS, Page(s) 2062 - 2071, 2000.
[4] MyungsikYoo, ChunmingQiao and Sudhir Dixit. ``Optical Burst Switching for Service
Differentiation in the Next-Generation Optical Internet'', IEEE Communications
Magazine, Page(s) 98 - 104, 2001.
[5] Mei Yang, S.Q. Zheng and Dominique Verchere. ``A QoS Supporting Scheduling
Algorithm For OBS DWDM Networks'', IEEE Global Telecommunications Conference,
Page(s) 86 - 91 vol.1, 2001.
[6] MyungsikYoo, ChunmingQiao and Sudhir Dixit. “Optical Burst Switching for Service
Differentiation in the Next-Generation Optical Internet'' IEEE Communications
Magazine, Page(s) 98 - 104, 2001.
[7] Vinod M. Vokkarane, Qiong Zhang, Jason P. Jue, and Biao Chen. “Generalized Burst
Assembly and Scheduling Techniques for QoS Support in Optical Burst-switched
Networks IEEE Global Telecommunications Conference, Volume 3, Page(s) 2747 -
2751 vol.3, 2002.
[8] Ching-Fang Hsu, Te-Lung Liu and Nen-Fu Huang. “On the Deflection Routing in QoS
Supported Optical Burst-Switched Networks'' Communications, 2002. ICC 2002. IEEE
International Conference, Volume 5, Page(s) 2786 - 2790, 2002.
[9] TzvetelinaBattestilli and Harry Perros, “An Introduction to Optical Burst Switching”
IEEE Optical Communications August 2003
[10] YunhanLuo, Sheng Wang. “An FDL-based QoS scheduling algorithm in OBS Networks''
IEEE, 2005.
[11] M. Casoni, E. Luppi and M. L. Merani. “Performance Evaluation of Channel Scheduling
Algorithm With Different QoS Classes''Networks, 2006. ICON '06. 14th IEEE
International Conference, Volume 2, Page(s) 1 - 6, 2006.

227


[12] FarhanSabir Ujager1, Zia-ul-Haq2, Muhammad Ramzan3 and S.M.H. Zaidi.“An
independent wavelength assignment, QoS Differentiation Scheme, in DWDM OBS
Networks, for zero high priority burst loss" IEEE CONFERENCE, Page(s) 274 - 279,
2010.
[13] M.Thachayani, Member IEEE and R.Nakkeeran. “Path Differentiated QoS Provisioning
Scheme for OBS Networks'', IEEE 2010 International Conference, Page(s) 1 - 4, 2010.
[14] Kostas Ramantas, Tito Raul Vargas, Juan Carlos Guerri and Kyriakos Vlachos. “A
preemptive scheduling scheme for flexible QoS provisioning in OBS networks'' IEEE
Sixth International Conference, Page(s) 1 - 6, 2009.
[15] V. Bapuji, R. Naveen Kumar, Dr. A. Govardhan and Prof. S.S.V.N. Sarma, “Maximizing
Lifespan Of Mobile Ad Hoc Networks With Qos Provision Routing Protocol”
International journal of Computer Engineering & Technology (IJCET), Volume 3,
Issue 2, 2012, pp. 150 - 156, Published by IAEME.
[16] Jayashree Agrakhed, G. S. Biradar and V. D. Mytri, “Optimal QoS Routing With
Prioritized Region Scheduling Over WMSN” International journal of Computer
Engineering & Technology (IJCET), Volume 3, Issue 1, 2012, pp. 289 - 304, Published
by IAEME.

228

Dropping based contention resolution for service differentiation to provide qo s

Recommended

Recommended

More Related Content

What's hot

What's hot (19)

Viewers also liked

Viewers also liked (9)

Similar to Dropping based contention resolution for service differentiation to provide qo s

Similar to Dropping based contention resolution for service differentiation to provide qo s (20)

More from IAEME Publication

More from IAEME Publication (20)

Dropping based contention resolution for service differentiation to provide qo s