A Novel Path Tracing Scheme In All-Optical Networks Using Benes Network

Pankaj Singh & Gurpartap Singh
International Journal of Signal Processing (SPIJ), Volume (7) : Issue (1) : 2013 66
A Novel Path Tracing Scheme In All-Optical Networks Using
Benes Network
Pankaj Singh pankaj1990@outlook.com
Department of Electronics and Communication
Lovely Professional University
Phagwara, 144401, India
Gurpartap Singh gurpartap.15882@lpu.co.in
Department of Electronics and Communication
Lovely Professional University
Phagwara, 144401, India
Abstract
A novel path tracing scheme is described in this paper which is known as Prime number encoding
scheme using Benes network. In this scheme every data packet consist a label which is default 1
and every node consist of a prime number tag, as this data packet pass through the network label
will be multiplied with the tag of the node. Prime number multiplication is done with encoder. At
the receiver end factorization is done which gives the information of travelled path. In this scheme
optical cross connects (OXC) is replaced with the Benes network which gives the better result
than OXC. System having Benes network gives less attenuation than OXC and complexity of the
system also decreases.
Keywords: Path Tracing Scheme, Optical Network Management, Optical Cross Connect (OXC),
Benes Network, All-optical Network (AON).
1. INTRODUCTION
In All-optical networks switching is an essential part, it helps to route the data from source to
destination. There are two types of switching in a network infrastructure: Circuit switching and
Packet switching, both techniques have own advantage and disadvantage. In circuit switching, a
guaranteed amount of bandwidth is allocated to each user and this connection available to the
user for all the time, once the connection is set up. The sum of the bandwidth of all the circuits, or
connections, on a link should be less than the link bandwidth. Example of circuit switching is
Public-switched telephone networks (PSTN), these networks are provide to support voice stream
and for other bulky data. Now days circuit switching is also known as private line service, which is
used for security purpose [1].
Another type of switching is Packet switching in which data is broken into small parts and known
as packet. Packet switching is used for small amount of data and it doesn’t create the physical
path between the source and destination. In All-optical networks packets are always carried on a
carrier that can be of different wavelengths, signal generated from one source can be delivered at
the different destination nodes using wavelength division multiplexing (WDM) which helps to route
the data in optical network. At each network node routing decision is made that based on its
current traffic loading and the destinations addresses of the data packets received. When an
optical data packet arrives at a node in network, its packet header that contains usually of lower
data rate is first extracted and detected, to retrieve its destination address. The high-speed
packet payload portion is buffered through fiber delay lines, before the optical packet is being
switched, via the optical cross-connect (OXC), based on the routing decision formed.

In this paper, a circuit switched based network infrastructure is used named as Benes network.
Benes network is basically a circuit switched network but it also used in the case of packet
switching [2]. It is well known that Benes network is a rearrange-able type of interconnection
networks. It can be used as a switching system in telecommunications or a communication
device in multiprocessor systems for linking processors and/or memories at its inputs and
outputs. The Benes network has less complexity compare to cross-bar interconnection network
(OXC) in terms of the number of switching elements. However, the Benes network is not easy to
setup as the network with O (N2) connections. The main problem is that Benes network needs
O (Nlog2N) time steps to realize N! Permutations between its inputs and outputs. Many studies on
fast algorithms to setup Benes networks have been made. Nonblocking conditions are the bases
of the setting-up algorithms [3].
For reliable data transmission and delivery in WDM networks the path should be well managed
and having high monitoring facility. During the travelling time packet can be routed to wrong
destination or alternate ports of the optical cross connects (OXC) due to error in switching
operations and malfunctioning of switches, this problem can be minimized with Benes network
that is implemented in this paper. So at reception of the optical data packets at the destination
node, identification of the exact physical network nodes or fibre links that the received optical data
packets have actually traversed, is very useful to derive and estimate its complete actual physical
path. This information is very useful to detect any possible network routing error due to possible
malfunction of the reconfigurable optical routing devices, and diagnose the possible causes of
signal quality degradation in the received optical data packets, by examining the optical
impairments along the retrieved path.
Moreover, when there exists any malicious or attack traffic, it will be useful to trace down the
source of the attack through examining the path information of the received packets. In addition, if
path tracing is performed at certain strategic nodes in the network, the traced path information on
the previously traversed network nodes or links of the data packets could be used to deduce the
actual or relative amount of accumulated optical impairments or temporal delay suffered by the
dynamically routed data packets. Such information is beneficial to estimate the signal quality, and
make strategic scheduling and routing decisions to meet the quality of service (QoS) requirement
of the network.
Many techniques proposed and implemented for path tracing but all techniques have some
advantage and disadvantage also very first technique was pilot tone based path tracing in which
pilot tones of low frequencies used to trace the path in the network. A pilot tone at a distinct
frequency was added to each input port of the OXC, as the input port identifier. By examining the
pilot tone frequencies contained in the switched optical signal at each output port of the OXC, the
switching connections of the OXC could be derived [4], [5].After that time delay recognition
technique come into picture every node have some delay instead of the pilot tones. Regarding to
the time-delay recognition schemes, the optical pulses at different input or output ports in an OXC
would experience different time delays, via some delay circuits. Hence, by examining the unique
temporal pulse patterns generated, connection states between the input and the output ports of
the OXC could be derived. The scheme could be further extended to realize path monitoring by
assigning different time delay patterns to different network nodes. However, the scheme suffers
from poor scalability, in terms of the amount of fibre delay required at each node in order to avoid
any ambiguity among between different possible paths. Besides, precise synchronization is
needed [6]-[9].
Recently, a novel of path tracing was proposed and implemented in which a distinct prime
number was assigned to each node as the path information tag. Through employing optical label
encoders based on prime number multiplication at the outputs of the network nodes, path
information tags carried by simple computation on the optical packet label at the receiving node.
Optical encoder can manipulate the labels on the fly [10].In this paper, prime number encoding
scheme further extended which helps to improve the Quality of Service (Qos) of the system. Next

section illustrates the principal of path tracing by employing the extended prime number encoding
technique.
2. PRINCIPLE OF PRIME NUMBER ENCODING PATH TRACING SCHEME
To trace the path in a network there are two ways one is network link tracing and other is named
as network node tracing. Network link tracing identifies all the links that the optical packet has
traversed. Network node tracing identifies all the nodes that the optical packet has traversed.
Both of schemes can be realized using extended path tracing scheme.
2.1 Network Link Tracing
Wavelength routing network with six nodes is shown in Figure 1and Table 1. Each link is
assigned with a prime number. In network link tracing every link has a prime number tag it can be
3, 7, 11, 13 etc. Whenever a signal passes through a particular link its label is multiplied with its
prime number tag. Therefore, all the fibre links that the optical data packet has traversed can be
identified at the receiving node, via prime-number factorization of the received label value. Figure
1 shows an example that the individual fibre links in the network have been assigned with their
distinct prime-number tags. Link every link tag is multiplied with its label which is default set as 1.
7 19
21
A1
A2 17
11 13
FIGURE 1: Example of Network link tracing.
A1 N1 N2 N6
Label Value 1 7 133
A2 N1 N4 N5 N6
Label value 1 3 39 633
TABLE 1: Example of Network link tracing.
2.2 Network Node Tracing
Wavelength routing network having six nodes is shown in Figure 2 and Table 2. Network node
tracing is modified from network link tracing technique, in this technique each node is comprises
Sender
Receiver
N1
N2
N3
N4
N5
N6

with AWG based OXC and assigned with a prime number. Whenever a signal passes through a
particular node its label is multiplied by the prime number of the node. Therefore, all the nodes
that signal traversed identified at the receiver end, by prime number factorization of the received
label value. An example of prime number encoding technique in which node assigned with a
prime number is shown in Figure 2.
A1
A2 A2
FIGURE 2: Example of Network Node Tracing.
A1 N1 N2 N3
Label Value 3 21 273
A2 N1 N4 N5 N6
Label value 3 15 165 2145
TABLE 2: Example of Network Node Tracing.
3. EXPERIMENTAL SETUP OF PRIME NUMBER ENCODING PATH
TRACING SCHEME USING OXC
To realize path tracing scheme laser diode is used as a source. Eight laser diodes are used to
generate eight signals. These signals are divided into two parts, first four signals are taken as a
data signals and another four signals are taken as a pilot signals. Data signals are of 193.1,
193.2, 193.3 and 193.4THz, all signals are having a power of 25dBm. Pilot signals frequencies
are 193.5, 193.6, 193.7 and 193.8THz that contains label value for each frequency, all pilot
signals are having a power of 10dBm. Transmitter module is shown in Figure 3(a). Further signals
are modulated using frequency modulation for transmission purpose.
Signals are further pass through the channel which consists of a OXC and Encoder, encoder is
used to calculate the travelled path of the packet on fly.
Fully implemented experimental setup is shown in Figure 3.
Sender
ReceiverN1:
3
N4:
7
N3:
17
N2:
5
N5:
11
N6:
13

Photodiode
(a) (b) (c)
FIGURE 3: (a) Transmitter generating eight signals, (b) Channel consist of Optical cross connect (OXC) and
Encoder, (c) Photodiodes at Receiver End.
At each output port of the OXC, the switched data wavelengths and their corresponding encoded
labels from different inputs are fed into an optical encoder to perform multiplication of its assigned
prime-number tag to the incoming label, and its structure and principle are illustrated in Fig. 4(a).
The data frequencies and the pilot frequencies (i.e. label) of the incoming composite signal are
first separated such that the label wavelengths are fed into an optical delay line circuit for
multiplication of the label values with the prime-number tag of the OXC. The optical delay line
circuit comprises an optical power splitter, an array of fiber delay lines, followed by an optical
power combiner. By setting appropriate number of fiber delay lines, it can generate an impulse
response which represents a particular binary number. Thus the resultant output pulse sequence
corresponds to the product of the input label value and the tag value [10].
For instance, as shown in the Fig. 4(b), when an incoming label with a value of 1 (i.e., one optical
pulses) is fed into the optical delay circuit with fiber delays of 0, τ, which represent a tag value of
3, the output will have two pulses with identical amplitudes and thus represent the decimal value
of 3 in binary form. Next, the label further passes through another optical delay circuit with fiber
delays of 0, τ, 2τ, which represent a tag value of 7, the output will have four pulses with relative
amplitudes 1, 2, 2, 1, respectively. By substituting these relative amplitudes as the coefficients of
the polynomial expression,1×y
3
+2×y
2
+2×y
1
+1×y
0
with y=2 , a decimal value of 21 is obtained and
this corresponds to the product of the input label value (3) and the tag value (7).
λ5
P
, λ6
P
, λ7
P
, λ8
P
optical delay
3τ
2τ
λ1
D
, λ2
D
, λ3
D
, λ4
D
λ1
D
, λ2
D
, λ3
D
, λ4
D
λ5
P
, λ6
P
, λ7
P
, λ8
P
τ λ5
P
, λ6
P
, λ7
P
, λ8
P
λ1
D
, λ2
D
, λ3
D
, λ4
D
(a)
LD
LD
LD
LD
MOD
MOD
MOD
MOD
OXC
ENCODER
ENCODER
ENCODER

t
1 1
Multiply with 3 multiply with 7 +
1 2 2 1
t t 1 1 t
1 1 1 +
1 1 t
(b)
FIGURE 4: (a) Structure of encoder for prime number multiplication. (b) Example showing Multiplication of
tag 3 & 7 with label 1.
4. EXPERIMENTAL SETUP OF PRIME NUMBER ENCODING PATH
TRACING SCHEME USING BENES NETWORK
Experimental setup of prime number encoding path tracing scheme using Benes network is
shown in Figure 5. Whole setup is divided into three parts that are Transmitter, Channel and
Receiver End. Transmitter part is shown in figure 5(a), which consists of eight laser diode
sources. Laser diodes generate the eight frequencies signals i.e. 193.1, 193.2, 193.3, 193.4,
193.5, 193.6, 193.7 and 193.8THz. Four signals are data signals having frequencies 193.1,
193.2, 193.3 and 193.4THz, data signals are of 25dBm power. Another four signals are pilot
signals having frequencies of 193.5, 193.6, 193.7 and 193.8THz, each pilot signal have a prime
number label. All pilot signals have power of 10dBm.
In this scheme OXC is replaced by Benes network which is reduce the complexity and increase
the power and also avoid the crosstalk like OXC. Basically Benes network is a switching network
it can be a multistage network for large networks as shown in Figure 5(b). The advantage of
Benes network is that connection between a large number of input and output ports can be made
by using only small-sized switches. A bipartite matching between the ports can be made by
conﬁguring the switches in all stages.
Photodiode
(a) (b) (c)
FIGURE 5: (a) Transmitter generating eight signals, (b) Channel consists of Benes network and Encoder, (c)
Photodiodes at Receiver End.
LD
LD
LD
MOD
MOD
MOD
BENES
ENCODER
ENCODER
ENCODER
MODLD

The Benes network is rearrangeable nonblocking network which can realize any arbitrary
permutation. The Benes network of dimension n is shown to be strictly nonblocking if only a
Suitable chosen fraction of l/n of inputs and outputs is used. In Benes network, the r-dimensional
Benes network connects 2
r
inputs to 2
r
outputs through 2r-1 levels of 2x2 switches. Here, each
level of switches consists of 2
r-1
switches, and therefore the size of the network has to be a power
of two. The Benes network has been proposed for use in telephone networks. It and other
closely related networks were also used as interconnection networks for parallel computers [11].
Basic structure of Benes network is shown in Figure 6.
0 0
1 1
2
2
3 3
4
4 5
5
6 6
7 7
FIGURE 6: Basis Structure of Nonblocking Benes Network.
Encoder functionality is same as explained in the previous section. At the receiver end eight
photodiodes are used, one for each frequency as shown in Figure 5(c). Basically photodiodes
converts the optical signals into electrical signals. At last eight signals are multiplexed. Next
section is about results analysis and comparison of both systems.
5. SIMULATION RESULTS
Prime number encoding techniques are implemented and simulated on optisystem software by
optiwave. As earlier discussed two types of technique are simulated, one technique is having
OXC and other technique is consists of Benes network. Both techniques are compared on the
basis of two parameters that are Complexity and power.
Complexity is main issue in optical networking less complexity gives better results. A simple
structure of optical cross connects, which is more complex than Benes network, OXC consists of
24 components. These components are 8 switches and 16 MUX/DEMUXs. Therefore these
components are responsible for much power consumption. MUX and DEMUXs consumes more
power and that’s by are MUX/DEMUXs are omitted in the proposed work. MUX and DEMUXs
leaks some information at every operation which leads to crosstalk. So reducing complexity also
reduces the crosstalk. Benes network, which have 20 components. It consists of 20 switches are
of 2x2. Complexity is decreased from the previous scheme i.e. using OXC; it also helps to
increase the power of the system. Less power consumption means less attenuation in the
network. If a system consume more power and received power is less than attenuation will be
high. Therefore, System with OXC have more attenuation but system with Benes network have
less attenuation that’s by much power is received in the case of Benes network.
Power is also a important factor in optical communication. Power received at receiver side
matters a lot, signal having high power will travels more distance. Optical spectrum of system with
OXC is shown in Figure 7(a), electrical signals spectrum shown in Figure 7(b) and optical power
meter is shown in Figure 7(c).Received power of system with OXC is just 7.269dBm.
2x2
2x2
2x2
2x2
2x2
2x2
2x2
2x2
2x2
2x2
2x2
2x2
2x2
2x2
2x2
2x2
2x2
2x2
2x2
2x2

(a)
(c)
(b)
FIGURE 7: (a) Optical spectrum of system having OXC, (b) RF spectrum of system having OXC, (c) Power
analyzer showing total received power.
System with Benes network has better results than system with OXC as shown in Figure 8.
Optical spectrum of received signals is shown in Figure 8 (a). It shows the power of individual
frequencies, power of data signals that are first four signals are higher than the power of pilot
signals that are remaining four signals. RF spectrum of electrical signals is shown in Figure 8(b)
and optical power meter is shown in Figure 8(c). Received power with benes network is
12.198dBm.
(a)
(b)
(c)
FIGURE 7: (a) Optical spectrum of system having Benes network, (b) RF spectrum of system having Benes
network, (c) Power analyzer showing total received power.
Therefore from the above results it is clear that by replacing OXC with Benes network gives better
performance in terms of power and it also reduces the complexity. As complexity decreases then
cost of the system also decreases. Therefore system with Benes network will reduce the cost of
the system.

6. CONCLUSION
Complexity and power are two important factors in optical communication. To measure and
improve the both factors two techniques are implemented, first is prime number encoding
technique using OXC and second is prime number encoding technique using Benes network.
Technique using Benes network gives better performance in terms of power and it also reduces
the complexity. Therefore Benes network can be used in the place of OXC to obtain better
results. Future work can be extended by making a new network with less complexity and less
switching. Network with high capability to reduce the crosstalk can replace the existing networks.
7. REFERENCES
1. R. Ramaswami and K.N Sivaranjan. Optical Networks. Academic Press, 2002.
2. R. Melen and J. S. Turner. “Nonblocking Networks for Fast Packet Switching” IEEE
journals, vol. CH2702, pp. 548-557, sep.1989.
3. GU and Shang-Jie. “Nonblocking Condition for Self-routing Benes network” IEEE tencon,
1993, pp. 203-206.
4. E.Kong, F.Tong, K.P.Ho, L.K.Chen, & C.K.Chan. “Pilot-tone based optical path
supervisory scheme for optical cross-connects,” Electronics Letter, vol. 35, no. 17, pp.
1481–1483, 1999.
5. S. Zhong, W. Chen, X.-H. Yang & Y.-J. Chen. “Transparent optical path and crosstalk
monitoring scheme for arrayed waveguide grating-based optical cross connect,” IEEE
Photon. Technology Letters, vol. 12, no.9, pp. 1249–1251, Sep.2000.
6. C.C.Lee,T.C.Kao,H.C.Chien,& S.Chi.“A novel supervisory scheme for OXC based on
different time-delay recognition,” IEEE Photonics Technology Letters, vol. 17, no. 12, pp.
2745–2747, Dec.2005.
7. J. Yu, L. K. Chen, G.-W. Lu & S.-T. Ho. “An improved OXC supervisory scheme based
on different time delay recognition,” in Proc. Joint Int. Conf. Optical Internet and Next
Generation Network (COIN-NGNCON), Jeju, Korea, Paper PS-13. 2006.
8. Z.Qian, G.W.Lu & S.-Y.Li.“Efficient OXC monitoring based on time delay recognition,” in
Proc. Int. Conf. Transparent Optical Networks (ICTON), Nottingham, U.K., Paper
We.B3.4, 2006.
9. Z.Qian,G.W.Lu,andS.-Y.Li.“Improved optical path supervisory scheme for optical cross
connects based on different time-delay recognition,” OSA J. Optical Networks, vol. 7, no.
1, pp. 80–87, Jan.2008.
10. K. H. Tse & C. KitChan.“A Path Tracing Scheme for All-Optical Packet-Switched
Networks”, IEEE Journal Of Lightwave Technology, Vol. 30, Issue. 11,pp. 1625-1631,
Jun.2012
11. Z. Jumandi, A. Samsudin and R. Budiarto. “optimized Arbitrary Size Networks” IEEE
journals, vol. 78, no. 03,pp. 665-666, Feb.2004.

A Novel Path Tracing Scheme In All-Optical Networks Using Benes Network

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