Centralized Monitoring and Self-protected against Fiber

World Academy of Science, Engineering and Technology
International Journal of Electrical and Computer Engineering
Vol:2, No:3, 2008
Centralized Monitoring and Self-protected
against Fiber Fault in FTTH Access Network
Mohammad Syuhaimi Ab-Rahman, Boonchuan Ng, and Kasmiran Jumari
International Science Index, Electrical and Computer Engineering Vol:2, No:3, 2008 waset.org/Publication/3862
Abstract—This paper presented a new approach for centralized
monitoring and self-protected against fiber fault in fiber-to-the-home
(FTTH) access network by using Smart Access Network Testing,
Analyzing and Database (SANTAD). SANTAD will be installed
with optical line terminal (OLT) at central office (CO) for in-service
transmission surveillance and fiber fault localization within FTTH
with point-to-multipoint (P2MP) configuration downwardly from CO
towards customer residential locations based on the graphical user
interface (GUI) processing capabilities of MATLAB software.
SANTAD is able to detect any fiber fault as well as identify the
failure location in the network system. SANTAD enable the status of
each optical network unit (ONU) connected line is displayed onto
one screen with capability to configure the attenuation and detect the
failure simultaneously. The analysis results and information will be
delivered to the field engineer for promptly actions, meanwhile the
failure line will be diverted to protection line to ensure the traffic
flow continuously. This approach has a bright prospect to improve
the survivability and reliability as well as increase the efficiency and
monitoring capabilities in FTTH.
Keywords—Fiber fault,
surveillance, MATLAB.
FTTH,
SANTAD,
transmission
I. INTRODUCTION
F
TTH is a broadband network technology that delivering
triple-play (data, voice and video) services with a high
speed to the home or business via optical fiber cable. FTTH is
the major role in alleviating the last mile bottleneck for next
generation broadband optical access network [1]. Today,
FTTH has been recognized as the ultimate solution for
providing various communications and multimedia services,
including carrier-class telephony, high-speed Internet access,
digital cable television (CATV), and interactive two-way
video-based services to the end users [2]. Owing the very high
capacity of optical fibers, FTTH can deliver greater capacity
as compared to copper-based technologies [3].
FTTH technology using passive optical network (PON)
with P2MP configuration or tree topology is the most
promising way to provide high quality broadband access.
PON has been early described for FTTH as early as 1986.
PON are nowadays extensively studied and some commercial
deployments are already reported [4]. The PON is commonly
deployed as it can offer a cost-efficient and scalable solution
to provide huge-capacity optical access [5].
Since this kind of architecture can accommodate a large
number of subscribers, when any fault occurs at one point in
an optical fiber line, the access network will without any
function behind the break point. It leads to affect the whole
services transmission. The upstream signal from multiple
ONUs at different customer residential locations to OLT at
CO or the downstream signal from OLT to multiple ONUs
after the break point will become unreachable if the fault
occurs in the feeder region [1]. However, if the fault occurs in
an individual subscriber’s infrastructure such as drop fiber or
customer premises equipment (CPE) (e.g. ONU), since the
signals from OLT are successfully shared among other
subscribers’ ONUs via a passive optical splitter, thus only one
subscriber’s service is affected [6]. Any service outage due to
a fiber break can be translated into tremendous financial loss
in business for the network service providers [7].
A failure due to fiber break in current optical
communication system could make the network service
providers very difficult to restore the system back to normal.
According to the cases reported to the Federal Communication
Commission (FCC), more than one-third of service
disruptions are due to fiber cable problems. This kind of
problem usually take longer time to resolve compared to the
transmission equipment failure [8]. Moreover, the laser source
used in optical communication system may explore at the
break point, it can caused the retina eye burning and may be
damaged temporarily or permanently (blind) in a few seconds
or even less time depending to the energy absorbed by the
retina eye [9]. Therefore, the survivability of the whole
network has to be examined more seriously. Lack of
survivability is one of main factor that FTTH is still not been
deployed in certain areas.
II. FIBER LOCALIZATION FAULT IN FTTH
This work was supported in part by the Malaysian Ministry of Science,
Technology and Innovation (MOSTI) under National Science Fund (NSF) 0101-02-SF0493.
Mohammad Syuhaimi Ab-Rahman, Boonchuan Ng, and Kasmiran Jumari
are with the Computer and Network Security Research Group, Department of
Electrical, Electronics and Systems Engineering, Faculty of Engineering and
Built Environment, Universiti Kebangsaan Malaysia, 43600 UKM Bangi,
Selangor, Malaysia (phone: +603-89216448; fax: +603-89216146; e-mail:
syuhaimi@vlsi.eng.ukm.my, ngbc@vlsi.eng.ukm.my, kbj@vlsi.eng.ukm.my).
International Scholarly and Scientific Research & Innovation 2(3) 2008
Fiber fault within FTTH becomes more significant due to
the increasing demand for reliable service delivery [5]. It is
important to be able to locate any fiber break after the
installation of FTTH access network. Furthermore, a simple
and effective monitoring configuration is highly desirable for
timely failure detection along the fiber [7]. A particular
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World Academy of Science, Engineering and Technology
International Journal of Electrical and Computer Engineering
Vol:2, No:3, 2008
International Science Index, Electrical and Computer Engineering Vol:2, No:3, 2008 waset.org/Publication/3862
problem in this regard is that a failure occurred at the drop
region must be located without affecting the service
transmission to other subscribers [10]. A good fault
surveillance system is essential to identify fiber fault without
interrupting the services, while other channels are still in
service to maximize the link utilization [7]. Therefore, an
optical line monitoring and testing system is essential for
failure detection to improve the service reliability and reduce
the maintenance costs of FTTH.
Optical time domain reflectometer (OTDR) was first
reported in 1976 [11] as a telecommunications application and
became an established technique for attenuation monitoring
and fault location in optical fiber network within the
telecommunications industry [12]. OTDR is a well-known
means of testing an optical fiber cable assembly in optical
networks. The OTDR launches a very narrow pulse into the
fiber and then records the response of the cable/connector
assembly to this pulse. Both reflections and absorption can be
observed in the cable, providing the troubleshooter with the
information needed to diagnose cable problems [13].
The OTDR measurements can easily be transmitted into
computer for advanced OTDR analyzing via RS-232 (serial
port) connection, high-speed universal serial bus (USB)
interface, ActiveX, General Purpose Interface Bus (GPIB),
Ethernet Transmission Control Protocol/Internet Protocol
(TCP/IP) connection, and extended memory option (manually
transfer through floppy disk or USB memory) in a proprietary
encoding format such as .TRC (trace). The users can convert
the OTDR traces into text file or American Standard Code for
Information Interchange (ASCII) format for subsequent use
by spreadsheet software (e.g., Microsoft Excel or Lotus 1-23).
Downstream (1490/1550nm)
Central Office
(CO)
Feeder Region
Upstream (1310 nm)
Remote Node Drop Region
(RN)
Home
ONU
Faulty Fiber
OLT
Feeder Fiber
1 x N Passive
Optical Splitter
Drop Fiber
Downed branch
OTDR
ONU
ONU
Active branches
Fig. 1 Identify faulty fiber and localize failure location in FTTH by using OTDR upwardly from multiple ONUs at different customer
residential locations toward OLT at CO (in upstream direction)
Fig. 2 Monitoring issue with using OTDR in the downstream direction from CO towards customer residential locations [15].
Conventionally, OTDR is used to identify faulty fiber in
FTTH upwardly from multiple ONUs toward CO as shown in
International Scholarly and Scientific Research & Innovation 2(3) 2008
Fig. 1 (in upstream direction). OTDR is the most costly
among the optical fiber test gears, but it is most frequently
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International Science Index, Electrical and Computer Engineering Vol:2, No:3, 2008 waset.org/Publication/3862
World Academy of Science, Engineering and Technology
International Journal of Electrical and Computer Engineering
Vol:2, No:3, 2008
used for characterizing a long haul communication link.
According to Chomycz [14], OTDR testing is the best method
for determining the exact location of broken optical fibers in
an installed optical fiber cable. Whenever a fault occurs, a
technician is called to plug OTDR manually to the faulty fiber
to detect where the failure is located. A high intensity optical
pulse is launched into a fiber and a high speed optical detector
recorded and graphically displays the observed reflection in
the screen. The technician can observe losses due to splice,
break, connector, and other attenuation in an optical line by
looking at the visual representation on the OTDR's screen.
However, this approach would require much time and
effort. Moreover, OTDR can only display a measurement
result of a line in a time. Therefore, it becomes a hindrance to
detect a faulty fiber with a large number of subscribers and
large coverage area in the fiber plant by using an OTDR.
Besides, it is difficult to detect a failure in optical line
equipped with passive optical splitter by using a conventional
OTDR in the CO downwardly from CO (in downstream
direction). The optical splitter will make the identification of a
fiber fault beyond the splitter very difficult. The OTDR testing
signal from all the splitter ports is added into one trace in
downstream direction as summarized in Fig. 2. Therefore it
can become very complicated to localize the failure in the
correct split branch of tree-based structured optical access
network [15].
Some researchers had discussed about the monitoring issues
with OTDR and recommended a number of possible methods
to overcome these problems to achieve desired network
survivability such as Centralized Optical Monitoring using a
Raman-assisted OTDR (proposed by Yuksel [5]) or OTDRbased testing system using reference reflectors or fiber
selectors (proposed by Tomita [16]). The faulty fiber can be
monitored without affecting other in-service channels.
However, these methods need relatively expensive additional
sources or devices that impose high-maintenance cost. Since
the network service providers need to keep capital and
operational expenditures (CAPEX and OPEX) low in order to
be able to offer economical solutions for the customers.
Therefore, improving network reliability performance by
adding redundant components and systems have shortcomings
in terms of implementation cost and flexibility [8]. Also these
methods are complex and difficult to implement has
prohibited them as a practical solution [2].
III. CONCEPTUAL DESIGN OF SANTAD
To reduce the cost and enhance the benefit, we proposed a
centralized monitoring and self-protected system named
SANTAD, which is involved in the failure detection,
automatic recovery, and increases the survivability and
maintainability of FTTH after taking consideration into the
requirement for network monitoring capabilities, maintenance
and repairing cost, restoration time, expandability,
dependability, and redundancy. SANTAD is a centralized
access control and surveillance system that enhances the
International Scholarly and Scientific Research & Innovation 2(3) 2008
network service providers with a means of viewing traffic
flow and detecting any breakdown as well as other
circumstance which may require taking some appropriate
action with the GUI processing capabilities of MATLAB
software.
SANTAD consists the new upgraded values of recent
FTTH technology toward the implementation of smart
(intelligent) network. It can reduce the time needed to restore
the fault to maintain and operate the FTTH more efficiently.
SANTAD is potentially to improve the survivability and
increase the monitoring capabilities in FTTH and capable to
overcoming the upwardly or downwardly monitoring issues
with OTDR. It has the same features of the OTDR and
computer-based emulation software for performing more
OTDR trace processing functions but with more additional
features and flexible to use in optical communication link
especially in FTTH.
A.
Measurement System Configuration
To locate a fiber fault without affecting the services
transmission to other subscribers, it is essential to use a
wavelength different from the triple-play services signals for
failure detection [17]. As illustrates in Fig. 3, a commercially
available OTDR with a 1625 nm laser source is used in failure
detection control and in-service troubleshooting in the
proposed scheme without affecting the triple-play services
transmission. OTDR is the instrument that used to measure the
fiber attenuation, locate fault, measure losses, and fiber
uniformity or the attenuation coefficient throughout the
installed fiber length.
The triple-play signals (1310 nm, 1490 nm, and 1550 nm)
are multiplexed with a testing signal (1625 nm) from OTDR.
When four kinds of signals are distributed, the testing signal
will be split up by the wavelength selective coupler (WSC) or
wavelength division multiplexing (WDM) coupler, which is
installed before the splitter. The WSC only allow the 1625 nm
testing signal to enter into the taper circuit and reject all
unwanted signals (1310 nm, 1490 nm and 1550 nm) that
contaminate the OTDR measurement. The downstream signal
will go through the WSC, which in turn connected to the
optical splitter before it reaches the multiple ONUs at different
residential location. On the other hand, the testing signal
which is demultiplexed by WSC will be split up again in
power ratio 99:1 by using directional coupler (DC) to activate
the microprocessor system. The 99% 1625 nm signal will then
be configured by using optical splitter which each output is
connected to single line of ONU. The operational of optical
switch is controlled by microprocessor system that is activated
by 1% of 1625 nm testing signal.
The OTDR is installed with OLT and connected to a
PC/laptop to display the troubleshooting results in a
proprietary encoding format with remotely controlled by
Ethernet Transmission Control Protocol/Internet Protocol
(TCP/IP) with Standard Commands for Programmable
Instruments (SCPI) commands for data archiving (Most of the
recent version OTDR are available with remote control
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World Academy of Science, Engineering and Technology
International Journal of Electrical and Computer Engineering
Vol:2, No:3, 2008
International Science Index, Electrical and Computer Engineering Vol:2, No:3, 2008 waset.org/Publication/3862
capabilities). The OTDR also can be remotely controlled
through GPIB with GPIB PC card (either built-in or external)
and the appropriate drivers to measure the optical fiber and
troubleshoot the optical access network.
SANTAD is interfaced with the OTDR to accumulate every
network testing result to be displayed on a single computer
screen for advanced OTDR analyzing. The analysis results
will be sent to field engineers or network service providers
through the mobile phone or Wi-Fi/Internet computer using
wireless technology for repairing and maintenance operation.
Any failure/breakdown occurs in the network will be diverted
to the protection (stand-by) line to ensure the traffic flow
continuously. The whole operation process can be simplified
in the flow chart as depicts in Fig 4. With the method
described in this paper, no any expensive additional
equipments or devices are required.
B.
The Network Testbed
Our technique has been tested on an optical access network
composed by 30 km fiber. The feeder fiber and drop fiber are
15 km long. The testbed network was set-up to serve as a
platform to study the mechanisms and characteristics of
optical signal in working (good/ideal) condition and nonworking (failure/breakdown) condition. We conducted two
experiments through the network testbed mainly focusing on
the identifying the faulty fiber and locating the failure location
in a failure link. As a first step, no default was introduced in
the network and OTDR measurements were performed.
During the experiment, the optical fiber is not connected to
any device at another end (unplugging) to represent the break
point in a testing line. It visualized the actual break point of an
optical line at that distance in a real condition.
Fig. 3 Centralized monitoring and self-protected against fiber fault in FTTH using SANTAD in the downstream direction
Start
Network
testing &
analysis
End
System
monitoring
Failure
detection
Option 1
Restoration
activation
Return to
normal
operation
Option 2
Information
delivery
Repair
Repeat
Fig. 4 The process flow for failure detection and restoration in SANTAD
After that, the OTDR measurement results for each line are
transferred into PC. The communication between OTDR and
PC was done over Ethernet connectivity. As a remark,
previously we are using RS-232 (serial port) connection for
data archiving. Transferring data between OTDR and PC
requires serial ports on both units and RS-232 serial cable
International Scholarly and Scientific Research & Innovation 2(3) 2008
(null modem cable) is required to establish connection
between OTDR and PC. However, some of the more recent
PCs are not equipped with such ports (Serial port and parallel
port) [18]. The instruments and measurement equipments used
in the experiment are summarized in Fig. 3 with the help of
schematic diagram.
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IV. EXECUTION DISPLAY FOR SANTAD
The developed program not only enables one to monitor the
system’s status and detect any failure in FTTH downwardly
from CO (in downstream direction), but also to determine
deployment, connection, and losses (connection losses, splice
losses, optical device losses, fiber losses or attenuation) in the
network system. The developed program also provides the
network service providers with a control function to intercom
all subscribers with CO. The mechanism of SANTAD
detection is illustrates in Fig. 5.
The functionalities of SANTAD can be generally be
classified into: (i) Network system configuration management,
(ii) Degradation management, and (iii) Fiber fault
management. SANTAD can help network services providers
and field engineers in FTTH network system to perform the
following the following activities:
x Network system configuration management - provides the
network service providers with a control function to
intercom all subscribers with CO.
x Degradation management - in order to keep the system
running and detect degradations before a fiber fault occurs
for preventive maintenance.
x Fiber fault management - detects any fiber fault that occurs
in the network system and troubleshoots it for post-fault
maintenance.
Degradation management tries to prevent fiber fault from
occurring. Although this is not always possible, however some
types of failure can be predicted and prevented. Even with
fiber fault prevention mechanisms, failures will still occur, so
fiber fault detection techniques need to test each optical line in
order to detect potential faults and precisely localize the exact
failure location. With detected alarms, fiber fault identification
processes will diagnose and determine the real causes.
Appropriate recovery actions are taken to treats the link and
fiber fault. In combination of the distinctive management
operations, the network service providers and field engineers
can centralize monitoring, testing, analyzing, configuring, and
troubleshooting the FTTH network system more efficiency to
provide the predefined quality of services (QoS) for customer
premises/subscribers.
Fig. 6 and 7 showed the ability of SANTAD to specify a
faulty fiber and failure location among a number of optical
fiber lines in FTTH by measuring the optical signal level and
losses. Every eight network testing results will be displayed in
Line’s Status window for centralized monitoring (in a single
computer screen), where the distance (km) represented on the
x-axis and optical signal level (dB) represented on the y-axis.
SANTAD used event identification method respectively
analyzes and identifies any faulty fiber and failure location
that occurs in FTTH. A failure message “Line x FAILURE at z
km from CO!” will be displayed to inform the field engineers
if it detect any fiber fault in the network system.
To obtain further details on the performance of specific line
in FTTH, every measurement results obtained from the
network testing are analysis in the Line’s Detail window. The
International Scholarly and Scientific Research & Innovation 2(3) 2008
developed program is able to identify and present the
parameters of each optical fiber line such as the line's status
(either in working or non-working condition), magnitude of
decreasing as well as the location, failure location, and other
details as shown in the OTDR's screen. The advantage of this
feature compare to the OTDR and computer-based emulation
software is SANTAD displayed every status for the tested line
in the Line’s Detail window.
A “Good condition” or “Decreasing y dB at z km” message
display at the line's status panel in a working condition (see
Fig. 8 and 9). However in the non-working condition, a failure
message “Line x FAILURE at z km from CO!” displayed to
show the exact failure location in the network system as
illustrated in Fig. 10 and 11. It is flexible and easily
Fig. 5 Flow chart for mechanism of SANTAD detection
to use for those who are inexperience in the optical fiber
testing by just reading the information gain from the
messages.
Once any fiber fault in the primary entity is detected, it will
automatically send the failure status to the field engineers
through the mobile phone or Wi-Fi/Internet computer using
wireless technology. The field engineers can determine
sharply the break point just connect a laptop or personnel
digital assistant (PDA) to a OTDR-based testing system
through Ethernet connection without making a site visit before
taking some appropriate actions, such as repairing or
maintenance operation. Meanwhile, the field engineer will
activate the restoration scheme to switch the traffic (service
delivery) from the failure (primary) line to the protection line
to ensure the traffic flow continuously.
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present or future field engineers or technicians solve a
similar problem.
x The frequency of the same kind of failure is an indication of
a major problem in the system. If a fault happens frequently
in one fiber/device/component at the same location (same
point), it should be replaced with a similar one, or the whole
network system should be changed to avoid the use of that
type of fiber/device/component.
x The statistic is helpful to another parts of network
management [18].
International Science Index, Electrical and Computer Engineering Vol:2, No:3, 2008 waset.org/Publication/3862
Fig. 6 Every eight measurement results are displayed on the Line’s
Status window
Fig. 7 A failure message displays to show the faulty line and failure
location in the FTTH network system
Fig. 8 An example of working line in the Line’s Detail window for
single event
Fig. 9 Another example of working line in the Line’s Detail window
for two events
Fig. 10 An example of failure line in the Line’s Detail window for
single event
This functionality alerts the service providers and field
engineers of a fiber fault before it is reported by the customer
premises or subscribers. After the restoration/maintenance
process, the traffic will be switched back to the normal
operation. The detail of the fiber fault must be documentation.
The record shows the faulty fiber, exact failure location,
possible cause (i.e. construction is conducted in the nearby
areas), action taken, cost, and time it took for each step. The
documentation is extremely important for several reasons:
x The problem may recur. Documentation can help the
International Scholarly and Scientific Research & Innovation 2(3) 2008
Fig. 11 Another example of failure line in the Line’s Detail window
for two events
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World Academy of Science, Engineering and Technology
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V. CONCLUSION
In this paper, we successfully bring up a new approach for
monitoring and controlling the FTTH network system to
ensure that it is running as efficiency as possible with
SANTAD using Operation, Administration, and Maintenance
(OAM) features. Service reliability must be considered
because a failure of broadband services may result in large
data loss for subscribers as well as tremendous financial loss
for network service providers. It is important to keep the
system running and detect degradations before a fiber fault
occurs for preventive maintenance. Although this is not
always possible, however some types of failure can be
predicted and prevented. Any failure should be localized
without affecting the service delivery and troubleshoot in a
short period to minimize the losses. It is a convenient and
cost-effective way to improve the service reliability of FTTH
and reduce the restoration time and maintenance cost with
SANTAD.
ACKNOWLEDGMENT
The authors are grateful to the Photonic Technology
Laboratory,
Institute
of
Micro
Engineering
and
Nanoelectronic (IMEN), Universiti Kebangsaan Malaysia
(UKM), Malaysia, for providing the facilities to carry out the
experiments.
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Mohammad Syuhaimi Ab-Rahman received the
B.Eng., M.Sc. and PhD degrees in Electrical,
Electronics and Systems Engineering from
Universiti Kebangsaan Malaysia (UKM), Malaysia,
in 2000, 2003, 2007 respectively.
He joined the Institute of Micro Engineering
and Nanoelectronics (IMEN) in 2003. He is
currently a senior lecturer in UKM, Malaysia. He is
also an associated research fellow of IMEN since
2006. His current research interests are in the area
of photonic networks and optical communication technologies such as optical
security nodes, device fabrication, photonic crystal, laser technology, active
night vision, plastic optical fiber, fiber to the home, fiber in automotive and
optical code-division multiplexing (OCDM). The current and interest project
is development of survivability and smart network system for customer access
network then can be called as an intelligent FTTH (i-FTTH), collaborated with
Ministry of Science, Technology and Innovation (MOSTI) of the Government
of Malaysia.
Boonchuan Ng graduated from UKM with a
B.Eng. in Computer and Communication
Engineering in 2008. In July 2008, he joined as a
researcher in the Computer and Network Security
Research Group, UKM. Currently, he is doing a
M.Sc. degree in Electrical, Electronics and Systems
Engineering at the Faculty of Engineering and Built
Environment, UKM. His current research interests
are in the area of optical communication and optical
access network.
Kasmiran Jumari is a professor in the Department
of Electrical, Electronics and Systems Engineering,
UKM. He received the B.Sc. and M.Sc. in Physics
and Instrument Design from UKM and University
of Aberdeen in 1976 and 1978, respectively. In
1985, he holds a PhD degree in Electronics from
University of Kent.
His research is in the area of security system,
intrusion detection system, signal processing,
image processing and computer communications
networks. Currently, he is also hold a position as
an associate research fellow of Institute of Space Science (ANGKASA).
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