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Integrated Fault Management System in PON: Research Challenges, Development and Future Issues:

Wider deployment of fiber in the last mile is driven by increased customer needs for high capacity

communication. This deployment requires solutions that reduce the operators OPEX. Passive optical

network (PON) is being considered as one of the best candidate for next-generation optical access

solutions. It is a fast emerging architecture that uses only passive components between the customer

and the central office. PON carries vast amount of bandwidth in the near future, thus issues relating totheir protection and maintenance are becoming more crucial. Yet the need of a cost-efficient fully

reliable and accurate monitoring solution supporting fault detection, identification, and localization in

different fiber access topologies will be a key part of those solutions. Moreover, PON operators need a

monitoring system for the physical layer to guarantee high service quality. This monitoring system is

necessary during the fiber installation, final network installation testing, regular operation of the

network, and for fault localization. To achieve this, a certain path redundancy should be added to a PON

by providing several alternative, diversely routed paths. Dissimilar access network environments may

require different protection schemes. Redundancy may be added to an entire PONs topology, or to only

a part of the PON. The International Telecommunication Union - Telecommunication Standardization

Sector (ITU-T) G.983.1 described a set of to two protection schemes, which are type B and type C

protection. This has two important consequences. First, the physical PON infrastructure is not entirelyvisible to the network management system (NMS) for fault management operations. Second, failures

within the fiber plant are likely to entail service disruption before being detected, leading to revenue

losses and customer dissatisfaction. In addition to those protection schemes, due to the high capital

expenditures incurred by the deployment of such protection, operators have resorted to

troubleshooting and restoration once faults are detected. Troubleshooting is an important network

maintenance function that involves locating and identifying any source of fault in the network. The

above-mentioned ITU-T protection configurations make no specific provisions to identify and localize

faults within the optical infrastructure and defer the task to maintenance standards (L series). ITU-T L.53

(2003) is the first standard to specifically address the maintenance of PONs by recommending the use of

optical time-domain reflectometry (OTDR)-based techniques for troubleshooting. However, a new

challenge has been appeared in PON networks. The network now becomes a point-to-multipoint (P2MP)

with passive optical splitter placed in the field. This network architecture introduces a new challenge for

network testing which requires enhanced test and measurement techniques. In addition, these

techniques must be capable of measuring the performance of a single bidirectional ber link that carries

three wavelengths simultaneously. Most of the monitoring techniques which are reliable and cost-

effective misses the fault localization feature which is a very important task for any monitoring

technique. This missed feature leads us to divide the monitoring procedure into two main steps. The

first step is fault detection to determine the faulty branch among the different branches in PON. This

should be achieved by using a reliable, cost-effective techniques. The second step is accomplished by

dispatching technicians to the faulty branch in the field and injecting an OTDR signal to exactly

determine the location of the fault. However, dispatching technicians increases the OpEx of the

network. Designing a centralized monitoring technique with full capability, i.e. a technique that

performs fault detection and localization from the CO without need for dispatching technicians is still anopen issue for further research. Therefore, there is a growing need for the monitoring of the PON fiber

plant. PON monitoring technology automatically identifies and localizes faults of the in-service PON

optical infrastructure. In doing so, it provides the NMS with enhanced optical infrastructure visibility in

real time, thus speeding up the detection and localization of faults. Monitoring avoids the operational

expenditures (OPEX) and large service restoration times of offline troubleshooting, thus enabling wider

service differentiation and stronger QoS guarantees. In addition, it paves the way to potentially

enhanced physical layer protection mechanisms. Furthermore, to operate in-service, the desired

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monitoring technology should act transparently to the data band signals such as the L and C bands.

Lastly, the protection schemes also should target higher performance, lower cost or scalability to the

next generation PON architecture (e.g., higher split ratio > 128 and beyond), including WDM, TDM over

WDM and LR-PON which intended to extend the reach from 20 up to 100 km distances and beyond.

Consequently, the monitoring technology requires simple design, fabrication, and implementation

procedures to minimize the cost.

The lack of a centralized, comprehensive, efficient and inexpensive solution for the PON fault

management still present many challenges and requirements for the physical layer monitoring system.

Possible Issues:

1. Architecture or technique that performs fault detection and localization from the CO without needfor dispatching technicians, thus increasing the QoS guarantees.

2. In-service monitoring technology that is performing monitoring without affecting the data bandsignals.

3. Centralized fault monitoring and restoration architectures or techniques that support NG-PONarchitecture such as: TDM-PON, WDM-PON and hybrid over WDM-PON.

4. The integration of physical layer with other surveillance functions in the higher layer protocols toproduce an efficient and complete monitoring system.