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Engineering Installation Works on FTTH-PON Laboratory Test Bed: Case Study

M.S. Ab-Rahman, B.C. Ng, R. Kasimin and K. Jumari
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This study introduces a low cost technique for testing and monitoring process that can be applied specifically for Fiber-to-the-Home Passive Optical Network (FTTH-PON). The simplest and low cost method would be using a Optical Power Meter (OPM) which is able to detect the total loss on the network. However, to identify faulty sections of a network, segmentation need to be done together with the optical power meter. Another testing and troubleshooting method would be using the Optical Time-Domain Reflectometer (OTDR). The OTDR within the network is able to detect the component that causes losses in the network. However, elements acting as a power splitter are not being able to be detected by the OTDR. Therefore, the Access Control System (ACS) is developed to bypass those elements and allows the use of OTDR entirely. This method is proven to be a faster method than the first. Additionally, it can be upgraded to monitor the line status by accumulate all the result in one display computer screen. But this mechanism is not interested to be discussed detail in this study. The new configuration of FTTH is named as modified FTTH. In the end, we compare the installation cost between the conventional and modified FTTH for different network size according to number of users.

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M.S. Ab-Rahman, B.C. Ng, R. Kasimin and K. Jumari, 2010. Engineering Installation Works on FTTH-PON Laboratory Test Bed: Case Study. Journal of Applied Sciences, 10: 29-36.

DOI: 10.3923/jas.2010.29.36



High Speed BroadBand (HSSB) deployments are frequently justified primarily by today’s applications rather than anticipated demands. For instant, streaming video content is considered by many as the ultimate bandwidth-hungry application. When one adds the bandwidth requirements of one High Definition Television (HDTV) stream, a few standard-definition streams and internet browsing, it may seem that 20-30 Mbps of bandwidth is sufficient in the long term. But historical data and projections indicate exponential long-term growth in bandwidth demand. Indeed, some service providers are already offering 1 Gbps access to residential customers today by means of GEPON and GPON and there are substantial deployments of 100 Mbps networks in some European countries. Even though the current bandwidth can be accommodated by the VDSL technology but the system is limited by the transmission distance which is less than 2 km and the rate is bounded by 100 Mbps only. Therefore, the VDSL technology is seemly not a future proof solution (Cisco, 2007). These huge bit rates can only be provided via FTTH technology. Fiber-to-the-Home (FTTH) technology provides residences with high-speed broadband access to digital services and the internet. The FTTH networks have now established their economic competitiveness by providing significantly reduced operating expenses and enhanced revenue opportunities for carriers. With the offer of novel high-bandwidth services such as triple play (voice, video and data transmission on the same platform) and high-definition video, a new market situation is rapidly emerging. For the first time, there exists a possibility to connect customers to these services at the required speed and at a fair cost. This represents a strong driving force for the further deployment of standard Passive Optical Networks (PONs) and the design of next-generation access technology (Kazmierski, 2008). It has long been thought that fiber’s very significant bandwidth would open the way to new applications by the consumer, but it is only recently with the advent of the Internet and the expansion of copper based broadband that this vision may become reality. Copper speed has the limitation but there is no limitation found in optical fiber. Projected data, video mail and downloads will soon provide huge benefits to businesses and residents, if they are fiber-connected.

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Fig. 1: PON architecture which consist of three main elements; OLT, optical splitter and ONU. The survivability and scalability scheme is not been recommended yet

The next generations of FTTH will be 4-100 times faster to keep pace with video driven bandwidth demands. The current transmission rate at commercialization point is 2.5 Gbps but in laboratory research the speed has already achieved 10 Gbps and it’s ready to be commercialized in market in near future (Kazmierski, 2008). With the advantages, the home business are feasible to be developed and this with reduce the risk or traffic congestion, office space consumption and also cost and time misspending. Super connectivity from home to office will give opportunity to the housewives to start their own business from home.

The PON is a Point-to-Multipoint (P2MP) fiber optical network with no active elements in the signal’s path. The signal transmission in a PON is performed between an Optical Line Terminal (OLT) installed in a Central Office (CO) or remote terminal and an Optical Network Unit (ONU) placed at the customer residence or in a building. OLT is active equipment that corresponds to the demarcation point between the access network and the metro backhaul network (Kim, 2003). The architecture of FTTH-PON is shown in Fig. 1. The optical splitter is the passive component which is used to distribute the application to all premises. The number of ONU in the network is associated with the size of optical passive splitter available (number of output port). Traffic from an OLT to multiple ONUs is called downstream (P2MP) and traffic from an ONU to OLT is called upstream (multipoint-to-point, MP2P). Two wavelengths are used: typically 1310 nm for the upstream transmission and 1490 nm for the downstream transmission. The video signal is sent downstream by using 1550 nm wavelength. In the downstream direction (OLT to ONUs), the signals are broadcasted by the OLT and extracted by their destination ONUs based on their Media Access Control (MAC) address (Mukherjee, 2006). In the upstream direction (ONUs to OLT), each ONU will use a time shared channel (TDM) arbitrated by the OLT. Since, the PON connectivity in a FTTH-PON 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 (Ab-Rahman et al., 2009a).

The upstream signal from multiple ONUs at different residential locations to OLT and CO or the downstream signal from OLT to multiple ONUs after the break point will become unreachable if the fault occurs in the drop region. However, if the fault occurs in an individual subscriber’s infrastructure such drop fiber or ONU, since the signals from OLT are successfully shared among other subscriber’s ONUs via a passive optical splitter, thus only one subscriber’s service is affected. From the analysis of the existing FTTH-PON network, some significant features cannot be found. For instance, the survivability scheme still unidentified and various proposals have been come out but the emphasizing is more on the feeder region and availability to handle the dysfunctional OLT (Ping et al., 2004). The schemes proposed to overcome failure occurs in the distribution are too little been discussed. Some research proposed the bridge to share the signal among the users in failure area but (Hwang et al., 2009) but before activate the restoration scheme needs the fast and efficient monitoring system. The faults identification and locator had implemented upwardly where the OTDR signal was injected from ONUs separately (EXFO, 2008). Although, the technique is efficient but it leads to the time and cost misspend.


We have proposed the restoration architecture that can be applied in FTTH-PON, especially in the drop region (from optical splitter to ONUs). Any failure occurs in this region will be sensed by Access Control System (ACS) by the 3% tapped signal that is connected to every access line. The activation signal is then sent to active the dedicated protection scheme. But if fault is still not restored, the shared protection scheme will be activated. The monitoring signal section is responsible for sensing fault and its location whereas generation of activation of signal is sent by activation section in ACS. The ACS is focusing on providing survivability through the Restoration Scheme Architecture (RSA) against failure by means of dedicated and shared protection that is applied in PON. The device used for the protection switching is Customer Access Protection Unit (CAPU). The ACS is used to monitor the status of the working and restoration fibers. The ACS recognized the types of failure and sent the activation signal to the related CAPU according to the activated protection mechanisms.

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Fig. 2: Schematic diagram of the monitoring system for FTTH-PON (a) SANTAD and ACS is used to increase the efficiency of monitoring and troubleshooting. (b) Once the OTDR Test signal bypasses the optical splitter, the status of FTTH-PON is able to be monitored centrally (Ab-Rahman et al., 2009c)

In our proposed system, we designed the RSA that enable to configure the faults until fourth order means the failures can occur at four communication lines but the signal can still be transmit to the users. This was explained detail in (Ab-Rahman et al., 2009b). For easier maintenance, we introduce Passive In-line Monitoring (PIM) device to define the fault specifically in which the device is installed along the line connected between Optical splitter and ONU.

In this study, we shared an experience in installing, testing and troubleshooting the network by using low cost equipment which are standard type power meter, OTDR and our own developed centralized monitoring program to monitor the status of each line connected to ONU onto one display screen (computer). The testing process is towards to the installation of Centralized Fiber Troubleshooting System (CFTS) (Ab-Rahman et al., 2009c, d). Our proposed centralized monitoring technique is the first reported up to this time. CFDS is then namely as Smart Access Network _Testing, Analysis and Database (SANTAD) for the commercialization strategy.

The proposed system architecture is shown in Fig. 2a. The proposed system is associated with optical monitoring, data analyzing, remotely controlling, failure detection, protection switching and automatic recovery apparatus. The CFDS installed in the network to divert the OTDR testing signal 1625 nm to bypass the Optical Splitter (OS) therefore the line status can be monitored by using OTDR. The ACS is the microcontroller based system that has been designed to handle the centralized line detection. The routing mechanism is shown in Fig. 2b. The ACS is function to divert the OTDR test signal to each line connected to the ONU. As a result, the monitoring graph can be observed at the static point where the OTDR injecting the signal (Ab-Rahman and Premadi, 2008). The communication system between CO and ACS is done via the copper-based LAN network to enable the controlled switch in ACS can be handled manually or automatically. The web-based is designed to interface the system to the user operator (Hassan et al., 2009).


The FTTH-PON network test bed at the Networking System Laboratory in Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia (UKM), Malaysia, was chosen to conduct our investigation as depicted in Fig. 3. Both fiber link between the OLT and optical splitter and optical splitter and each ONU were about 10 km. In normal operation, both upstream and downstream signals traveled through a transmission distance of 20 km from OLT towards each ONU.

The optical signal level is measured by using one unit of FOT-600 Optical Loss Test Set manufactured by EXFO Electro-Optical Engineering Inc., one is designated as 1310/1550 nm light source, while the other one reserved as power meter for studying the parameters of loss as shown in Fig. 4. The laser source is emitting and passing the conventional network (do not pass through the taper circuit). Using OPM, 1550 nm wavelength is injected at the center office (downstream test) and 1310 nm wavelength is injected at the ONU (upstream test). The values of the optical signal level at the respective points are listed in Table 1 and 2. The optical power for 1550 nm wavelength much lower as compared to 1310 nm because it is more sensitive to the bending of optical fiber lines in the network system.

Using point-to-point measurement, we observed maximum loss occurs in line 2 and further inspection had identified that terrible leakage happened in the WSC device. To combat the problem, the device has to be replaced.

Analysis: The further analysis to identify the components failure is by using the segmentation. Line 2 is divided into few partitions and the troubleshooting process is implemented part by part. Our observation using the quantitative method has found the loss contribution is due to the Wavelength Selective Component (WSC or WDM coupler) that has high insertion loss. Three units of WSC that is cascaded together to enable the OTDR signal been injected from the CO. The leakage occurs in this devices has increase the dynamic range. Further investigation shows each device has loss about 10 dB and line 1, line 3 and line 4 has one unit of WSC except 3 units in line 2. Therefore, the exact loss for each line is approximately 24 to 28 dB. Replacing the failure component will improve the system performance.

Table 1: Measurement results of optical signal level from CO using 1550 nm light source
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*Loss is found bigger at line 2

Table 2: Measurement results of optical signal level from customer sides using 1310 nm light source
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*Loss is found bigger at line 2

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Fig. 3: FTTH-PON network test bed in UKM

The next step is testing the network using OTDR which represents a simple and faster technique to identify the fault location. To enable the operation can be done downwardly, we introduce a new equipment named as Access Control System (ACS) to bypass the OTDR signal across the optical splitter.


After the connectivity of lines is already performed, the next step is the line troubleshooting utilizing OTDR. Our new network configuration (embedded with ACS) has enable the process could be perform downwardly and stationed/centralized at OLT. FTB-400 Universal Test System manufactured by EXFO Electro-Optical Engineering Inc used as an OTDR to investigate the network system. The 1625 nm light source is selected to test the network system in downstream direction, from CO towards ONUs using the injection point same as 1550 nm laser source as shown in Fig. 4. The laser source is entered into the taper circuit and bypassing the optical splitter in the conventional network. The waveform and event table for the network testing four lines connected to ONU are presented in Fig. 5-8. Here, the loss of every component, fiber joins and the span can be defined.

Analysis: The high loss at point 2 at line 1 (Fig. 5) and line 2 (Fig. 6) is caused by the leakage that is introduced by the WSC. Our customized specification of WSC is the main element in which any leakage occurs in the device will fail the testing process. The OTDR test result obtained has support the point-to-point test by suing the optical power meter but with OTDR the specific attenuation occurs in the line can be defined specifically. Figure 7 and 8 show, respectively the OTDR output display after the components have been replaced for line 3 and line 4.

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Fig. 4: Experimental setup for measuring the optical signal level using one unit of FOT-600

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Fig. 5:

The network testing results for line 1 for the OTDR trace of downwardly testing in the proposed system architecture and the event table for OTDR trace

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Fig. 6:

The network testing results for line 2 for the OTDR trace of downwardly testing in the proposed system architecture and the event table for OTDR trace

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Fig. 7:

The network testing results for line 3 for the OTDR trace of downwardly testing in the proposed system architecture and the event table for OTDR trace

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Fig. 8:

The network testing results for line 4 for the OTDR trace of downwardly testing in the proposed system architecture and the event table for OTDR trace


Our modified FTTH has tremendously offers high and effective solution for customer premises and bandwidth demand by introducing prototypes to increase the system performance such as SANTAD, ACS, PIM and CAPU. These equipments offer low cost and simple installation. The SANTAD offers fast monitoring and failure detection on one screen display. Any failure/breakdown occurs in the network will be restored by switching the traffic to protection line while the status of the failure will be sent automatically to field engineer for repairing and maintenance operation. The failure status will be determined by SANTAD while the restoration scheme will be activate by ACS and CAPU is the routing device to handling the switching function. The information will be sent to field engineer and PIM is used to determine sharply the point of failure before it is been repaired. Besides that, the specified line test is also applicable to be activated by field engineer. This section calculates the cost budget between ordinary FTTH and modified FTTH and according to the network sizes. The cost for each upgraded devices are also included and this can be observed detail in Fig. 9. Figure 10 shows the cost comparison between ordinary FTTH, total improvement and modified FTTH according to the network size.

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Fig. 9: Bar chart shows the cost comparison for different splitting ration which is 1:8, 1:16, 1:32 and 1:64 for conventional FTTH and modified FTTH include the support elements such as SANTAD, ACS, CAPU

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Fig. 10: Bar chart shows the cost comparison for conventional FTTH, total support elements and modified FTTH according to the splitting ratio which are 1:8, 1:16, 1:32 and 1:64

The cost is in Ringgit Malaysia (RM) which is equivalent to USD (1/3.80). Although, modified FTTH is much higher and obviously for the big size network but the features offer by modified FTTH is exclusive. The status of all the time can be monitored and ready to be restored is breakdown or something faulty happens in the line.


Testing and troubleshooting an FTTH-PON network can be done either by using an optical power meter or by OTDR. While using the OPM can be proved simplest, this device only allows measurement on the loss of the entire network only, unless segmentation is done. By using OTDR, on the other hand, proves to be a faster and better method than the OPM. Even though elements acting as a power splitter cannot be detected by the OTDR, but through the use of ACS, it allows the use of OTDR in troubleshooting a FTTH network downwardly. Our proposal is expected the increase the efficient of monitoring scheme that previously used upwardly and from one ONU to the other ONU. Even though our modified FTTH has high cost installation as compare to the conventional FTTH, but the safety and survivability issue have already been solved efficiently. Our solution is the first reported up to the current time.


This research work was supported by the Ministry of Science, Technology and Innovation (MOSTI), Government of Malaysia, through the National Science Fund (e-Science) 01-01-02-SF0493 and University Research Support Grant UKM-GUP-TMK-108.

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