Troubleshooting a faulty passive optical point-to-multipoint network (PON) can be more complex than a point-to-point network. This application note looks at the use of non-intrusive or active fiber testing for troubleshooting PON networks.
Point-to-Point FTTx Network
Point-to-Point FTTx Network
When a failure occurs on a point-to-point FTTx network, the network completely shuts down. It is then easy to disconnect the fiber without further affecting the customer issue.
Point-to-Multipoint FTTH Network (PON) Topology
Troubleshooting a point-to-multipoint fiber-to-the-home (FTTH) network (also defined as a PON net-work) differs significantly.
The International Telecommunications Union (ITU-T) and Institute of Electrical and Electronic Engineers (IEEE) have created several standards for optical access systems based on PON architecture (G.982, G.983 or G.984 for ITU and 802.3ah or 802.3av for IEEE). As Figure 2 shows, a PON network consists of one optical line terminal (OLT) connected via a splitter to multiple optical network terminals (ONTs) (one for each subscriber, up to 64 subscribers). Sometimes, a second splitter can be connected in cascade to the first splitter (as Figure 3 shows) to dispatch services to buildings or residential areas.
Using the network monitoring system at the Network Operation Center (NOC), operators can easily determine which subscribers are affected. They can also identify possible fault elements such as how many customers are affected and whether the PON is cascaded.
The cases below describe each possible scenario:
PON Case 1: Simple PON - Only One Customer is Affected
When only one subscriber cannot receive service, three potential faults are probable, see Figure 4:
‒ Fault in the distribution fiber between the customer and the closest splitter
‒ Fault in the ONT equipment
‒ Fault in the customer’s home wiring
PON Case 2: Cascaded PON and all Affected Customers are Connected to the Same Splitter
When all customers connected to the same splitter cannot receive service, but others connected to the same OLT can, the cause may be because of one of the following (see Figure 5):
When all customers connected to the same splitter cannot receive service, but others connected to the same OLT can, the cause may be because of one of the following (see Figure 5):
‒ Fault at the last splitter
‒ Fault in the fiber link between the cascaded splitters
PON Case 3: All Customers are Affected (at the OLT level)
Whether or not the PON is cascaded, all customers dependant on the same OLT may be affected. If all cus-tomers are affected, the cause may be from of the following:
‒ Fault in the splitter closest to the OLT
‒ Fault in the feeder fiber/cable of the fiber network
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