Signal Quality and Performance Monitoring in FTTX Networks
The global broadband market is shifting towards fiber-optic technologies, with a subscriber growth rate in Europe of 28% from 2021-2023 [1]. FTTX networks are a generalization for different configurations of fiber deployment. Fiber can be deployed all the way to the premises (FTTB – Fiber to the Building, FTTH – Fiber to the Home), where Ethernet or coaxial cables are used for the final connection. Alternatively, fiber can reach a central node, while the final connection relies on copper lines (FTTN – Fiber to the Node, FTTC – Fiber to the Cabinet).
Challenges in FTTX Networks
There are multiple challenges that the operators face when deploying the FTTX networks:
Signal Quality and Performance,
Network Security and Reliability
Scalability and Compatibility
To ensure that the network offers a satisfactory level of signal quality and performance, the network needs to be monitored. One possible approach is by using the well-defined protocols, supported by the Optical Line Terminals (OLTs) and Optical Network Terminals (ONTs). This approach does not include any additional elements in the network, such as probes, and it will be the focus of this blog.
Network security is a very important topic in every communication network, and special attention needs to be paid to protecting against eavesdropping, spoofing, and unauthorized access. To ensure reliability, it is very important to contain mechanisms to efficiently detect and resolve network issues, and also mitigate the impact of temperature, humidity, and physical damage on the infrastructure.
Related to scalability and compatibility, the network should be upgradable to higher capacity to meet the possible growing demand. Interoperability needs to be ensured as well to enable seamless operation between different vendors.
Signal Quality and Performance
Signal Quality and Performance Monitoring mainly relates to ensuring a suitable power level set for the expected fiber length and split ratios, and that there are no signal strength reductions in the network. Unexpected signal quality and performance values might be an indication of connector loss (poor or dirty fiber connectors), splicing loss (misalignments in fiber splices), and physical bends or micro-bends in the fiber. The introduction of a larger number of splitters can introduce additional loss as well.
Relevant KPIs
Detection of unexpected changes can be done by monitoring Receive and Transmit Power levels on ONTs and OLTs and comparing them. Both transmit and receive power values are available from ONTs and OLTs via SNMP or TR069/TR369 protocols. While deploying the network or updating hardware or software, these values are always configured and adjusted. Because of aging and degradation of laser diodes or possible inconsistencies in manufacturing, it is necessary to monitor these values over time.
Additional KPIs
To be able to estimate the overall health of the ONTs, we introduced a specific KPI that can be correlated to the customer's Quality of Experience (QoE). The Network Health Index is a numerical value that is primarily determined by the relationship between the aforementioned receive and transmit power levels.
Network Health Index, with some additional KPIs, is shown in the Customer Support Portal (CSP) per single CPE. Network Health shows the general status of the ONT and takes into account if the packets are discarded, and if there are some losses in optical power transmission. Additional KPIs include Optical Intermittence, a valuable parameter that refers to irregular, sporadic interruptions or fluctuations in an optical signal transmitted over a fiber optic network. In such cases, the light signal, instead of maintaining a stable and continuous flow, experiences brief drops or interruptions in intensity. As a result, this can cause packet loss, jitter, and increased latency, and consequently degrade performance and interrupt services that require stable, continuous data flow (e.g., VoIP and video).
Network Health Index equation takes into account the parameters that are shown in the following table. The calculation is executed every time the parameters are received from the CPE.
For each parameter, the weight is calculated based on the following table. In the end, Health is calculated in a way that the sum of weights for each parameter is divided by the sum of total weights for each parameter considered good.
AXTRACT FTTX Bundle
Network Health Index is a part of Axiros AXTRACT FTTX Bundle, which enables monitoring of the most important parameters of ONTs and OLTs. Apart from the Customer Support Portal (CSP) with information about single ONTs, it also provides additional dashboards for showing the status of the whole fleet of OLTs, and additional information per OLTs, line cards, and Passive Optical Network (PON) ports. This solution provides a valuable insight into the FTTX access network.
Written by Pavle Skocir, PhD
Pavle Skocir is working in Axiros as a Technical Account Manager. He is an IoT enthusiast and has previously worked on numerous applications in the smart home environment, as well as solutions for the IoT interoperability. Currently his focus in Axiros is on solutions for WiFi and access network monitoring and analytics.
References
[1] FTTH Council Europe: FTTH Market Panorama – Report by country, September 2023