With high speed internet connectivity and seamless data flow becoming a necessity, the demand for optical fibre networks is growing at an astonishing pace. The demand for fibre in India is also being driven by the government’s Digital India push through initiatives such as BharatNet and the Smart Cities Mission. As part of the BharatNet project, the government has laid over
0.56 million km of optical fibre cable (OFC) as of end February 2022. The government has set a target of laying an incremental 3 million route km of OFC as part of the National Broadband Mission. The Smart Cities Mission has also generated significant opportunities for the industry as OFC is fundamental to enabling services such as Wi-Fi, video surveillance and security, smart lighting, smart parking and smart traffic management.
Another key factor contributing to the surge in demand for OFC is the growing proliferation of fibre-to-the-x (FTTX) networks. FTTx is a generic term for any broadband network architecture that uses optical fibre to provide last-mile telecommunications to premises (FTTP), homes (FTTH), buildings (FTTB), etc. Through FTTx, operators can deliver services directly to the end-user location from the switching equipment, thereby avoiding connectivity issues at the last mile. Given the limited availability of wireless spectrum and the data deluge that is currently being witnessed owing to the growing adoption of next-generation technologies such as internet of things and big data, FTTH is emerging as a key contender to wireless technologies for delivering broadband to the last mile.
To ensure optimal service quality in an FTTx network architecture, it is vital that service providers choose the appropriate network topology and put in place enough troubleshooting mechanisms that are able to locate, identify and fix issues in the least possible time.
tele.net takes a look at the network topologies available to deploy FTTx networks, the various business models that operators can choose from and the need for testing of fibre networks…
FTTx network topologies
Telecom operators can choose from a variety of FTTx network architecture to deploy their fibre networks. The most widely adopted framework among these is FTTH in which the fibre connection is laid all the way to customer premises (home or private network), thereby ensuring the maximum bandwidth. However, FTTH is costly to roll out, especially in cases where an existing copper-based
architecture is to be replaced with fibre. FTTH is therefore usually preferred only in greenfield projects. Another network topology is fibre-to-the-antenna (FTTA) in which optical fibre is used to connect the remote radio head (RRH) to the base station in new antennas, or retrofitted in the existing ones, to replace all or part of the coax local loop. Fibre optic cables are lighter than coax cables, and therefore easier to install. FTTA ensures low latency, provides high speed backhaul and increases traffic bandwidth.
An alternative to FTTH and FTTA is the FTTB framework in which the service provider lays the OFC till the boundary of the building, such as the basement in a multi-dwelling unit, while the final connection to individual premises is made through alternative means. Further, every subscriber’s optical network terminal is connected to a fibre distribution hub (FDH) through fibre distribution terminals. The FDH cabinet, which contains splitters, patch panels and fibre management elements, is connected to the central office.
The other architecture available is fibre-to-the-curb in which the fibre is made to run from a central office to a curb-side distribution point, such as in a pole or an enclosure, in the vicinity of customer premises. The curb-side distribution point is connected to subscribers through twisted pair copper cables. FTTA can be used to deliver services to a smaller cluster of customers.
Fibre-to-the-node (FTTN) offers a cost-effective way to deliver telecommunication services to a large number of consumers from a single node, without having to roll out the fibre all the way. In an FTTN topology, the optical fibre ends at a street cabinet, with final connections being made through existing legacy copper or coaxial cables.
While FTTx remains a promising growth strategy for operators, the viability of the stand-alone FTTx model remains uncertain owing to the requirement of large-scale investments and low revenue realisations. To this end, operators can explore alternative business models such as build-your-own-infrastructure, build-operate-transfer (BOT), fibre grid and fibre network convergence to provide telecom services through fibre networks.
In the build-your-own-infrastructure model, cable and network operators can build their own infrastructure and lease the capacities to users/operators. The infrastructure could either be in the form of an outright duct or a dark fibre lease to operators on an indefeasible right-of-use basis.
An alternative to the traditional capex model is the BOT model in which a specialist can build and manage the capacities, and decide on revenue sharing on a per byte bandwidth delivered, or on a per home connect basis. Meanwhile, in a fibre grid model, the fibre assets of all owners are aggregated to build a one-stop shop for dark fibre on a pan-Indian basis. These owners together can operate and maintain the entire pool of fibre assets and drive planned expansions. In the case of fibre network convergence, multiple services are combined within a single access network. A single OFC pipe can be used to deliver multiple forms of communication services such as a distributed antenna system, small cells and Wi-Fi.
Testing of FTTx networks
A fibre network needs to be tested properly during installation, activation and maintenance in order to deliver superior quality of service and network coverage to customers. While most components are tested during the manufacturing process, they need to be tested again after the splicing and installation of splitters and access terminals. Further, field testing must be undertaken to ensure that no excess loss or reflectance has been introduced due to micro-bends in the installed fibre and the connectors are properly aligned, otherwise the network might deliver a poor performance. Four tests are commonly done to ensure proper functioning of a fibre network – connector inspection, insertion loss test, optical return loss test and optical time domain reflectometry.
Connector inspection and cleaning during installation and maintenance are among the most effective methods for ensuring that an optical network will deliver the expected performance. Connector inspection is typically performed using an optical microscope and is used to check for any kind of connector contamination or damage in the network. Meanwhile, an insertion loss test measures the end-to-end loss of the installed link by injecting light with a known power level and wavelength at one end, and measuring the received power level output from the other end. The measured difference between the
transmitted and received power levels indicates the optical loss through the network. Insertion loss is considered acceptable when the measured loss level is lower than the budgeted loss level.
An optical return loss test injects light with known wavelength and power level into one end and measures the power level returned to that same end. The difference between the injected power level and the measured return level is the return loss. Return loss is considered acceptable when it is higher than the budgeted return loss target. A low return loss value is often an indication of one or more sources of excess reflection in the network under test, typically due to dirty or damaged connectors or a fibre break. Meanwhile, an optical time domain reflectometer (OTDR) scans the fibre network to measure the length, loss and optical return loss of an optical network. It also locates and measures reflective and non-reflective events in the network due to splices, connectors, micro- or macro-bends, splitters or faults.
An ever-increasing demand for higher bandwidths and the growing use of data-intensive applications is leading to a surge in the demand for FTTx networks. Moreover, FTTx has presented an alternative growth strategy to operators to diversify their revenue streams since FTTx services can be bundled with service and content offerings. However, given that FTTx deployments are highly capital intensive, it is imperative for the operators to choose the network topology and the business model that makes their investments financially viable. Regular testing of the FTTx networks is also necessary to reduce the costs associated with product malfunctions, repairs, replacements, product call backs and repeat production, and deliver better network coverage, superior data performance and best uptime to consumers. s