Broadband networks are built with the aim of lasting for decades and they need to support increasingly heavy traffic at higher bandwidths. Factors that contribute to the network’s reliability and longevity, such as the need for good fibre/cable management and highly reliable connections throughout the network, have been accepted as necessary. However, in addition to meeting today’s needs, operators need to build networks with an eye to future requirements.
The optical fibre network installed today enables us to make phone calls, access the internet and stream video, and will typically see four generations of transmission systems over the network’s expected lifetime. Indeed, the amount of data traffic will continue to increase dramatically with the number of global internet users forecasted to rise to 3 billion users in 2015, with nearly 15 billion fixed and mobile networked devices. In addition, a fourfold increase in fixed broadband speeds since 2010 is forecasted for 2015, as the average fixed broadband speed of 7 Mbps in 2010 is expected to rise to 28 Mbps in 2015.
New standards and technology
New technologies and standards in the development of fibre-optic cabling and connectivity directly impact operators’ network considerations. Single-mode optical fibres are being designed to operate with wavelengths ranging from 1260nm to 1650nm, supporting advanced broadband service delivery. Longer wavelengths mean increased attenuation can arise by bending of the fibre which can degrade service quality. A minimum bend radius of 20mm can be accepted for ITU-T G.652D fibres, however, when installing fibre at customer premises, this is not practical. To support customer premises cabling, ITU-T G.657 A2 bend insensitive fibres were introduced as a solution. When these fibres are stored with a bend radius of 10mm, the macro-bending loss is 10 to 20 times lower than that of G.652D fibres with the same bend radius.
When bend-insensitive fibres were introduced in FTTH rollouts, ITU-T recommendations in passive optical network (PON) resulted in “looser” specifications for operators, allowing them to employ people with lower technical skills in building FTTH networks. While operators aim to reduce costs, save time and stay competitive, they must also pay greater attention to the selection of materials and the network architecture. For example, proper fibre splicing requires skill, training and experience, but fully-trained splice technicians are expensive and increasingly rare. A network architecture that minimises the number of splice locations, concentrating them, and increasing their individual splice density, can help reduce costs, but it must be planned from the beginning of the network’s design.
Many FTTH network business cases were calculated to have pay-back in shorter timeframes and focused primarily on initial costs. This resulted in reduced specifications of optical fibre cables and optical connectors, and reduced attention to installation practices. While it is tempting to save costs on the quality of materials used, or training installation crews in proper practices, these up-front “savings” are costly in the long-term as new generations of transmission equipment increase the demands on the fibre.
Downtime affecting residential customers has also historically not been the highest priority for network operators, but customer expectations have changed. Fortunately, standards and technologies have responded by opening up a wider portion of the fibre spectrum to assure that expensively deployed networks are built to last.
Building to meet future requirements
The next-generation stage 2 (NG-PON2) transmission standards under discussion at ITU-T allow operators to increase the FTTH networks’ bandwidth capacities and reduce deployment costs by sharing the same fibre with more connected customers or sharing networks with multiple operators. NG-PON2 standards employ more of the same fibre and allow seamless overlays of new services to existing Gigabit PON (GPON) networks. However, a wider spectrum and a less forgiving customer base will no longer allow components with reduced specifications to be used in access networks.
The NG-PON2 downstream channels will operate in the wavelength band between 1600nm and 1625nm. Surprisingly, the current ITU-T and IEC performance standards for cables and connectors do not always reflect the requirements for these transmission wavelengths. For future-proof networks, all network components should be specified for use at 1625nm. Standardisation bodies like ITU-T and IEC will pay attention to this in the revisions of the standards for cables and connectors.
Ultimately, operators need to build networks with an eye to future requirements because changes will keep happening. What form the change will take is not clear, but future use of wavelengths up to 1625nm is a certainty. The lessons learnt from the past – including training crews to handle fibre properly, using solutions supporting correct cable management, using connectors with the right performance specification – provide both short and long-term benefits to operators and customers alike.
Post time: Dec-01-2018