By Sam Leeman, senior manager of application engineering for EMEA, TE Connectivity
As pressure and expectations from both business and residential customers increase, technology and networks have evolved. Factors contributing to reliability and longevity, such as reliable connections and good fibre and cable management systems throughout the network, are necessary. To survive and grow, operators must build networks that consider the future.
Today’s situation
New technologies and standards in the development of fibre optic cabling and connectivity directly impact operators’ network considerations. Single-mode optical fibres are designed to operate with wavelengths ranging from 1260nm to 1650nm, supporting advanced broadband service delivery. Bends in fibre cause an attenuation increase at longer wavelengths and 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.
Business cases
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. But assuring that materials and installation meets real, long term network (and customer) needs is typically a very small part of the network’s total cost of ownership.
It’s important to remember that the initial CAPEX of an FTTH deployment consists mainly of civil costs, cost of actives and civil hardware. Passive equipment, with generally long service lives, make up a relatively small part of overall CAPEX. However, their impact on later OPEX, due to costs involved in replacing them, can be huge, yet seem to be ignored during fibre access/FTTH network builds.
Let’s consider how ITU-T G.657 bend-insensitive fibres impact CAPEX and OPEX. Although optical performance of macro-bending has improved greatly, the probability of mechanical failure increases. A failure ratio of 10-5 is considered acceptable for FTTH applications, but for long haul networks a much lower probability is required.
The expected reliability of fibre lines depends on the type of network; in core, metro and long haul fibre networks, attention was traditionally paid to the network’s long term reliability. These networks were built to last for decades and to support increasingly heavy traffic at higher bandwidths. In the critical last mile, where the network connects to the end customer, the same attention to long term reliability is equally important, so that network quality and minimum downtime is assured.
Downtime affecting residential customers was historically not 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.
Future requirements
The new 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. NG-PON2 standards deploy 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 into today’s future generation 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 futureproof 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 change will happen. 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.
TE Connectivity designs and manufactures highly engineered connectors, sensors and electronic components essential in our increasingly connected world.
