Reducing Operating Expense in Fibre Access Networks

The access network accounts for over 90 percent of cabling in most Telecommunications systems. The big push now within the industry is the transition to fibre to improve broadband speeds and services. This is a major task, as the number of European households set to be connected by 2017 will double to over 40 million by 2017 (source FTTH Council).

A Challenge for Operators

Whilst this will be great for customers, operators will have to tackle the maintenance and repair issues that will certainly result from this expansion. Street furniture connecting switches and major concentration points will need to be placed in more vulnerable areas than the existing infrastructure.

Fibre optics have in general proved to be very reliable and not prone to failure if properly installed. However where people have access and cables are open to human error, this can change.

It is simple to introduce faults in fibres by using poor practice, lack of training or simple carelessness. In addition to having telecommunications staff having access to the fibres, with cables laid in the street or on overhead drops, other utilities may also come across fibre cabling and unwittingly cut or bend them.

To add further to these issues, end users now have great expectations from the new services and are quick to complain when things do not work as they should. To run a high quality service operators will be forced to take a new approach to fault detection.

Not Starting From Scratch

Operators have had to overcome similar challenges in access networks over the years. In the early days of copper, vast numbers of technicians armed with a variety of test equipment were deployed to look after the networks. For some operators this group of people often made up the majority of the workforce. There was little or no option for operators for many years but to invest heavily in this part of the business.

With the arrival of digital services, testing became more important but also costly when carried out in the traditional manner, even with the evolution of more intelligent technology.

To combat this, centralised test equipment and solutions were developed that would enable tests to be performed remotely by lower skilled staff. Additionally routine overnight testing could identify problem areas often before the customer realised he had a problem. The effect of this has been for the operators to be able to reduce the number of technicians and also expensive test equipment and training without jeopardising quality.

Centralising Fibre Testing

Overall, operators have managed to reduce the numbers of staff employed dramatically, by more than 50 percent in many cases and thus enjoyed the associated operating cost reductions whilst improving overall customer service.

The challenge in fibre networks is to be able to replicate what has already been achieved with copper network test success. Testing fibre is, in many ways, easier than testing copper, with its lower susceptibility to external factors such as electrical fields or water.

Optical Time Domain Reflectometry (OTDR) has been successfully used for many years on installation, maintenance and fault finding. The field technician units have their faults too though being relatively expensive, require skilled operators and only testing one fibre at a time. They also require the fibre to be taken out of service and for the whole operation to be reactive with faults only being reported after they are noticed. On top of these less than ideal conditions the Passive Optical Network (PON) architecture of many fibre access networks means that today's handheld tests can only be performed from customers' premises, unless all customers using that PON are taken out of service just for testing.

One advantage of modern PON transmission equipment though is that the Optical Line Terminals (OLT) and Optical Network Terminals (ONT) constantly communicate, allowing statistical analysis that will show failings in the electronics and possibly issues with the physical layer. Whilst useful, this does not help in locating the nature and location of such issues.

A New Dimension in Access Fibre Testing

Recent advances in OTDR technology combined with low cost optical switches have introduced a new way to test fibre. By using an "out of band" testing wavelength which does not interfere with the transmission, it is possible to test from the OLT or switch end of the PON. Whilst in the past it has been problematic to view all the customers on PON individually, breakthroughs have been made that allow this to be done with very high resolution, even where 128 customers are on one PON system. One OTDR combined with a switch can test many PON systems and reduce the overall cost and complexity of testing.

Field testing of such systems have shown huge benefits in finding faults on PON Networks, up to and beyond the splitter. It is now even possible to see issues such as dirty connectors, ONTS disconnects, micro bends and breaks. The OTDR systems can also be integrated with GIS mapping software to show the real location of faults and get repair teams despatched with the correct equipment.

A management system operating on this basis could monitor alarms generated by the transmission equipment to detect a fault when it occurs allowing the OTDR to swiftly find the nature and location of the fault and a suggested remedy.

The Future's Bright, the Future Uses Non-Interfering Wavelengths

In future, finding faults on PON systems will no longer be a "dark art" with armies of trained technicians finding issues. Faults that do occur will be pinpointed with instant corrective actions identified immediately. Maintenance will be determinable by routine testing and planned with new customer connections that are made instantly verified.

The cost savings of the adoption of these systems is huge with staff numbers being dramatically reduced, personal test equipment almost eliminated, costly training reduced, plus a better working system and happier customers. I think this is a goal we can all relate to!