The increasing use of fiber in the access network has made GPON one of the fastest growing broadband access technologies today. In many countries GPON is moving from the pilot phase to mass deployment, opening new opportunities for service providers, along with new challenges.
In the early days of GPON service providers cared primarily about getting the service to work, and the easiest way to ensure this was to purchase an end-to-end GPON solution from a single vendor, who was responsible to make it work. Providers that used multiple vendors in their network divided their service area into different regions, and within each region used the same vendor for the OLT and the ONUs or ONTs.
In today's competitive environment providers are looking for ways to speed up the service bring-up for new customers and reduce the costs associated with capital investment, installation and continuous operations. Cost-competitive ONUs, including the emerging small-footprint-ONUs from new vendors, are aimed to enable self installation by the end customer.
However, as some of the service providers told us, these new ONUs put much more responsibility on their own people, since they are the ones who have to integrate the equipment from different vendors and ensure that it delivers proper service, and in case of a problem they are likely to find the OLT and ONU vendors pointing fingers at each other and reluctant to resolving it. In my previous blog post I discussed the negative implications of a rogue ONU, which is just one example of a problem that is likely to happen if you didn't select your ONU carefully or didn't test it well enough before deployment. Further down in this article we will talk about the testing that should be done for selecting the right devices.
On paper if both ends comply with the relevant GPON standards, you should be able to connect any ONU with any OLT and deliver your service. It's just like you can buy a mouse from one brand and plug it into the USB port of a PC from another brand. During the last few years standards bodies and industry forums have put significant efforts to allow service providers to mix GPON vendors, including the development of test plans and the arrangement of GPON interoperability events. But still today, if you buy the ONU and OLT from different brands, they often don’t work together. Let's try to understand why this happens and what a service provider can do to handle this.
When an ONU connects to an OLT, it first has to complete the activation process, sometimes called ranging. The OLT may then request the ONU to identify itself by a password, which is an optional means of security applied in some networks. After this phase, the OLT will setup the ONU's service configuration with OMCI messages and then the ONU is ready to deliver the service.
But when mixing GPON equipment vendors any of these phases might fail. In fact, in many cases the ONU will complete the activation process but will not be able deliver service, and this may be a result of anything from a simple password conflict to a more complex OMCI service setup issue.
Some service providers rely on their vendors with their internal debugging logs to figure out where the failure occurs, but this requires resource investment from the vendors' side, which will often not be their highest priority. Other providers have adopted a more proactive approach of using a GPON analyzer for viewing the message exchange on the PON at the different layers and pointing out conflicts and errors. This puts them in a much stronger position to demand their vendors to resolve the issues. We have seen many cases in which GPON analysis reports created by a service provider were acceptable by equipment vendors as evidence of an interoperability issue, especially if the vendors use the same GPON analyzer and are familiar with its analysis capabilities. This prevents finger pointing between vendors and significantly speeds up the process of getting the OLT and ONU ends to work together.