The global GPON market is expected to grow at an annual rate of about 10% over the next 10 years, driven by broadband initiatives, for example, undertaken by government agencies.
Currently, operators are gradually deploying a new version of the XGS-PON standard in parallel with the older GPON solutions still present in their networks, while considering future-proof concepts such as NG-PON2.
Providers face challenges in ensuring supply chain continuity for today’s deployments and future needs for the evolving xPON access and the diverse new use-cases and business models.
In response to these challenges, many Communications Service Providers are adopting a multi-vendor strategy, moving away from the model of a single homogeneous network containing equipment from a single provider with full responsibility for the correctness of all their functionality.
In particular, the wholesale service providers’ sales model assumes that the OLT they use must work together with ONT subscriber equipment selected by the retail operators concerned, which may come from many different suppliers.
According to the Broadband Forum, interoperability is a key factor in the success of GPON deployments around the world. In order to ensure (multi-vendor) interoperability between selected OLTs and the numerous ONU options available to operators, it is necessary to test all the functionalities in advance.
The situation is further complicated by the possibility of operators using multiple OLT solutions based on branded, white-box or virtual solutions.
Frequent changes in software versions of station and subscriber equipment repeatedly increase the number of tests needed to be carried out over the period of use.
All PON solutions are based on the standards published by ITU-T:
The entire ONT Management Control Interface (OMCI) layer is also described in the G.988 standard (successor to the G984.4 standard) containing about 400 unique elements – Management Entities (MEs), so in theory all devices complying with the standard should work together.
In the OMCI description, only a small part of the MEs is mandatory for providers, and more than 300 of them are left as vendor-specific, and each OLT and ONT may interpret them a little differently, as if, despite using a common language, they spoke different dialects of it.
The situation is not helped by the fact that more than 20 versions of the G.988 standard were compiled between 2004 and 2020, and the structure of the interdependencies between different MEs is very complicated.
Providers often take advantage of the freedom of interpretation contained in the standard’s description to emphasize the distinctiveness of their solutions, distinguish themselves with additional functionalities or even apply a vendor lock-in strategy for customers.
These are the main reasons for the lack of interoperability between equipment from different vendors:
It is obvious that in the context of accelerating the rollovers of tens of thousands more ONTs, it is necessary to first thoroughly test all their functionalities and correct the operation with all versions of OLTs present in the network.
It would seem, however, that the need for interoperability testing applies only to operators using equipment from multiple vendors, while in the case of homogeneous networks based on the solutions of a single provider, the provider is entirely responsible for their correct interoperability.
This is somewhat true, but the situation can change dynamically, such as after the provider ceases production, introduces new software versions, introduces a service and network leasing model (NetCo / ServCo), cooperates with multiple retail service providers, or merges with an operator using equipment from another provider. The provider’s top-down corporate policy may also force the introduction of equipment supplier diversification, leading to capital expenditure savings.
Equipment providers are not necessarily interested in offering interoperability testing services with competing devices, and often their integrator services are expensive and their terms and conditions not flexible enough.
Of course, the operators’ engineering teams can undertake interoperability testing tasks themselves, but typically encounter the following challenges and problems:
Taking an independent view of GPON and XGS-PON standards compliance has become a necessity for many Communication Service Providers. An evaluation of the interoperability between OLTs and ONUs, and identifying functional deficiencies, is a part of any deployment of this technology.
Given the magnitude of the potential complications, ONT testing becomes an unwanted necessity prior to deploying devices to the network. This engages teams of experienced engineers whose basic role in the telcos company is completely different, distracting them from their daily tasks.
This becomes more burdensome when the visible issue is not easily traceable back to its root cause, and due to the frequent changes of the device firmware, the tests can become an almost everyday chore. Moreover, an in-depth analysis of the interoperability issues isn’t possible without an additional cost outlay, including the acquisition of equipment, specialist competencies, and human resources.
Fortunately, testing the interoperability of xPON solutions doesn’t require telcos to build and manage a dedicated team of specialists, which could jeopardize their operating costs.
Outsourcing testing to an independent and experienced third party ensures objective results and OPEX control. External engineering support helps clear the testing backlog and accelerates the development of xPON infrastructure.
Further, recommendations on the tested platform from a third party and a proposed solution to any encountered problems provide telcos with an independent view and full assessment of interoperability issues and improvements for future test runs.
Such a partner with skills, engineering teams, and experience becomes a knowledge and competence center, able to mirror the telco’s infrastructure in their lab with specialized test equipment enabling in-depth and detailed analysis of the problem. As an independent third party, the testing partner will provide arrangements with suppliers, while representing the operator’s interest.
A big advantage of having a partner to run the tests is a guarantee of network and service development continuity and guidance in the fast-changing and dynamic xPON technology landscape.