With more and more CableLabs member operators deploying or preparing to deploy ITU-T-based passive optical networking (PON) technologies such as XGS-PON, interoperability of equipment from different vendors is more important than ever. One well-known source for the lack of cross-vendor interoperability of XGS-PON equipment stems from differing implementations of the ONU Management Control Interface (OMCI) — primarily specified by ITU-T Recommendation G.988.

Last year, the CableLabs Common Provisioning and Management of PON (CPMP) working group set out to tighten some of the gaps in G.988, via the publication of the first version of the Cable OpenOMCI specification. This specification aims to enumerate the set of management elements from G.988 that are most important to CableLabs member operators and clarify how those elements must be supported in XGS-PON equipment intended for sale to those operators.

At a recent  XGS-PON Interop·Labs event at CableLabs, multiple suppliers of PON optical line terminal (OLT) and PON optical network unit (ONU) equipment exercised their gear’s ability to interoperate. It was the industry’s first opportunity to exercise equipment implementations conformant to the requirements defined in the Cable OpenOMCI specification.

But the event, held April 28–May 1 in our Colorado labs, exercised more than just OMCI interoperability. It also included a continuation of the DOCSIS Provisioning of XGS-PON config file interoperability testing, first initiated during our February interop. Please see my blog post from March for a deeper description of the concept of DOCSIS Provisioning of XGS-PON and the scope of that event.

Supplier Participation in the XGS-PON Interop

Interoperability events enable participants to collaborate and problem-solve on specific technologies and goals. The participation of vendors is critical to advancing technology solutions for the entire industry.

Participants at our April Interop·Labs event included XGS-PON OLT suppliers — showcasing their OMCI and DOCSIS Adaptation Layer (DAL) implementations — as well as XGS-PON ONU suppliers, who showcased the OMCI aspects of their ONUs.

These XGS-PON OLT suppliers included Calix, Ciena and Nokia. In particular, Calix tested using their E7-2 OLT and DPx DAL. Ciena brought their Tibit MicroPlug OLT, MCMS controller and DAL system. And Nokia tested using their Lightspan MF-2 OLT and Altiplano controller. While the primary focus of the event was on XGS-PON technology, Ciena also brought their pre-production 25GS-PON OLT and 25GS-PON ONU, and demonstrated DOCSIS provisioning of that equipment, as well as traffic forwarding through it.

In addition to the OLT supplier participants, XGS-PON ONU suppliers in attendance included Askey, Cambridge Industries Group, Hitron, MaxLinear, Sagemcom and Sercomm. While Sagemcom brought an ONU embedded in a residential gateway, most suppliers brought bridging ONUs. Numerous ONUs from additional suppliers (including Calix, Ciena/Tibit and Nokia) were also on hand for interested OLT vendors to test with their OLT and DAL implementations.

The XGS-PON OMCI Test Cases

The OMCI test plan executed during the event was based on the requirements defined in the I01 version of the Cable OpenOMCI specification. Interested OLT and ONU suppliers met over the course of several weeks prior to the event to define the test cases that would be included in the interop test plan.

Following the general contents of the Cable OpenOMCI specification, the following test cases were defined:

• The MIB upload component of OMCI configuration management
• Create and get methods of OMCI configuration management
• Performance monitoring via OMCI
• ONU software image download
• ONU software image activation

During the first three test cases, the lab’s 100GE traffic generation system was used to transmit and receive traffic via a given OLT and ONU combination under test. And during each of the five test cases, an XGS-PON analyzer or OMCI debug capabilities of the OLT were used to capture and examine the message exchanges between the ONU and OLT. One participating OLT vendor indicated that, during the event, they tested with 12 different ONU models, inspecting close to 100 OMCI management elements for each ONU.

The results of the interop testing were encouraging and showed that the participating suppliers have already begun implementing the requirements of the Cable OpenOMCI specification in their software. As expected, the testing also uncovered additional OMCI interoperability issues. Those issues will inform the next set of work items for the CPMP working group to tackle.

New Issues Bring New Fixes

With a wide array of OLT and ONU vendor implementations on hand at the event, new issues were bound to be discovered — which is exactly why we hold interoperability events.

Now, the CPMP working group will discuss our findings and prioritize solutions for them via an engineering change process to the Cable OpenOMCI specification. Fixes for the simpler issues will likely be included in the upcoming release of the I02 version of the spec. More complex issues may take more time for the working group to solve and will therefore be addressed in a later version of the spec.

Join Us Next Time

CableLabs is planning two more PON Interop·Labs events this year, with the next event scheduled for the week of Aug. 4. Stay tuned for more details.

The August event will provide an opportunity for OLT and ONU suppliers to return to test interoperability based on compliance with an anticipated I02 version of the Cable OpenOMCI specification. We also welcome OLT suppliers to return to exercise their DAL solutions for ONU and config file interoperability.

At the recent DOCSIS® Provisioning of XGS-PON Interop·Labs event at CableLabs, suppliers of PON optical line terminals (OLTs) exercised their systems’ ability to configure XGS-PON optical network units (ONUs) via the use of DOCSIS-style configuration files. The event took place February 24–28 at our headquarters in Louisville, Colorado.

CableLabs member operators have long been familiar with the method of using a configuration file to provision services on a DOCSIS cable modem. Beginning a decade or so ago, DOCSIS-style configuration was also utilized by many operators to simplify the provisioning of IEEE EPON systems compliant to the DOCSIS Provisioning of EPON (DPoE) specifications. These DPoE virtual cable modem (vCM) config files enabled an operator to use the same service provisioning back-office systems that they originally deployed for DOCSIS cable modems to provision services on DPoE EPON networks.

Fast-forward to today, and many CableLabs member operators are deploying or preparing to deploy ITU-T-based PON technologies, including XGS-PON, 25GS-PON and 50G HSP.

Some XGS-PON OLT suppliers have now also adopted the vCM config file method for provisioning ONU services by adding a DOCSIS adaptation layer (DAL) software function to their system offering. The DAL solution performs the well-known cable modem DHCP and TFTP transactions on behalf of each ONU registering on each OLT managed by the system. The DAL parses the contents of each config file and translates those contents into directives on the OLT. This provides the OLT with the necessary details to complete the service configuration of a given ONU.

Using an OLT with a DAL capability isn’t the only method to configure services on each ONU. Other methods include the use of SDN-based procedures and protocols such as Netconf or OLT supplier-provided RESTful APIs. But the use of the DAL and DOCSIS-style config files can ease the transition of member operators into ITU-T-based PON technologies, without the need for wholesale replacement of the operator’s service provisioning back-office.

Supplier Participation in the Provisioning of XGS-PON Interop

We thank the supplier participants who helped make the February interop event so successful. The primary participants were XGS-PON OLT suppliers who showcased their DAL implementations.

These OLT suppliers included Calix, Harmonic and Nokia. In particular, Calix tested using their E7-2 OLT and DPx DAL. Harmonic brought their Pier OLT and cOS virtualized core software platform. And Nokia tested using their Lightspan MF-2 OLT with Altiplano controller and a DAL from their solution partner, ZCorum. As a bonus, Nokia demonstrated that the DOCSIS provisioning method can also be used to provision services on a 25GS-PON optical network unit (ONU).

In addition to the OLT supplier participants, MaxLinear was in attendance with their reference-design XGS-PON ONU, and TraceSpan participated with their NG-PON Xpert analyzer, whose DPoX Validation capability was instrumental for validating the correctness of the OMCI configurations that were set by the OLTs.

How the XGS-PON ONU Test Cases Unfolded

During the interop event, CableLabs provided an identical set of XGS-PON ONUs of various makes and models to each of the three OLT suppliers. CableLabs also provided a set of standard config files — one for each of the test cases defined in the interop test plan.

By utilizing a common set of ONUs and config files, we could see how each OLT-plus-DAL system reacted to a given config file on a given ONU. The overall goal of the event was to work towards a given ONU having an identical service configuration — for a given test case — across all the OLTs.

The test plan executed at this event was derived from the DOCSIS Provisioning of ITU-T PON tech report, which CableLabs published in December 2024. Test cases included basic HSD configuration of ONUs with a single Ethernet port as well as ONUs with multiple Ethernet ports. When configuring services on ONUs with multiple ports, a config file construct called a Cable Modem Interface Mask (CMIM) Classifier was utilized to control which ports on the ONU were active. Testing also included a triple-play (HSD, IP Voice and IP Video) test case, which utilized Differentiated Services Code Point (DSCP) traffic classifiers in the config file. A final test case that was executed from the interop test plan included the use of an ONU with an integrated eRouter functionality.

In cases where an OLT supplier was not initially able to successfully configure a given ONU for a given test case, we allowed the supplier to make customizations to the standard config file. This enabled the supplier to execute the test case and note where changes in their software might be needed to successfully use the standard config file in the future.

Each test case executed during the event made use of the lab’s 100GE traffic generation system, the lab’s standard DHCP and TFTP server infrastructure, and a PON analyzer to decode the ITU-T-specified ONU Management and Control Interface (OMCI) message exchanges across the PON. Many thanks to Charter Communications and TraceSpan Communications for supplying additional NG-PON Xpert analyzer units, enabling each OLT supplier test setup to utilize a dedicated analyzer.

Beyond the primary DOCSIS provisioning focus of this February event, we were pleasantly surprised that one of the supplier participants in this event brought OLT and ONU software versions that demonstrated partial compliance to the Cable OpenOMCI I01 specification. We look forward to seeing many more suppliers follow suit in the near future.

Applying the Lessons Learned

Overall, the results of the event were encouraging, with both established as well as new supplier entries into this product space showcasing their abilities to provide common service configurations across a wide variety of ONU makes and models.

The implementations exercised at this event indicate that these suppliers believe that a DOCSIS Provisioning of XGS-PON solution will be an important part of their product portfolio for the foreseeable future. We plan to take the lessons learned from this event and apply them to a future update of the DOCSIS Provisioning of ITU-T PON tech report.

Join the Next PON Interop

CableLabs is planning three more PON Interop·Labs events to be held in our Louisville, Colorado, labs in 2025. Our next event is scheduled for the week of April 28, 2025.

The April event will provide an opportunity for OLT suppliers to return with their DAL solutions to once again test ONU and config file interoperability. In addition, ONU and OLT suppliers with software implementations compliant to the Cable OpenOMCI I01 specification will be invited to exercise the capabilities defined in that specification.

In the broadband industry, network operators and vendors are continually working together to advance interoperability and streamline operations — but the puzzle pieces don't always fall into place easily. Passive optical networks (PONs), for example, face the ongoing challenge of achieving interoperability without stifling innovation. PON standards are intentionally written to be flexible and to encourage innovation. When translated to practical implementation, this approach has led to diverse interpretations, creating interoperability challenges.

PON standards establish functional and behavioral requirements that span a network’s operational layers. These standards alone do not guarantee interoperability among vendors. For network operators, lack of interoperability leads to fragmentation and vendor lock-in. This includes bookended deployments, in which optical network units (ONUs) and optical line terminals (OLTs) must be provided by the same vendor. These limitations and challenges drive up operational costs, increase network complexity and extend time to market as operators grapple with compatibility issues.

Early in the evolution of PON, CableLabs’ DOCSIS®️ Provisioning of EPON (DPoE) specifications and certification program represented a significant advancement in addressing these challenges. By implementing rigorous interoperability testing between ONUs and OLTs, DPoE demonstrated that detailed specifications combined with collaborative industry efforts can achieve multi-vendor PON equipment compatibility. This success provided valuable insights for advancing interoperability across the broader PON ecosystem.

But DPoE's scope was focused on PON based on IEEE standards, so it did not address the interoperability challenges present in PON based on ITU-T standards. This is particularly evident in the deployment of XGS-PON, which is becoming the predominant ITU-T-based PON technology worldwide. As the industry moves toward newer technologies like 25GS-PON and 50G-PON, establishing robust interoperability standards becomes increasingly critical.

BBF has made significant strides in advancing PON interoperability through its comprehensive testing framework. By developing detailed test plans and guidelines, the organization addresses the implementation gaps in ITU-T PON standards. Its cornerstone documents — TR-255 “GPON Interoperability Test Plan,” TR-309 “PON TC Layer Interoperability Test Plan” and TP-247 “G-PON & XG-PON & XGS-PON ONU Conformance Test Plan” — establish rigorous testing protocols for various network scenarios, from traffic management to fault handling.

Advancing Interoperability Together

CableLabs recently hosted a PON Plugfest interoperability event on behalf of the Broadband Forum (BBF). CableLabs, a member of the Broadband Forum, provides the technologies, experts and tools to advance ideas from research to real-world deployment. CableLabs is well equipped to offer testing services for hybrid fiber coax (HFC), fiber to the premises (FTTP) and mobile network equipment — making our state-of-the-art facilities ideal for interoperability testing and an event like this.

This event provided a neutral environment in which vendors could work collaboratively to test their products for interoperability — for both XGS-PON and 25GS-PON implementations — according to test plans created by the Broadband Forum.

Collaborate With Us

It is essential for industry partners like CableLabs and BBF to work together to chart the next phase of specification development and drive interoperability standards for OLTs and ONUs. We invite our members and the vendor community to join us in CableLabs’ Interop·Labs events and in other opportunities for collaboration, such as our working groups, to gain valuable insights into key industry technologies and interoperability challenges and opportunities.