This supplement defines a test plan whose purpose is to verify interoperability between an OLT and an ONU in the ITU-T G.983-series of Recommendations which refer to a Broadband Passive Optical Network (B-PON). When testing peer-to-peer interoperability, such as between SONET/SDH ADMs, both network elements are usually considered to reside at the same hierarchical level, but in a technology such as B-PON, with a master/slave relationship, it is more appropriate to evaluate interoperability relative to a baseline, or master, equipment. In this supplement, the OLT is regarded as the baseline equipment, against which the ONU is evaluated. This is not to be understood as an assertion that the OLT is necessarily right in the event of incompatibility, merely to reflect the reality that a network operator is likely to have OLTs in place and is interested in qualifying additional ONUs for use on these OLTs. From this perspective, the unit under test is an ONU.Interoperability testing is conducted by, or on behalf of, four interests: the OLT vendor, the ONU vendor, one or more network operators who are potential customers, and possibly a third-party testing lab. As a preliminary to an interoperability testing campaign, all interests are expected to agree on features, functions and configurations. Only the features supported by both OLT and ONU need be tested but all test cases need to be addressed with either a test result or an indication why there is no result (Not supported, etc.). As to test configurations, the vendors may be requested to supply equipment (of a given vintage), and the network operator may be interested in testing in the presence of other ONU makes and models, or with particular ODN characteristics. The testing lab needs to have the necessary power, space, test equipment and expertise for the agreed campaign.In this supplement, the manufacturers are referred to as the OLT vendor and the ONU vendor respectively, while tests are deemed to be conducted by a test operator. The term ONU includes ONTs as well, and the term OLT includes the entire network element at the head end of the PON, not just the G.983 interface.