A passive optical network has a shared medium in the upstream direction, and the passive ODN combines all ONU outputs towards the OLT. Therefore, an ONU that is not transmitting in a manner consistent with parameters specified in the standard can threaten all upstream transmissions on the PON causing interference and disrupting communications of all ONUs on the PON. An ONU that transmits optical power up the PON in violation of the parameters of the standard is called a "rogue ONU". This kind of situation is not unique to PONs, as many wireless and RF-based systems use the same shared channel scheme. However, under certain hardware and software conditions (attributed to circumstances including design, manufacturing, device failure, environmental, external, or other influences), an ONU may exhibit behaviour that disrupts the operation of other ONUs on the same PON. Such rogue ONU behaviour can cause performance issues or outages for one or more ONUs on the PON. Also, diagnosing and isolating the offending ONU can be difficult since the affected ONUs are not always the ONUs causing the disruption. This Supplement raises the awareness of rogue ONU behaviour and provides system designers and implementers with techniques and tools to facilitate the prevention, detection, isolation, and removal of the offending ONU to avert or minimize service interruptions to other ONUs on the PON. This treatment distinguishes a rogue ONU from a unit that intentionally or maliciously transmits optical signals that are not in accordance with the standard. In the strictest sense, these devices or intentional jammers are not ONUs, since they are not following the ITU-T Recommendations that describe ONUs. They are essentially illegal devices that intend to deny or steal service from the network. However, these devices may exhibit behaviour and use processes that are similar to rogue ONUs and, therefore, considerations contained in this Supplement may assist in mitigating their potential impact. Security measures are specified in the standard to further assist in reducing threats from malicious sources. The following clauses consider several rogue conditions that can occur and the design measures that can be employed to address them. Rogue ONU prevention, detection, isolation, and mitigation techniques are intended to avert or minimize service interruptions on a PON when a rogue condition occurs, and are not intended to be a substitute for solid engineering practice and adherence to the standards. Clause 4 provides the expansion of abbreviations and acronyms.