In a passive optical LAN (POL), upstream data is transmitted in time division multiplexing (TDM) mode. The OLT allocates independent bandwidth and timeslot to each ONU.

In a Passive Optical LAN (POL) system, which is based on Passive Optical Network (PON) technology, the upstream transmission from multiple Optical Network Units (ONUs) to a single Optical Line Terminal (OLT) is managed using a multiple access protocol to prevent data collisions. This protocol is Time Division Multiple Access (TDMA), where the OLT grants specific transmission timeslots to each ONU. The ONUs can only transmit data during their allocated timeslots. This mechanism is a form of time-division multiplexing where access is shared over time.

This statement is factually correct. The alternative, False, would be incorrect because without a time-division access scheme like TDMA, simultaneous upstream transmissions from multiple ONUs would interfere with each other, making communication impossible.

1. Huawei Enterprise. (2020). GPON Technical White Paper. Section 2.3, "GPON Upstream Transmission." This section states: "In the upstream direction, various ONUs send data to the OLT. If the ONUs send data at will, data conflicts will occur on the optical fiber. To avoid data conflicts, the OLT uses the time division multiple access (TDMA) mode to centrally schedule data transmission of the ONUs."

2. Huawei Enterprise. (2022). Huawei Campus OptiX Solution White Paper. Section 2.1, "What Is a POL Network?" This document describes the underlying GPON technology, which employs TDMA for upstream traffic management.