Method, apparatus and system for allocating uplink bandwidth in passive optical network

Disclosed is a method for allocating a bandwidth in a passive optical network, which is characterized in that the method comprises: an ONU receiving multiple downlink frames from an OLT, wherein each of the downlink frames carries a Bandwidth map (BWmap), the BWmap comprises N subfields for allocating bandwidths for N TCs, and N is an integer greater than 512; the ONU parsing the BWmap, and obtaining the bandwidths allocated to the TCs of the ONU; and the ONU sending uplink data based on the obtained bandwidths of the TCs. According to a preceding technical scheme, a number of bandwidths allocated to each frame can be expanded from 512 to 2047, significantly reducing an allocation period, and reducing a requirement on a buffer of the ONU.