In this paper, we present a proposal of extensions to the already existing Multi Point Control Protocol (MPCP), as defined in the IEEE 802.3 ah standard, clause 64. Current MPCP system allows for two LLID assignment policies, namely 1 LLID per ONU or 1 LLID per queue, resulting in significant frame delineation or excessive scheduling overhead in the upstream channel, respectively. First, we examine the impact of both LLID assignment policies on the overall system performance, and then we propose the extended GATE / REPORT MPCP DUs. Backward compatibility issues as well as coexistence of standard and extended flow control messages in the same network structure are addressed and dealt with in a satisfactory manner, proving the inter-operability of the proposed solution. Gradual system upgrade from legacy into extended version is thus possible.