Ethernet Passive Optical Networks (EPONs) are considered one of the most promising architectures for Fiber-to-the-Home deployment. EPONs combine a point-to-multipoint fiber topology, variable-sized Ethernet packets, and a centralized in-band scheduling protocol to deliver subscriber′s traffic at low operational cost.

However, EPONs present network designers with several challenges. Large propagation delays, burst-mode operation, and specifics of access network environment do not allow easy adaptation of existing scheduling algorithms.

• static slot allocation
• derivation of formula for packet delineation overhead (unused slot remainder)
• attempts to improve utilization by packet scheduling within slot

• dynamic slot allocation
• specific measures to eliminate walk times and reduce scheduling overhead (BW consumed by control messages)

• support of multiple priority queues per ONU
• discovered unexpected behavior where queuing delay for lower-priority classes decreases with increased network load (light-load penalty phenomenon)
• suggested two schemes to fight light-load penalty: two-stage buffering and CBR-crediting

• support of multiple services with independent QoS
• use of service envelopes to achieve farness among services in a truly hierarchical scheduler (one GATE and one PERPORT per physical ONU)
• cousin-fair vs. sibling-fair schedulers