EPON Study

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.

Ethernet PON (ePON): Design and Analysis of an Optical Access Network
  • static slot allocation
  • derivation of formula for packet delineation overhead (unused slot remainder)
  • attempts to improve utilization by packet scheduling within slot

Interleaved Polling with Adaptive Cycle Time (IPACT): A Dynamic Bandwidth Distribution Scheme in an Optical Access Network

IPACT: A Dynamic Protocol for an Ethernet PON (EPON)
  • dynamic slot allocation
  • specific measures to eliminate walk times and reduce scheduling overhead (BW consumed by control messages)

Supporting differentiated classes of service in Ethernet passive optical networks
  • 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

Fair Queuing with Service Envelopes (FQSE): A Cousin-Fair Hierarchical Scheduler for Subscriber Access Networks
  • 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