Ethernet Passive Optical Networks

1. Ethernet Passive Optical Networks • PON Definition • Point to multipoint optical networks • Architecture build up from two elements • An Optical Line Terminal (OLT) at Network Provider's premises • Multiple Optical Network Units at users' premises • Fiber to the home solution (FTTH) • Fiber to the business solution (FTTB) • Fiber to the curb solution (FTTC) • Transmissions occur between OLT and the ONUs • No active elements in signals' path • Employ passive combiners, couplers and splitters only. • Ethernet PON • Data is encapsulated in Ethernet frames • IEEE 802.3ah – Ethernet in the first mile

2. Ethernet Passive Optical Networks Example of EPON architecture for Access Networks

3. Ethernet Passive Optical Networks Transmissions in an EPON Downlink Broadcasting ONUs select their packets based on MAC address Uplink ONUs compete for using the channel CSMA cannot be used, since collisions cannot be avoided Solution : TDM with polling arbitration scheme (MPCP protocol) Scheduling in EPON Uplink transmissions require scheduling Two parts Inter-ONU (arbitrated by the OLT) Given by the dynamic bandwidth allocation algorithm Intra-ONU IEEE 802 family : Strict priority scheduling, class based

4. Ethernet Passive Optical Networks Scheduling in EPON Intra-ONU scheduling can be arbitrated either by the OLT or by the ONU Both approaches have drawbacks When arbitrated by the ONU, fairness among users from different ONU cannot be assured. When arbitrated by the OLT, scalability issues arises. Number of classes must be small Session-by-session scheduling is unachievable

5. Ethernet Passive Optical Networks • Our proposal • We propose an hierarchical scheduling approach to circumvent both drawbacks • A utility function is defined for each session • For a given session, the utility function represents the benefit of receiving some amount of bandwidth • The utility functions reflect either the demand or the target performance of the sessions • A weight is assigned to each session • For the system, the weights represent the benefit of allocating some amount of bandwidth to each session • The weights reflect either the priority or the willingness-to-pay of the sessions • Bandwidth is dynamically allocated so that the weighted sum of the utility is maximized over time (utility-based fairness approach) • OLT consolidates the demand of all ONU • ONU performs the intra-ONU based on the global demand information received from OLT and the utility of the sessions

6. Ethernet Passive Optical Networks Advantages QoS orientation Individual bounds on performance metrics (latency and delay) can be obtained Fairness Utility-based fairness Fairness is assured even among sessions from different ONUs Scalability Session-by-session scheduling is achieved Limit is mostly given by the capacity of the network Simplicity The arbitration process requires less information and computation Most of the computation is performed at ONU or at the users premises, in a distributed manner MPCP arbitration messages can be made shorter