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

Ethernet Passive Optical Networks Example of EPON architecture for Access Networks

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

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

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

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