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