Next Generation EPON-based Access Network Architecture

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Next Generation EPON-based Access Network
Architecture
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Access Network
Link between the customer premises and the first
point of connection to the network
infrastructurea point of presence (PoP) or
central office (CO).
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Ethernet in the Last Mile
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Access Bandwidth
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Optical Access
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What is Passive Optical Network

• Passive Optical Networks (PON) are
  point-to-multipoint optical networks with no
  active elements in the signals path from source
  to destination.
• Advantages of PON
• PON allows longer distances between CO and
  customer 20 km for PON vs. 5.5 km for DSL
• PON provides higher bandwidth.
• Allows downstream continuous broadcasting
  (video).
• Eliminates electronic devices in the middle of
  the network.
• Allows easy upgrades to higher bit rates or
  additional wavelengths.

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Basic Architecture of PON
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EPON Downstream
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EPON Upstream
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EPON Configuration
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EPON Performance

• EPON Media Access Control (MAC) uses Ethernet
  framing and line coding.
• Downstream channel uses true broadcast.
• Packets extracted by the MAC addresses.
• Not different from any shared-medium Ethernet
  LAN.
• Upstream transmission uses multiple access.
• Which multiple access scheme? (Problem)

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Multiple Access Schemes
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Statistical TDMA

• Time synchronization among ONUs cannot be easily
  achieved
• Who drives the clock?
• How do we achieve synchronization?
• Ethernet in the first mile task force (IEEE
  802.3ah) recommends Multipoint Control Protocol
  (MPCP).
• Work is still in progress.
• MPCP is not concerned with a particular
  bandwidth-allocation scheme.
• MPCP supports mechanism that can facilitate
  various implementation of bandwidth allocation
  algorithms.

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Timing Issues

• Ranging - RTT Measurement
• 1. OLT sends GATE at absolute T1
• 2. ONU receives GATE at T2,
• and resets local counter to show T1
• 3. ONU sends REPORT at time T3, showing timestamp
  T4
• 4. OLT receives REPORT at absoluteT5
• RTT T2-T1T5-T3
• RTT T5-T4
• T3-T2 T4-T1

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Multipoint Control Protocol (MPCP) Operation

• This protocol relies on two Ethernet messages
  GATE and REPORT.
• (Additionally MPCP defines REGISTER REQUEST,
  REGISTER, and REGISTER ACK messages used for an
  ONUs registration.)
• A GATE message is sent from the OLT to an ONU.
• It is used to assign a transmission timeslot.
• A REPORT message is used by an ONU to convey its
  local conditions (such as buffer occupancy, and
  the like) to the OLT to help the OLT make
  intelligent allocation decisions.
• Both GATE and REPORT messages are MAC (media
  access control) control frames (type 88-08) and
  are processed by the MAC control sublayer.

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Statistical multiplexing

• Burst time and size are hard to predict.
• Must use schemes with feedback (like polling).
• Hub polling would work, but walk times are very
  large.
• Roll-call polling also works, but it requires
  ONUs to listen to each other.
• PON should be deployed as a broadcasting star or
  passive ring (too restrictive).
• Proposed IEEE EFM standard solution Interleave
  polling routines in time.

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Interleaved polling scheme
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Advantages of Interleaved Polling Scheme

• Bandwidth utilization.
• If only one ONU is active, it can use up to 600
  Mbps (with 5 µs guard band).
• Lower delay.
• Delay is bounded by RTT, not frame time. Under
  maximum load behaves like TDMA system.
• No ONUs synchronization necessary.
• ONU sends data immediately on receiving
  (processing) the control message (Grant). No
  centralized framing necessary.
• All smarts are in OLT.
• OLT may use various scheduling algorithms based
  on SLA, type of traffic, etc.
• Fast detection of disconnected ONU.
• Disconnected ONU consumes only 0.0005 of PON
  bandwidth.

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Ethernet TCP/IP Frame
100Base CU Burst 31 1518Byte Frames per Burst
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DBA Scheme

• This algorithm is cycle-based, where a cycle is
  defined as the time that elapses between two
  executions of the scheduling algorithm.
• The ONU will be granted the requested number of
  bytes, but no more than a given predetermined
  maximum WMAX (maximum transmission window). If
  Reqi is the requested bandwidth of ONUi and
  Granti is the granted bandwidth, Granti is then
  equal to

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Class-of-Service Considerations

• Performance in EPON can be characterized by
  several parameters
• bandwidth
• packet delay (latency), delay variation, jitter
• packet-loss ratio
• Quality of service (QoS) refers a networks to
  ability to provide bounds on some or all these
  parameters on a per-connection (flow, session)
  basis.
• Not all networks, however, can maintain
  per-connection state or even identify
  connections.
• To support diverse application requirements,
  networks separate all the traffic into a limited
  number of classes and provide differentiated
  service for each class.
• Such networks are said to maintain classes of
  service (CoS).

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Overview of IEEE 802.1D Support for Classes of
Service

1. Network control. Characterized by a must get
   there requirement to maintain and support the
   network infrastructure.
2. Voice. Characterized by less than 10-ms delay,
   and hence maximum jitter oneway transmission
   through the local-area-network (LAN)
   infrastructure of a single campus.
3. Video. Characterized by less than 100-ms delay.
4. Controlled load. Important business applications
   subject to some form of admission control, be
   that preplanning of the network requirement at
   one extreme to bandwidth reservation per flow at
   the time the flow is started at the other.
5. Excellent effort. Or CEOs best effort, the
   best-effort-type services that an information
   services organization would deliver to its most
   important customers.
6. Best effort. LAN traffic as we know it today.
7. Background. Bulk transfers and other activities
   that are permitted on the network but that should
   not affect the use of the network by other users
   and applications.

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Dynamic Bandwidth Allocation
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Timeslot utilization is less than 100

• Packets cannot be fragmented.
• If the next packet to be transmitted is larger
  than the remainder of timeslot, the packet will
  wait for the next timeslot gt the timeslot will
  be transmitted with an unused remainder at the
  end.

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Why timeslot adjustment wont work

• Why timeslot adjustment wont work
• Linear increase in offered load requires
  exponential increase in timeslot size.
• Increased timeslot size will increase timeslot
  period gt will increase packet delay.
• Timeslot adjustment should be based on traffic
  load.
• However, due to burstiness of traffic at every
  timescale, no load prediction is possible based
  on previous load.

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Drawbacks of OLT based DBA

• OLT-ONU is 20km and a control messages (REQUEST
  and GRANT) consumes significant portion of the
  valuable upstream bandwidth.
• ONUs traffic changes dynamically and very bursty
  in nature thus most recent buffer status is not
  at hand when OLT makes DBA allocation.
• CoS cannot be truly support by centralized DBA
  decision as OLT relies on inter-ONU scheduling
  for optimal solution and hence fails to take into
  account critical QoS parameters while arbitrating
  between ONUs.

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Proposed New PON Architecture (In-band Signaling)
ONU
Redirected 1310nm signal
OLT
1550nm
1310nm
ONU
Splitter/ Combiner

• Control Plane
• 1310nm channel
• Data Plane
• Upstream 1310nm channel
• Downstream 1550nm channel

ONU
ONU
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Algorithm (DBA)
Control
Data
Time
Individual ONU update messages
Individual ONU data messages
a) First Phase
a) First Phase
Combining of ONU update messages
Combining of ONU data messages
b) Second Phase
b) Second Phase
Combined ONU update messages
Combined ONU data messages
Combined ONU data messages
Combined ONU update messages
c) Third Phase
c) Third Phase
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Distributed DBA for EPON In-band Control Plane

• Using (Splitter/Combiner) we reflect 1310nm
  upstream bound signal.
• We use REQUEST Control frames to update all ONUs
  of the current ONUs buffer info.
• After receiving all updates from all ONUs (max.
  64), each ONU independently run DBA and arrive at
  one unique timeslot allocation per ONU.
• A copy of the REQUEST also propagates to OLT and
  it also can run the same DBA to know which ONU is
  transmitting when.
• CoS could be easily factored into the DBA
  decision.

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Distributed DBA for EPON In-band Control Plane
(Cont.)

• A portion of the upstream bandwidth is consumed
  to establish the control plane, however it is
  very small (less than 5).
• Time synchronization among ONUs is an issue
• Fixed downstream frame sizes could be used to
  derive time synchronization.
• The average radius from the Splitter/Coupler to
  ONUs is less than 1km and we propose to have a
  fixed distance of 1 km to avoid time delay
  issues.
• The proposed cycle time (window size) is 2ms
• Optimized cycle time would be investigated under
  various traffic load and QoS requirements.

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Proposed New PON Architecture (Out-of-band
Signaling)
ONU
Splitter/ Combiner
OLT
ONU
1550nm
1310nm

• Control Plane
• Fixed Wireless LAN
• Data Plane
• Ethernet Passive Optical Network

ONU
ONU
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Distributed DBA for EPON Out-of-band Control
Plane
Control Plane
i
Control
Data
Data Plane
i1

• Since ONUs are with in less than 2km diameter, we
  can use fixed wireless to establish the control
  plane.
• Control information from the ith window is used
  to run DBA for timeslot allocation per ONU.
• Out-of-band signaling relieves the upstream
  channel to be fully utilized for data traffic
  only.

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Thesis Proposal

• To develop and implement a fully distributed
  EPON-based dynamic bandwidth allocation
  algorithm.
• The work will be carried out in two stages
• Simulation studies using OPNET and other tools.
• Physical implementation of DBA in the lab test
  bed.
• Simulation data will be compared to the empirical
  data obtained from the lab experiments.
• The proposed Next Generation EPON-based
  Architecture will unleash the Access bandwidth
  bottleneck and support total packed-based QoS
  guaranteed new applications.

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Testbed SETUP
Wireless Access Card
SM Fiber (500 m)
GigE Card
Workstation1 (ONU)
3X3 Splitter/ Combiner
Workstation2 (ONU)
Isolator
SM Fiber (500 m)
SM Fiber (500 m)
SM Fiber (20 Km)
GigE Card
Server (OLT)
Workstation 3 (ONU)