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Next Generation EPON-Next Generation EPON-based Access Networkbased Access Network
ArchitectureArchitecture
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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).
Customer
PremiseAccess Link
Merto PoP / CO
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Ethernet in the Last MileEthernet in the Last Mile
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Optical AccessOptical Access
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What is Passive OpticalWhat is Passive Optical
NetworkNetwork Passive Optical Networks (PON) are point-to-Passive Optical Networks (PON) are point-to-
multipoint optical networks with no active elementsmultipoint optical networks with no active elementsin the signals path from source to destination.in the signals path from source to destination.
Advantages of PONAdvantages of PON PON allows longer distances between CO and customer: 20PON allows longer distances between CO and customer: 20
km for PON vs. 5.5 km for DSLkm for PON vs. 5.5 km for DSL
PON provides higher bandwidth.PON provides higher bandwidth.
Allows downstream continuous broadcasting (video).Allows downstream continuous broadcasting (video).
Eliminates electronic devices in the middle of the network.Eliminates electronic devices in the middle of the network.
Allows easy upgrades to higher bit rates or additionalAllows easy upgrades to higher bit rates or additionalwavelengths.wavelengths.
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Basic Architecture of PON
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EPON DownstreamEPON Downstream
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EPON UpstreamEPON Upstream
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EPON ConfigurationEPON Configuration
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EPON PerformanceEPON Performance
EEPON Media Access Control (MAC) uses Ethernet framingand 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 SchemesMultiple Access Schemes
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Statistical TDMAStatistical TDMA
Time synchronization among ONUs cannot beTime synchronization among ONUs cannot beeasily achieved:easily achieved: Who drives the clock?Who drives the clock?
How do we achieve synchronization?How do we achieve synchronization?
Ethernet in the first mile task force (IEEE 802.3ah)Ethernet in the first mile task force (IEEE 802.3ah)recommends Multipoint Control Protocol (MPCP).recommends Multipoint Control Protocol (MPCP). Work is still in progress.Work is still in progress.
MPCP is not concerned with a particular bandwidth-MPCP is not concerned with a particular bandwidth-allocation scheme.allocation scheme.
MPCP supports mechanism that can facilitate variousMPCP supports mechanism that can facilitate variousimplementation of bandwidth allocation algorithms.implementation of bandwidth allocation algorithms.
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Timing IssuesTiming Issues
Ranging - RTTMeasurement
1. OLT sends GATE atabsolute T1
2. ONU receives GATE at T2,and resets local counter to
show T13. ONU sends REPORT at
time T3, showingtimestamp T4
4. OLT receives REPORT atabsoluteT5
RTT = T2-T1+T5-T3
RTT= T5-T4
T3-T2 = T4-T1
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Multipoint Control ProtocolMultipoint Control Protocol
(MPCP) Operation(MPCP) OperationThis protocol relies on two Ethernet messages: GATEThis protocol relies on two Ethernet messages: GATE
and REPORT.and REPORT. (Additionally MPCP defines REGISTER REQUEST, REGISTER, and(Additionally MPCP defines REGISTER REQUEST, REGISTER, and
REGISTER ACK messages used for an ONUs registration.)REGISTER ACK messages used for an ONUs registration.)
A GATE message is sent from the OLT to an ONU.A GATE message is sent from the OLT to an ONU. It is used to assign a transmission timeslot.It is used to assign a transmission timeslot.
A REPORT message is used by an ONU to convey itsA REPORT message is used by an ONU to convey itslocal conditions (such as buffer occupancy, and the like)local conditions (such as buffer occupancy, and the like)to the OLT to help the OLT make intelligent allocationto the OLT to help the OLT make intelligent allocationdecisions.decisions.
Both GATE and REPORT messages are MAC (mediaBoth GATE and REPORT messages are MAC (mediaaccess control) control frames (type 88-08) and areaccess control) control frames (type 88-08) and areprocessed by the MAC control sublayer.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 InterleavedAdvantages of Interleaved
Polling SchemePolling Scheme Bandwidth utilization.Bandwidth utilization.
If only one ONU is active, it can use up to 600 Mbps (with 5If only one ONU is active, it can use up to 600 Mbps (with 5s guard band).s guard band).
Lower delay.Lower delay. Delay is bounded by RTT, not frame time. Under maximumDelay is bounded by RTT, not frame time. Under maximum
load behaves like TDMA system.load behaves like TDMA system. No ONUs synchronization necessary.No ONUs synchronization necessary.
ONU sends data immediately on receiving (processing) theONU sends data immediately on receiving (processing) thecontrol message (Grant). No centralized framing necessary.control message (Grant). No centralized framing necessary.
All smarts are in OLT.All smarts are in OLT.
OLT may use various scheduling algorithms based on SLA,OLT may use various scheduling algorithms based on SLA,type of traffic, etc.type of traffic, etc.
Fast detection of disconnected ONU.Fast detection of disconnected ONU. Disconnected ONU consumes only ~0.0005% of PONDisconnected ONU consumes only ~0.0005% of PON
bandwidth.bandwidth.
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Ethernet TCP/IP FrameEthernet TCP/IP Frame
100Base CU Burst: 31 1518Byte Frames per Burst
S h
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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). IfReqi is the requested bandwidth of ONU
iand Grant
iis the granted bandwidth,
Grantiis then equal to
{ MAXiiMAX
iMAX
WReqifReq
WReqifWiGrant
the timeslot will be
transmitted with an unused remainder at the end.
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Why timeslot adjustment wontwork
Why timeslot adjustment wont work Linear increase in offered load requires
exponential increase in timeslot size.
Increased timeslot size will increase timeslotperiod => will increase packet delay.Timeslot adjustment should be based on
traffic load.
However, due to burstiness of traffic atevery timescale, no load prediction ispossible based on previous load.
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Drawbacks of OLT based DBADrawbacks of OLT based DBA
OLT-ONU is 20km and a control messagesOLT-ONU is 20km and a control messages(REQUEST and GRANT) consumes significant(REQUEST and GRANT) consumes significantportion of the valuable upstream bandwidth.portion of the valuable upstream bandwidth.
ONUs traffic changes dynamically and veryONUs traffic changes dynamically and very
bursty in nature thus most recent buffer statusbursty in nature thus most recent buffer statusis not at hand when OLT makes DBA allocation.is not at hand when OLT makes DBA allocation.
CoS cannot be truly support by centralized DBACoS cannot be truly support by centralized DBAdecision as OLT relies on inter-ONU schedulingdecision as OLT relies on inter-ONU scheduling
for optimal solution and hence fails to take intofor optimal solution and hence fails to take intoaccount critical QoS parameters whileaccount critical QoS parameters whilearbitrating between ONUs.arbitrating between ONUs.
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OLT
ONU
ONU
ONU
ONU
Control Plane: 1310nm channel
Data Plane: Upstream: 1310nm channel Downstream: 1550nm channel
1550nm
1310nm
Redirected
1310nm signal
Splitter/
Combiner
roposed New PON Architecture(In-band Signaling)
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3xNS/C
ONU
ONU
ONU
OLT
3xNS/C
ONU
ONU
ONU
OLT
3xNS/C
ONU
ONU
ONU
OLT
3xNS/C
ONU
ONU
ONU
OLT
Control Data
a) First Phase
b) Second Phase
c) Third Phase
3xNS/C
ONU
ONU
ONU
OLT
3xNS/C
ONU
ONU
ONU
OLT
a) First Phase
b) Second Phase
c) Third Phase
Algorithm (DBA)
Individual ONU update messages
Combined ONU
update messages
Individual ONU data messages
Combined ONU
data messages
[Time]
Combining of ONU update messages Combining of ONU data messages
Combined ONU data messages
Combined ONU
update messages
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Distributed DBA for EPON:Distributed DBA for EPON:
In-band Control PlaneIn-band Control Plane Using (Splitter/Combiner) we reflect 1310nmUsing (Splitter/Combiner) we reflect 1310nm
upstream bound signal.upstream bound signal. We use REQUEST Control frames to update allWe use REQUEST Control frames to update all
ONUs of the current ONUs buffer info.ONUs of the current ONUs buffer info.
After receiving all updates from all ONUs (max.After receiving all updates from all ONUs (max.64), each ONU independently run DBA and64), each ONU independently run DBA andarrive at one unique timeslot allocation per ONU.arrive at one unique timeslot allocation per ONU.
A copy of the REQUEST also propagates to OLTA copy of the REQUEST also propagates to OLTand it also can run the same DBA to know whichand it also can run the same DBA to know which
ONU is transmitting when.ONU is transmitting when. CoS could be easily factored into the DBACoS could be easily factored into the DBA
decision.decision.
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Distributed DBA for EPON:Distributed DBA for EPON:
In-band Control Plane (Cont.)In-band Control Plane (Cont.) A portion of the upstream bandwidth isA portion of the upstream bandwidth is
consumed to establish the control plane,consumed to establish the control plane,however it is very small (less than 5%).however it is very small (less than 5%).
Time synchronization among ONUs is an issue:Time synchronization among ONUs is an issue:
Fixed downstream frame sizes could be used to deriveFixed downstream frame sizes could be used to derivetime synchronization.time synchronization. The average radius from the Splitter/Coupler to ONUsThe average radius from the Splitter/Coupler to ONUs
is less than 1km and we propose to have a fixedis less than 1km and we propose to have a fixeddistance of 1 km to avoid time delay issues.distance of 1 km to avoid time delay issues.
The proposed cycle time (window size) is 2msThe proposed cycle time (window size) is 2ms Optimized cycle time would be investigated underOptimized cycle time would be investigated under
various traffic load and QoS requirements.various traffic load and QoS requirements.
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OLT
ONU
ONU
ONU
ONU
Splitter/
Combiner1550nm
1310nm
Control Plane: Fixed Wireless LAN
Data Plane: Ethernet Passive Optical Network
roposed New PON Architecture(Out-of-band Signaling)
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Data Data Plane
i
i+1
Control PlaneControl
Distributed DBA for EPON:Distributed DBA for EPON:
Out-of-band Control PlaneOut-of-band Control Plane
Since ONUs are with in less than 2km diameter, we canSince ONUs are with in less than 2km diameter, we canuse fixed wireless to establish the control plane.use fixed wireless to establish the control plane.
Control information from the ith window is used to runControl information from the ith window is used to runDBA for timeslot allocation per ONU.DBA for timeslot allocation per ONU.
Out-of-band signaling relieves the upstream channel toOut-of-band signaling relieves the upstream channel tobe fully utilized for data traffic only.be fully utilized for data traffic only.
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Thesis ProposalThesis Proposal
To develop and implement a fully distributed EPON-To develop and implement a fully distributed EPON-based dynamic bandwidth allocation algorithm.based dynamic bandwidth allocation algorithm.
The work will be carried out in two stages:The work will be carried out in two stages: Simulation studies using OPNET and other tools.Simulation studies using OPNET and other tools. Physical implementation of DBA in the lab test bed.Physical implementation of DBA in the lab test bed.
Simulation data will be compared to the empirical dataSimulation data will be compared to the empirical dataobtained from the lab experiments.obtained from the lab experiments.
The proposed Next Generation EPON-basedThe proposed Next Generation EPON-basedArchitecture will unleash the Access bandwidthArchitecture will unleash the Access bandwidthbottleneck and support total packed-based QoSbottleneck and support total packed-based QoS
guaranteed new applications.guaranteed new applications.
Testbed SETUP
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3X3
Splitter/
Combiner
Isolator
Workstation1 (ONU)
Workstation 3 (ONU)
Workstation2 (ONU)
Server (OLT)
Wireless Access Card
GigE Card
GigE Card
SM Fiber (500 m)
SM Fiber (500 m)
SM Fiber (500 m)
SM Fiber (20 Km)
Testbed SETUP