Analytical Approach to Dynamic
Bandwidth Allocation Algorithm
used in LRPON
MS Thesis Defense + PhD Qualifiers
Anu Mercian
Committee Members:
Martin Reisslein (Chair)
Michael McGarry
Cihan Tepedelenlioglu
Yanchao Zhang
Agenda
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Passive Optical Networks (PON)
Long-Range PON (LRPON)
Dynamic Bandwidth Allocation (DBA)
Part 1: Multi-threading Polling
Part 2: Parallel Polling
Part 3: Multi-polling techniques
Conclusion
Future Works
INTRODUCTION
• We live in a bandwidth-hungry world with services
demanding superior performance in voice, data and
video services
Passive Optical Networks
• When the physical layer is Optic Fibers, bandwidth
obtained in the higher layers is promising
© wikipedia
Structure of PON
Downstream
Traffic
Upstream
Traffic
© [20] G. Kramer, G. Pesavento. Ethernet Passive Optical Network(EPON): Building a next
Generation Optical Access Network
Evolution of PON
• APON – ATM passive optical networks
• BPON – Broadband PON (~622Mbps)
• EPON – Ethernet PON (more widespread(easy
overlay))
• GPON – higher bandwidth (larger variable length
packets) (ITU G.984)
• GEPON – within the Ethernet, gigabit availability
• LRPON – long-reach to allow >20km (~100km)
© Glen Kramer, Gerry Pesavento; Ethernet Passive Optical Network(EPON): Building a
Next Generation Opitcal Access Network
Importance of LRPON
• High CapEx and OpEx involved in PON deployment to cover
large area with a OLT/Central office for every 20Km of
distribution
• LRPON covers 100Km reducing CapEx and OpEx
• Reduction in active sites leads to larger distances
Multi Point Control Protocol
IEEE 802.3ah standard
© Michael P.McGarry, Martin Reisslein, Martin Maier; Ethernet
Passive Optical Network Architectures and Dynamic Bandwidth
Allocation Algorithms
Dynamic bandwidth allocation
• Static Bandwidth Allocation – Each link is given a standard
BW allocated.
• Disadvantages of SBA
• Necessity of Dynamic Bandwidth Allocation – Statistical
Multiplexing
• Design Space [22]:
– Grant scheduling framework
– Grant sizing schemes
– Scheduling Policies
© [22] M.P. McGarry; M. Reisslein. Investigation of the DBA Algorithm
Design Space for EPONs
Grant Scheduling framework
• Online or IPACT(Interleaved Polling with Adaptive
Cycle time)
• Offline
Grant sizing schemes
• Fixed
• Gated
• Limited
Scheduling Policies
• Shortest Propagation Delay
Where τ is the half RTT
• Shortest Grant or Shortest Processing Time
First(SPT)
Problem Statement I
• LRPON promises less OpEx and CapEx but the large
propagation delay gives poor delay performance.
• A Solution – Multi-thread polling (MTP)[16].
• Discrepancies in MTP: MTP gives good delay
performance when compared to offline scheduling
framework. But is it better than online technique?
© [16] H. Song et. al. Multi-thread polling: A Dynamic Bandwidth
Distribution Scheme in LPON
Delay Analysis
• Polling delay
• Granting delay
• Queuing Delay
• Channel Utilization[22]
Multi-Thread Polling
• Idea is to send request before the previous Gate
message is received creating a new thread
© [16] H. Song et. al. Multi-thread polling: A Dynamic Bandwidth
Distribution Scheme in LPON
Features of MTP
• Tuning Multiple Threads
• Inter-thread Scheduling
• Achieving Fairness
Reduced Delay in MTP
• Polling delay
• Granting Delay
• Queuing delay
MTP: Analysis
• MTP based on design space is (multiple-offline,
excess)
• Polling delay for MTP is less because it has another
opportunity in the same cycle
• Granting delay for IPACT is less because IPACT is
online, and does not involve wait time
• Overall delay for IPACT is lower
Experiment Settings
• Simulator used: Simulator developed using CSIM
discrete event simulation library
• Channel settings
– Channel Capacity C = 1 Gbps
– Number of ONUs M = 16
– Max Grant size = 7688bytes
• Self-similar traffic
– Quad model packet size distribution
– 60% 64bytes, 4% 300bytes, 11% 580bytes, 25% 1518bytes
• Same distance between ONU and OLT
Results
Distance between ONU and OLT = 100Km
Overall Delay
Results
Distance between ONU and OLT = 20 Km
Channel Utilization
Overall Delay
Problem Statement II
• Offline technique was extended to obtain a multithread process which gave delay performance better
than offline but not as good as IPACT. What if online
was extended as a multi-process?
Concept of Parallel Polling
• Multiple online processes in parallel
• Motivation:
– IPACT performs better than Multiple-offline threads so
multi-online could be even better
– Issues in Multi-thread process: Problem of wait time or idle
time
– Fairness Issue
– Void formation
Parallel Polling: A possible solution
• Each cycle time has two threads in parallel with each
one services as online
Advantages of PP
• PP is based on online grant scheduling framework,
therefore low idle time and hence high utilization
• No issue of fairness issue as GRANT is given as per
REPORTed
• Thread tuning will be required and compared
between the effective cycle load
• Easy and simple implementation
Delay performance of PP
• Polling delay
• Granting delay
• Queuing delay
Delay Comparison
• Polling delay of PP will be slightly less than MTP as
the cycle length of online process is less than the
offline
• Granting delay for PP is very less when compared to
MTP because of online technique
• Queuing delay is same for same simulator settings
• Therefore,
Results
Distance between ONU and OLT = 100Km
Channel Utilization
Overall Delay
Results
Distance between ONU and OLT = 20Km
Channel Utilization
Overall Delay
Problem Statement III
• MTP is better than offline scheduling framework
• PP is better than online scheduling framework
• So multiple polling of OLT is advantageous for
LRPON?
Multiple polling techniques
• Multi-thread polling[16]
• Parallel Polling
• Double Phase polling[2], can be also called Multigroup polling
© [2] S.Y. Choi et. al. Double Phase Polling Algorithm Based on Partitioned ONU Subgroups
for High Utilization in EPONs
Results
Distance between ONU and OLT = 100Km
Channel Utilization
Overall Delay
Results
Distance between ONU and OLT = 20Km
Channel Utilization
Overall Delay
Conclusions
• MTP is good for LRPON when compared to offline
but not when compared to online
• PP gives comparatively best delay performance for
LRPON
• Multiple polling techniques in one cycle time gives
promising results for LRPON with QoS awareness
• Channel utilization of PP and IPACT are high when
compared to Multi-group, offline and MTP
Future Work
• Can scheduling policies be useful for techniques
based on offline grant scheduling framework?
• Can fairness be achieved in PP using online excess
bandwidth distribution (OEBD)
• PP a new technique and can be explored further. will
it be promising for GPON as well?
• Can multiple polling techniques be of use to LRPON
• Consideration of performance of Real-time polling
with respect to current multi-polling techniques
• How will these DBA schemes perform with video
and voice traffic.
• What if distances between ONU and OLT are
random, how will the techniques perform?
• How can delay performance for PP be improved for
SRPON.
THANK YOU
and
Questions?
References
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BACK UP
Basis study
• Availability of many DBA schemes in research
brings a need to classify these DBA schemes based
on their importance
Classification Description
• Existent classifications cover QoS aware and unaware
but their usability is not explicitly mentioned
• Connecting scheduling framework to user traffic type
and demand
– Direct
– Predictive
– Intelligent
EPON-LRPON Classification
Usability
• Direct – User’s that require high throughput but do
not compensate on fairness
• Predictive – User’s that have a flexible requirement
• Intelligent – When user’s of high load and low load
are combined
Results: Poisson
20Km
100Km
Channel Utilization
Overall Delay
Results: Poisson
20Km
100Km
Channel Utilization
Overall Delay
Results: Poisson
20Km
100Km
Channel Utilization
Overall Delay
Design Space Equations
• Offline
• Online
• DPP
• MTP
• PP
Idle time Equations
Multi-thread Polling
Parallel Polling