Analytical Approach to Dynamic Bandwidth Allocation Algorithm
used in LRPONMS Thesis Defense + PhD Qualifiers
Anu Mercian
Committee Members:
Martin Reisslein (Chair)
Michael McGarry
Cihan Tepedelenlioglu
Yanchao Zhang
Agenda
• 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 PONDownstream Traffic
UpstreamTraffic
© [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
• Shortest Grant or Shortest Processing Time First(SPT)
Where τ is the half RTT
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
ResultsDistance between ONU and OLT = 100Km
Overall Delay
Results
Channel Utilization Overall Delay
Distance between ONU and OLT = 20 Km
Problem Statement II• Offline technique was extended to obtain a multi-
thread 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,
ResultsDistance between ONU and OLT = 100Km
Overall DelayChannel Utilization
ResultsDistance 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 Multi-
group polling
© [2] S.Y. Choi et. al. Double Phase Polling Algorithm Based on Partitioned ONU Subgroups for High Utilization in EPONs
ResultsDistance between ONU and OLT = 100Km
Channel Utilization Overall Delay
ResultsDistance between ONU and OLT = 20Km
Overall DelayChannel Utilization
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?
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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
Channel Utilization Overall Delay
20Km
100Km
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
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