1. M. K. Multani, Arif-ur-Rahman, Asfand-e-yar
Partially Online Dynamic Bandwidth Allocation Algorithm for Hybrid TDM/WDM EPONs
M. K. Multani, Arif-ur-Rahman, Asfand-e-yar

2. Outline Motivation Related literature Methodology Results Conclusion
Future Directions

3. Motivation

4. Increase in Bandwidth Demand
In recent years there has been a tremendous increase in access network traffic due to the introduction of bandwidth-hungry applications
High definition TV
Video Conferencing
High Definition Internet Gaming
The existing copper infrastructure has become insufficient for satisfying these applications.
This has led to the increasing deployment of fiber optic networks

5. Passive Optical Network (PON)
A PON uses a single trunk fiber that extends from a central office to a passive optical splitter, which then fans out to multiple optical drop fibers connected to subscriber nodes CO
OLT
ONU 1
ONU 2
ONU 32
Optical
Splitter
Fig 1. Passive Optical Network
Backbone
Networks
Users
An OLT typically supports up to 32 ONUs. The OLT provides the interface between the PON and the backbone network. The main functionality of the OLT is to adapt the incoming traffic (Voice and Data) from the metropolitan rings into the PON transport layer. OLT sends optical signals out, which are immediately broken into several streams. ONU terminates the PON and presents the heterogeneous service interfaces to the user. ONU receives traffic in optical-format from OLT and transforms it into customer-format (Ethernet, IP multicast, POTS, T1, etc.).

6. Key EPON Schemes TDM EPON
Upstream: The common wavelength channel is shared among ONUs by time slot allocation
TDM EPON
Single wavelength channel is used for Upstream transmission and similarly a single channel for Downstream
Downstream: broadcast
Upstream: channel is common so it is shared either:
Statically: each ONU is given a fixed time slot
Dynamically: time slot allocation is dynamic considering the ONU traffic demand and overall network load
OLT
ONU 1
ONU 2
ONU 3
ONU 4
Downstream: The traffic is broadcast to all the ONUs over the shared wavelength channel

7. Key EPON Schemes WDM EPON
In WDM EPON each ONU is given an individual wavelength channel for upstream and downstream transmission
Bandwidth available to ONU for Upstream / Downstream transmission is not shared
In WDM EPON there is a need for wavelength allocation
Upstream/Downstream: Each ONU enjoys the full bandwidth of the wavelength channel allocated to it

8. Increase in Bandwidth Demand
TDM EPONs
Limited Bandwidth shared among multiple users
Cost-effective
WDM EPONs
Dedicated Bandwidth to each user for transmission
Costly
Objective:
Increase Bandwidth from the limited bandwidth provided by TDM EPON
Keeping the EPON Cost-effective
Method:
Hybrid TDM/WDM EPON

9. To design a bandwidth allocation algorithm to reduce average packet delay thus improving bandwidth utilization in Hybrid TDM/WDM EPON
Problem Definition

10. Related Literature

11. Related Literature
[1] Ahmad R. Dhaini, Chadi M. Assi, Martin Maier and Abdallah Shami, “Dynamic Wavelength and Bandwidth Allocation in Hybrid TDM/WDM EPON Networks”, Journal of Lightwave Technology, Vol. 25, No. 1, January 2007.
[2] Ahmad R. Dhaini, Chadi M. Assi, and Abdallah Shami, “Dynamic Bandwidth Allocation Schemes in Hybrid TDM/WDM Passive Optical networks”, IEEE CCNC proceedings, pp
[3] J. Zheng, “Efficient bandwidth allocation algorithm for Ethernet passive optical networks”, IEE Proc-Commun, June 2006.
[4] J. Zheng, and S. Zheng, “Dynamic Bandwidth Allocation with High Efficiency for EPONs”, IEEE ICC, 2006.

12. [1, 2] DWBA-2 Type: Hybrid TDM/WDM Approach: Dynamic
Control: Centralized
Motivation: To provide bandwidth allocation in Hybrid TDM/WDM PON with smaller average packet delay by reducing idle time
Mechanism: On the fly allocation on the basis of minimum guaranteed bandwidth
BiMIN = BMIN = ( (Tcycle − N × Tg) × RN × K) / (8 × N)
Extract: Aggregated BW grants, On the fly allocation to Lightly loaded ONUs
Benefit: Aggregated, On the fly allocation to Lightly loaded ONUs reduces the idle time between the reception of all REPORT messages at the OLT and the sending of GATE messages to the lightly loaded ONUs, thus reducing overall packet delay
Weakness: The OLT has to wait until all REPORT messages in a cycle have been received before it allocates bandwidth to highly loaded ONUs. This causes packet delay to increase.
[1, 2] DWBA-2
[1] Ahmad R. Dhaini, Chadi M. Assi, Martin Maier and Abdallah Shami, “Dynamic Wavelength and Bandwidth Allocation in Hybrid TDM/WDM EPON Networks”, Journal of Lightwave Technology, Vol. 25, No. 1, January 2007.
[2] Ahmad R. Dhaini, Chadi M. Assi, and Abdallah Shami, “Dynamic Bandwidth Allocation Schemes in Hybrid TDM/WDM Passive Optical networks”, IEEE CCNC 2006 proceedings, pp

13. [1, 2] DWBA-3 Type: Hybrid TDM/WDM Approach: Dynamic
Control: Centralized
Motivation: To provide bandwidth allocation in Hybrid TDM/WDM PON with smaller average packet delay by reducing idle time
Mechanism: On the fly allocation on the basis of minimum guaranteed bandwidth
BiMIN = BMIN = ( (Tcycle − N × Tg) × RN × K) / (8 × N)
Extract: Two separate BW grants to highly loaded ONUs, On the fly allocation to Lightly loaded ONUs
Benefit: On the fly allocation to Lightly loaded ONUs reduces the idle time between the reception of all REPORT messages at the OLT and the sending of GATE messages to the lightly loaded ONUs, thus reducing overall packet delay
Weakness: The algorithm splits up the grant for highly loaded ONUs into two separate grants. This means that bigger packets cannot be transmitted by the ONU in the smaller grant windows and causes increased packet delay. Aggregating the grants would provide better results.
[1, 2] DWBA-3
[1] Ahmad R. Dhaini, Chadi M. Assi, Martin Maier and Abdallah Shami, “Dynamic Wavelength and Bandwidth Allocation in Hybrid TDM/WDM EPON Networks”, Journal of Lightwave Technology, Vol. 25, No. 1, January 2007.
[2] Ahmad R. Dhaini, Chadi M. Assi, and Abdallah Shami, “Dynamic Bandwidth Allocation Schemes in Hybrid TDM/WDM Passive Optical networks”, IEEE CCNC 2006 proceedings, pp

14. Network Architecture
In this architecture time/wavelength are shared among all ONUs
Sharing is arbitrated by OLT using Dynamic Wavelength & Bandwidth Allocation (DWBA)
Optical Fiber
OLT Tx Rx
ONU1
ONUn
Users
Tunable Laser
Splitter/Combiner
k Wavelengths
Algorithm Simulated for 64
ONUs with 2 λs in [1, 2]
Algorithm Simulated for 16,
32, 64 ONUs with 2 λs in [5]
The service contents are multiplexed and broadcast downstream; then these broadcast signals are fanned into individual fibre connected to ONUs by the splitter. Upstream transmissions from all ONUs are controlled and scheduled in a timely manner by the OLT [6]
This WDM PON proposed is identical to the single channel PON except that the OLT is equipped with multiple transceivers to support parallel transmission in the fibre. [6]
The ONUs support all the wavelengths in use in the network
[5] K. H. Kwong, D. Harle, and I. Andonovic, “Dynamic bandwidth allocation algorithm for differentiated services over
WDM EPONs,” in Proc., IEEE ICCS, Singapore, Sep. 2004, pp. 116–120.

15. Assumptions Initially Lightly Loaded ONUs ONUs transmitting at 10Mbps
Initially Highly Loaded ONUs
ONUs transmitting at 20, 30, … 100Mbps
Each ONU is serviced at least once in each cycle
Each ONU gets a minimum guaranteed bandwidth in each cycle
There are two upstream wavelengths. OLT keeps track of when each λ will become free
Assumptions

16. Type: TDM
Approach: Dynamic
Control: Centralized
Motivation: To reduce delays in TDM EPON by reducing idle time
Mechanism: On the fly allocation on the basis of minimum guaranteed bandwidth
BiMIN = ( (Tcycle − N × Tg) × RN × wi) / 8
Extract: On the fly allocation to LL ONUs, granting accumulated excess BW to highly loaded ONU before all lightly loaded ONUs are processed if no REPORT is received from a lightly loaded ONU by time (tend – RTT/2) where tend is the end of the time slot of the last scheduled ONU.
Benefit: On the fly allocation to lightly loaded ONUs reduces idle time and thus packet delay. Allocating bandwidth to highly loaded ONUs based on time condition and not receiving REPORT message from a lightly loaded ONU also reduces idle time and improves bandwidth utilization
Weakness: Waiting till time (tend – RTT/2) before allocating excess bandwidth to highly loaded ONU can cause delay.
[3, 4] Efficient bandwidth allocation algorithm for Ethernet Passive Optical Networks
[3] J. Zheng, “Efficient bandwidth allocation algorithm for Ethernet passive optical networks”, IEE Proc-Commun, June 2006.
[4] J. Zheng, and S. Zheng, “Dynamic Bandwidth Allocation with High Efficiency for EPONs”, IEEE ICC, 2006.

17. Mechanism:
Lightly loaded (LL) ONUs are granted bandwidth on the fly
Excess bandwidth from these LL ONUs is accumulated
Grants Minimum Guaranteed Bandwidth to Highly loaded (HL) ONUs if no REPORT is received from a lightly loaded ONU by time (tend – RTT/2) where tend is the end of the time slot of the last scheduled ONU
[3, 4] Efficient bandwidth allocation algorithm for Ethernet Passive Optical Networks
[3] J. Zheng, “Efficient bandwidth allocation algorithm for Ethernet passive optical networks”, IEE Proc-Commun, June 2006.
[4] J. Zheng, and S. Zheng, “Dynamic Bandwidth Allocation with High Efficiency for EPONs”, IEEE ICC, 2006.

18. Our Solution
Use of Bandwidth Threshold for immediate (online) Bandwidth allocation for lightly loaded ONUs 1
Aggregated Bandwidth grants 2
ASAP allocation to least loaded ONUs among highly loaded ONUs 3

19. By incorporating Aggregated ASAP allocation to as many highly loaded ONUs as possible we can transmit the traffic in a timely manner & improve efficient allocation of bandwidth for upstream transmission measured by different performance parameters
Average Packet Delay
Average Queue Size
Bandwidth utilization
Rationale
The algorithms discussed before performed On the fly bandwidth allocation for lightly loaded ONUs but the key difference is in how they handle the grants to the highly loaded ONUs.
In one algorithms, the OLT waits till all REPORT messages in a cycle are received before granting BW to highly loaded ONUs. This grant is an aggregated grant (not split up).
In the second algorithm, the OLT splits the GRANT message for the highly loaded ONUs into two windows, one of Minimum Guaranteed Bandwidth and another is the share of the ONU in the excess bandwidth at the end of the cycle.
In the third algorithm, the OLT waits until time (tend – RTT/2) before granting Minimum Guaranteed BW to the highly loaded ONUS if, no REPORT message has been received from a lightly loaded ONUs until that time.

20. Methodology

21. Assumptions Initially Lightly Loaded ONUs ONUs transmitting at 10Mbps
Initially Highly Loaded ONUs
ONUs transmitting at 20, 30, … 100Mbps
Each ONU is serviced only once in each cycle
Each ONU is guaranteed the minimum guaranteed bandwidth in each cycle
There are two upstream wavelengths. OLT keeps track of when each λ will become free
OLT arbitrates time slot and wavelength allocation at the same time
Wavelengths are shared among all ONUs
Each ONU has a tunable laser and supports all wavelengths
Based on MPCP (Multipoint Control Protocol): uses REPORT and GATE messages for bandwidth management (extended to incorporate λ allocation)
For every REPORT message received OLT allocates next available channel

22. Simulation Parameters
The maximum link capacity was 1Gbit/s, even though 1.25Gbit/s is endorsed in the EPON specification. The difference is a result of adopting the 8b/10b channel encoding scheme, which decreases bandwidth utilization by 20%. [4]
Parameter
Description
Value N
No. of ONUs 64 RN
OLT to ONU Link rate
1 Gbps RU
User to ONU Link rate
100 Mbps K
No. of λs supported by OLT & each ONU 2 Q
ONU buffer size
1 MB L
Distance between OLT and ONU
20 km
Tcycle
Maximum Cycle Time
2 millisec Tg
Guard Time
1 µsec HL
Highly Loaded ONUs 32 22

23. ParOnD Bireq ≤ BMIN Start: Get REPORTs from ONUs
(sorted w.r.t arrival time)
i=0, Bexcess= 0
ParOnD
Pick REPORT[i] with Bireq
All BW requests for
current cycle granted?
Bireq ≤ BMIN No
Yes
Bigate = Bireq
Send GATE msg (next available λ)
Bexcess += BMIN – Bireq
i++ No
Yes
Find minimum Bjreq from
highly loaded ONUs
i++
Update REPORT table
i =0
Bexcess=0
All BW requests for
current cycle granted?
Yes No
Bexcess>(Bjreq – BMIN)
Yes
Bgate = Breq
Bexcess=Bexcess–Bjreq+BMIN
Send GATE msg (next available λ) No No
Last report of cycle?
For all BW requests > BMIN in current cycle
& not already served
Bgate = BMIN + (Share of ONU in Bexcess)
Send GATE msg (next available λ)
Yes

24. Results

25. Average Queue Depth (per cycle)
ParOnD reduces the average
queue depth of lightly loaded
ONUs by a minimum of
2400Bytes to a maximum
of 6000Bytes

26. Average Queue Depth (per cycle)
ParOnD reduces the average
queue depth in a cycle
of highly loaded
ONUs at low loads ( )
by a minimum of Bytes
to a maximum of 25000Bytes
and at medium loads ( )
by 1200 to 5200Bytes

27. Average Packet Delay ParOnD reduces average
packet delay at low loads ( )
by a minimum of 417 μsec
& a maximum of μsec,
and at medium loads ( )
by a minimum of 232 μsec
& a maximum of 631 μsec

28. Average Bandwidth Wasted

29. Average Bandwidth Wasted (per cycle) by ONUs at load 0.5

30. Conclusion

31. ParOnD reduces packet delay and average queue size at low to medium loads
DWBA-2 performance is minimally better than ParOnD at high loads
ParOnD reduces average queue sizes in ONUs to ultimately reduce the average number of heavily loaded ONUs in a cycle
ParOnD improves bandwidth utilization by reducing bandwidth wasted by each ONU in a cycle
E.g. at load 0.5, bandwidth wasted by a highly loaded ONU is reduced from 781 bytes per cycle to 412 bytes per cycle
Thus ASAP allocation of highly loaded ONUs improves the performance of our bandwidth allocation algorithm
Conclusion

32. Future Directions
Monitor the offered load and employ a modified version of this algorithm to overcome the packet delay at higher loads 1
Investigate the criteria for allocating bandwidth to highly loaded ONUs online (employ heuristics) 2
Incorporating wavelength assignment with restrictions on wavelengths supported by different ONUs 3

33. Thanks

34. [1]. Ahmad R. Dhaini, Chadi M
[1] Ahmad R. Dhaini, Chadi M. Assi, Martin Maier and Abdallah Shami,”Dynamic Wavelength and Bandwidth Allocation in Hybrid TDM/WDM EPON Networks”, Journal of Lightwave Technology, Vol. 25, No. 1, January 2007.
[2] J. Zheng, “Efficient bandwidth allocation algorithm for Ethernet passive optical networks”, IEE Proc-Commun, June 2006.
[3] J. Zheng, and S. Zheng, “Dynamic Bandwidth Allocation with High Efficiency for EPONs”, IEEE ICC, 2006.
[4] Dawid Nowak, “Dynamic Bandwidth Allocation Algorithms for Differentiated Services enabled Ethernet Passive Optical Networks with Centralized Admission Control”, (PhD Thesis) 2005
[5] K. H. Kwong, D. Harle, and I. Andonovic, “Dynamic bandwidth allocation algorithm for differentiated services over WDM EPONs,” in Proc., IEEE ICCS, Singapore, Sep , pp. 116–120.
[6] Kae-Hsiang Kwong, David Harle, Ivan Andonovic, “WDM PONs: Next Step for the First Mile”, HET-NETs 2004
[7] A.Banerjee,Y.Park,F.Clarke,H.Song,S.Yang,G.Kramer,K.Kim, and B. Mukherjee, Wavelength-division-multiplexed passive optical network (WDM-PON) technologies for broadband access: A review, OSA J. Opt. Netw., vol. 4, no. 11, pp , Nov
[8] Michael P. McGarry, Martin Reisslein,and Martin Maier, WDM Ethernet Passive Optical Networks, IEEE Comm. Mag., Feb. 2006, pp. S18- S25.
[9] Michael P. McGarry, and Martin Reisslein, Investigation of the DBA Algorithm Design Space for EPONs, IEEE J. Lightwave Technology, vol. 30, no. 14, pp , 2012
References

35. End