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Frontiers of Optoelectronics

Front. Optoelectron.    2019, Vol. 12 Issue (4) : 422-432
Heuristic polling sequence to enhance sleep count of EPON
Bhargav Ram RAYAPATI(), Nakkeeran RANGASWAMY
Department of Electronics Engineering, Pondicherry University, Pondicherry 605014, India
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Next-generation passive optical networks (PONs) demand power conservation to create a green environment. A reduction in power consumption of the traditional Ethernet passive optical network (EPON) can be achieved by increasing the sleep count in optical network units (ONUs). In this paper, this is accomplished by introducing a first-in-last-out (FILO) polling sequence in the place of a fixed polling sequence to increase the number of ONUs entering sleep mode (sleep count). In a fixed polling sequence, the optical line terminal (OLT) allocates idle time to the ONUs based on the overall load of the ONUs. This leads to a situation that whenever the idle time does not meet the wakeup time threshold of sleep mode, the ONUs are put into doze/active mode, which consumes more power. In the FILO polling sequence, the first polled ONU in the current cycle is made to be polled last in the following cycle. Polling continues in this way, and by this rearrangement, the idle time of delayed poll ONUs increases; hence, it helps to reduce the power consumption. Additionally, a modified load adaptive sequence arrangement (MLASA) method is suggested, where the ONUs are categorized into doze ONUs and sleep ONUs. A numerical simulation of the FILO polling sequence with a vertical cavity surface emitting laser (VCSEL) ONU shows a maximum reduction in power consumption of 15.5 W and a 20% improvement in energy savings compared with the traditional fixed polling sequence. The MLASA method results in better power consumption with minimum delay than that of the proposed FILO and existing LASA methods.

Keywords Ethernet passive optical network (EPON)      optical network unit (ONU)      polling sequence      power conservation     
Corresponding Authors: Bhargav Ram RAYAPATI   
Just Accepted Date: 24 June 2019   Online First Date: 07 November 2019    Issue Date: 30 December 2019
 Cite this article:   
Bhargav Ram RAYAPATI,Nakkeeran RANGASWAMY. Heuristic polling sequence to enhance sleep count of EPON[J]. Front. Optoelectron., 2019, 12(4): 422-432.
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Fig.1  Basic EPON architecture [2]
Fig.2  Traditional fixed polling sequence [16]
Fig.3  Idle time partition
Fig.4  FILO polling sequence with n ONUs
Stepwise algorithm:
1. In each cycle, the REPORT Messages in CBR traffic are sent from the ONU to the OLT.
2. For the chosen MLASA FILO or fixed polling methods, compute Tidle and Tcycle of the ONUs based on the average bandwidth.
3. The variations in the CBRs lead to variation in the idle time of ONUs with constant cycle time/variation.
4. for Tidle=1 ms:0.2 ms:3 ms
5. if (Tidle>2 ms)
6. TsleepONU=Tidle−2, SLcount=SLcount+1;
7. else (Tidle>330 ns)
8. TdozeONU=Tidle−330, DZcount=DZcount+1;
9. end.
10. Tsleep= total sleep time of ONUs, Tdoze= total doze time of ONUs, Tact=total wakeup time of ONUs, including sleep to active time and doze to active time.
11. Compute network (power cumulative, energy savings, and maximum delay).
S. No. parameter value
1 number of ONUs 10
2 upstream line rate (Ru) 10 Gbps
3 delay constraint 4 ms
4 VCSEL Pactive 3.985 W
5 VCSEL Psleep 0.75 W
6 VCSEL Pdoze 3.85 W
7 VCSEL sleep to active time 2 ms
8 VCSEL doze to active time 330 ns
9 DFB laser Pactive 5.052 W
10 DFB laser Psleep 0.75 W
11 DFB laser Pdoze 3.85 W
12 DFB laser sleep to active time 2 ms
13 DFB laser doze to active time 760 ns
14 distance reach 10 km
15 idle time variations 1 ms:0.2 ms:3 ms
Tab.2  Parameters considered for analysis [6]
Fig.5  Power cumulative of polling methods against idle time
Fig.6  Energy savings of polling methods against idle time
method idle time=2 ms idle time=1.6 ms idle time=1 ms
Pc/W η/% Pc/W η/% Pc/W η/%
traditional fixed polling DFB 38.5 23.7 38.5 23.7 38.5 23.7
traditional fixed polling VCSEL 38.5 3.38 38.5 3.38 38.5 3.3
LASA method 29.0 23.6 29.0 12.9 50.5 0
FILO VCSEL method 23.0 23.3 26.0 14.6 38.5 3.3
FILO DFB method 23.0 28.9 26.0 22.1 38.5 23.7
MLASA method 10.6 8.4 16.8 6.4 38.5 23.7
Tab.3  Performance comparison of different polling methods
Fig.7  Performance evolution of the LASA method and MLASA method
Fig.8  Delay exploration against idle time
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