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Energy-Efficient PON with Sleep-Mode ONU Progress, Challenges, and Solutions

Speaker: Shieh-Chieh ChienAdvisor: Dr. Ho-Tin Wu

2013/09/23

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Outlines• Basic knowledge• Background• Current progress • Challenges in Energy-Saving PON • SLA-Based Energy-Efficient Scheduling Scheme

– Put ONU into sleep mode – Guard time – Sleep time state transition – Reserving slots for sleeping ONU – High-priority frame come to the sleeping ONU – Compare graph

• Conclusion • References

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Basic knowledge

• PON = Passive Optical Network• OLT = Optical Line Terminal • ONU = Optical Network Units

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Basic knowledge(Cont.)

• Control message– Grant(Gate)• Downstream direction(broadcast)• Allows an ONU to start sending data.• Include ONU_ID, window size(in bytes)

– Request(Report)• Upstream direction• Include how many bytes in ONU’s buffer.

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Background

• The subscribers’ ever increasing demands for bandwidth.

• The line rate increase in the access network and it will brings more power consumption.

• PON consumes significantly less energy than its counterparts based on copper, wireless, or active optical technologies.

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Current progress

• Methods proposed for power saving so far:– Better IC design– Power shedding of non-essential parts– Slowing down link rate– Putting network elements in sleep mode

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Current progress(Cont.)

• No ONU energy saving function is included in the EPON standard.

• Power saving schemes in different domain– GPON• ONU shedding, dozing, and sleeping

– Sleep mode also used in wireless communication– IEEE 802.3az Energy Efficient Ethernet(EEE)• Low Power Idle (LPI) mode

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Challenges in Energy-Saving PON

• When do the ONU go to sleep or wake up?– > Trade-off between • power saving vs. network performance

• Frequent mode switching– > Energy wasted in wake up process– > Extra Overhead (2 ms) from sleep to active

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SLA-Based Energy-Efficient Scheduling Scheme

• According to experienced traffic to adjust the sleep time.

• Allowing ONU to quit sleep mode before the predetermined sleep time is up in order to send high-priority packets.

• Add an extra guard time at the end of the active period.

• Proposal is within the IEEE P802.3ah/av control schemes and requires minor changes in the control signal flow.

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SLA-Based Energy-Efficient Scheduling Scheme(Cont.)

• The scheduling scheme categorizes packets into two classes with different SLAs.– High-priority class is expedited forwarding(EF)– Low-priority class is best effort(BE)

• Three-bit priority value to store in the frame header defined by IEEE P802.1p.

• Preemptive queues are used at both OLT and ONU.• Credit-based bandwidth allocation is used by the

OLT to assign bandwidth dynamically.

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Put ONU into sleep mode

• When ONU into sleep mode– Stop sending REPORT– All low-priority frames will be stored in its buffer

until sleep period expires.• Pros and cons– In worst-case all the low-priority frames

experience an extra delay.– High-priority frames in upstream direction will be

guaranteed a small delay.

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Guard time

• If (after the end of the transmission on both directions) then {wait extra guard time}

/*This time is used to identify whether the current traffic burst is over or not.*/

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Sleep time state transition

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Reserving slots for sleeping ONU

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High-priority frame come to the sleeping ONU

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High-priority frame come to the sleeping ONU(Cont.)

• In upstream direction– The frameh is from the users, the ONU will wake

up immediately.• In downstream direction– OLT has no means to inform the ONU.

→ frameh still encounter delay.─ Delay could be alleviate

→ implement a cross-layer design

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Compare graph

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Conclusion

• To design a energy-efficient PONs with sleep-mode ONUs, the challenge is to find the optimal scheduling scheme.

• SLA-based energy-efficient scheduling scheme could meet these challenges and solve the problem of frequent mode switching.– Adjusts the sleep time according to traffic– Extra guard time before into sleep period– Can quit sleep mode for high-priority frames

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References• [1] L. Shi, B. Mukherjee, and S. S. Lee, "Efficient PON with

Sleep-Mode ONU: Progress, Challenges, and Solutions," IEEE Network Magazine, vol. 26, no. 2, 2012, pp. 36-41.

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Thanks for listening

• Q&A