Power saving in (X)GPONs

1
Power saving in (X)GPONs
Joint ITU/IEEE Workshop on Ethernet - Emerging
Applications and Technologies(Geneva,
Switzerland, 22 September2012)

• Frank Effenberger
• Rapporteur Q2/15
• VP Access RD, Futurewei

2
Introduction

• Power saving in the ITU
• Supplement G.45
• Actual power consumption

3
Initial activities

• First contributions were made by semiconductor
  vendors, to consider signaling methods
• The Q2/15 group thought these were premature
• The requirements for power saving were not clear
• The impact on existing systems was not clear
• There was a concern it would degrade the user
  experience
• It was agreed that a survey would be made of the
  operators to learn their requirements

4
Power saving survey 1

• Survey gathered information on
• Basic power supply designs
• Who pays, Who changes the battery?
• Overall requirements and interest in power saving
• The most telling result was Which is a higher
  priority, service availability or power savings?
• The answer was overwhelmingly Service quality is
  much more important that saving power
• Apparently, the Green Revolution had not yet
  happened

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Power saving surveys 2 and 3

• Survey 2 focused on the case of power failure
• What UNIs are in common use?
• How do they get powered down if the main power
  fails?
• Who can control this powering down process?
• Survey 3 focused on regulations about lifeline
• Are their regulations that force the maintenance
  of service during a power failure?
• How do those regulations vary from service to
  service (POTS vs. video vs. Internet)?

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Outcome of the surveys

• It was clear that there was interest in power
  saving
• For the most part, power saving was seen as a way
  to lengthen the life of the battery during an
  outage
• Operators were not willing to compromise much in
  the name of power saving
• Cant cost any more
• Services cant be effected
• This set the stage for the G.sup45 document

7
Introduction

• Power saving in the ITU
• Supplement G.sup45
• Access power consumption

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Outline of G.sup45

• Requirements
• Classification of techniques
• Signaling of ONU operations
• Comparative analysis
• Conclusions

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Requirements

• Surveys were used as a primary requirement
• Power saving mode should be triggered by power
  failure, and NOT low traffic or unused ports
• EU CoC
• The current state of these power targets was
  reviewed
• The low power mode was noted to be only half of
  full power mode
• There are two main requirements
• To maintain service during a power failure
• To save power at all times
• No operator consensus on the balance between
  these two requirements

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Classification of techniques
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Power Shedding

• When triggered, the ONU turns off the UNIs
• Turn off in this context means fully powering
  down the circuit (not just deactivating service)
• Each UNI type can have a different shut-down
  period (e.g., video can turn off after 30
  minutes, but POTS is maintained for several
  hours)
• When to trigger is a question
• During power failure, some UNIs can be turned
  off safely (e.g., video, because the TV sets will
  not have power in most cases)
• During normal times, it is difficult to judge if
  UNI is busy
• This is the least service effecting method
• ONU maintains contact with OLT at all times

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Dozing

• When triggered, the ONU should stop transmitting
  in the upstream, even if it is given BW
  allocations
• This allows transmitter circuitry to go into low
  power mode
• Lower than normal off in between bursts
• May take longer to recover (10s of milliseconds)
• Trigger would be the inactivity of the ONU
• Difficulty is that data services (and VoIP) tend
  to chatter all the time
• Downstream receiver and signal chain remains on
• ONU can be signaled by the OLT
• Incoming calls can be received without delay
• This impacts services slightly
• Outgoing communications might suffer a delay, as
  normal bidirectional communication is
  reestablished

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Fast Sleep

• When triggered, the ONU shuts off entire PON
  interface for a short period of time
• ONU periodically wakes up to see if OLT has
  anything to say
• During the shutdown, the ONU could conceivably
  have nearly zero power drain (only the wake-up
  timer would be powered)
• Key issue is how fast can you wake up the optics
• Normal transceiver designs are not optimized to
  turn on fast
• However, proper optimization could get times down
  to 1 ms
• Side note Recent result have shown circa 60
  reductions
• This method can have relatively low service
  impact
• ONU maintains contact with OLT (albeit
  transiently)
• Interactions with higher layer protocols must be
  considered

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Deep Sleep

• When triggered, the ONU completely shuts off
• Services are definitely impacted, no apologies
  for that
• Power drain is zero, or nearly so
• Challenge How to wake up?
• Snow White method A prince (the user) kisses the
  deep sleeper (presses a button on the ONU)
• Rip Van Winkle method Deep sleeper wakes up
  after a preset time, and sees if anything has
  changed
• This method only appropriate for long outages
• It seems that the usual obligations are excused
  if power is out for a long time, and users and
  regulators understand that

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Signaling of ONU operations

• Dying gasp Enhancing the existing message
• For G-PON, not accepted, because it changes the
  TC-layer
• PLOAM-based Signaling for fast sleep method
• For G-PON, not accepted , because it changes the
  TC-layer
• OMCI-based Configuration of power features
• For G-PON, OMCI additions have been made
• Extended Power shedding Detailed control
• For G-PON, fine-grain control of shedding has be
  standardized
• Implicit signaling OLT suppresses alarms
• No standards impact, so OLT vendors are free to
  implement
• Security aspect Impostor attack
• When the ONU is asleep, impostor can more easily
  jump in

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Comparative analysis

• Model of ONU power consumption is given, and used
  to evaluate the savings for each type power
  saving
• This model is only an example, based on a
  particular ONU design and circuit power values
  (these change over time)
• Key findings of this evaluation
• Power shedding accomplishes a lot (70) of power
  saving
• The other methods have increasing implementation
  difficulty and declining efficacy of power saving

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Conclusions of G.sup45

• Power saving is an important topic
• Main object is to improve handling of power
  failures
• Recommendations to improve power usage
• Continuous improvement of design (ASIC, optics,
  power conv. Etc.)
• Power shedding should be supported and activated
• Dozing can be implemented with little cost
• Aggressive sleeping modes are of lowest
  priority
• Final note G-PON saves power in ICT field and
  other industries, so some credit should be given
  for that

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Introduction

• Power saving in the ITU
• Supplement G.45
• Access power consumption

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System architecture of a VDSL system
DSLAM
CPE
LT
SW
LT
WAN
LT
CPE
SW
LT
WAN
LT
CPE
Typical VDSL linecard consumption today is 2W
per line (i.e., per user)
Typical VDSL HG CPE consumption is 10W per user
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System architecture of G-PON system
OLT
ONU
LT
SW
LT
WAN
LT
ONU
SW
LT
WAN
LT
ONU
Typical OLT linecard consumption today is 7W per
PON port (_at_ 28 users/PON 250mW/user!)
Typical GPON HG CPE consumption is 10W per user
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Central office / Node power crunch

• Central office dissipation is dictated by NEBS
• Typical US number 2000W per bay, 3 racks per bay
• Typical DSLAM has 16x24 lines 768W per rack
• This barely fits in the 2000W number
• Typical OLT has 16x8 PONs 896 W per rack
• Have to leave 1 rack-space empty!
• Is PON hitting the crunch? NO!
• One OLT serves 3584 users, while a DSLAM serves
  only 384 users
• We need 9 times fewer OLTs than DSLAMs

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Trend in broadband access CO equipment

• The power per chassis is increasing marginally
• Perhaps a 30 increase generation-over-generation
• The capability per chassis is increasing
  incredibly
• Aggregate bandwidth increases 410x per
  generation
• Users per chassis increased 10x from copper to
  fiber
• Total access power per user is already declining
• Driven by the acceptance of fiber access
• Power density is increasing
• Suggests a rethinking of the CO power design
  guidelines
• Perhaps even a redesign of the cooling method
  entirely
• Diffused air cooling (typical in todays CO) is
  inappropriate for intense point heat loads

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The CPE power issue - Functional blocks
Mem
POTS Interf (x2)
MAC
WAN interface
Ethernet Interf (x2)
Typical Single family home gateway CPE
consumption is 10W
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Breakdown of ONU (VDSL is similar)
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Observations on baseline consumption

• Power consumption is reasonably balanced amongst
  functions there is not one bad actor
• The majority of power (60) lies in functions
  that are not particularly related to PON
• You find them in any access system
• Many are legacy dictates (ringing a bell)
• They are designed for reliability and performance
• E.g. Power converters consuming 20 of the power
  why? To handle the stress environment that Telco
  requirements give us
• Flexible hardware (e.g., CP instead of ASIC) is
  used
• The flexibility is a meta requirement of the ever
  changing market
• But, this is never the most power efficient way
  to build equipment
• If the true power cost of all the requirements
  was rationalized, just imagine what we might save!

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Power saving technologies

• Most natural path is intrinsic improvement
• Current designs were not designed with power as a
  key requirement
• Time to market, performance, and simplicity were
  always more important to the designer
• Example burst mode laser driver
• The average ONU duty cycle is 3 (32 ONUs per
  PON)
• But, the typical laser driver consumes current
  100 of the time
• Why? Because it was easier that way
• This is straightforward to fix
• The designers only need to be guided that power
  consumption is an important goal that has value
• This process is underway already!

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Always on means always polluting

• Recall the original telephone network
• You only used power when off hook very
  efficient, and natural behavior to the user
• Data separated the session from user
• Ideally, users interact with their computer, and
  the computer establishes the (logical) sessions
  automatically
• User involvement in session control (dial up) was
  slow and painful
• This quickly drove the always on model
• Power consumption was not considered!

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Sleep modes for access equipment

• Protocols for sleeping and dozing are
  standardized in the XG-PON system

ONU state diagram
OLT state diagram
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Future possibilities

• OLT power consumption could be reduced in future
  PON systems
• OLT shedding If a port is not used, it should
  be powered down
• As deep into the card as possible
• OLT sleeping If a TWDM-PON is underused,
  reduce the active waves
• ONUs would be concentrated onto fewer channels
• This could improve the load-dynamic power
  consumption of the CO

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Getting a good nights sleep

• Standardization is only the beginning
• The hardware must be designed to use it
• Optoelectronics must have fast turn-on/off
• Logic devices must support the protocols
• Switching must recognize that link is transient
• The operators must be motivated to use it
• Operators respond to competitors and users
• In a choice between performance and power-saving,
  which wins?
• Example ADSL has power saving for some years now
  almost never used

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Conclusions

• Current access power consumption is trending in
  the right direction, considering the incredible
  BW improvements
• The CO-side solution is in our hands deploy PON,
  and you cut your CO power by an order of
  magnitude
• The CPE-side is much larger problem
• Legacy interface requirements are an issue
• If we could only redesign POTS
• If only Telcos could agree on a service profile
  and stick to it
• Power saving modes have good potential
• Changing always on into always available
• Already standardized we just have to do it