Joint ITU/IEEE Workshop on Ethernet - Emerging
Applications and Technologies
(Geneva, Switzerland, 22 September2012)
Power saving in (X)GPONs
Frank Effenberger
Rapporteur Q2/15
VP Access R&D, Futurewei
Introduction
Power saving in the ITU
Supplement G.45
Actual power consumption
2
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
3
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
4
Power saving surveys #2 and #3
Survey #2 focused on the case of
power failure
What UNI’s 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)?
5
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
Can’t cost any more
Services can’t be effected
This set the stage for the G.sup45
document
6
Introduction
Power saving in the ITU
Supplement G.sup45
Access power consumption
7
Outline of G.sup45
Requirements
Classification of techniques
Signaling of ONU operations
Comparative analysis
Conclusions
8
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
9
Classification of techniques
10
Power Shedding
When triggered, the ONU turns off the UNI’s
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 UNI’s 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
11
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 (10’s 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
12
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
18
System architecture of a VDSL system
DSLAMLT
WAN
SW
CPE
LT
LT
WAN
SW
CPE
LT
LT
Typical VDSL linecard consumption
today is 2W per line (i.e., per user)
CPE
Typical VDSL HG CPE
consumption is 10W
per user
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System architecture of G-PON system
WAN
OLT
LT
SW
LT
LT
WAN
SW
LT
ONU
ONU
LT
ONU
Typical OLT linecard consumption
today is 7W per PON port
(@ 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
21
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 4~10x 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 today’s CO) is
inappropriate for intense point heat loads
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The CPE power issue - Functional
blocks
Mem
WAN
interface
POTS
Interf (x2)
MAC
Ethernet
Interf (x2)
Typical Single family home gateway CPE
consumption is 10W
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Breakdown of ONU (VDSL is similar)
PON optics
10%
Power Conv.
20%
MAC
30%
SLIC
20%
Ether
20%
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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!
27
Sleep modes for access equipment
Protocols for sleeping and dozing are
standardized in the XG-PON system
ONU state diagram
OLT state diagram
28
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 night’s 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 powersaving, 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 Telco’s 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
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