Transcript Document
Energy-Efficient Solutions
for 10Gbps Ethernet
Yury Audzevich, Alan Mujumdar,
Philip Watts, Andrew W. Moore
MSN 2012 workshop
Friday, July 13th, 2012
Introduction
Energy-efficiency of transmission systems is one of the key priorities with respect
to the next generation of networking equipment.
Open questions:
What is the power contribution
of the ‘lower layer’ transmission
protocols?
What is the power impact of
Servers
vs Network for a Google cluster (fat trees topology)
the encoding
blocks?
(Energy proportional datacenter networks, Abts et al. ISCA 2010)
The focus of the research
Which effect DC-balanced codes do have on the optical transmission system?
…and in particular: what is
- the effect on optical power requirement?
- front-end power contribution, like PMA and PMD?
- the power consumption of line coding block itself?
???
???
10Gb/s optical link simulations
Optical link – transmission system:
• 219 bits PRBS is used as an input, the baud rate is adjusted after encoding
Optical link parameters:
• 100m Single Mode Fibre with parameters satisfying requirements for 10Gbps
Ethernet over SMF
Optical link – receiving system:
• Optical receiver with direct detector and AC coupling achieved using High Pass Filter
• BER is calculated using the complementary error function
10Gb/s optical link simulations (cont.)
better
better
• The transmission system is relatively insensitive to the DC-balanced codec choice
• Taking 100MHz HPF cut-off frequency and assuming 20dB link budget, the laser
power requirement is lower for encoded sequences (0.3mW of savings) in
comparison to PRBS
Physical Coding Sublayer – 8B10B (and 64B66B)
8B10B line code:
1) Encoder/Decoder – implemented 3B4B and 5B6B codes plus disparity control
check for DC-balance
64B66B line code:
1) Encoder/Decoder – decoding from XGMII into 10GBASE-R format
2) Scrambler/Descrambler – mixing of data to avoid long sequences of 0s/1s
• Codecs were implemented in Verilog HDL and Synthesized using 90nm
and 45nm technical process libraries
• Industry standard estimation tools were used for power measurements
Early-days results – 8B10B PCS power
10Gb/s link results: obtained for 30 microseconds simulation periods, with a
symbol clock frequency of 625MHz for both 45nm and 90nm tech. process
Inverse of
energy-proportionality
• IDLE sequences costs MORE to encode
• Low leakage 45nm library provides decrease in power by a factor of 2
Power estimates – 64B66B PCS
10Gb/s link results: Identical pattern sent for 30 microseconds of simulation
periods, with a symbol clock frequency of 156.25 MHz
64B66B
10GBASE-SR / 10GBASE-LR
(commonly used)
8B10B
10GBASE-LX4
(less common)
• Power consumption of 64B66B codec is actually more data proportional
• Scrambling & gearbox modules have a fixed power cost (~1.5-2.5 times larger
power dissipation than the combination of encoder & decoder power)
Physical Medium Attachment – 8B10B and 64B66B
PMA components are built using both CMOS and MCML logic families
• CMOS designs were synthesized using standard cell libraries
• MCML designs were built, optimized and analysed using HSPICE tools
PMA power – 8B10B and 64B66B
64B66B
• MCML power is independent of the operating frequency but is strongly related to the
optimization criteria
• At high clock frequencies MCML designs become more power efficient than their CMOS
counterparts
• Even well power-optimized PMA designs may require 5x-10x times higher power than the
corresponding PCS blocks!
Implications
• Our recent analysis of realistic trace data(10Gbps) showed average link
utilization of only 8.79% - in concordance with [1].
• The majority of the networks are overprovisioned to sustain peak loads and
underutilized most of the time
• Current implementations of Ethernet standards require continuous
transmission of IDLE code words (even in the absence of MAC traffic)
So…
May be, we need a system that has good energy-proportionality and can
quickly restart
Sounds like we need a new MAC…
[1] T. Benson, A. Akella, and D. A. Maltz. Network traffic characteristics of data centers in the wild. In Proceedings of ACM
IMC '10, pp. 267-280, New York, USA, 2010.
Or an old energy-efficient MAC
Remember this one? Ethernet – CSMA/CD
Many features/ideas we don’t want, but one we do:
• Preambles give clocks valuable re-sync. time and allow photonic systems to
turn back on
Energy-efficient MAC
Where do we get energy-savings from:
Powering down the codecs when no data is present
Using a synchronization preamble prior to data transmission for fast CDR
Is the protocol going to make a difference?
89%
93%
93%
87%
With avg. Ethernet frame size of 1150bytes and 64bits of preamble, the effective energysaving is ~93%
Key take-aways
Optimal laser power is independent of the DC-balanced codec chosen
Codec power consumption is not always data-proportional
Serialization/deserialization power dominates over all the other power
groups
New MACs (off when idle) do save significant power
How do we test, build, trial?
regular NICs don’t help
Need something programmable but FAST…
Thank you!
QUESTIONS?