Re: [STDS-802-3-25G] Power Consumption of of 25G RS-FEC

[Jonathan King <jonathan.king@xxxxxxxxxxx>]

Thank you, Scott, for laying out the power question in detail (and for supplying all the references).

jonathan

 

From: Scott Kipp [mailto:skipp@xxxxxxxxxxx]
Sent: Tuesday, July 14, 2015 4:27 PM
To: STDS-802-3-25G@xxxxxxxxxxxxxxxxx
Subject: [STDS-802-3-25G] Power Consumption of of 25G RS-FEC

 

802.3by,

 

Yesterday, there was considerable debate about power consumption due to the RS-FEC used in 25GbE.  In goergen_3by_02_0715.pdf, the power consumption for RS-FEC was approximated to be 300mW.  I did a quick search and found these estimates:

http://www.ieee802.org/3/bm/public/sep12/wang_01_0912_optx.pdf = 45mW on slide 3

http://www.ieee802.org/3/bj/public/mar12/gustlin_01_0312.pdf = 90 mW on page 6

http://www.ieee802.org/3/bs/public/adhoc/logic/oct21_14/wangz_01_1014_logic.pdf, Wangz concludes: In practice, either KR4 or KP4 FEC is easy to implement and not much power-consuming.

 

A conservative estimate is 100mW for 100GBASE-KR4.  25GBASE-KR4 will consume 1/4 of this power or 25mW based on a one of the four lanes.

 

I propose that 25mW is a practical power consumption for RS-FEC.  Let’s calculate the cost of the power consumption for the server over a 3-year lifespan.

 

	Goergen_3by_02_0715	My proposal
Power of RS-FEC (mW)	200 (value used in calculation)	25
Power Consumption over 3 year lifespan of server (kWh)	5.25	0.66
Cost of kWh ($/kWh)	0.11	0.05
Power cost/server for RS-FEC	$0.58	$0.03

 

Another correction that I wanted to make is to the estimate is the cost of electricity.  Hyperscale data centers that consume megawatts of power buy electricity at wholesale rates.  Many are located near electric power plants so that Google pays about $0.04/kWh according to this article:

http://www.oregonlive.com/silicon-forest/index.ssf/2013/09/google_reaches_new_data_center.html

 

The wholesale electricity industry is regulated and current pricing is available for this site and shows electricity ranges in 2015 has varied from $0.036/MWh to $0.065/MWh.  Read more here:

http://www.eia.gov/electricity/wholesale/

 

I used a conservative $0.05/kWh.

 

My estimate is that the cost of RS-FEC per server is about $0.03 over the life of the server.  Three cents is basically in the noise for our purposes and should not be a fundamental driver for 3m cabling without FEC.

 

Kind regards,

Scott Kipp