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Bi-PON could reduce FTTH energy consumption tenfold

25 April 2012
Alcatel-Lucent has proposed a new time-division multiplexed passive optical network (TDM-PON) protocol that could cut energy use in fibre to the home (FTTH) networks by a factor of 10 compared to current technologies.
The proposal was described in a recent technical paper by engineers from systems vendor Alcatel-Lucent and its research arm Bell Labs. IMEC Ghent University in Belgium, a research organization specialising in nanoelectronics and nanotechnology, also contributed to the work.
Called bit-interleaved PON or Bi-PON, the new protocol lowers energy consumption by reducing the amount of data processing in the optical networking unit (ONU) in the subscriber’s home. 
“In today’s broadcast-and-select based TDM-PON system, every ONU on the PON must perform intensive processing on all of the data that is broadcast from the optical line terminal (OLT) in the central office to select the data relevant for the respective ONU. When this energy-intensive processing is complete, 97% to 99% of the original bits are dropped because they are intended for other ONUs on the PON,” the paper explains.
“With the bit interleaving protocol, every ONU still receives every bit that is broadcast on the PON. But it can immediately determine which bits are intended for other units and drop them before they undergo heavy processing. Bell Labs testing confirms the bit interleaving protocol reduces power consumption in the ONU by a factor of 10 — from about 2 W to less than 200 mW — compared to today’s conventional TDM protocols as specified in the standards.
“With much less data to process, the processing stages in the customer optical networking unit can now operate at the clock speed matched to the customer’s rate, typically 10 Mbps or 100 Mbps, which is much lower than the line rate of 10 Gbps.”
The development is one of 25 projects taking place in the GreenTouch Consortium, which aims to reduce energy consumption in optical networks by factor of 1000 by 2020.
Bell Labs has applied for four patents on Bi-PON, according to a report in EE Times.  The members of the GreenTouch Consortium have agreed to share intellectual property on a royalty free basis, but can charge fees to outsiders.
However, it is likely to be some time before Bi-PON becomes commercially available – analysts reckon deployment could be six to ten years away, and the technology will first need to be standardised by the relevant bodies.
By Pauline Rigby