FEATURE MID-REACH
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efficiencies and operational gains: radio cell capacity can be moved around as required unlike current systems where maximum capacity is provisioned for each cell even though it is rarely required. And virtualisation and cloud computing techniques could be used to implement the base station functionality on standard servers rather than specialist hardware. Optics is needed here as significant traffic is
generated between the remote radio heads and the base stations. Dubbed mobile front-hauling, this is where cheaper 100-Gig interfaces could play a role. ‘In the wireless network market, there is a large
consortium shares a common goal but does not work as closely as companies developing an MSA that sign a non-disclosure agreement and share intellectual property. Te specifications of the CLR4 and CWDM4 are
The backers of CWDM4 and CLR4 are working to align their specifications
very similar. Both include forward error correction (FEC), not in the module but as part of the system design, but whereas FEC is fundamental to the CWDM4, it is optional with the CLR4. ‘We have focussed on the FEC-enabled [CWDM4] version so that optical manufacturers can develop the lowest possible cost components to support the interface,’ said Mitchell Fields, senior director in the fibre-optics product division at Avago Technologies. Te FEC adds flexibility, he says, not just in relaxing the components’ specification but also by simplifying module testing. By having FEC only as an option, the CLR4
Alliance’s interface avoids the delay associated with FEC, suiting applications such as high-frequency trading where latency is an issue. Te backers of CWDM4 and CLR4 are working
to align their specifications and while it is likely that the two will interoperate, it remains unclear whether they will merge. Te CWDM4 specification is set for completion in September, said Avago. Te similarity of the CWDM4 and CLR4 means that both designs will come to market simultaneously. ‘If you have specific applications that emerge that require one [design] or the other, you basically have both covered,’ said Ram Rao, product marketing, senior manager at Oclaro. Finisar highlights how the emergence of 2km
100-Gig interfaces could also be used in wireless networks. One emerging trend in the radio access network is separating the radio equipment from the base station in order to pool the base station functionality. Using simple remote radio units and centralising the base station units promises greater
32 FIBRE SYSTEMS Issue 5 • Autumn 2014
and emerging need for optics that will go up to 2km,’ said Ward. For now, though, front-hauling is an emerging application and 10-Gig optical links is sufficient for front-hauling. Wireless also requires industrial-temperature optics operating between -40C and 85C whereas data centre optics operate in a more controlled environment. Te industry’s view is mixed as to how the four
mid-reach 100 Gig designs will fare. Oclaro, a member of the CWDM4 and PSM4
MSAs as well as the CLR4 Alliance, says it is seeing end-user interest in both the parallel and duplex modules. ‘With the PSM4 and the CWDM4/CLR4, you are matching up with the [data centre] cabling infrastructure,’ said Rao. Ciena, while having joined the CLR4 Alliance,
welcomes all four developments. ‘Te CLR4 Alliance as well CWDM4, PSM4, and OpenOptics are promising initiatives as they are focussed on identifying new ways to scale network capacity in a more cost-effective manner,’ said Alexander. But D’Ambrosia of the Ethernet Alliance regrets
that four specifications have emerged. ‘My own personal belief is that it would be better for the industry overall if we didn’t have so many choices,’ he said. ‘But the reality is there are a lot of different applications out there.’ Avago’s Fields says it is hard to give guidance as to
how the market will develop. Avago believes that the 100GBASE-LR4 will become the smallest of the segments as it will take time before it appears in a QSFP28. Te hyper-scale data centre operators will be the early adopters of the mid-reach 100 Gig QSFP28s, whether PSM4 or CLR4/CWDM4, skewing the market towards single mode. But, once enterprises start adopting 100 Gig widely, more and more 100-Gig multi-mode modules will be used. LightCounting expects the PSM4 and a merged
CWDM offering to find strong market traction. ‘Avago, Finisar, JDSU and Oclaro are participating in both categories, demonstrating that each has its own value proposition,’ concluded Murray.l
Roy Rubenstein is editor of Gazettabyte.
www.gazettabyte.com
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