DCN April 2016 - Page 26

cabling Some transceiver solutions now leverage Wave Division Multiplexing (WDM), a technology that enables a single fibre to support multiple wavelengths (in effect, separate ‘data lanes’). The IEEE 100GBaseLR4 standard – supported by every major vendor – establishes four 25Gb/s lanes on each of two single mode fibres to deliver an aggregated 100Gb/s, enabling 100GE links with a reach of up to 10km. The 100GBase-CWDM4 standard uses exactly the same structure to deliver 100GE over 2km on just two single mode fibres. There are also several multimode fibre WDM solutions on the market that are not currently standards approved. Another approach is through a well known industry leader’s bi26 directional (BiDi) transceivers. BiDi requires multimode fibre and can support 40Gb/s transmit speeds by aggregating two 20Gb/s optical lanes – one per fibre – with the receive link put together in the same way. Distances over OM3 and OM4 are down to 100-150m but then we’re talking about the backbone of a data centre here, not some elongated campus LAN. But hang on a moment – will any aggregated 2-fibre solution really be able to attain the blistering high speeds of future standards like 400G, over any kind of usable distance? And when the maximum capacity of two fibres eventually reaches its zenith, isn’t there a risk that data centres which have taken this path will be ‘locked-in’ to the proprietary roadmap of their transceiver manufacturer? Some will find that a reassuring prospect, but others will be concerned that such a wide variety of choice is no longer available to them. Another school of thought favours parallel optics and the aggregation of greater numbers of fibres. Using the current Base-12 cabling standard creates links based on increments of 12 fibres rather than two, and makes use of MTP connectors. MTP has become the norm for many data centres, and that’s important as far as future flexibility is concerned. Even where LC connectors still feature heavily at the end of links, the backbone connectivity is increasingly MTP domina