JOHN WILLIAMSON EXTENDING WAVELENGTHS
Fixes For Looming Optical Network Traffic Jams? BATTLE OF THE BANDS
As is widely reported, the amount of traffic carried over the world’s optical fibre networks has been growing on some routes at a prodigious rate in recent years, and the expectation is that the volumes involved should only get larger in the future. In that eventuality it’s likely that the development and introduction of effective measures to circumvent conceivable optical system traffic jams will become more commonplace, writes veteran tech journalist John Williamson .
NOT A WALK IN THE PARK However, the use of L-band and
the only extant C- and L- band subsea system is Pacific Light Cable Network. There could be others in the pipeline, but Howard Kidorf, Managing Partner at Pioneer Consulting, reasons that C+L, is not the preferred method of the undersea system suppliers for increasing the capacity of an undersea cable. “Space- Division Multiplexing (SDM) – i.e. just more fibre and amplifiers - and to a lesser extent multi-core fibre (MCF), are preferred as the engineering is more straightforward and by some metrics, the capacity is greater,” reckons Kidorf.” Putting more fibre in the cable is a relatively small additional cost to a cable.” TERRA IS FIRMER, THOUGH The C- and L-band pairing picture is somewhat different in the long-haul terrestrial cable sector. As described by Brown, many of his company’s Communications Service Provider (CSP) customers are utilising spectrum-based C+L-band DWDM solutions in terrestrial networks to effectively double the capacity per fibre pair and avoid the cost of leasing additional fibre pairs. “Although commercial C+L-band solutions have existed for several years, the recent availability of more highly integrated and application-optimised line system solutions has enabled a broader adoption of C+L in metro and long-haul networks by CSPs (and) cable operators, as well as enterprises,” adds Brown.
Daryl Inniss, optical fibre and device expert with a focus on commercialising technologies, says that, on the fibre side, there is industry debate on how to support traffic growth at some 30% per year. Inter alia, Inniss sits on the European Conference on Optical Communications (ECOC) Market Focus Committee. Fleshing traffic volumes out, and citing his own company’s ‘Global Network Traffic 2030’ report, Dave Brown, Senior Product Marketing Manager, Line Systems, Nokia Optical Networks, says overall global network traffic demand is expected to reach between 2,443 to 3,109 Exabytes per month in 2030. This is around 100 times the total monthly Internet traffic generated in 2012 WAVELENGTH COMBINATIONS? One possible capacity augmentation strategy is to use different or additional wavelengths to the C-band. “The thought is by 2030 the industry will need more bandwidth per fibre; higher transmission rate in the C-band is not sufficient,” judges Inniss. Referring to potential C- and L-band combinations, he observes that transmission lines have to be provisioned with hardware to accept both C- and L-band transponders. “While the line may not use L-band today, the necessary hardware is going in so that it is easy to increase capacity,” Inniss contends. The C-band currently dominates DWM systems in the trans-national submarine cable arena. But it’s reported that, so far,
combination C- and L-band frequencies isn’t necessarily a slam dunk. “For better or worse now there’s been a huge amount of investment within the C-band. And like with any technology, you get economies of scale. So you now have extremely cost effective solutions within the C- band,” admits Rob Shore, Senior Vice President of Marketing at Infinera. “L-band is much, much less utilised because you need a completely different type of amplifier to amplify frequencies in that range.” Kidorf points out that the L-band is not disadvantageous, per se, but the need to manage C-band and L-Band introduces additional design constraints on equalisation, cross-talk, fibre testing and many other areas. “Even after this work, the separate L-band amplifier in the repeater still requires space and electrical power,” he comments. .”L-band amplifiers are not the most straightforward way to maximise the number of Terabits transmitted per Watts of electrical power.” Kidorf clarifies that these caveats apply to both submarine and terrestrial to some extent, but are a much larger issue with submarine due to the limitations on space and deployment complexity. The considerations for terrestrial application are extremely small by comparison. Cost and earnings are, of course, pivotal considerations in shaping which proposed capacity enhancement
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| ISSUE 36 | Q1 2024
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