@fibresystemsmag |
www.fibre-systems.com
FEATURE TERABIT NETWORKS
provisioning of long haul optical transmission capacity in 2013. Infinera collaborated with DANTE (Delivery of Advanced Network Technology to Europe) to install and activate an 8Tbps long-haul super-channel across a section of the GÉANT Network, from Vancis Amsterdam, the Netherlands to GlobalConnect Hamburg, Germany. Te GÉANT network is a high bandwidth pan-European research and education backbone that connects national research and education networks (NRENs) across Europe. Sixteen of Infinera’s 500Gb line cards and 32-fibre connections were deployed at each end of the link, and once the super-channels were in operation, a 100-Gigabit Ethernet (GbE) service was provisioned over the fibre. Geoff Bennett, director of solutions and
technology at Infinera said: ‘Service providers have to be able to deal with the exponential increase in demand on modern core networks, and 500G super-channels are a great way to do that. With the world record attempt, we showed how robust and scalable a super-channel solution can be.’ Te total time from the insertion of the first
super-channel line card to the activation of the 100Gb service was 19 minutes and one second, resulting in a provisioning rate of 26.02Tbps per hour. All of these trials demonstrated that terabit networks can be achieved using long established fibre that has been deployed for 20 years in some cases. According to Fischer, some users might decide
that the increased modulation route might be a good solution for metro/regional networks or for short-distance high-capacity interconnects between data centres – they may just accept that the range goes down. However, the solution does not work for the full network, he added. ‘Currently no one builds dedicated networks
for special-use cases. Te most efficient way is to have one network that can cover a number of different services. It is very important that these kinds of specific solutions can co-exist with other traditional services on the same network,’ he continued. Tat was one of the issues showcased in the Australian experiment. All three of the company’s trials used
super-channels to achieve terabit-per-second network capacity. However, this technology needs high modulation states; this increases noise, shortening the maximum distance that can be achieved. Currently this presents a trade-off that network providers must balance to achieve the results that customers want – by increasing the modulation state there must be more signal shaping and some kind of forward error-correction.
Older network architectures used QPSK
modulation, but the move to 8 or 16 QAM presents some new challenges. Xenos said: ‘In QPSK, the four constellation points, also called symbols, are well separated from each other, but with 16QAM, there are 16 constellation points in the same space. Tis means there is significantly less separation between constellation points or symbols, hence much higher sensitivity to noise.’ As modulation technology becomes the
standard to achieve high capacity across fibre networks, each company has had to develop solutions to combat this issue of increased noise. Fischer pointed out that for 8QAM the spectral
efficiency is improved by a factor of 1.5. Going to 16QAM does not doubling the 8QAM improvement again, but increases the spectral efficiency by another factor of 1.3. ‘However this trades against reach, because you suffer from more noise in the system,’ he added. Bennett, of Infinera, said: ‘Te optical
transmission capacity from a super-channel can be compared to the torrent of water from a fire
All three of the trials used super channels to achieve terabit-per- second network capacity
hydrant. Something has to manage that torrent so that it can be used in an effective way by lower-speed client services.’ Each network provider will have their own
solution for squeezing the signals as close together as possible in technologies like 16QAM. Tis involves squeezing the traditional band gap and processing the signal using a DSP installed in the network. Xenos said: ‘Different vendors’ solutions will
have different types of performance, depending on the type of forward error correction that they are using and the DSP that they have. Tis means that not every solution at 16QAM will be the same, either. ‘Soſt-decision forward error correction is a key
enabler to a longer distance optical transmission, but not everybody’s forward error correction is the same. You will be able to tell, with the kind of deployments that are coming out, who has the better solution because of the types of distances that can be achieved,’ she concluded.
Infinera has been utilising photonic integrated
circuit technology in its super-channel solutions, because of the space, power and reliability benefits associated with the reduced number of optical components. Bennett said: ‘Super- channels have become the favoured technology for implementing DWDM capacity at 100Gbps and beyond. As we scale the number of wavelengths in a super-channel it seems obvious to do that using a highly integrated approach like the PIC – and the service provider market obviously agrees because PIC-based super- channels are now one of the most popular ways to implement long-distance transmission capacity.’ He continued: ‘A PIC is the optical equivalent
of a multi-core Pentium CPU – and shares all of the same advantages of electronic integration; namely smaller footprint, lower power use, higher reliability, and lower cost compared to a line card built from discrete optical components.’ Other providers have developed their own
solutions. At Coriant, Flexigrid technology is a key component of DWDM it allows the flexible assignment of optical bandwidth to channels enabled by FlexiGrid technology. Tis allows higher bit rate transmissions by maximising flexibility in channel spacing. FlexiGrid also introduces the concept of virtualisation of physical layer resources. An operator can adapt the wavelength grid to the needs of high capacity, long reach transport as well as increase spectral efficiency and thus the overall capacity of the system. Fischer said: ‘You have multiple carriers
travelling on different optical wavelengths, or you could consider them as different colours. In a typical system, you have a filter that acts as a grid. It provides a filter gap between all the channels. Tis means you have one band, which is 50GHz apart from the other, and the transmission bandwidth of that band is roughly 37GHz. In between, there is a band gap where, if you were to apply a signal there it would just not go through, so you have filtering between the different colours. ‘Now if you separate the colours by electrical
signal processing, then you can avoid the filtering in between the different colours. Tis removes the pass bands between the different transmission bands, allowing you to utilise the gaps in the signal by squeezing the transmissions closer together. ‘Tere are specific ROADM devices that allow
this,’ said Fischer. ‘Tey allow you to program, in a flexible fashion, the transmission pass band and they also allow you to avoid any filtering in between the different pass bands.’ Signal shaping is important to reduce
Issue 5 • Autumn 2014 FIBRE SYSTEMS 35
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45