The NXT equipment is a high performance Submarine Line Terminal (SLTE) specifically designed for Repeatered Submarine Links with submerged repeaters. It offers capacities up to 160 x 10 Gbit/s per fiber, depending on the bandwidth of the system. It also offers monitoring capability for submerged equipment which uses either command/response supervisory, or is fitted with high loss optical loop-backs/reflectors. Designed as a general purpose submarine terminal, the main application of the NXT is in adding capacity to existing submarine systems, where it produces significant increases to the original design capacity. For example, a long-span system originally designed for 16 x 2.5 Gbit/s was upgraded to 24 x 10 Gbit/s and has since been operating trouble-free for over two years. A further fiber pair will soon be upgraded to 40 x 10, using Differential Phase Shift Keying (DPSK) transmission at 20 Gbit/s per wavelength. This allows a class-leading spectral density of 10 Gbit/s per 25 GHz.
Apart from significant capacity increases, the NXT also supports new types of traffic – such as 10GE LAN PHY, 10GE WAN PHY and G.709 OTU2 – as well as offering 2.5 Gbit/s clear channel transmission to handle legacy traffic.
The NXT can be deployed in parallel with existing equipment, which minimizes the expense and disruption of replacing equipment and migrating traffic, and Xtera has worked with its customers to develop procedures for connecting the NXT into existing operational systems rapidly and with minimal disruption.
To achieve even greater capacity increases, the NXT should be deployed to replace existing equipment. Xtera has experience of both types of upgrade.
The addition of capacity above the original design target, and the ability to add new types of traffic, allows significant investment return on the submerged parts of a repeatered system. Eliminating the need to procure and install a new system not only reduces direct expenditure, but also allows new capacity to be accessed more quickly.
Resources
At Xtera we have a highly experienced team of people that cover all aspects from initial system assessment through to long-term support of deployed equipment. We have a mixture of computer simulation, lab test facilities and specialised test equipment which aim to assess how much extra traffic can be added with as little intrusion as possible – in some cases zero impact on existing traffic. The people involved in installation follow a similar policy, aiming to work with local staff and make installation as painless as possible.
Design
Our terminal is designed to maximise capacity and the latest channel cards use Differential Phase Shift Keying (DPSK) combined with 20 Gbaud transmission to achieve a spectral density of 10 Gbit/s per 25 GHz. This technology has now been field tested on a variety of operational submarine systems, the longest of which included 9000 km of un-regenerated transmission. With an eye to the future, we are now looking at ways to get even more capacity – for example by placing the wavelengths even closer together – and also determining the best way to transport 40 Gbit/s traffic.
Our design also focuses on operational factors. The NXT’s channel cards are fully tuneable and can be configured to any of the 10 Gbit/s rates/formats, thus simplifying sparing. Once plugged in, a card will download all its configuration information – no operator actions are required beyond connecting optical leads. It can also be re-configured to a different traffic type via the network management system. To safeguard network operation, the Management System will detect and block unauthorized requests and warn of actions which may be hazardous to traffic.