Squeezing the stone (part two)

05 January 2016 | Benoit Kowalski


Benoit Kowalski

Blog Author | Infinera; director, subsea

Extracting more capacity and achieving enhanced differentiation in subsea transmission, Geoff Bennett, director of solutions and technology, and Benoit Kowalski, director of subsea, Infinera continue to explain in part two.

Adding cashflow efficiency

It is tempting to assume that opex for subsea operators could be driven down by simply implementing super-channel line cards with ever-more capacity. But is this a viable approach from a cashflow perspective? In other words, while the network planning department would readily embrace a 500Gbps or even a 1.2Tbps line card in which all of the wavelength planning is done in one step, the finance department might be reluctant to pay for it until there are revenue-generating services that need to use it.

With a super-channel line card it is possible to license the capacity in 100Gbps “chunks” (note that while this is technically possible for any vendor’s super-channel line card, you should check if your vendor offers this as a commercial option). With this approach, all of the wavelengths of the super-channel are lit from day one (avoiding the need for idler channels to be taken in and out of service), the network operator can pay for 100Gbps slices of capacity as needed. More importantly these 100Gbps bandwidth slices can be activated “instantly” (ie. within the timeframe of the financial approval, and not usually limited by the technology activation timeframe).

This is a radical change in service delivery capability for a typical subsea network. An un-forecast subsea transponder might have a lead time of the order of nine to twelve months, whereas a new 100Gbps slice of an existing super-channel line card could be activated in minutes.

A novel option would be to allow a network operator to maintain a “floating pool” of bandwidth licenses. These could be moved around the network if spare capacity exists on a given link, and an obvious application would be as part of a service protection strategy.


In Figure 2 we can see how this would work. Let’s assume a cable fault (eg. caused by a fishing trawl, ship’s anchor dragging, or a subsea earthquake) occurs between A and B. Protection techniques such as ITU-T Shared Mesh Protection can ensure service continuity against SLAs, but in this case it may be that the protection path over A-D-C-B is now carrying more traffic than the network operator’s traffic engineering guidelines recommend. By activating a number of time-based bandwidth licenses it is possible to rebalance the traffic matrix and remain within traffic engineering parameters. When the original link is repaired, the licenses can be returned to the “pool”.

This capability was used earlier this year on the AJC cable system after a subsea cable fault in 7,000 to 8,000 metres of water depth. Over 400Gbps of traffic was rerouted in just a few minutes using this “instant bandwidth” capability on the existing super-channels. This type of temporary capacity increase can come at no additional cost, and the licenses are simply returned to the bandwidth pool, in this case following the cable repair.


Conclusion: Subsea service differentiation

The move to 100Gbps coherent transmission for SLTE upgrades is now well under way. Existing cable capacity can be increased by perhaps a factor of ten – and new cable types offer even greater capacity, while taking full advantage of second generation coherent technologies.

But capacity on its own does not offer a clear differentiation for subsea operators. New technologies based on super-channel line card designs offer dramatic reductions in operational scalability while an “instant bandwidth” capability on these line cards reduces new capacity deployment times from months to minutes.

As internet demands, driven by cloud services, higher video quality, and high definition mobile devices, continue to grow exponentially there has never been a clearer reason for subsea operators to look to innovative network upgrades.