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ANALYSIS OPINION
Topology Abstraction
Path Computation
Service Provisioning
Figure 1
can’t be programmed is just a brick’. In this context, if the underlying data plane resists automation for any reason then it makes the job of a control plane extremely challenging. In this case an optical layer built on conventional transponders is ‘just a brick’ – and this probably explains why most DWDM vendors have avoided automating this part of their architecture to date. Fortunately there is a DWDM technology
that solves this problem. DWDM super- channels were first shipped in mid 2012, and have rapidly become a favored approach for deploying capacity at the ‘beyond 100G’ level in the Western world. A super-channel is an evolution of DWDM
technology that implements multiple, coherent optical wavelengths on a single linecard, and which is brought into service in a single operational cycle. So all of the wavelength planning associated with multiple 100G transponder installation is done at one time, and the wavelengths are ready for new service activation, or to protect existing services in the event of link failures. Current super-channels have been deployed
at the 500Gb/s data rate, but what if the service provider doesn’t need 500Gb/s of capacity on day one? In this case the super-channel can be ‘sold’ in units of 100Gb/s – a feature called instant bandwidth because the “dormant” 100G sub-channels can be activated in seconds through the network management system. Referring back to Figure 2, the dotted lines
between the super-channel line card represent the ‘virtual capacity’ of the super-channel that has not yet been activated, and is not being paid for by the service provider. When the new routers come along, or if the network load has to
Figure 2
be rebalanced in the event of a link failure elsewhere in the network, these chunks of virtual capacity can be activated and made available in seconds. Note that Figure 2 is a very simplistic example of the power of this technique. In a larger, meshed network the possibility for closely matching rapid response to demands with cashflow efficiency are extremely exciting. Te first service provider to publicly support
instant bandwidth was TeliaSonera International Carrier. Mattias Fridstrom, the company’s CTO, also presented in Nice and it
to a survey by analyst firm Infonetics, 90 per cent of the service providers they questioned are deploying, or plan to deploy an integrated OTN/DWDM core transport platform. Te addition of OTN means that DWDM capacity, and the switching of that capacity, is now totally deterministic. Tis contrasts with the idea of only using
These chunks of virtual capacity can be activated and made available in seconds
was reassuring to hear a service provider talking about how these kinds of innovations are driving new revenue streams, and not simply about ways to drive cost out of the network!
The power of three Instant bandwidth is one of three elements needed to make the optical data plane programmable. Te second is to recognise that OTN and DWDM belong together – in the same network element. Tis is a prime example of how it makes sense to integrate certain functional elements in the network. According
optical switching in the network. Optical switching is extremely cost-effective, but when an optical switching decision is requested by the control plane it may be seconds or even minutes before the capacity becomes ready for service. Even worse is that it may not be possible at all to complete the switching decision if the optical switch (called a reconfigurable optical add/drop multiplexer, or ROADM) encounters blocking for one of many possible reasons (eg. wavelength blocking). In fact the third element to ensure a
programmable optical data plane is that ROADMs have to be engineered to be free of any risk of blocking – a design known as colourless, directionless and contentionless (CDC). CDC ROADMs that are able to manage flexible grid super-channel wavebands are now becoming available, and the technology is a perfect complement to instant bandwidth and non-blocking OTN switching. In summary, all the elements are now in
place so that the optical layer in a modern transport network can be programmed by a carrier grade control plane – whether that’s generalised MPLS (which is widely used today) or carrier SDN in the future. Te end result is that service providers can now become more responsive to new service demands, or changing traffic patterns while keeping OpEx costs low.l
Issue 5 • Autumn 2014 FIBRE SYSTEMS 15
Infinera
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