When talking about wavelength division multiplexing you should also remember that it refers to connections between large data centres. Taking a closer look at the connections, you can notice that the majority of them use the same paths, and what’s more, they rely on point-to-point architecture. So, with that in mind, should you use the same technology as in telecommunication connections when building such systems? And will the increasing demand for broadband between data centres force you to rely on coherent solutions?
But let’s start from the beginning.
Data Centre Interconnect (DCI) is a technology of connecting two or more data centres on short, medium and long distances with the use of packet-optical connection. There is no doubt that the connectivity at long distances and high speed requires coherent transmission, but this subject has been discussed in separate articles (links at the end of the article). Here we want to discuss whether it is possible to find a more economical solution which, at the same time, will enable you the scalability of your network.
When deploying DCI you should consider the following key aspects:
- Distance - it is of key importance when choosing topology for building connections between data centres. The distance will determine whether the best solution will be dark fibre, alien wavelength technology or your own DWDM system. Fortunately, the technology known today enables you to find an optimal solution for each of the above mentioned alternatives,
- Capacity - data centres store and process huge amounts of data calculated not as before in gigabytes but in terabytes or petabytes. To cope with such a load of data, network devices must be able to ensure reliable connections of large capacity, which can be easily and flexibly scalable,
- Cost - huge amounts of data which is sent between data centres must be transmitted at the lowest cost possible as the network traffic increases by 30 per cent every year. If data centres are to be economical, the cost of data transmission cannot rise at the same pace as capacity.
So, what solution are we looking for? Let’s start with the interface. The switches/routers installed or owned by data centres are in majority equipped with QSFP+/QSFP28 ports. If you were able to install a transportation solution directly in such devices, then you could eliminate additional transportation devices and significantly lower the costs of implementation and network maintenance.
The QSFP28 DWDM solution relies on advanced pulse-amplitude modulation and thus, it provides the capacity of up to 4 TB/s on one fibre and facilitates connecting data centres located at a distance of even 120 km. A great advantage of this solution is the fact that the modules are installed directly in network devices and their signal is transferred directly onto multiplexers. Thanks to this approach we can have both an economical and scalable solution.
What else is needed to apply our solution? You already know that QSFP28 DWDM transceivers can be directly installed in network devices and connected to multiplexers. And this is exactly what you need – a multiplexer, and, to be more precise, an optical link that can work with the transceivers specified above. The entire solution will require the right multiplexers, optical amplifiers and chromatic dispersion compensators. The good news is that it is a one-time investment made at the stage of launching the first 100 Gbps transmission. To start another 39 channels of 100 Gbps transmission you just need to use the right transceivers.
The case of connecting data centres has been analysed by ACG Research experts. Their research shows that depending on the required bandwidth and the costs of fibre lease, the application of QSFP28 DWDM transceivers installed directly in network devices allows you to save 58-67% on TCO, in comparison to the use of dedicated transportation solutions in data centres situated at a distance of up to 80 km.