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Connecting modern data centres with DWDM technology

Marcin Bala

Marcin Bala

CTO at Salumanus Ltd
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DWDM

Traditionally, data centres were seen as compartmentalised facilities that did not offer much flexibility to companies. If a company wanted to expand its data capabilities, it had to invest in acquiring more server space in the data centre, but this did not address security concerns, as all data was stored in only one location. With the rapid advancement of telecommunications, two or more data centres can be connected in a versatile and cost-efficient way using DWDM technology.

European data centres attracted approximatively £23.5 billion worth of investment in the first half of 2020, despite the impact of Covid-19, according to The Knight Frank Data Centre Report. This is an impressive increase from only $2 billion investment volumes in 2019, and companies such as Amazon, Facebook and Google are continuously expanding their hubs.

As the size and number of companies choosing to host their information in data centres grows, so does the demand for stronger capabilities and higher bandwidth. Data centres can host data from giant corporations like Google together with the assets of smaller companies, meaning that they must meet the needs of a small business that requires 1GbE or 10GbE connectivity, as well as a multinational corporation with needs of 100GbE or even 400GbE connectivity.

They also need to be interconnected geographically to minimise the risk of external threats on customers’ networks, as well as to increase their backup capabilities. Strong encryption protocols with strict accessibility rules are also required to avoid costly data breaches.

To respond to companies’ demand for capacity, distance and security, data centre operators can use Wavelength Division Multiplexing (WDM) technology, which allows data centres to virtually multiply their existing fibre backbone infrastructures and meet their customers’ demand for bandwidth.

CWDM or DWDM?

The traditional solution used by data centres is Coarse Wave Division Multiplexing (CWDM), which is a convenient and low-cost technology that allows up to 18 channels to be connected over a fibre pair. However, although the 18 channels will work efficiently for distances of up to 40 kilometres, only eight will function properly for up to 80 kilometres.

The channels are transmitted through a single optical fibre at the same time, with a distance of 20 nanometres between the central wavelength of each channel. Because of the large distance between the channels, CWDM cannot be amplified. Due to technology limitations, the speed of data transmission is around 10 Gigabit Ethernet and 16Gb Fibre Channel.

Unlike CWDM, DWDM connections can be amplified using an optical amplifier, and therefore can be used for transmitting data at a much longer distance, even a few thousand kilometres. DWDM is capable of supporting anywhere between 40 and 160 separate wavelengths. To support 48 channels for a 100GHz grid, there is 0,8 nanometres spacing, while the spacing to obtain 96 channels for a 50 GHz grid is 0,4 nanometres. This means that enormous amounts of data can be transmitted over a single fibre, with each channel at a speed of 400 Gbps and 64 channels per fibre pair.

Another advantage of DWDM is that the networks are carried on distinct wavelengths and the channels do not interfere with each other, meaning they can use different data formats and be transmitted at different data rates. This feature is essential for maintaining data integrity and ensuring any security-related partitioning where there are multiple tenants in the same data centre.

For these reasons, DWDM technology is a more appropriate solution for large capacity data transport and connectivity over long distances. It is also useful for densely populated data centres, especially hyperscale cloud service providers or colocation providers for their densely multi-tenanted spaces.

Data Centre Interconnect

Data Centre Interconnect (DCI) is a technology that connects two or more data centres together over short, medium and long distances with the use of packet-optical connection.

To achieve an effective DCI strategy, companies can choose to use muxponders. However, for large corporations that require more than 100G connection at a reasonable cost, a more suitable option is the use of QSFP+/QSFP28 ports. By installing a transportation solution directly in such devices, users can eliminate additional hardware and significantly lower the costs of implementation and network maintenance.

QSFP28 DWDM solutions rely on advanced pulse-amplitude modulation and thus provide a capacity of up to 4 TB/s on one fibre and facilitates the connection of data centres located at a distance of even 120 km. A great advantage of these solutions is the fact that the modules are installed directly in network devices and their signal is transferred directly onto multiplexers. Thanks to this approach, companies can have an economical but scalable solution.

The entire solution will require the right multiplexers, optical amplifiers and chromatic dispersion compensators. This is a one-time investment made at the stage of launching the first 100 Gbps transmission. However, a recent analysis conducted by ACG research showed that the application of QSFP28 DWDM transceivers installed directly in network devices allows users to save 58 to 67 per cent on the total cost of ownership (TCO) of transceivers, compared to the use of dedicated transport solutions in data centres situated at a distance of up to 80 km. This ensures a fast ROI for companies, while also giving them the possibility to scale up. For example, to start another 39 channels of 100 Gbps transmission, data centre managers just need to use the right transceivers.

Not only does a QSFP+/QSFP28 port reduce the total transport solution costs, as it takes up minimal rack space, but it also lowers the power consumption per transmitted bit. This makes it ideal for connecting data centres over distances of up to 120km, while maintaining a sustainable installation and deployment.

Modern data centres require modern and advanced solutions. They are no longer seen as just locations for storing data, but increasingly as a viable solution for scaling up businesses and improving customer satisfaction by offering them secure and easy access to their data. DWDM is the ideal technology for connecting data centres and responding to companies’ demands. Higher speeds, more channel capacity and longer distances makes DWDM the technology of choice for modern enterprises.

Salumanus Ltd is a telecommunications networks specialist.

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