FEATURE SubTelForum.com/Cablemap
TAILORING THE NETWORK FOR LOW-LATENCY AND HIGH AVAILABILITY BY STEINAR BJØRNSTAD
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n today’s market the need for low-latency and high availability services is growing, pushed by users in high-speed financial trading and the gaming industry, as well as new applications like Augmented Reality and Virtual Reality (AR/VR). One of the key goals of the introduction of 5G network technology is to address these emerging applications and markets. Communication technology is continuously evolving and in combination with 5G targeting critical services in the automation of the industry (Industry 4.0). All demonstrating a strong drive for providing services with increasingly demands to high availability and 47612792ultra-low latency for supporting existing and emerging markets. Figure 1 shows a map with Tampnet’s fibre routes in and out of Scandinavia. Tampnet has from the earliest days of the company had an ultra-reliable low latency (URLL) building methodology in mind when deploying sub-sea fibre cables and building new fibre-routes. Let’s have a deeper dive into which building practices that should be followed for minimizing latency. In legacy long-distance fibre systems that predate modern optical coherent technology, dispersion compensation as part of the fibre link was mandatory. A commonly used method was to insert a so-called Dispersion Compensating Fibre (DCF), with the inverse and a higher dispersion than the transmission fibre. As a result, dispersion was managed
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and pulse distortion avoided. However, as inserting a piece of DCF fibre meant adding an extra segment of fibre, this resulted in added latency on the link. If DCF fibre is utilised the extra added segment typically corresponds to 2025 % of added length. On a fibre segment of 1,000 km, the DCF may add as much as 200 km in length, corresponding to 1 millisecond of delay. Alternatively, Fibre Bragg Grating (FBG) based modules with the ability to compensate the dispersion while adding insignificant delay. This is a compensation method found in more recent long-haul fibre installations deployed before the current state-of-the-art coherent technology was taken into use. Hence, one of the important principles Tampnet follows when building fibre routes is to use up to date optical coherent technology and minimize, or avoid, the use of DCF fibre.
OPTICAL SWITCHING
To enable high availability, Tampnet has from its inception deployed optical switching elements like Reconfigurable Optical Add Drop Multiplexers (ROADM) and Wavelength Selective Switches (WSS). The optical switches enable high-speed switching to alternative routes and are used for redirecting traffic to alternative links in cases of planned work or failures on a link. Looking at optical switching from a latency perspective, the signal is transported optically and transparently through the