FEATURE WHEN SHOULD YOU CONSIDER AN UNREPEATERED SOLUTION? BY ANDERS LJUNG, TONY FRISCH AND LYNSEY THOMAS
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facing cable and fiber manufacturers and system suppliith the increasing popularity of Space Division ers. For links around 250km we would expect to achieve Multiplexing (SDM) on repeatered systems, and around 18Tbps per fiber with standard fiber, and up to with new high fiber count transoceanic cables being 24Tbps by using more specialist fiber with a larger effeccontracted every month, it is worth reviewing how all this tive area. This aligns unrepeatered systems of this length traffic is carried within regions. Traditionally a mixture of small repeatered systems, unrepeatered festoons and point to with the per fiber capacity capabilities of their transocepoint links have been used, but how do we determine which anic counterparts, but what happens when we stretch the distance, moving design makes the most towards 350, 400 and economic sense and 450km? over what distances The graph below should we opt for one shows us that the solution over another? number of 100G’s an Historically unreunrepeatered system peatered links have can carry declines been used to connect exponentially after transoceanic systems 350km. This has often from one landing been the gating factor point to its neighfor system builders bour, and potentially who have then opted onwards in a festoon to install repeatered arrangement. UnFigure 1 Comparison of Capacity vs Unrepeatered System Length links for distances repeatered designs over 400km. We know that with the use of Remote Opoffer a low-cost solution and are often less complex than tically Pumped Amplifiers (ROPA) and powerful pre and creating large and complex powered systems with many branches. Unrepeatered systems do away with the need for post amplification we can make significant steps towards improving the capacity that can be carried – moving from power feeding equipment, repeaters and line monitoring equipment and can therefore utilise a different [more cost a handful of 100G channels at 400km, to 80 x 100G with a ROPA, and well over 100 x 100G by adding specialeffective] type of cable, making them attractive for parts ist fiber to the mix. On top of this, the high fiber count of the world where resources are limited. But they have offered by unrepeatered systems means they can now always been distance-limited, and that is the challenge JULY 2019 | ISSUE 107
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