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Best practice for preventing service interruptions in the event of a fibre cut calls for protection using a working fibre and a protecting fibre between locations, ideally using different routes and even different providers. The traditional approach for protection in point-to-point networks has been to use a dedicated fibre pair for the working fibre, with one transmitting and one receiving and a separate pair for the protecting fibre (see Figure 3). Leasing four fibres for each part of the network can get very expensive.
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25T Example
PL-4000G 4.8T transponders and PL-300 mux/demux passive devices, can build a point-to- point topology with redundant fibre pairs to protect against fibre cuts (see Figure 5). This solution leverages a 64 channel DWDM system that is capable of transmitting a total of 25.6T.
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As wavelengths can propagate through a fibre in opposite directions simultaneously without interfering with each other, it is possible to use one set of wavelengths for transmitting and another set of wavelengths for receiving. The technique requires careful attention to distance, channel spacing, and data rate limitations to maintain signal quality but it can provide significant savings, especially for complex networks.