OTN

flex-grid-optical-networks

Fiber Optic cable — Channel Capacity:

Frequency = Speed of Light (m/s) / Wavelength (nm)

C-Band(Conventional Band): 1530 nm to 1565 nm
Spectrum is Available in C Band:
$$
(\frac{299792458}{1530} - \frac{299792458}{1565}) \times 10^9 = 4.4 THz
$$

Flex-grid

  • Flex-grid removes the fixed cubbyhole walls and lets the service provider define the spectral width of each wavelength independently.

  • The optical spectrum is no longer pre-partitioned into 96 fixed slots of 50 GHz but rather a continuous 4,800 GHz wide block of spectrum.

  • the emergence of Flex-grid allows the service provider to carve the optical spectrum of their fiber to transport wavelengths of various spectral widths.

    Flex-grid-ROADM-Diagram

Spectrum planning with Flex-grid

  • The flexibility of Flex-grid offers a great benefit but it can also be a bit of a double edge sword. If channel assignment is not properly planned, it can lead to stranded spectrum within the optical band.

  • Wavelengths typically require at least a 50 GHz spectral width in order to provide a minimum of 100 Gb/s capacity over a typical metro DWDM network. An operator should be careful in ensuring that they are not leaving unassigned spectrum components between wavelengths that are not at least 50 GHz. The presence of small slices of unusable spectrum is commonly referred to as spectrum fragmentation.

  • The emergence of unusable stranded spectrum can actually occur over time. Optical circuits are dynamically created and deleted and this dynamic nature can unintentionally create spectrum fragmentation.

reference

Share