Colorless Directionless Contentionless Flex Grid
The review considers the key provisions that determine the ROADM technology (Reconfigurable optical Add/Drop Multiplexer), supporting the functionality of the new generation of the CDC-F type
C – Colorless
Ability to connect optical channels to any port of the multiplexing equipment and remotely adjust the wavelength of each channel
D – Directionless
Ability to add/drop optical channels from or to any direction of transceiver and remotely change the direction of the channel transmission
C – Contentionless
Add/drop of optical channels using the same wavelength to different directions in multi-degree node
F – Flex Grid
Flexible frequency grid
On existing transport networks built using OTN/DWDM technology, most often for optical channels use a standard fixed frequency grid (Fixed Grid) with a step of 50 or 100 GHz. To build such a communication line, the simplest equipment is used, but this approach has a number of limitations.
Firstly, a high level of spectral efficiency of the DWDM system is not achieved, especially in cases where optical signals with a spectral width much smaller than the fixed frequency grid step are used.
Secondly, it is not possible to use optical channels with a high symbol rate, the spectrum width of which exceeds the fixed frequency grid spacing.
To overcome the restrictions provided, telecommunications equipment that supports the Flex Grid functionality is used (ITU-T G.694.1 (10/2020) «Spectral grids for WDM applications: DWDM frequency grid»). In such equipment, it is possible to adjust the frequency grid flexibly, allocating a frequency band for each channel, consistent with the spectrum width of this channel. The minimum tuning step of the central wavelength of the channel is 6.25 GHz. More information on Flex Grid technology are provided in ITU-T Rec. G.694.1.
Application of Flex technology Grid provides the possibility to increase the level of spectral efficiency and throughput of the DWDM system, as well as increase the transmission distance without 3R regeneration (without the use of an intermediate OEO transform) by using channels with a high symbol rate and with lower level modulation formats.
Due to the denser packing of the frequency spectra of individual optical channels in the DWDM group signal spectrum (spectral defragmentation), it becomes possible to build new, previously unavailable, routes for optical channels on a network with a complex topology.