The EGN model (download EGN model paper) provides excellent accuracy in predicting the amount of non-linearity (or non-linear interference noise, NLI) affecting each channel in a WDM system.

See below the June 2014 news for more details. However, the EGN model is substantially more complex than the GN model. 

Now, the accuracy of the EGN model can be obtained with similar complexity to the GN model, for most practical systems.

The breakthrough is the GN model closed-form correction formula, derived from the EGN model, which we just published on the IEEE/OSA Journal of Lightwave Technology. A pre-print version is available on arXiv, to download it click here.