Migrating to an Ethernet-centric Infrastructure

Thanks for touching base again, Michael.

The topic of ROADM and ASON is an interesting one. The ASON architecture includes both an internal and external network node interface definition (I-NNI and E-NNI, respectively). The E-NNI ASON interface is compatible with optical networks that contain ROADMs, as the E-NNI is able to make use of an abstract view of a network domain. In a sense, the E-NNI never needs to know there is a ROADM inside the domain; it just needs to learn what connectivity the domain can establish.

In the case of an I-NNI, the status is quite different for ASON standards concerning a network domain including network nodes that are ROADMs. Although the ASON architecture encompasses photonic network elements and all-optical network reconfiguration, no standards yet exist for a photonic layer I-NNI, and I am not aware of any standards under active development. This is also the case in the I-ETF, in the GMPLS drafts.

There are significant technical difficulties in obtaining and interpreting necessary analog parameters for a photonic layer path computation. Additionally, vendors of optical networking equipment use different technologies, with significantly different propagation performance. Therefore, the practical application of multi-vendor photonic layer interworking is not near, at least not for the general networking case. There will always be specific situations where distances are short and nonlinear effects small, where photonic interworking will be achievable without a great deal of difficulty.

In summary, the emphasis of standards work in the ITU is on developing an E-NNI, and this seems to be a good solution for the electronic layer as well as the photonic layer, where ROADMs are included.