Adaptation describes how data from a (client layer) Port is encoded in another (server layer) Port.

There are two proposals to describe these relations in NML.

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Option 1: As adaptation service. (similar to a switching service)

egress server layer Port --(hasService)--> adaptation Service
adaptation Service --(providesPort)--> egress client layer Port*

ingress server layer Port --(hasService)--> de-adaptation Service
de-adaptation Service --(providesPort)--> ingress client layer Port*

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Option 2: As Adaptation or DeAdaptation object (similar to a Link object)

egress client layer Port* --(isSource)--> Adaptation
egress server layer Port --(isSink)--> Adaptation

ingress server layer Port --(isSource)--> DeAdaptation
ingress client layer Port* --(isSink)--> DeAdaptation

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*Port or PortGroup, if we decide to allow descriptions of multiple Ports -eg. all VLANs- as a group for efficiency 
purposes.

Option 1 is more natural choice for dynamic adaptations, e.g. VLANs in Ethernet.
Option 2 is more natural choice for static adaptations, e.g. Ethernet over a wavelength.

We can even allow both: option 1 for dynamic adaptations, and option 2 for static adaptations.