However no official rules or models exist for these types of units.

An important fact is that this model (B210) just existed in 1974.

The project was abandoned in the late 1960s and two different models exist.

That model will no longer exist other than as the Z06.

As a result, different models exist for the channel holding time distribution.

Of course, since no such closed model exists, one could argue not to regulate at all.

This model didn't even exist before 2007 so it's exciting for me to see the success we've achieved in such a short time.

Fortunately, a model exists for creating one: the air traffic control system.

I am one of those who consider that a European social model exists.

It is indeed a challenge, because no such model currently exists.