Difference between "fallback" and "fall back"? [closed]

I am struggling to understand when to use fallback and when fall back (with a space).

• http://en.wikipedia.org/wiki/Fallback
• http://en.wikipedia.org/wiki/Fall_back_and_forward

Basically I have to say

This application implements a fallback [without space?] scheme: the application will fall back [with space?] to the next option if the first wasn't sufficient.

In general, grammatically, fallback is a single word, normally a noun. The meanings are what you see on the wikipedia page and notice that in all cases, they're nouns. On the other hand, fall back is two separate words, a verb and an adverb (except in the case of the fall back and forward protocol). So you can fall back, but you can't fallback. You can have fallback, but you can't have fall back.

In the context of data communications, "fallback" is an algorithm used in some protocols. As a verb, "fall back" is used. As a noun, "fallback" is used with no space. So a modem will fall back to a lower speed. The amount of fallback is negotiated between the communicating modems.