How do you determine constraint length,k is small value or large value?

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[For small values of k, this is done with a widely used algorithm developed by Viterby(Forney, 1973]

My question is how do they determine k value is considered small or big? What is the threshold value for k? For example, length of this code is 7 and they considered it as small value. How about 10? or how about 20? Are they considered as small value or large value? I’m curious about the threshold value of k.

This is an excerpt from Computer Network Book by Andrew S. Tanenbaum

The data link layer(chapter 3), Page 208, Fifth edition.