No that is one specific implementation of a DoS attack. There are CPU exhaustion attacks, memory exhaustion attacks, and all kinds of attacks that have nothing at all to do with bandwidth exhaustion. I believe what you just named is an open socket exhaustion attack, it doesn't even have to do with bandwidth. The most commonly known of form for a DoS attack is bandwidth exhaustion, but the term is so incredibly broad that it applies to all kinds of almost completely unrelated things. It is like saying "2 + 2 IS NOT ADDITION 1 + 1 IS ADDITION".