The SW-21 switch is definitely not a 22KHz switch, nor is it a 0v/12v switch.
Therefore, it must be some type of DiSEqC switch, but it is not the same as a typical DiSEqC switch. There is something unique about it that makes it slightly different from what we are familiar with as a DiSEqC switch as it won't work (as far as I know) if you try to set it up in a STB's menus as a generic DiSEqC switch.
Some FTA receivers have an option to utilize this switch (which is good because this switch seems to be extremely durable and flexible for many applications). They are a great little switch and tough!
I wish that I could present you with more information than just this, but maybe someone else will respond with more explicit information.
Either way, make certain that you keep that switch. If it is still functional (and I expect that it is) it is a valued switch.
If I recall correctly, the sw21 is very much like a 22KHz switch but it operates on a different frequency. I think DirecTV has one that operates on 21KHz or lower. I can't remember what DNet's switch is, it could be 20KHz... And just for your info, I understand the "SW" does not stand for switch, I wish I could remember these things... errr! So don't quote me on this.