Linux: how to create a sysctl variable?

Hello,
I have a debian kernel 2.6.32 machine and i making changes to the tcp stack.
To make this i need to create a new sysctl variable.

can anybody tell me in which files i have to declare, define.. the variable and what are the steps to do so?

Thanks in advance

I don't know, but since you know what they are, then perhaps you could find other examples of sysctl variables in the code base, and see how they do it.

Then it's follow the examples you find.