18th letter in the Arabic alphabet.

Ain: Hebrew: Not, or Nothing. This is the final of the three negative veils beyond the Primal Unity described on the Qabalistic Tree of Life as Keter, the Crown. Thus it is the most sublime dimensional state descriptable in linguistic terms. All comes from naught and goes to naught. Not negating itself becomes Not-Not, (Not Nothing), or Ain Soph, "No Limit." Thus the second veil is a double negative, two zeros adjoined, an infinity. Contradict this, and there is Not-Not-Not,(Not Not-Nothing), called Ain Soph Aur, "Light Without Limit." Such is the only way to describe the source behind Unity, as Unity is both essentially limited and unlimited. Thus the Qabalists described everything as, ultimately, nothing. There is also some speculation that the three negative veils are themselves a primal mirror of the three supernal spheres on the Tree, or perhaps, the other way round...

AIN is the acronym for Advanced Intelligent Network. It is the SS7 TCAP service that allows custom applications to be developed that use the SS7 network. Any of the other TCAP services could be duplicated with this, or you could create your own way of using it. The total subjectivity of its use makes it impossible to give a description of how it operates. The specifics depend solely on how the service in question was designed to work.