GTT

Global title translation (GTT) is the SS7 equivalent to IP routing. Translation examines the destination address (e.g. the number being called) and decides how to identify it over the telephone network. This process can include global title analysis, which is the act of looking up the number and finding a result address, and global title modification.

It is possible for the result of Global Title Translation to be Route on SSN. This means that, instead of the Global Title routing, lower level MTP routing will be used for this message from this point on. Equivalently, in a system using SIGTRAN, the result from Global Title Translation may be to a route to an IP server.

Reference

http://en.wikipedia.org/wiki/Global_Title