Oh,I just remembered.Another story that I'm currently reading also references portals.It's called Project Sunflower.I hope it helps with the concept but in all actuality you can make up whatever comes to mind and it will probably work.

One of the great thing about stories are the fact that they reflect the author and his/her creativity are always unique.So either build off of anothers theory or create your own.Either way is a win-win.:)