We are looking to upgrade our existing fiber backbone which is currently running at gigabit speeds, and is approximately 10-12 years old. Consequently it won't run any faster speeds over the link lengths we are currently running. What I am wondering is what standard fiber should I be looking at upgrading it to? I want the new fiber to at a minimum to be able to run 10gigabit, and possibly short lengths of 100gigabit. We are currently running 12 core, and will probably want to replace it with 20 or 24 core fiber. Can anyone give me some advice on what standards I should be looking at?