The transmission data is very precise. It contains no content on transmissions. It does not reveal substance, the meaning, or the purpose of the communication. It more or less identifies a type direction data—the date, duration, and so forth. So it's actually similar to phone call data today. If I were to make a phone call I know that this number called that number. So it' the same thing with this computer calling that computer. So we're establishing the link.
On May 15th, 2014. See this statement in context.