Associated data is data about a communication. It defines not the content of the communication, but it defines the communication event. The purpose of associated data is to help the network route to the information through the network.
A very simple example would be that associated data would be a phone number, so the number that is called. Well, the reason that associated data is there is to actually route the telephone conversation to the right destination. That is what we were trying to explain when we said that associated data is used by the network to actually deliver information.
Again, to reiterate, associated data does not describe the content of the communication. It simply describes the context. Classic examples would be date, time, duration, phone number dialled, etc.