A person who's not naturally talkative (like me) is a block-data communicator. I send a block of data, I stop talking, I wait for the other person to process it and respond, they send a block of data, and when I hear a cue (like a falling tone or a pause in speech) I know it's my turn to process the data and reply with a new block of my own.
With stream-data communicators, there's no cue, because the other party is expected to process the data continuously and respond whenever they feel like it. The other party isn't expected to wait for an invitation - they just jump right in! Unlike block communicators, they're not peevish about being 'interrupted' because for them that's a perfectly natural, normal way to communicate.