One channel, the get-state-request channel, goes from an observer to the subject; an observer sends the state request on that channel. The other channel, the get-state-reply channel, goes from the subject back to the observer; the subject sends the state reply on that channel. All of the observers can share the same request channel, but they will probably each need their own reply channel. Each observer needs to receive not just any response but the particular response for its specific request, and the easiest way to ensure this is for each observer to have its own reply channel.
