rsync's usage of ssh

[a.]

I am trying to understand how rsync uses ssh. From what I understand of
the source, it simply opens a ssh connection and then simply pipes
rsync's data. But somehow my stomach tells me that this is not the whole
story.

For one, that would mean the whole (?) of rsync's protocol is only used
for not-ssh transmission. The biggest question for me right now is,
whether rsync, when transmitting remotely over ssh, is binding sockets
of some kind or if it is completely dependent on ssh for that.

For every bit of enlightenment in this regard I am very grateful!

alex.