Are endpoints and pipes unidirectional?



Hi folks,

I am reading USB 2.0 spec. and trying to get basic understanding about
USB 2.0 and OTG.

My question is "Are endpoints and pipes unidirectional?" I will
appreciate if anyone can give me some help .
The explanation of direction of endpoint and pipe on the specification
seems conflicted.
From page 33:

Each endpoint is a simplex connection that supports data flow in one
direction: either input(from device to host) or output (from host to

This means "Endpoints are unidirectional," isn't it?

On page 34

5.3.2 Pipes
A USB pipe is an association between an endpoint on a device and
software on the host.

So, pipes are unidirectional as well, but on page 36

Message pipes allow communication flow in both directions.

It said pipes are bidirectional. How come the explanation is

On page 34,

The pipe that consists of the TWO endpoints with endpoint number zero
is called the Default Control Pipe.

=> The Default Control Pipe possesses two pipes with endpoint number
zero, but on page 36

The Default Control Pipe is always a message pipe.

There is only ONE pipe associated with Default Control Pipe. How come?


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