An OSI Transport connection is an end-to-end connection. It is a
    reliable two-way, data-transfer path between two OSI Transport
    users. An OSI Transport connection has three phases:

    o  Setting up the connection -- an OSI Transport user (the
       initiating user) on one end system (the initiating host) sends a
       connection request TPDU to another OSI Transport user (the
       responding user) on a second end system (the responding host).
       When a successful connection is made, data transfer can take
       place in either direction.

    o  Using the connection to transfer data through -- OSI Transport
       connections support two kinds of data transfer:

         - Normal data transfer --- for usual message exchange or

         - Expedited data transfer --- bypasses any blockage
           due to the flow control applied to normal data; only for
           sending small amounts of data; has its own type of TPDU
           and transmission rules.

    o  Releasing the connection -- either transport user can release the
       OSI transport connection by sending a disconnect TPDU.