An SMPP session between an SMSC and an ESME is initiated by the ESME first establishing
a network connection with the SMSC and then issuing an SMPP Bind request to open an SMPP
session. An ESME wishing to submit and receive messages is required to establish two network
connections (TCP/IP or X.25) and two SMPP sessions (Transmitter and Receiver).
Alternatively, in this version of the protocol an ESME may establish an SMPP Transceiver
session over a single network connection.
During an SMPP session, an ESME may issue a series of requests to an SMSC and shall receive
the appropriate responses to each request, from the SMSC. Likewise, the SMSC may issue
SMPP requests to the ESME, which must respond accordingly.