The command to enter Point to Point Protocol mode (PPP) is used when an external stack configuration is needed. PPP is useful if the stack resides in the host computer, providing multiple sessions and complete control over all aspects of each session. PPP is quickly becoming the new standard for dial-in-networking. PPP provides more flexibility and requires fewer items that need to be explicitly set.
The PPP session is usually controlled by DTR, unless the modem has been configured to ignore DTR by programming register S211. DTR, when used, must be asserted to initiate a session and de-asserted to terminate a session. If the modem has been programmed not to use DTR Control, then the command AT\APPP can be sent without asserting DTR. To exit PPP in this case, the host must either power down the modem or use the escape sequence. To terminate a PPP session, DTR must be de-asserted or the escape sequence can be activated or the modem can be powered down.