User's Guide

User’s Guide CDPD Operation
2110059 Rev 1.1 Proprietary and Confidential Page 53
The listening port (+WS212) must be set to the desired port number to communicate over. Both
the client and server must share this port number.
In a server session, the host does not originate transmissions, but rather waits for service requests
from a calling client. The modem does not enter data state until a successful TCP handshake has
been negotiated.
Receiving
Incoming requests for TCP connection are accepted from the network only if the IP of the sender
is on the Friends List or the list is empty (Friends Only disabled) and the destination port matches
the listening port. Any connection requests or packets arriving from an IP other than those
accepted are ignored.
Once the session has been started, the modem will only receive packets from the connected client
IP. This will remain in effect until the session is closed.
If the modem has been placed in command state but is still in on-line condition, incoming data
will be buffered. There is an automatic remote flow control between the modem and the network
to prevent overflow.
Transmitting
Once in data state, the modem uses its PAD management services to assemble the data coming
from the host into packets. See Section 5.9 for a discussion of these services.
All outgoing packets are directed to the connected client IP until the connection is closed.
5.8.3.5. Escaping Data State
Escaping data state to allow the issuing of AT commands to the modem is handled exactly the
same way as a client session. See Section 5.8.3.2 above for details.
5.8.3.6. Closing a TCP Server Session
Closing a server session can be handled in three ways.
• The server host can close the session exactly the same way as a client session. See
Section 5.8.3.3 above for details.
• The client can disconnect. The server host will receive the “NO CARRIER” message and the
Carrier Detect (DCD) signal will go inactive indicating the session has closed.
• The modem can close the session if the PAD Inactivity Timeout in register S30 expires. This
timer is disabled by default (set to 0) but can be set to a value from 1 to 20 minutes to prevent
the modem from holding an idle session open. If this mechanism closes the session the
modem will send the message “NO CARRIER” and return to command state. The Carrier
Detect (DCD) signal will also go inactive indicating the session is closed.
Provided the modem is set to auto-register and ATH1 is not used to close the session, the modem
is ready for the next server session without further configuration. Auto-answer will remain
enabled and the modem registered on the network.
To disable auto-answer, you must set register S0=0. This will prevent the modem from opening
any further server sessions.