User's Guide

User’s Guide CDPD Operation
2110059 Rev 1.0 Proprietary and Confidential Page 43
registration is enabled, the modem will switch off DCD (closing the current session) but will
remain registered.
If the session has been kept open, the host can re-enter data state by issuing the On-line command
(O). The modem will respond with CONNECT and data state is restored.
5.7.2.3. Closing a UDP Session
To end a UDP session, escape data state as described above. If the &D2 DTR option is used then
the session is closed.
If TIES or the &D1 DTR option is used then you must hang-up with either ATH0 or ATH1 to
close the session. Both of options of the Hook Control (H) command will close the current
session. If the modem is set to manual registration, it will also be de-registered by both of these
options.
ATH1 will force de-registration of the modem even if auto-registration is enabled. The modem
will remain de-registered. Although auto-registration remains enabled, the modem will not
resume auto-registration until the register is reset (+WS173=1) or the modem itself re-enters
CDPD mode (a modem reset or power cycle on CDPD-only modems).
NOTE: There is a PAD Inactivity Timeout in register S30 that can also close a session. 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 “OK” to the host and return to command state. The Carrier Detect (DCD) signal
will also go inactive indicating the session is closed.
5.7.2.4. Opening a UDP Server Session
Server sessions are those in which your modem answers a “call” from another system.
A detailed discussion of this type of session follows the outline of steps to open a UDP Server
Session. (AT is omitted for brevity):
1. +WS46=4 to place the modem in CDPD mode (only required on the SB320).
2. +WS45=0 to select UDP packet service.
3. Optionally assign a channel with +WPCHAN=n where n is the channel to use.
4. Optionally verify the channel acquisition with +WPRSSI looking for the second value in the
return string to be 3.
If the modem is using auto-registration (+WS173=1) skip to step 7.
5. +WS197=n where n is the index (1-4) of the NEI to register, to select the NEI
6. +WPREG to register on the CDPD network. The modem will reply as noted in the section
above on manual registration.
7. +WS56? to query the registration status. Repeat this command until it returns a value of
1 (registered) or until the host chooses to timeout, failing the connection.
8. +WS212=<port> where <port> is the port number (1025-4999) that the modem will listen
to. The modem will only accept packets addressed to this port. The factory default is 2100.
9. S0=1 sets the modem into auto-answer mode. The modem will remain in command state
until a message is received from the network.
The session is not actually opened until the first acceptable packet is received.
In server sessions the modem will check all incoming packets for the source IP address. If Friends
Only is enabled, the originator’s IP address is checked against entries in the Friends List. If no
match is found the packet is discarded. If there is a match, or the Friends List is empty, the
modem will also verify that the destination port is matched to the listening port set in register
+WS212. If so, the session is opened (if necessary) and the packet is passed to the host (DTE).