User's Guide

User’s Guide CDPD Operation
2110059 Rev 1.1 Proprietary and Confidential Page 45
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.
5.8.2.4. Opening a UDP Server Session
Server sessions are those in which your modem answers a “call” from another system. The
modem is enabled or disabled from handling server sessions by the setting in +WS212 (Listening
Port). A setting of 0 disables the modem from answering server requests. Setting the register to a
valid port will enable the server side of the protocol stack.
Answering server connection requests is handled independently from enabling the service.
Provided the service is enabled, the modem can be configured to auto-answer or leave answering
up to the host with a manual answer command. Register S0 controls the answering scheme. A
setting of 0 disables auto-answer and will require the host to issue the Answer – Manual (A)
command. Setting the register to 1 will enable auto-answer and the modem will automatically
switch to data state for incoming server session requests.
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. Optionally set S0=1 to enable 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.
Provided an incoming packet is acceptable, the modem will then toggle the RI signal and issue the
RING message to the host. The RI signal is toggled on for one second and off for four seconds. If
the DTR signal is inactive, the toggle is issued a total of three times for each connection attempt.
The RING message is sent to the host once only regardless of the state of DTR.