User's Guide

User’s Guide CDPD Operation
2110059 Rev 1.1 Proprietary and Confidential Page 51
When the TIES is received by the modem, it will enter command state but remain registered and in
on-line condition (the session is kept open). If data arrives at the modem while the session is open
and the modem is in command state, the data is buffered as described above. See below for
instructions on closing the session.
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.
DTR Option
An alternative to TIES is to pre-set the DTR Options (&D) to either 1 or 2 and then switch DTR
off to escape data state. If the option is set to 1 (&D1), the modem will enter command state and
remain registered with the current session still open. If the DTR Option is 2 (&D2) then the
modem will close the session, de-register, and return to command state. Note that if auto-
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.
5.8.3.3. Closing a TCP Session
To end a TCP 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 these command options 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 NO CARRIER and return to command state.
The Carrier Detect (DCD) signal will also go inactive indicating the session is closed.
5.8.3.4. Opening a TCP 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 TCP Server
Session. (AT is omitted for brevity):
1. +WS46=4 to place the modem in CDPD mode (only required on the SB320).
2. +S31=0 to disable logic sleep.
3. +WS175=0 to disable CDPD sleep.