User's Guide
The Operational View SB300 Series
Page 52 Proprietary and Confidential 2110059 Rev 1.1
4. +WS45=1 to select TCP packet service.
5. Optionally assign a channel with +WPCHAN=n where n is the channel to use.
6. 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 9.
7. +WS197=n where n is the index (1-4) of the NEI to register, to select the NEI
8. +WPREG to register on the CDPD network. The modem will reply as noted in the section
above on manual registration.
9. +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.
10. +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.
11. Optionally set S0=1 to enable auto-answer mode.
The modem will remain in command state until a TCP handshake is completed with a calling
client.
The session is not actually opened until a TCP connection handshake is negotiated with an
accepted IP address on the listening port. 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 handshake will fail and the
host will not be advised of any activity. This is handled entirely within the modem.
Provided connection request 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.
If auto-answer is enabled, the modem will then open the session. If DTR is off (indicating the
host is unavailable), incoming packets are buffered. At this time, there is no DTR flow control.
Any incoming packets received while DTR is off are held in the modem buffers until one arrives
at a time when DTR is on. At that point, all buffered packets are forwarded to the host.
If auto-answer is disabled, the modem will wait for the host to issue the Answer – Manual (A)
command before completing the TCP connection handshake. If the host is slow to answer, the
caller may timeout (get a NO ANSWER result).
Once the session is opened the host is notified with the CONNECT <ip> message (where <ip> is
the address of the client station). The CONNECT message provides a “caller ID”. Note that
quiet mode (Q) will suppress the word CONNECT but not the IP caller id.
At this point the modem changes from command state to data state. Incoming packets are then
presented to the host and the modem is ready to accept host reply data for packet assembly and
transmission to the client.
Detailed Discussion
The first four steps simply place the modem in CDPD TCP mode. The modem’s sleep features
are disabled to prevent delays in TCP acknowledgements, which would cause excessive re-
transmissions and possibly loss of connection. The modem’s packet service is set in register
+WS45 (Packet Service) by step 4. Setting this value to 1 will enable the modem’s TCP stack.
This can be done before or after registration on the network so auto-registration can occur before
this step.
The registration process can be more closely controlled with steps 5 through 8. Steps 5 and 6 can
be used in auto-register as well as manual register settings.
The network registration is verified by testing register +WS56. Once registered the modem is
configured to receive calls.