User's Guide

User’s Guide CDPD Operation
2110059 Rev 1.0 Proprietary and Confidential Page 47
11. D<dest> where <dest> is the destination IP and port number to send your data to. See the
AT Command Reference for details on this command. The modem will reply with
CONNECT at which point you are in data state.
The modem is now ready to accept host data for packet assembly and transmission to the network.
Any incoming packets, from an originator other than the <dest> will be ignored. Incoming
packets from the <dest> address will be passed to the host. This allows the host to exchange data
in a point-to-point connection on a specified port with a specific station.
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.
To send data over the network in a TCP client session the user must enter a data state connection
to the network with a specific IP address and port number.
The On-line command (O) can only be used after a session has started. The Dial command must
be used to establish the TCP point-to-point connection. Once established, the host can escape data
state and then use this command to return to data state with the point-to-point connection still
intact.
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.
The IP of the destination can be any valid IP. Client sessions do not apply the Friends Only
restrictions. If the Dial command is given bad syntax including an invalid destination IP or port
number, then it will return the ERROR result code.
The Dial command can handle the network registration process using the NEI indexed by the auto-
register index or the one specified with the N=v dial modifier. See the AT Command Reference
for details. This means steps 3 through 6 can be omitted if desired.
Note that two timers are used for the connection process. +WS198 (Registration Wait Time) is
used to timeout the network registration process. The default is 30 seconds. A second timer at S7
(TCP PAD Timeout) is used to time the TCP connection handshake. This timer defaults to 30
seconds as well. The TCP PAD Timeout starts when the Dial command is issued. If modem was
not already registered, then network registration will consume time from this timer as well. In
other words, the TCP PAD Timeout can run concurrently with the Registration Wait Timer.
The response to the Dial command when TCP is enabled does not depend on the setting of register
+WS179 (Registration Wait Status). The CONNECT code is only returned on the successful
network registration and TCP negotiation with the destination. A failure to register or negotiate
TCP is reported to the host by either a NO CARRIER or NO ANSWER result code. The response
can be one of the following:
CONNECT The modem has successfully registered and established the TCP
connection. You can now communicate with your destination.
NO CARRIER The modem failed to register with the network within the time allowed
by +WS198.
NO ANSWER The modem could register with the network but could not negotiate the
TCP handshake with your destination within the time allowed by
register S7.
ERROR An invalid IP or port number was specified or there was some other
error in the Dial command syntax.