User's Guide
User’s Guide CDPD Operation
2110059 Rev 1.1 Proprietary and Confidential Page 43
Any incoming packets, from a remote 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
with a specific station.
Detailed Discussion
The first two steps simply place the modem in CDPD UDP mode. The modem’s packet service is
set in register +WS45 (Packet Service) by step 2. Setting this value to 0 will enable the modem’s
UDP 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 3 through 6. Steps 3 and 4 can
be used in auto-register as well as manual register settings.
To send data over the network in a UDP 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 be used
with the modem using the default IP address and port. Unfortunately, there is no way for you to
verify what this destination is, so we recommend you issue the dial command with an explicit
destination each time you start a client session.
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. This is also true if a “quick dial” index points
to an empty or invalid entry in the Friends Only list.
The Dial command can handle the network registration process using the NEI indexed by the auto-
register index. See the AT Command Reference for details. This means steps 3 through 6 can be
omitted if desired.
The response to the Dial command will depend on the setting of register +WS179 (Registration
Wait Status). If the setting is 0 (the default) then the CONNECT code is returned regardless of
the success or failure of the modem to register. If the modem was not registered then the dial
command must perform the task. The UPD PAD is ready and you may start assembling data into
a packet while the registration process proceeds in parallel. The modem will buffer the data until
the modem registers. A failure to register is NOT reported to the host, and the packet can be lost.
If the Registration Wait Status register is set to 1, then the modem will not respond to the dial
command until the registration process terminates. In this case, the response can be one of the
following:
CONNECT
The modem must have successfully registered and you can
communicate with the network.
NO CARRIER
The modem failed to register with the network within the time allowed
by +WS198.
ERROR
An invalid IP or port number was specified or there was some other
error in the Dial command syntax.
It is important to understand that CONNECT does not mean that you have established a
communication link with the destination. UDP is “connectionless”, meaning that you only have a
connection to the network. Data packets are not guaranteed to reach their destination using UDP.
Transmitting
Once in data state, the modem uses its PAD management services to assemble the data coming
from the host into packets. See Section 5.9 for a discussion of these services.
Receiving
When the connection is established actively (by a D (Dial) or O (On-line) command), the modem
treats the connection as a client session. Incoming packets are accepted from the destination
address specified in the Dial command (or defaulted in the On-line command) regardless of
whether or not it is contained in the Friends list.
Any packets arriving from an IP other than that in the Dial command are ignored.