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Configuration and Use DART 300 Modem
Page 84 2110212 Rev 1.0
9.2.2. Using PPP Service
With a modem configured as noted immediately above, the local host needs to do the following to
connect to the network.
(AT is omitted for brevity):
1. On start-up, either monitor the DART 300 for the OK result code, or check for an assertion of
the CTS control line to indicate the modem is ready.
2. Optionally verify CDPD channel acquisition and registration. You can manage this process
as suits your need. If manual registration is selected, 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.
3. D (Dial); any parameters are ignored. This command forces the modem to attempt to register
regardless of the setting of auto-registration. This allows the modem to go on-line using just
the one command, but network registration is not guaranteed unless +WS179 was set to 1 in
the configuration.
The modem will reply with CONNECT at which point PPP is used to negotiate the session
parameters between the modem and local host. If the host does not handshake the PPP
negotiation promptly, the modem will drop the connection and revert to command state with
the OK result code.
An alternative process is to issue O to go on-line (start the session). This should only be used
if you know the modem has successfully registered on the CDPD network.
The modem is now operating under PPP control to pass host packets to the network. Any
incoming packets, from any calling client or responding server, will be passed to the local host.
This allows the host to send and receive packets to and from multiple destinations asynchronously
provided the host can manage multiple socket connections.
Once in data state, the modem acts as a pipe through which data passes. All PAD and IP protocol
stacks as well as PPP framing must be implemented on the local host (DTE) system. Windows
Dial-up Networking can provide these services.
9.2.2.1. Transmitting
Data packets received from the local host (DTE) are forwarded to the network in 128 byte
segments. They can be buffered on the modem up to 14 segments (1792 bytes). Beyond this,
there is local hardware flow control (RTS/CTS) with the host to prevent overflow.
9.2.2.2. Receiving
Incoming data from the network is buffered (up to 14 x 128 bytes) and is passed to the local host
as it arrives. If the modem has been placed in command state but is still in on-line condition,
incoming data will be buffered. There is an automatic remote flow control between the modem
and the network to prevent overflow when the modem’s buffers are full.
9.2.3. Closing a PPP Session
To end a PPP session, escape data state via PPP or by using DTR in conjunction with the &D2
DTR option.
If the PPP escape sequence or the &D1 DTR option is used then you must hang-up with either H
or H1 to close the session. Both of these will close the current session. If the modem is set to
manual registration, it will also be de-registered by both of these commands.
H1 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 resets or power
cycles.