User's Guide

User’s Guide CDPD Operation
2110059 Rev 1.1 Proprietary and Confidential Page 41
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 configurations.
To send data over the network in SLIP mode the user must enter a data state connection to the
network. There is no explicit destination in SLIP mode so the Dial command is not supported.
You are better advised to verify the modem has registered and simply go on-line. Registration is
verified with a response of 1 to the query of register +WS56.
If there are problems with registration, the host should manage a timeout on this process.
Continue to repeat the +WS56? query until you get a response of 1 (registered) or the host timer
expires.
The O command will switch the modem to data state regardless of the registration condition. This
should only be used if you know the modem has successfully registered on the CDPD network.
Once in data state, the modem acts as a pipe through which data passes. All PAD and IP protocol
stacks as well as SLIP framing must be implemented on the host (DTE) system. Windows Dial-up
Networking can provide these services.
Transmitting
Data packets received from the 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.
Receiving
Incoming data from the network is buffered (up to 14 x 128 bytes) and is passed to the 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.
Escaping Data State
To escape data state in SLIP mode, the host can issue the escape sequence <0xC0>+++<0xC0>
to the modem. The hexadecimal value 0xC0 is the SLIP frame character. This means the modem
will be sent a frame containing nothing but the escape code (+++). This is parsed by the modem
as an escape and it will not forward the packet to the network.
Entering the 0xC0 character from the keyboard is accomplished one of two ways: using the
numeric keypad to enter Alt+0192, or using Character Map, a Windows accessory program.
The modem 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.
An alternative to the escape sequence 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 the same as if the escape sequence was issued; it will 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.
5.8.1.2. Closing a SLIP Session
To end a SLIP session, escape data state as described above. If the &D2 DTR option is used then
the session is closed.
If the escape sequence or the &D1 DTR option is used then you must hang-up with either H0 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.