User's Guide

User’s Guide CDPD Operation
2110059 Rev 1.0 Proprietary and Confidential Page 39
4. 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 7.
5. +WS197=n where n is the index (1-4) of the NEI to register, to select the NEI
6. +WPREG to register on the CDPD network. The modem will reply as noted in the section
above on manual registration.
7. +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.
8. O to start the session. The modem will reply with CONNECT at which point you are in data
state.
The modem is now ready to pass host packets to the network. Any incoming packets, from any
originator, will be passed to the host. This allows the host to send and receive packets to multiple
destinations asynchronously provided the host can manage multiple socket connections.
Detailed Discussion
The first two steps simply place the modem in CDPD SLIP mode. The modem’s session state is
set in register +WS45 (Packet Service) by step 2. Setting this value to 3 will place the modem in
SLIP mode. 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 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.