Across the Boards
Communications Device Drivers
Section 5 - General Configuration and Usage Information
Page 200
cfSOFTWARE Confidential,
2000
5.14 cfPPP Driver Usage
Several
Across the Boards
TCP/IP drivers with embedded TCP/IP and PPP stacks are available. Several special
considerations apply when using these drivers.
General Program Flow
The use of cfPPP based drivers proceeds in three steps: link startup, application driver usage, and link shutdown.
The application driver usage stage is usually unchanged from the usage of a “normal” TCP/IP driver, while the
startup and shutdown steps are new.
Special care must be taken to not close the driver until link shutdown occurs. If the driver is closed the link will
drop. This may require removing XAPI Close requests, CFXDIAL Close-Device requests, and/or setting the
APPX PPX-no-device-close switch in various places in the application.
Link Startup
The cfPPP drivers present a TTY-like terminal for use during link startup. Normal CFXDIAL script statements
can be used to start the link (alternatively, the function can be performed with raw XAPI function calls, but this
is not generally recommended).
Four special SEND functions are available in cfPPP mode:
XAPI Keycode
SEND Keyword Function
ApkSysReq SYSREQ Starts PPP negotiation process
ApkTest TEST Shut down PPP connection (forces hard
shut down if used twice)
ApkAttn ATTN Enter cfPPP command mode
ApkClearBuf CLEARBUF Clears TTY screen (without sending any
data to the host)
A normal modem setup and dial sequence should be performed to the PPP access router. A PPP connection will
usually require the following communications port settings:
8 Data Bits
No parity
1 Stop Bit
No Xon/Xoff flow control
In addition, it is recommended to turn on hardware flow control (usually RTS/CTS) and to enable compression
and error correction on the modem.
A PPP access router will usually expect that a user ID and password be supplied via the PAP or CHAP
protocols. The correct protocol is negotiated automatically, but the driver needs to be be told what the user ID
and password are. This is accomplished with the commands “userid=“ and “password=“ entered in command
mode (
see below
). These should be set before the SysReq key is sent to start PPP negotiation. Usually the user
ID and password would be set before the modem dials.
In some cases (notably Compuserve), the “logon” occurs via a TTY style interaction rather that with PAP or
CHAP. This should be scripted as appropriate.
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