Technical information

Chapter 2: AT+i Commands Reference
May 31, 2008 AT+i Commands Reference Manual 2-83
During RAS PPP negotiations, W24 will replies only to (+++) (escape sequence) and AT+iRPn
commands. Specifically, W24 replies "Connecting as RAS" to the AT+iRP2 (W24 status)
command. The escape sequence can be used to abort the RAS session at any time. The AT+iRP2
command is the only means for the host processor to determine that a PPP session is in progress.
W24 manages the RAS protocol internally and does not transfer any information to the host. Any
other commands received from the host are disregarded by W24.
Once the PPP connection has been fully negotiated and established, W24 responds to all AT+i
commands as when it is online. Specifically, W24 replies "RAS Connected" to the AT+iRP2
command.
As part of the PPP negotiation, W24 assigns itself the default IP 192.168.0.1 and allocates
192.168.0.2 as the client IP. However, if the client requests a specific IP, W24 always grants the
client's request and uses the client's IP minus 1 as its own IP.
The following restriction to the minus 1 rule applies: If the IP requested by the client minus 1 is
an IP address that ends with 0x00 or 0x255 as the last nibble, W24 assigns itself with the client's
IP plus 1 instead of minus 1. This is done to assure that the IP that W24 assigns itself never
violates the rule that defines that a network or host IP segment may not be all binary 1's, nor all
binary 0's.
After a RAS PPP connection is established, W24 automatically activates the internal web server,
if the AWS parameter is set to a non-zero value. Thus, the remote client can browse W24's
website.
Auto PPP RAS Mode
W24 allows combining RAS and direct modem-to-modem communication sessions. A special
mode, named Auto PPP RAS, supports dialing into the W24 with a PPP dialer or a regular
modem.
Auto PPP RAS mode is enabled by enabling RAS mode and adding a +100 offset to the RAR
parameter, where [<RAR>-100] determines the number of RINGS after which W24
automatically picks up the line and negotiates a PPP connection. The host processor can instruct
the modem to pick up the line beforehand by issuing the ATA (modem) command or by setting
the modem to auto-answer after less than [<RAR>-100] RING strings. This is normally done in
order to manage a direct modem-to-modem (non-PPP) communication session.
When W24 is in the Auto PPP RAS mode, it monitors the data stream following the modem
CONNECT line. If the first character transmitted by the remote end is (~) (0x7E), W24 defers to
PPP negotiation. The (~) is the last character transmitted to the host end to signal that W24 has
taken over the negotiations. Upon this event, W24 continues to negotiate a PPP connection
internally in a manner similar to the procedure that occurs when W24 picks up the line after
receiving <RAR> RING strings. If, however, the first character received from the calling end
after the CONNECT line is not a (~) (0x7E), W24 remains in Transparent mode, and a regular
modem-to-modem data session takes place.
SerialNET Mode
The RAS can also be enabled while W24 is in SerialNet mode. In this case, however, the modem
RING strings are not forwarded to the host serial port. Once the PPP connection is established,
W24 proceeds to act as it would after receiving a RING event and creating a PPP connection to a
remote RAS server. That is, a listening socket is established on the LPRT socket, available for a
SerialNET connection. This provides an alternative means to wake-up a SerialNET server device.