Technical information

Appendix D: Use Cases
May 31, 2008 AT+i Commands Reference Manual D-5
Upon entering Gateway/Router mode, W24 immediately goes online on the WiFi side and the
Cellular. If an IP is not configured, W24 attempts to resolve one using its DHCP client. After
establishing both connections, W24 holds two IP addresses, each associated with one of the
physical interfaces.
Figure D-2: Gateway/Router Data Mode
For example of gateway/router mode configuration see “The mode configuration” on page 1.
In Gateway/Router mode, W24 can be configured using the following methods:
• AT+i commands coming from the host application.
• From the WiFi end, W24's internal configuration website can be accessed by any browser.
Routing inside of W24
W24 routes packets between the two communication platforms according to the following rules:
• IP packets received on the WLAN end, where the destination address is different than its
own, are routed to the Cellular end.
• IP packets received on the Cellular end are normally routed to the WLAN end, with the
exception of a fixed port set aside for W24 web-based configuration.
Routing is determined at the IP layer, where source and destination IP addresses are extracted.
Before routing a packet between the physical interfaces, W24 exchanges the relevant source or
destination IP address, as normally performed by a Network Address Translation (NAT) process,
to conceal the WLAN end's 'false' address. The IP exchange is performed according to the
following rules:
• In IP packets sent from the WLAN end, the source IP is exchanged with W24's Cellular end
IP.
• In IP packets arriving from the Cellular end, the destination IP is exchanged with the host's
WLAN end IP, unless received on a fixed port set aside for W24 configuration.
UART
USB/H
UART#1
USB/D
GPIO
IGN,ON/OFF
CTL
Mic,SPK
Audio
W24
GPIO
SIM
SIM
UART#2
USB/H
UART#0
SPI
UART#1
G24
USB/D
UART#2
UART
Cellular
Network
WiFi
Network
Host