Technical information

SerialNET Theory of Operation
2-86 AT+i Commands Reference Manual May 31, 2008
Server Devices
Server devices linger until approached by a remote client. The remote client must know W24's IP
and listening port address in order to establish communications.
WLAN-based devices and dial-up devices linger differently.
A WLAN device is normally online and may thus have an associated listening (passive) socket
ready to accept remote socket connections. While in SerialNET mode, W24 establishes a
listening socket on the port defined in its LPRT parameter. A remote client terminal can connect
to that port.
A dial-up device is normally offline and must be awakened to go online at a precise moment.
Moreover, once it connects to the Internet, it usually receives a dynamic IP address. This address
must be communicated in some way to the client device in order to establish a link across the
Internet. W24 resolves these problems by supporting a wake-up call and automatically
implementing one or more IP registration procedures. This allows a client to wake up a W24 in
SerialNET mode and retrieve its dynamic IP address from a registration server.
The W24 or in dial-up mode is offline by default, but waits for a RING signal on the modem to
trigger it into activity. In this case, the remote client device dials directly to the W24 and hangs up
after two rings. When contacted, W24 (under SerialNET mode) waits for the RING to subside
and then dials into its ISP and connects to the Internet. If the RRMA parameter contains an e-mail
address, W24 registers its IP address using the Email registration method. W24 then listens on the
LPRT port for a socket connection. The recipient of the e-mail can use the registered IP address
and port to create a link to W24's SerialNET socket.
If the RRSV parameter contains a server name and port, W24 registers its IP address using the
Socket registration method.
If the RRWS parameter contains a URL, W24 registers its IP address using the Web server
registration method.
Once connected, W24 transfers all arriving data from the local device over the serial link. Device
responses are routed back to the initiating client. Data flows freely between the two systems until
a predefined activity termination event is triggered, upon which the remote connection is
dropped.
In a WLAN environment the W24 continues to listen on the port server listening socket, while in
a dial-up environment, W24 goes offline and waits for another RING trigger.
The W24 MSEL signal (see W24 datasheet) can be lowered to GND to emulate the RING event.
This is useful for testing and debugging purposes of the SerialNET connection procedure or as a
means to cause W24 to activate the ring response procedure as a result of some TTL hardware
signal.
Client Devices
Client devices initiate communications to a server. When a client device first sends data on its
serial link, W24 (in SerialNET mode) buffers the incoming data bytes and attempts to establish a
connection to a remote server. After going online, W24 performs an IP registration process
according to the RRSV, RRWS, and RRMA parameters.
Once the socket connection is established, W24 transmits the buffered data collected during the
connection period. The MBTB parameter dictates the maximum number of bytes to buffer. If
additional bytes are received on the serial port before the connection is established, they are
discarded.