AT+i Programmer's Manual - SE Spezial-Electronic AG

LAN-based devices and dial-up devices linger differently.
SerialNET Theory of Operation
A LAN device is normally online and may thus have an associated listening (passive)
socket ready to accept remote socket connections. While in SerialNET mode, iChip
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. iChip resolves these problems by supporting a wakeup
call and automatically implementing one or more IP registration procedures. This
allows a client to wake up an iChip in SerialNET mode and retrieve its dynamic IP
address from a registration server.
The iChip 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
iChip and hangs up after two rings. When contacted, iChip (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, iChip registers its IP address using the
Email registration method. iChip 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
iChip‘s SerialNET socket.
If the RRSV parameter contains a server name and port, iChip registers its IP address
using the Socket registration method.
If the RRWS parameter contains a URL, iChip registers its IP address using the Web
server registration method.
Once connected, iChip 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 LAN environment the iChip continues to listen on the port server listening socket,
while in a dial-up environment, iChip goes offline and waits for another RING trigger.
The iChip MDSEL signal (see iChip 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 iChip to activate the ring response procedure
as a result of some TTL hardware signal.
28.4 Client Devices
Client devices initiate communications to a server. When a client device first sends data
on its serial link, iChip (in SerialNET mode) buffers the incoming data bytes and attempts
to establish a connection to a remote server. After going online, iChip performs an IP
registration process according to the RRSV, RRWS, and RRMA parameters.
Once the socket connection is established, iChip transmits the buffered data collected
during the connection period. The MBTB parameter dictates the maximum number of