User manual
605M-D1 GPRS Modem User Manual
man_605M-D1_1.5.doc Page 34
Open the Connection with the Internet Host
With the command #SKTD (socket Dial) the TCP/UDP request to connect with the internet host starts:
• Eventually does the DNS query to resolve the IP address of the host name internet peer
• ELPRO 605M-D1establishes a TCP/UDP (depending on the parameter request) connection with the given internet
host
• Once the connection is up the module reports the code: CONNECT
Note that the peer specifications of this socket Dial are within the command and not the one stored with #SKTSET
command.
From this moment the data incoming in the serial port is packet and sent to the Internet host, while the data received
from the host is serialized and flushed to the Terminal Equipment.
NOTE: this command differently from the AT#SKTOP DOES NOT automate all the process of
activating the GPRS, if no GPRS is active the command reports ERROR; therefore before issuing this command the
GPRS shall be activated with AT#GPRS=1 command.
In the same manner, when disconnecting the #SKTD command does not close the GPRS context, leaving it active
for next connections until an AT#GPRS=0 command is issued or the network requests a context closing.
Close the Socket without deactivating the context
The connection can be closed because of:
• remote host TCP connection close
• socket inactivity timeout
• Terminal Equipment by issuing the escape sequence "+++"
• Network deactivation
NOTE: if in the raw data to be sent there's an escape sequence, then the TE must work it out and sent it in a
different fashion to guarantee that the connection is not closed.
The pause time is defined in the parameter S12.
On the reception of an escape sequence if the socket was opened with the AT#SKTD command, the ELPRO 605M-
D1 closes the connection, does not deactivate the GPRS context and returns to command mode issuing the NO
CARRIER code.
4.2.8 EASY GPRS Incoming Connection
The EASY GPRS feature provides a way to accept incoming TCP/UDP connections and keep the same IP address
after a connection, leaving the GPRS context active.
The steps that will be required to open a socket in listen, waiting for connection requests from remote hosts and
accept these request connections only from a selected set of hosts, then close it without closing the GRPS context
are:
• configuring the GPRS Access
• configuring the embedded TCP/IP stack behaviour
• defining the Internet Peer that can contact this device (firewall settings)
• request the GPRS context to be activated
• request the socket connection to be opened in listen
• receive connection requests
• exchange data
• close the TCP connection while keeping the GPRS active
All these steps are achieved through AT commands.
As for common modem interface, two logical status are involved: command mode and data traffic mode.
• In Command Mode (CM), some AT commands are provided to configure the Data Module