Telit Wireless Solutions Easy GPRS Manuel D’Utilisation

 
 
 
 

 
 

80000ST10028 Rev. 0 - 02/01/07  

  

Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved 

 

page 19 of 35 

 

 
NOTE: if there is an escape sequence in the raw data to be sent, 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 
Telit module closes the connection, does not deactivate the GPRS context and returns to command 
mode issuing the NO CARRIER code. 

2.1.2 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 (see par. 2.1.1.2) 

•  defining the Internet Peer that can contact this device (firewall settings) (see par. 2.1.2.1) 

•  request the GPRS context to be activated (see par. 2.1.1.4) 
•  request the socket connection to be opened in listen (see par. 2.1.2.2) 

•  receive connection requests (see par. 2.1.2.3) 

•  exchange data 

•  close the TCP connection while keeping the GPRS active (see par. 2.1.1.6) 

 
All these steps are achieved through AT commands. 
As for common modem interface, two logical statuses are involved: command mode and data traffic 
mode. 
 

•  In Command Mode (CM), some AT commands are provided to configure the Data Module 

Internet stack and to start up the data traffic. 

•  In data traffic mode (Socket Mode, SKTM), the client can send/receive a raw data stream which 

will be encapsulated in the previously configured TCP / IP packets which will be sent to the other 
side of the network and vice versa. Control plane of ongoing socket connection is deployed 
internally to the module. 

 

2.1.2.1  Defining the Internet Peer that can contact this device (firewall settings) 

 
The Telit module has an internal Firewall that controls the behaviour of the incoming connections to 
the module. 
The firewall applies for INCOMING (listening) connections, OUTGOING connections will be always 
done regardless of the firewall settings. 
Firewall General policy is DROP, therefore all packets that are not included into an ACCEPT chain 
rule will be silently discarded.