User's Manual

TECHNICAL MANUAL
Telit GM862-GPS
Quad Band GPS Data Terminal Module
Pag.28 of 79
Rev. 0
will be sent to the other side of the network and viceversa. Control plane of ongoing
socket connection is deployed internally to the module.
3.10.9.1 Defining the Internet Peer that can contact this device (firewall settings)
The GM862-GPS 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.
When a packet incomes from the IP address <incoming IP>, the firewall chain rules will be
scanned for matching with the following criteria:
<incoming IP> & <net mask> = <ip_address> ?
if the result is yes, then the packet is accepted and the rule scan is finished, otherwise the
next chain is taken into account until the end of the rules when the packet is silently
dropped if no matching was found.
For example, let assume we want to accept connections only from our devices which are
on the IP addresses ranging from :
197.158.1.1 to 197.158.255.255
We need to add the following chain to the firewall:
AT#FRWL=1,"197.158.1.1","255.255.0.0"
3.10.9.2 Request the socket connection to be opened in listen
With the new command #SKTL (socket Listen) the TCP request to start listening for
connection requests is executed:
- GM862-GPS opens a listening socket on the port specified, waiting for incoming TCP
connections (depending on the parameter request) with the internet hosts
The parameters that shall be specified are the local port where packets shall be received,
the type of socket and the closing behaviour.
3.10.9.3 Receiving connection requests
Once the connection request is received, the module reports an indication of connection
with an unsolicited code
+CONN FROM: <remote address>
- then connection is accepted and once it is up the module reports the code:
CONNECT
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 serialised and flushed to the Terminal
Equipment.