Page
59
February 2010
3.16
Socket Routing
TCP/IP Port forwarding
The WI-MOD-E is primarily a TCP/IP
Routing Server
, to which a number of external TCP/IP
Clients
may connect. Since TCP/IP connections are point-to-point only, Socket Routing allows a
number of remote TCP/IP clients to connect to the WI-MOD-E simultaneously, the WI-MOD-E can
then route data between the separate remote client devices as necessary.
Socket routing requires that the remote devices initiate the connection, so they must be acting as
TCP/IP clients. Once a connection has been established, the WI-MOD-E can keep it open using
'keep alive' messages which are configured at specific pre-configured time intervals.
In order to route data between connected devices efficiently, the WI-MOD-E would need to have
detailed knowledge of the
protocol
comprising that data. Alternatively, if the protocol is not known
by the module, then any data frame arriving from a given device can simply be forwarded to all
other devices (i.e. broadcast). The WI-MOD-E Routing Server supports ModBus RTU routing
mode, a generic master/slave protocol mode, and a broadcast mode.
The example below illustrates the type of topology that would typically be used in conjunction with
the WI-MOD-E – that is, an existing Wifi network using WI-MOD-E modems to connect remote
devices back into a corporate LAN. At the same time a server located on the LAN uses
port
forwarding
to forward TCP/IP data arriving from remote GPRS modems to the WI-MOD-E. In this
case, the fixed IP address of the WI-MOD-E is used by the server for port forwarding, whereas the
remote GPRS modems connect to the server using a
domain name
and TCP port number.
