Digi Cellular Gateway Application Guide Connecting Ethernet Devices using IP Port Forwarding 6/19/2007 rev A Digi International 1 of 3 Scenario : The Digi cellular gateway connects one or more remote devices via a cellular IP network. Communications is typically initiated either from the host system but can also be initiated from the device(s). Sample Diagram : Wireless Network Digi Connect WAN Internet/ Frame Relay Host Application polls or sends to remote Remote Site HQ Host Initiates Traffic Hub / Switch Theory of Operation : Communications applications such as SCADA polling, remote printing, or other host-initiated traffic can be sent over the cellular network to the remote device or devices via the Digi cellular gateway.
The Digi cellular gateway forwards IP traffic destined for a specific port or port range on the cellular interface, to a private IP address on the Ethernet "side" of the Digi cellular gateway. This process uses NAT (Network Address Translation) where only the mobile IP address is visible to the outside and TCP/UDP port forwarding. Port-forwarding entries direct traffic from the Digi cellular gateway 9s mobile IP address to the appropriate device.
For example a SCADA application on the host computer uses Modbus/TCP to poll three remote ... more. less.
devices. Modbus/TCP uses TCP port 502 by default. If multiple Modbus devices are at the remote location, the application must allow the user to define a different Modbus/TCP port number for each device.<br><br> Port-forwarding entries on the Digi cellular gateway then direct the traffic to the appropriate device based on the external (or source) TCP port number. This same concept can be used for most any remote polling or host initiated / remote terminated communication application. GSM APN Type Needed : A wireless plan that supports Mobile Terminated Data is required.<br><br> Some plans allow only outgoing connections and/or use private IP addresses behind NAT firewalls. For example, AT&T (Cingular) Internet and wwan.ccs APNs, and most Sprint and Verizon Wireless plans support mobile terminated connections. Check with your cellular provider for details.<br><br> Connecting Ethernet Devices using IP Port Forwarding Example Configuration 1 3 Modbus/TCP Three devices are attached to the Digi 9s Ethernet port (refer to the diagram). The devices 9 IP addresses are 192.168.1.2, .3, and .4. The Digi cellular gateway 9s Ethernet port is 192.168.1.1; its mobile IP address is 188.8.131.52.<br><br> The Digi cellular gateway will be configured with a TCP port-forwarding table for Modbus/TCP such as: External TCP Port Internal IP Address Internal TCP Port 12001 192.168.1.2 502 12002 192.168.1.3 502 12003 192.168.1.4 502 Note the devices can still use the default Modbus/TCP port number of 502 since the Digi cellular gateway 9s port forwarding can use different source and destination port numbers. The Modbus application must be then able to direct traffic to the Digi cellular gateway mobile IP address and the appropriate port. So, the application would use the following ports: Remote Device Internal IP Address Internal TCP Port One 184.108.40.206 12001 Two 220.127.116.11 12002 Three 18.104.22.168 12003 The Digi cellular gateway will now direct the Modbus polls to the appropriate destination.<br><br> Other applications and protocols, such as HTTP, FTP, printing, etc. can be handled in similar fashion. Remote Devices 9 Default Gateway : The remote devices 9 default gateway must point to the Digi cellular gateway 9s Ethernet port IP address, which in this case is 192.168.1.1.<br><br> 6/19/2007 rev A Digi International 2 of 3 Connecting Ethernet Devices using IP Port Forwarding Example Configuration 2 3 Remote Device HTTP Server The remote device attached to the Digi 9s Ethernet port has an HTTP (web) server that needs to be accessed remotely. The device 9s IP address is 192.168.1.100. The Digi cellular gateway 9s Ethernet port is 192.168.1.1; its mobile IP address is 22.214.171.124.<br><br> The device 9s HTTP server uses the default TCP port 80. The Digi cellular gateway also uses TCP port 80 for its built-in web server. To avoid conflicts there are two methods: 1.<br><br> Change the Digi 9s web server to use TCP port 8080 and use the standard port 80* to access the device: a. Change the Digi 9s default HTTP server port to 8080 via Configuration > Network > Network Services. b.<br><br> Add a TCP port forwarding entry as: External TCP Port Internal IP Address Internal TCP Port 80 192.168.1.100 80 c. Access the device 9s web server via the cellular WAN via http://126.96.36.199 into the browser 9s address bar. 2.<br><br> Keep port 80* for the Digi 9s web server; and use port 8080 in the browser for the application to access the remote device 9s web server. a. Add a TCP port forwarding entry as: External TCP Port Internal IP Address Internal TCP Port 8080 192.168.1.100 80 b.<br><br> To access to the device 9s web server via the cellular WAN enter http://188.8.131.52:8080 into the browser 9s address bar. * NOTE : Some cellular network plans block port 80. Check with your provider.<br><br> If so, change the Digi 9s HTTP web server to use port 8088 (or any port other than 80 or well-known port) as shown in 1.a. above; and use port 8080 as shown in 2.a. for the device 9s web server.<br><br> HTTPS can also be used to access the Digi. Further information and assistance is available on the included Digi documentation CD, or at www.digi.com or by calling Digi at 952-912-3444. 6/19/2007 rev A Digi International 3 of 3<br><br>