manual

APPLICATION NOTE - Configuring the CX111 for J Series and Branch SRX Series Devices

Power over Ethernet

When available, Power over Ethernet (PoE) can be used to power the CX111. In the event that the CX111 is connected

through a switch or a gateway that does not support PoE, an external power supply can be used (provided with the

basic install kit).

When PoE is used, the device will require about 3.5 watts of power per modem connected, so plan your power

budget accordingly.

Dial Modes

The CX111 can be configured in two modes: “always on” or “dial on-demand.” In the “always on” mode, the CX111

connects to the 3G network after booting. The connection is always maintained, as long as there are no network or

connectivity problems.

In “dial on-demand” mode, the CX111 only initiates a connection when it receives traffic from the interface connecting

the CX111 and gateway. In particular, DHCP request messages will trigger a connection. Similarly, the connection will be

dropped after a configurable inactivity timeout.

Regardless of the mode, the CX111 can accept multiple cards simultaneously. In the event of a failure or inability

to connect, the remaining card(s) will be used. The connection priority is user configurable through the CX111’s

management interface.

The default mode at shipping is ‘dial on-demand’ and set at 20 minutes idle timeout. Most carriers prefer the modem

to disconnect if there is no interesting traffic. After the modem times out, the DHCP requests from the SRX Series

device will result in a 192.168.30.x/24 response from the CX111. If interesting traffic is observed by the CX111, the modem

re-dials. Modem connection takes about 15 to 20 seconds generally. After that, the next DHCP request from the SRX

Series device will fetch the actual 3G IP address and internet connection is re-established.

Deployment Scenarios

In the following section, we will discuss several common deployment scenarios and provide the associated configurations.

CX111 Used for Primary Connectivity

This first scenario shows the gateway configuration when the 3G network is used as the primary WAN link. This can be

achieved by simply connecting the CX111 to any interface in the untrust zone. On the SRX Series device, this is ge-0/0/0

when using the default configuration.

Figure 2: 3G network as the primary link

192.168.1.0/24

Trust Zone

CX111

SRX210

OFFICE

INTERNET

ge-0/0/0.0 connected to the CX111