Smart factories are increasingly reliant on network connectivity.
PLCs upload equipment status to the MES, industrial PCs submit production data to servers, HMIs require remote maintenance, and vision inspection, code-scanning and traceability systems all depend on the local area network. During normal production operations, it is easy to assume that since the factory already has switches, optical fibers and an enterprise network, adding an extra industrial cellular router adds little value.
However, after completing on-site deliveries, equipment manufacturers will find that problems almost always occur after network anomalies take place.
Maintenance of the plant's core switch, accidentally cut optical fibers during construction, enterprise IT network adjustments, or broadband operator failures can all suddenly disconnect a normally running production line from the MES or remote operation and maintenance platform.
Therefore, for critical production lines, the key consideration is not just "whether there is a network", but whether there is a second available path when the primary network fails.

1. What Exactly Does a Backup Router Protect Against?

Take an automatic packaging production line as an example. The equipment is equipped with internal PLCs, HMIs, industrial PCs and a vision inspection system, which normally connects to the MES via the factory's wired network.
The PLC itself will not shut down immediately when the external network is disconnected, but three subsequent problems may arise:

Production data cannot be uploaded, and the MES fails to receive equipment status updates;
When program or parameter anomalies occur, the equipment manufacturer cannot remotely access the on-site devices;
Server-dependent services such as production traceability and code scanning may be disrupted.
If you rush to set up a temporary 4G hotspot and rewire connections at this point, valuable fault handling time will already be wasted.
A more reliable approach is to design the backup communication link into the system during the equipment delivery phase.
For example, use the USR-G806w as the industrial cellular router on the equipment side. Under normal conditions, traffic runs over the wired WAN; when the wired network fails, the system switches to the 4G or WiFi link according to pre-configured policies. The G806w supports Failover among wired, cellular and WiFi connections, and is equipped with 4G, WiFi and 3 Ethernet ports.
In this way, the backup network is not a temporary setup after a fault occurs, but a pre-designed component from the equipment design stage.
2. Which Equipment Deserves a Dedicated Backup Network?

Not all equipment in the factory needs a dual-network configuration.
If an ordinary auxiliary device going offline for half an hour will not affect production, it can continue to use the factory's unified network without additional modifications.
The equipment that truly justifies a backup industrial cellular router is usually critical process equipment with high reliance on remote after-sales support.
Typical examples include packaging machines, filling machines, CNC processing equipment, robot workstations, automated warehouses, and key inspection devices. Once these devices shut down, both upstream and downstream processes will be affected; and most of their faults can be quickly located by remotely checking the PLC, HMI or industrial PC.
For equipment manufacturers, installing the G806w inside the control cabinet can establish the following architecture:
PLC / HMI / Industrial PC
↓
G806w
↓
Primary Link: Factory Wired Network
Backup Link: 4G / WiFi
↓
MES / IoT Platform / Manufacturer Remote Operation & Maintenance
This architecture also makes it easier to clearly separate the enterprise internal network and the remote maintenance entry for equipment manufacturers.

3. Why Can't You Wait Until the Network Fails to Take Action?

In industrial sites, what disrupts production is often not the fault itself, but the recovery time.
For example, an optical fiber fault may take several hours to repair, but a PLC program issue can usually be located by an engineer remotely in just a dozen minutes. If remote operation and maintenance has to rely on this already broken optical fiber, even a minor equipment problem can only be resolved after the engineer arrives on site.
The value of the backup 4G link is to ‌isolate "network faults" from "equipment faults" as much as possible‌.
Even when the factory's primary network is under maintenance, the equipment manufacturer can still access the devices for diagnosis through the authorized backup channel.
The G806w supports VPN protocols including IPSec, OpenVPN, PPTP, L2TP and GRE, and is equipped with firewall, access control, IP/MAC filtering and port mapping functions. Therefore, for remote maintenance, the more reasonable practice is to access the devices via VPN or the enterprise's authorized network, rather than directly exposing PLC ports to the public internet.

4. How to Deploy the Backup Network to Avoid It Becoming a Useless Ornament?
4.1 Conduct Actual 4G Signal Testing

Many manufacturers configure the router in the office and ship it directly. But after the equipment arrives at the factory, the control cabinet may be located in an underground workshop, inside stainless steel equipment, or in a corner of the plant. Metal cabinets will significantly attenuate wireless signals, so the antenna position must be tested under the final installed state of the equipment.

4.2 Actively Test Network Switchover

Before delivery, you can directly unplug the WAN Ethernet cable to verify that the system switches to 4G according to the preset policy; after restoring the wired network, confirm that services switch back to the primary link normally.

4.3 Clarify the Bandwidth Target for the Backup Link

The 4G backup network should first guarantee the transmission of PLC status, alarms, key MES data and remote maintenance traffic, instead of carrying a large volume of video streams by default. It is best to classify critical and non-critical services in advance.

Finally, test the full cabinet restart. The G806w adopts a dual hardware and software watchdog design, supports DC 9–36V power supply, and has an operating temperature range of -20℃ to 70℃, making it suitable for installation inside industrial control cabinets. During final acceptance, you still need to confirm that the wired, 4G, VPN and remote connections can all automatically resume after power is restored.

For smart factories, the "backup industrial cellular router" does not actually ensure that the factory never loses network connectivity. Instead, it guarantees that when the primary network fails, critical equipment still has a channel to continue uploading data, send alarms and perform remote maintenance.
For equipment manufacturers, adding this backup link consideration during the design phase is far more efficient than repeatedly dispatching engineers to the site for troubleshooting after equipment delivery due to customer network faults.
This is especially true for equipment delivered across regions with a high proportion of remote after-sales services. The architecture where the primary network handles daily production and the 4G industrial cellular router acts as a fallback under abnormal conditions is far easier to maintain in the long run than relying solely on the customer's plant network.