Moxa ioLogik W5312-T [110/194] Known issues of cellular monitoring systems
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Moxa ioLogik W5312-T [110/194] Known issues of cellular monitoring systems

Moxa ioLogik W5312 [110/194] Known issues of cellular monitoring systems
ioLogik W5300 Planning and Assistance
5-2
Known Issues of Cellular Monitoring Systems
Cellular technology is well-suited for remote monitoring and alarm systems that cover a wide area, such as
pipeline monitoring of public water supplies or natural gas systems. Using cellular technology to implement a
remote monitoring system can save development, deployment, and maintenance time.
However, problems such as dynamic IPs, low bandwidth, and unexpected disconnections must be overcome for
the cellular monitoring system to achieve greater stability.
Known Issue 1: Dynamic or Private IP over a Cellular Network
Although cellular technology can make device communication easier, cellular networks were not designed for
industrial devices, but for mobile phones. Since mobile phones only need a temporary IP to connect to the
Internet, cell phones get a different temporary IP each time the mobile phone accesses the Internet. This is
referred to as the Dynamic IP issue. Most telecom service providers assign temporary IPs when a mobile phone
requests access to the Internet. A remote monitoring system using a cellular communications ioLogik W5300
should request a permanent IP to ensure stable bidirectional communications. For this reason, you may need
to apply for a special data plan from the service providers or the mobile virtual network providers (MVNOs).
As opposed to using the so-called “pull” or “passive” architecture, Moxa’s ioLogik W5300 utilizes active edge
communications, which works with the powerful cellular device management middleware, Active OPC Server.
Active OPC Server runs on a central network computer that uses a static IP. Even if the cellular I/O
units work in a dynamic or private IP environment with a general data plan that is for a mobile phone, since the
ioLogik W5300 contacts the Active OPC Server (and not the other way around), once a connection is
established the two sides of the connection can proceed with bi-directional communication. In addition, the
built-in front-end intelligence called Click&Go control logic enables the ioLogik to report its I/O status, and send
alarms and log data actively. Centralized software such as a SCADA system is now able to leverage this
technology by connecting the Active OPC Server using Modbus/TCP or OPC Client Drivers instead of connecting
to the remote ioLogik's IP address directly.
Known Issue 2: Low Bandwidth and slow response time
Cellular networks provide only low bandwidth transmission compared with wired CAT-5 Ethernet networks.
Generally speaking, the response time of the GPRS network is about 4 to 10 seconds, and 1 to 3 seconds for
3G/HSPA networks.
This means that the latency of data for one round trip is much slower than a millisecond level Ethernet network,
resulting in system overload or shutdown when a large number of remote sites and large amount of information
need to be exchanged. A better approach is to use an “active” architecture such as the ioLogik, and the Active
OPC Server to reduce traffic and improve response time and decrease the use of the bandwidth.
Another factor that could cause unexpected disconnection is the cellular signal strength. In some places,
several communication channels could exist simultaneously, with each device accessing a different channel and
using a different signal strength. This kind of random signal strength could result in unexpected disconnection.
SMS (short messages) will not respond in time as expected, especially when using a data plan that is only for
data transmission or at specific times, such the end of the year, when traffic volume is much higher.
Known Issue 3: Unexpected Disconnection from Cellular Networks (Carriers)
Although cellular network transmissions are charged by number of packets and not connection time, most
vendors still refer to their service as “Always On.” However, a better description might be “always accessible”
since in reality, cellular carriers optimize their IP resources, time slots, and the base station capacity by
disconnecting connections that have been idle for a certain period of time. During this period, the mobile
devices will not be aware of the disconnection, and this lapse in the actual connection could introduce a certain
amount of unreliability in your remote monitoring and alarm system. If using “Always On” to keep your
connection alive is not stable enough for your purposes, you must configure additional “Cellular Reconnection”
settings to prevent being kicked off the network accidentally or without notification. See Chapter 4 for detailed
settings.

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