Ethernet-APL Network Topologies: Building Stable and Future-Proof Process Networks
The Challenge: Rising Demands on Process Networks
The process industry is under growing pressure to increase efficiency, ensure safety in hazardous environments, and accelerate digital transformation. Traditional Fieldbus infrastructures, while robust, were not designed for the data-rich, connected environments that Industry 4.0 demands.
Ethernet-APL (Advanced Physical Layer) provides a promising answer and is set to be the new standard for the process industry. It is based on the 10BASE-T1L specification as per IEEE 802.3cg and facilitates two-wire Ethernet to the field. The primary advantage of Ethernet-APL is the interoperability and flexibility achieved by the seamless connection of field devices with rapid data transmission on the information layer, in both small networks at short distances as well as in large networks covering long distances.
Importantly for the process industry, Ethernet-APL also supports the intrinsically safe ignition protection type “Ex i” in Ex Zones 0, 1, and 2. With the Ethernet-APL technology, the future digitalization of automation networks is relatively easy to implement, assuming several preconditions concerning network topology are considered as part of the equation.
Three Network Topologies for Reliable Ethernet-APL Connectivity
Given the large number and variety of plant types, the network system should be easy and inexpensive to expand. It should also provide redundancy options.
Additionally, it must meet the specific needs of the process industry. This includes working in harsh environments or operating in potentially explosive atmospheres. The Ethernet-APL Engineering Guideline escribes different network topologies for Ethernet-APL networks. However, the conditions for Ethernet-APL spurs are the same for all topologies.
Ethernet-APL devices can be connected to a switch using a Category IV cable. This should not be longer than 200 meters. Devices can communicate at a transmission rate of 10 Mbps. The following section provides a detailed examination of three selected variants.
Variant 1: Direct Connection with APL Field Switches
In this setup, APL field switches are connected directly to a standard Industrial Ethernet network. The installation environment largely determines their placement – either in a control cabinet or out in the field.
In this version, the APL switch connects to the control network via standard Ethernet copper cables or fiber-optic cables. The typical transmission rate in this part of the network is 100 Mbps.
This structure is similar to today’s Fieldbus systems and is designed to support existing brownfield plants. These plants were originally built before the rapid pace of digitalization could be anticipated, while they are now expected to keep up with modern industrial demands.
Variants 2 and 3: Trunk Technology with Power and Field Switch Options
These variants use a network structure similar to Variant 1 but are based on trunk technology with standard APL switches.
The difference lies in the type of switch deployed:
- One option uses an APL power switch with its own autonomous energy supply.
- The other uses an APL field switch that requires an additional external power source.
For installations in ATEX environments, it is also important to mention the 2-WISE explosion protection model (2-Wire Intrinsically Safe Ethernet). This model builds on the proven FISCO (Fieldbus Intrinsically Safe Concept).
Managing Network Load to Ensure PROFINET Stability
To keep a PROFINET network both stable and fail-safe, it is important to monitor the load on Ethernet-APL devices. Continuous monitoring of load peaks helps prevent sporadic outages of individual devices caused by overloading.
This is achieved by limiting ingress and egress data traffic at the switch ports – a practice also recommended by the IEEE (Institute of Electrical and Electronics Engineers). The reason is that when networks transition from 100 Mbps in the control network to 10 Mbps on the spurs, the higher load in the control network becomes critical for Ethernet-APL devices. After all, 10 Mbps represents only 10% of the throughput compared to the 100 Mbps control network.
Ethernet-APL Switch Takes Care of Net Load Rate Limits
Network load remains a critical challenge, and Softing now offers Ethernet-APL switches that actively limit net load rates to maintain stability without overloading. These switches support both copper and fiber-optic links and are fully available today.
They’re particularly well-suited for Variant 1 topologies. Two models are offered:
aplSwitch Field: A 16-port “2-WISE” switch installed in Zone 2 that transparently connects intrinsically safe Ethernet-APL field devices to higher-level industrial networks, providing intrinsically safe power to those devices.
aplSwitch Field PA: Also a 16-port switch in Zone 2, but with an integrated PROFINET-PROFIBUS PA proxy. This allows connection of both Ethernet-APL and Profibus PA devices on the same switch and enables seamless migration of existing PA infrastructure.
Both switches support stable network operation via ingress/egress rate limiting and offer extensive diagnostics (including PROFINET diagnostics, local displays, and FDI support).
