Industrial Optical Bus
Technical Background
Currently, network cables in factories are unreliable and vulnerable to strong-current interference. In addition, the maintenance mode is outdated. On the other hand, the network deployment and coverage are too rigid to adapt to frequent production line changes due to manufacturing work changes, and routing cables again can be very costly. In the future, factories will become more automated, and various industrial automation devices must have high-speed and high-precision motion control capabilities, posing higher requirements on the network bandwidth, latency, and jitter.
To meet the increasing requirements on bandwidth, latency, and jitter on the industrial control networks, the industrial optical bus technology in the industrial optical network can be used below PLC. Based on optical communication network technologies, the industrial optical bus combines the multi-level optical splitting and multi-terminal access capabilities of the optical distribution network to provide competitive performance indicators for the field bus, further improving the bandwidth and reducing the latency of the industrial bus. The application of the all-optical network accelerates the digital transformation of industrial manufacturing.
Position of the Industrial Optical Bus in the Industrial Internet Architecture
In the industrial Internet architecture, the industrial optical bus is located in the onsite industrial production network (see the preceding figure). Optical head modules are built inside the PLC of the master station, and optical terminal modules are built in devices such as servers, I/O devices, and industrial cameras. Through the star-topology optical distribution network, control data can be efficiently transmitted between the master station PLC and slave station devices.
The industrial optical bus technology reshapes the physical layer and data link layer. The link layer changes the serial communication mechanism of the original industrial protocol to the parallel communication mechanism, and shortens the data transmission period to reduce the latency at the physical link layer. The new industrial optical bus technology has two working modes:
| Common industrial protocols | Working mode 1 | Mode 2 |
|---|---|---|
| Application layer | Original industrial protocols | Optimized new industrial protocols |
| Data link layer | Optical data link layer | Optical data link layer |
| Physical layer | Optical physical layer | Optical physical layer |
Mode 1: Transparently transmit original industrial protocols, such as Modbus, EtherCAT, ProfiNet, ProfiBus, and CC-LINK. Industrial optical bus technology defines the optical physical layer and optical data link layer, and original industrial protocols are transparently transmitted. The data link layer of the industrial optical bus does not change various types of data in the original industrial protocols, and only loads the data into the payload of the communication packets of the industrial optical bus and transmits the payload to the peer end. Limited by the interaction mechanism of the original upper-layer industrial protocols, this working mode does not significantly reduce the total system latency.
Mode 2: The industrial optical bus technology defines the optical physical layer and optical data link layer, and works with the optimized new industrial protocols to reduce the total system latency. Reducing the latency is an important optimization direction of the industrial bus protocol. The key method is to optimize the application layer protocol and reduce the PLC cycles by parallel communication.
