As the two most important distribution network communication solutions at present, industrial Ethernet switches and industrial EPONs have their own characteristics. This paper makes a simple comparison of the two schemes from the aspects of protocol, degree of industrialization, networking mode, and maintainability.
Protocol standardization
The switch has been mature and commercialized for many years, and the standardization of its protocols has already been completed, including the underlying protocol, network redundancy protocol, management protocol, network precise clock transmission protocol, etc. The products of different manufacturers have good interoperability and can realize hybrid networking.
The EPON standard was officially released in 2004, and the industrial EPON standard has only been gradually improved in recent years. Therefore, the standardization of many specific implementation details needs to be unified, such as: dynamic bandwidth DBA algorithm, ranging implementation method, encryption algorithm, etc. From the perspective of the current state, there is still a certain risk of interoperability, which will take some time.
degree of industrialization
The concept of industrial Ethernet has been proposed since 2000, and after more than ten years of rapid development, the entire industry chain is very mature, both in terms of chips and markets, and industrial features such as EMC, high and low temperature can fully meet industrial needs. market has been widely used.
As a relatively new technology, EPON has a short industrialization time, and is mainly concentrated in the power industry, with insufficient practical operation experience. Its optical splitter is a passive device with high stability. However, OLT and ONU are active devices, and the degree of industrialization is mostly inferior to industrial Ethernet equipment.
Networking method
EPON can form a point-to-multipoint network mode through an optical splitter, which is very suitable for the actual distribution of the distribution network. Each ONU is connected in parallel, with strong resistance to multi-point failure. Its possible disadvantage is that all business processing is concentrated on the OLT, and the stability of the OLT is crucial. After the OLT takes effect, the entire network will be paralyzed, and the communication between the underlying nodes will also be interrupted. Due to the insertion loss of the optical splitter, the network cannot be too large, and the longest cannot exceed 20 kilometers. For the expansion of new nodes, the direction can be increased by replacing the optical splitter, which is very convenient.
Industrial Ethernet switches mainly use segmentation redundancy, intersecting rings, and tangent rings to improve the reliability of networking, and have weak resistance to multi-point failures. In its peer-to-peer communication mode, the failure of a single node will not have a fatal impact on the entire network. By selecting the appropriate optical module, the transmission distance can be up to 100 kilometers. For capacity expansion, the switches of the connected nodes need to be replaced to support more optical ports, and the cost will increase.
For the single-fiber bidirectional advantage of EPON, first of all, only one optical fiber is not distributed during wiring, and industrial Ethernet can also support single-fiber transmission through a single-fiber optical port.
network management
Industrial Ethernet switches are classified into two types, managed and unmanaged, according to whether they support the SNMP protocol. The unmanaged switch is developed from the hub. It can realize the routing function of messages from one port to another port, which is more intelligent than the hub. Unmanaged switches can automatically detect the network speed of each network device. In addition, it has a feature called "MAC address table" that can identify and remember devices on the network. In other words, if port 2 receives a message with a particular identifier, the switch will then send all messages with that particular identifier to port 2. This intelligence avoids message collisions and improves transmission performance, a huge improvement over hubs. However, unmanaged switches cannot implement any form of communication detection and redundant configuration.
Compared with unmanaged switches, managed switches have more and more complex functions, and the price is much higher. Usually it is 3 to 4 times that of an unmanaged switch. Managed switches offer more functionality and are usually fully configurable through a network-based interface. It can automatically interact with network devices, and users can also manually configure network speed and flow control for each port. Some older devices may not be able to use the automatic interaction function, so manual configuration is essential.
Most managed switches also typically offer some advanced features, such as SNMP (Simple Network Management Protocol) for remote monitoring and configuration, port mapping for diagnostics, VLAN (Virtual Local Area Network) for grouping network devices, A prioritization function to ensure that priority messages pass through, etc. With managed switches, redundant networks can be built. Using a ring topology, managed switches can form a ring network. Each managed switch can automatically determine the optimal transmission path and the backup path, and automatically block the backup path when the priority path is interrupted.
The managed switch can be managed in three ways: through RS-232 serial port (or parallel port) management (or out-band network management), web network management and through SNMP network management software management (or in-band network management). Which method is used? When the switch is initially set up, out-of-band management is often required; after the IP address is set, in-band management can be used. In-band management can realize remote management because management data is transmitted through a public LAN, but the security is not strong. The out-of-band management is communicated through the serial port, and the data is only transmitted between the switch and the management machine, so the security is very strong; however, due to the limitation of the length of the serial port cable, remote management cannot be realized. So which method to use depends on your requirements for security and manageability. Sugarnms Zhihe network management platform has been well applied in remote monitoring and management of industrial switches.
Epon usually consists of OLT, ONU and optical splitter. Generally, the OLT supports the SNMP protocol, but the ONU does not support SNMP and does not even have an IP address. Optical splitters are completely passive devices and do not support any form of management protocol. Therefore, for the operation and maintenance management of the EPON network, the OLT can be managed through the SNMP network management software, and the ONU is attached to the OLT device in the form of device resources. There is a one-to-many relationship between them. way of communication. The NMS does not communicate directly with the ONU, and all configurations must be delivered through the OLT. Since the optical splitter is a passive device, it can only be managed manually by the administrator. For Epon networks of different manufacturers, through the secondary development of the Sugarnms Zhihe network management platform, the remote management and maintenance of the Epon network can also be well realized.
In general, industrial Ethernet switches and industrial EPON, as the two mainstream communication methods for distribution networks, each have their own characteristics and are currently used in the pilot stage. coexist.
Zhihe Network Management Platform (SugarNMS) is a professional industrial Ethernet switch and EPON network management platform. For more industrial Ethernet switches and EPON network management content, please visit www.zhtelecom.com.