Ethernet is a flexible, reliable, robust, expandable, controllable and dynamic transport system! Dynamic, in terms of being a transport mechanism over different mediums for a variety of different protocols.
Progression of Ethernet in Utilities
The growing concern of lack of communication compatibility between devices ultimately lead to the creation of the IEC 61850 Standard. This was completed when the Utility groups turned to the Electric Power Research Institute (EPRI), along with IED manufacturers and leading utilities such as American Electric Power, they collaborated to develop the Utility Communications Architecture Standard (UCA2.0) which has now been released as the international standard IEC 61850. Part of the standard defines a set of standards and specifications with a common application layer protocol to ensure everyone speaks the same language and caters for several communication protocols with Ethernet as the transport mechanism to ensure everyone resides on the same physical network.
Progression of Ethernet in Industrial applications
In the process control industry (i.e. industrial automation) a similar transformation has taken place with most major vendors of process control IED’s now providing Ethernet connectivity to the degree that many have espoused the notion that “Ethernet is becoming the RS232 and more for process control”. Protocols such as Common Industrial Protocol (CIP) and Modbus TCP are helping Industrial applications migrate reliably to Ethernet.
General Ethernet Progression
Most Programmable Logic Controllers (PLC) and Remote Terminal Units (RTU) vendors are now making their equipment with Ethernet interfaces forcing the migration to Ethernet based systems. It is now possible to manage/configure/control a PLC/RTU in the field and even have live visual confirmation (for safety or confirmation purposes) over existing infrastructure such as: fiber, Satellite, GSM , Wifi or WiMAX.
The selection of a communication backbone vendor for any Automation Systems is critical since failure of equipment or design will impact production or processes. Safety, uptime and cost are possibly the most important factors!
In today’s world with automation systems in place, the communication infrastructure is like the central nervous system for the automation processes and should therefore have the highest amount of available uptime.
In order to have high amounts of uptime the following points stand out in importance:
- Message Prioritization and Class of Service for real-time control per IEEE 802.1p Priority Queuing
- Network redundancy and fault tolerant architectures per IEEE 802.1w Rapid Spanning Tree protocol
- Virtual LAN’s which allows for traffic isolation and system security per IEEE 802.1Q VLAN
- Multiple Spanning Tree Protocol (MSTP) which allow for redundant links to be on a per VLAN basis, allowing for better traffic balancing across the network, as different VLANs can be configured to use different paths.
- Correct Network Vendor selection for the right environment (e.g. Devices without fans for cooling as these can become a weak point in the system; High Quality power supplies, with different input options and dual redundant supplies where required)
- Vendor Support is critical
- Network Management Solution in order to correctly and reliably manage the network
- Fast recovery times
- High Mean Time Between Failures (MTBF)
Bringing the past equipment forward to Ethernet with a simple converter
The reality is that if you have an existing plant it is not always a financially feasible option to replace all older PLC’s/RTU’s to the new age technology with embedded Ethernet Ports. In such a case, use of a Serial Device Server would be required in order to convert existing RS232/422/485 Serial communication to Ethernet. There are two methods for making use of these converters:
Method 1
The first method involves using two serial device servers (two pieces of hardware), one on each end of the serial link. The serial port of the first serial device server would connect to a device in the field with serial, the Ethernet port of this serial device server in the field will connect to a switch on the network. On the other side we would have a second serial device server connecting to the Ethernet network and the second port (the serial port) would then connect to the serial device partner/Serial port on a server.
Method 2
This method requires a Virtual Port Software Package on the PC end and one serial device server for in the field. The software will create multiple virtual Com Ports as needed and communicate directly with the Serial Device Servers in the field as if directly connected with Serial cable.
Typical Serial Conversion to Ethernet would require the device to understand the Serial Protocol being used (WIN, TIN, DNP3, Microlok). Ruggedcom are able to convert these known protocols and even legacy Serial Protocols as a RAW Serial Data Encapsulation. If you are using a legacy Serial Protocol then this method would be a good choice for you since no further development would be required, in effect, you would be simply extending your Serial Network through your existing Ethernet Infrastructure.
Communication Mediums
Ethernet typically uses a standard Unshielded Twisted Pair Cable (UTP) with a category rating based on the performance required. The cable is fairly inexpensive but has a distance limitation to 100m (This is without any interfering factors). When a connection is required further than 100m then you would look at the following options to extend the connection:
- Introduction of an additional switch to repeat and regenerate the signal which would propagate it a further 100m (This is a limited and costly option)
- Fiber optic cabling can also be used to extend distances:
- Use switches with embedded/modular fiber ports. This is the preferable option due to having the intelligence of the switch for statistics on the fiber link condition.
- Fiber to be used is Multimode or Singlemode
- The selection of fiber is based on the distance/speed you require
- Fiber can handle longer distances
- Fiber is immune to EMI
- Wireless
- This is typically used in applications where it is not possible or practical to install new fiber or copper runs.
- Wireless can be used from a few meters to a few Km’s, this is based on whether you are using un/licensed frequencies.
Communication solutions used for industrial and utility sites needs to be highly reliable, and as such the equipment should be carefully selected for the application. Equipment needs to be able to handle harsh environments without failing or losing data. Such environments could include high temperature ratings, high EMI (Electro-Magnetic Interference) or high vibration environments. Certain environments would require conformal coating on the circuit boards to prevent against high humidity and air-born chemicals/dust particles that are conductive/corrosive and if they intrude on the unit they could lead to downtime. The selection of product basket should also be able to offer reliable communication on a range of mediums:
- Copper Cables
- UTP/FTP/STP Cabling
- Pilot, Telephone Cabling (EoVDSL – Ethernet over VDSL)
- Fiber Optic cables
- Wireless
- IEEE802.11 Wifi b/g
- IEEE802.16/e Wimax with mobility option
- Serial RS232/422/485 conversion to IP to extend serial communication
- GSM
- E1/T1 Lines
Logical Network Separation
Before we separate the logical portions of the network we need to understand how a network initiates and completes its required communication. Once you have your physical network topology in place, you need to confirm what the network will be used for. i.e. Scada, PLC’s, IP Video, VoIP (Voice), seismic, protection etc…
An IP Address and Subnet mask are used on the end devices in order specify the network they are logically connected to as well as to specify their individual host address on that network. 192.168.0.0/24 would represent an IP Address range from 192.168.0.1-254. So any device assigned with a 192.168.1.0/24 range would not be able to communicate to 192.168.0.0/24 range without routing the traffic between the networks.
In order to understand a portion of how this takes place we need to understand the different types of addressing structures such as:
Unicast This is a standard message from one device to another device
Broadcast This is a message that is sent from 1 device to EVERY device on the network (subnet)
Multicast This is a message block that is sent from one device to one device or to many devices but not necessary to all devices on the network(subnet)
If device “A” wishes to send data to device “B”, Device “A” will send a broadcast message requesting for information on the location of Device “B”. This Broadcast message is intense on the network in that it will travel to ALL devices on the same subnet and each device will process the broadcast packet. Therefore with too many Broadcasts the network will suffer along with the end devices, yet without any Broadcasts the network would not work at all, so it is important to be able to tailor configure your network based on your applications requirements.
The same if an Intelligent Ethernet Device (IED) in a 192.168.0.X range wishes to communicate to a PLC in the same range, a Broadcast will be sent to the 192.168.0.0 range and no other subnet range.
From this we can see the importance to logically separate the network if running multiple various systems over the same existing Ethernet Infrastructure. Such examples would include PLC, Scada, VoIP, IP Video and protection networks.
Virtual Local Area Networks (VLAN’s) is a method of creating virtual logical networks within a single infrastructure. There are 3 main types of VLAN’s namely:
- Port Based VLAN’s
- MAC Address Based VLAN’s
- IP Based VLAN’s
These different options are based on the different layers referred to by the 7 Layer Open System Interconnection (OSI) which were developed by International Standardization Organization (ISO). It is not uncommon practice to use L1 and L3 based VLAN’s on a single infrastructure for further network control purposes.
Industrial Ethernet IP Camera Management Solution for ADDITIONAL SAFETY
Traditionally CCTV Systems have been analog based and have required a specific Control Room in which they can view all camera feeds. A CCTV user would then sit in the Control Room and attempt to view relevant camera feeds for feedback.
This can become a tedious task if for example, there is only one operator attempting to view over 64 camera feeds and determine their relevance in the production scheme.
Industrial Video and Control is one excellent solution to this problem, as opposed to having an operator find the camera of relevance during a specific part of the process, rather have the Camera of relevance popup on a monitor in the control room and bring attention of the operator to the part of the process that requires his/her attention.
IP camera solutions provide many other benefits (to mention a few):
- Multiple points of viewing without additional software, from anywhere on the network that can access the RSS (Relay Station Server)
- Can be easily integrated into a SCADA/HMI by using IV&Cs mature Active-X functionality
- Can be implemented across previously built IP networks
- Can manage network utilization for individual events such as recording, viewing from the same subnet and viewing from a remote subnet
With the integration of IP Camera’s, the possibilities to add safety is enhanced by the fact operators can now control the Scada while having a live visual on the actual location.
A further development is now to migrate towards the ability to view a trend from a Historian Server and synchronize this with an operators recorded screen (including mouse movement) with a recorded camera feed from in the field to verify certain conditions. This means that in the case of any fault it can be easily determined exactly what happened at the time, allowing for quick response in fixing the problem, as well as the capability to analyze and prevent the problem occurring again.
Figure 1 – Integration of trending and video
How to manage your Ethernet Network:
From the above details you can see the importance of the network and how it can act as your central nervous system, hence the importance to manage and maintain it! In order to manage an Ethernet Network effectively, you would require to have all your Ethernet Switches/Routers enabled for Simple Network Management Protocol (SNMP) and if possible to have the end devices also configured with this standard protocol. Certain vendors offer more in depth Management Information Bases (MIB’s) for more in depth detail pertaining to that specific unit.
A network management station is an intelligent piece of software that communicates via the network using SNMP to communicate to all managed devices to gain information regarding their state of operation and their health status thus assisting to be proactive rather than reactive to any potential maintenance required on the network.
If a problem occurs, the system will automatically notify the person on shift with a relevant notification regarding the state of the network or device.
Figure 2 – RuggedNMS Network Topology Screen
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