ISA 100.11A PDF
In ISA a, the network layer uses IETF. IPv6 and 6LoWPAN formats, and the transport layer provides connectionless UDP IPv6 service with compressed or. of wireless industrial automation standards: ISAa and WirelessHART networking technology developed by the ISA Committee of the ISA. ISA A: Wireless systems for industrial automation: Process control and related applications.
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System Integration: Field wireless networks – ISA
So, I want to give thanks to the many people of the ISA who work on securing the future of the organization just as the original founders had. ISA was and is forged and founded from true honesty and integrity that you will not find in to many other professions. The use of wireless transmission is part of everyone’s life. Every day, companies develop and update products with wireless capabilities. The benefits of mobility make the use of wireless equipment almost a necessity.
The online life is now possible not only through computer desktops but also through cell phones, tablets, notebooks, and TVs, which makes wireless transmission the first choice of the communication interface. When one looks to the industrial environment, it is natural to ask if the “wireless wave” will reach industrial applications to be used in automation and instrumentation projects.
This question will only be answered in the future. However, when one looks to the near past, very few people could have imagined a scenario in which wireless communication took over the world. So, it is reasonable to assume a similar speed of change will occur within a few years in industrial automation.
The use of wireless networks in industrial automation has increased in the past few years. It can be explained due to several advantages wireless technology presents, such as the reduction of time and cost to install new devices, since there is no need to provide a cabling infrastructure, along with the possibility of installing new devices in hard-to-reach or hazardous areas and the flexibility to alter existing designs. With adopting wireless technology, many important requirements should be considered regarding the solutions presented by the new standards, protocols, methodologies, and support tools.
The most important requirements are: Various solutions proprietary or not exist in the market to issues with using wireless transmission in an industrial environment. This article describes the main features and the solutions adopted, in order to facilitate the comparison between them.
The article also briefly discusses some open issues that will have to be addressed in future versions of these standards. The main purpose of the ISA committee is to provide a family of standards for industrial wireless networks, which will address the needs of the whole plant, such as process control, personnel and asset tracking and identification convergence of networks, and long-distance applications.
It describes a mesh network designed to provide secure wireless communication to process control. It presents routing and non-routing field devices, backbone routers, a system manager, a security manager, and gateway. It is worth mentioning that routing devices perform an important role in mesh networks. In this topology, data is transmitted from source to the destination through several hops, and the routers are responsible to make sure that the data arrives at the right destination.
They can even use alternative paths to improve reliability. The backbone router is responsible to route the data packets from one subnet over the backbone network to its destination, which can be another subnet or the gateway. The gateway acts as an interface between the field network and the plant network and control host applications.
The system manager is the administrator of the network and it is responsible for communication configuration e. The security manager is in charge of the policy security management of the standard. Figure 2 shows the ISA It is important to note that the ISA This will allow the ISA The application layer is very flexible and is capable of performing tunneling. This allows users to maintain the compatibility with legacy protocols that are currently in use in their plants.
WirelessHART was the first standard developed for wireless communication for process control. It means that a field device does not have to communicate directly with the gateway; it only needs a neighbor device to transmit its data, which will be responsible for sending the data to another field device until it arrives at the gateway.
The mechanism extends the network range and also creates redundant communication paths, which increases the network reliability. It can be seen that the new layers were included in order to make the HART protocol work in a wireless network. The physical layer defines the mechanical and electrical interfaces and the procedures to establish and disestablish the physical connection to transmit the information coded in bits.
These radios operate in 2. This band is divided in 16 channels, uses DSSS direct sequence spread spectrum and Kbps raw data transmission rate. It is a medium access control method that provides time diversity i. The duration of the time slot can be configured 10 to 14 ms to better accommodate the application needs. All the time slots needed to allow the network communication form what it is called a superframe.
In order to provide better support applications with strict time requirements, besides the use of TDMA, there is a flow control method with priority assignment. Messages can be given two different levels of priorities. The communication reliability is increased through frequency diversity. In channel hopping, the communication between devices uses a different channel on every transmission. The choice of channel follows a pseudo-random sequence of the available channels hop sequence.
It increases data communication reliability, because it increases immunity against interferences.
Another strategy used to improve reliability is the ARQ automatic repeat request. The transmitted messages need to be acknowledged by the destination device. If it does not happen, then the message is retransmitted automatically in another channel.
Based on the data received from the field device, regarding the RF spectrum, the system manager can interdict prohibit the use of one or more channels for a certain period of time. These forbidden channels go to a ” channel blacklist ” and they are not used in the hop sequence. The adaptive hopping is similar to channel blacklistingwith the exception that the decision is taken by the field device based on the statistical data of some wireless parameters.
The traditional HART protocol isz token-passing as medium access control.
The medium access control is also TDMA to assure temporal determinism and to optimize the use of the device battery. The duration of the time slot is fixed 10 msand the time slots are organized in a superframe, which are periodically repeated to accommodate different types of traffic.
The slot can be dedicated-in order to obtain minimum latency-or can be shared to allow better use of the bandwidth. To avoid interferences, disturbances, and collisions with other communication systems, WirelessHART also uses channel hopping, but only one scheme was defined. Regarding spectrum management, channel blacklisting is also used. In this topology, a field device can be used to route the messages from the other devices to its final destiny.
It increases the network range and also creates redundant paths routesmitigates problems with interferences and obstacles without user intervention, and helps increase network reliability. The routes are configured by the manager of the network based on the information received from the devices. Hence, the redundant routes are continually updated based on the spectrum condition. It means that ISA The security mechanisms must be evaluated using the following criteria: The confidentiality of information guarantees that only the authorized network members will have access to the information.
These keys have an expiration time and can be updated. The MIC message integrity code is added to the data that will be transmitted. It allows the receptor to verify if data were corrupted or altered by an attacker.
Additionally, the MIC and symmetric keys can be used to authenticate data packets transmitted between the network nodes.
Devices that are willing to join the network listen to and capture advertisement messages from routers. These advertisements contain the required information about the network to allow the device to assemble a join request. This request is sent to the system manager to ask permission to become a member of the network.
The system manager processes this request with the security managerwhich is responsible for verifying whether the new device presents all the security credentials.
Once the request is approved, the system manager sends a response to the router and admits the new device in the network. For example, the ISA The transport layer uses the nounce to indicate when the data packet was created. The join process can also make use of asymmetric keys, which does not require a secure initial exchange with a joining device.
The joining process is similar to the one described previously. The device that is willing to join the network sends a join requestand if all goes well, it receives a join response from the network manager. Since in both standards there is a central entity responsible for keeping a record of the devices belonging to the network, the probability that successful node replication attacks occur is very low. The availability of the information can be threatened by interference continuous or intermittent in the communication channels.
In the case of continuous interference in several isz, the channel blacklisting provides an efficient solution.