I have a client who wants to connect a CP6606 to a SCADA-server on a BACnet/IP network.
In short, this CP6606 is controlling an automatic waste collecting system, and now the customer wants to have all alarms and so on sent up to this SCADA-system which acts as a central operation unit.
Do we need a gateway, or can this be done from TwinCAT?
How to proceed?
Not sure I can help much, but I know that we can a vendor using TwinCAT via a Beckhoff PLC, and they seemed to need to write their own BACnet gateway (- but I'd probably recommend one that is already available & tested - be it one that might be provided via TwinCAT, or a piece of hardware that can already do it for you - if TwinCAT doesn't provided such an offering).
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I have created an OPCUA server with eclipse milo that is installed in the same machine where the clients are installed, so the communication works fast and reliably.
I did a bit of sniffing with wireshark to see how much communication involves under the hood and apparently there is a lot going on when monitoring variable, alarms, etc....
So I am thinking what issues I may expect in terms of performance and scalability if the server gets deployed in the cloud. I have seen that people talks about OPCUA cloud services, but not being this a hot topic is hard to foresee what challenges may come, and how well it scales and performs.
I would imagine that OPCUA uses sticky sessions, which means that you only can support a max number of users/requests, so dynamic scaling may not be an alternative right?
I tried the samples provides by eclipse milo, which are stored somewhere in the network, and it took long timeto connect to it. If that is the performance one may expect then the perception of the service for non-technical users would be that it does not work well.
Is the cloud a right place to use OPCUA considering the network overhead? Any recommendation to stick to local networks (intranet) only and skip the cloud?
Any feedback would be appreciated, thanks!
If you wanted to get into more detail and share Wireshark captures we might be able to go over parameters that would reduce traffic.
If bandwidth is a concern because you're using cellular or other constrained connections then sure, OPC UA may not be the best fit.
I'm curious what kind of delays or latency you experienced running the examples - connecting over the internet generally does not take very long, so perhaps you were also measuring the time it took to compile and start the example or there was something going on with your network.
I am expected to design the solution for collecting/processing samples from a PLC device, and working with some control tags of the device. Please, suggest the approach. Sorry for the long question. I will split it to more questions after learning what are the smaller and more reasonable subjects/questions.
The solution for the company is built almost from scratch. There are some PLC devices, and there is a KEPServerEx (without the IoT Gateway). The PLC devices are already used through the third party proprietary software. But there is no "bigger framework" for future. From that point of view, I can introduce a modern design, but the budget is restricted.
From what I have learned so far, it seems that the KEPServerEx is a good choice for accessing PLC devices, but I have no hands-on experience with it. It seems to me that the OPC UA should be the choice over the older OPC (DA). I am also aware of the ladder way of working with PLC.
From what I have learned about "IoT Gateway" (which will not be used) for KEPServerEx, the KepServer can set the sampling frequency at the PLC tag level. And also the frequency of transferring the data can be set by IoT Gateway. The IoT Gateway then uses an internal (memory) buffer for storing the sampled values, and the tuples (tagID, value, quality, timestamp) can be read and passed to third party.
What is not clear to me is, how to do that without the IoT Gateway. I assume that it must be a basic operation. Is the (tagID, value, quality, timestamp) generic for working with PLC through any OPC server? Or is it generic only for KEPServerEx, or is it special for the IoT Gateway (optional) plugin?
I have learned that OPC Foundation added recently the Publih/Subscribe mechanism to the OPC UA. Does it require also newer version of KEPServerEx? Or can it be used with any earlier OPC server?
I am fairly experienced in programming and database things. I also have some technical background in industrial sensors, actuators,... However, I have never worked with digital automation in industry.
Thanks, and have a nice day.
Depending on the PLC you want to communicate with, and the communication network your devices will be transmitting data on, you need to purchase the appropriate driver package so that KEPServerEX can communicate with it.
For example:
If your PLC is an Omron NJ PLC, and it is on an Ethernet network with the server that KEPServerEX is residing on, you will need to use the "Omron NJ Ethernet" driver in the suite package Kepware offers called the "Omron Suite".
Regarding your question about the IoT Gateway:
From what I have learned about "IoT Gateway" (which will not be used) for KEPServerEx, the KepServer can set the sampling frequency at the PLC tag level. And also the frequency of transferring the data can be set by IoT Gateway. The IoT Gateway then uses an internal (memory) buffer for storing the sampled values, and the tuples (tagID, value, quality, timestamp) can be read and passed to third party.
This can be done without the IoT Gateway, by using the appropriate aforementioned driver, and then using another driver package to send the PLC data to wherever you would like (ODBC client, SQL Server database, etc.). It depends on what you want to do with the data you are acquiring.
When you talk to a specific device you need to know the protocol that the device uses and those protocols can vary really much.
Sometimes the manufacturer of a device provides an OPC server that shields you from this or as you mention a 3rd party Connectivity server like KepServerEx or Matrikon can be used presenting an OPC interface for your client to use.
I don't know anything about the KepServerEx or your particular requirements but normally an OPC server has a cache where values are stored from which the client can read from alternatively read directly from the hardware. Subscriptions can be configured similarly e.g. frequency, threshold etc.
The protocol from the OPC sever/3rd party to the device determines the frequency in which you can sample values. E.g. some protocols need the device to be polled for values, some are more elaborate.
If you create an OPC client then you are pretty much free what kind of OPC server you connect to whether it is a 3rd party or an OPC server from the manufacturer and having the client storing values whenever items in a subscription changes is pretty trivial.
If you are familiar with Visual Studio, then AdvancedHMI may be a possible solution. You did not mention any specific PLCs, but AdvancedHMI includes many PLC communication drivers as part of the free package. This gives you the ability to write VB or C# for transferring the values from the PLCs to a database. The drivers are not OPC drivers, but are designed to be much simpler to use and more efficient.
I need to make TCP based decentralised chat app for local network. By decentralised I mean there is no central server. Each entity on a network should have server/client architecture. When app starts it should check which user is online ( already running the app ). My question is how can i check that? Can i do it by trying to connect via connect() function from socket library? I'm new to programming, especially socket programing, so if it's a dumb question sorry in advance.
You should definitely study how other decentralized applications do this. There are lots of techniques.
Each instance of the application should, as part of its server functionality, track the addresses of other instances of the application. Each instance should, as part of its client functionality, keep track of a few instances it can connect to. Prefer instances that have been around for a long time.
The software should include a list of servers that have been running for a long time and are expected to typically be available. You may wish to include a fallback method such DNS, maintained by anyone willing to keep a list of well-known servers offering access through a well-known port. The fallback method can also be IRC or HTTP.
If you want to stay decentralized, you might want to try multicasting or broadcasting a request packet to all hosts on the network to discover other instances of your chat application.
Something similar has been implemented in Pidgin, named Bonjour. It works quite nicely and provides chatting capabilities on a local network. More specifically, it is defined as a Serverless Messaging part of XMPP.
If you are looking for code examples, have a look at one of my projects where I use multicast to discover hosts on the local network that provide a specific service: Headers and implementation.
I have a client company with a simple web application (Python Flask) and I need to add a phone notification functionality to it.
The main requirement is that the app should call users, play a certain sound file and accept some tone input ("Hello! This is an automated message from your WebApp account. You have a meeting with $John today at $5pm. Please press 1 to confirm").
The other requirement is that the solution should be relatively cheap and fast to market.
I have done some research already and it seems that there are a few consequent steps to achieve that:
Set up an Asterisk or a FreeSwitch server;
Set up a SIP account;
Write some business logic for the Asterisk server which allows to make calls and play sounds via a SIP account;
Write an API at the Asterisk server and expose it to the Python Flask web app.
Do I miss something here? Can any of the steps be omitted anyhow? Can I do it simpler?
the fastest way to get it working is to use one of the cloud voice services with speech synthesiser. Here's a short list to check out:
Twilio
Tropo
Plivo
Here I listed some details.
Those services charge you per minute, plus you may have to pay some monthly fee.
If you want to run an independent and standalone service, I would recommend FreeSWITCH instead of Asterisk. It's got reach integration possibilities and API. You will need to read the FreeSWITCH book in order to understand how it works and how to build your service.
I agree with Stanislav Sinyagin on the cloud based solutions, but I would add one more, Voxeo Prophecy. Tropo is from Voxeo, but they have offered Prophecy as a solution for a lot longer and it supports the open standards CCXML and VoiceXML. The advantage of CCXML for outbound notification applications is you have a lot more control of the notification process.
The Prophecy platform has excellent call progress analysis (CPA) which will allow you to determine whether a machine or a human answered and handle the call accordingly. For example, it does not make sense to ask a machine to "...press one to confirm". Instead you may want to leave a message that provides a call back number for the user to confirm with after they have listened to the voice message. The CPA can be used to leave a message on a machine at the correct time (when the greeting message has stopped) so that you do not get clipped messages in the voice mail. CPA will also allow you to provide detailed reports on who was notified and for those that did not it can tell you whether it was a bad number (received a SIT tone), a modem or fax answered, or ring-no-answer (pretty rare these days). These type of details can factor into your retry process for failed notifications.
The other advantage to using Prophecy and open standards is your application will be portable to other IVR systems that are VoiceXML/CCXML compatible if you ever want to migrate. Tropo, Twilio, and Plivo all use proprietary API's which does not allow you to move your applications to other services. Prophecy is also available as a software solution so that if you want to take it out of the cloud you can run it on premise. You can get a two port version for free to try it out.
There is excellent documentation on developing outbound notification systems on Voxeo's developer site. Take a look at the CCXML documentation in section F on Outbound Dialing.
Not sure which development languages you are familiar with, but if you are used to ASP.NET MVC there is an open source project called VoiceModel that makes it easier to develop VoiceXML applications. The other advantage of VoiceModel is that you develop your application once and it will run on any VoiceXML compatible platform and Tropo. They are currently working on adding outbound notification support in this project that will work for both Tropo and VoiceXML.
Third party solutions listed are your easy choice. Running your own asterisk is also suitable for what you want to do, but i think for only this much it would be overkill, from an operational perspective.
In asterisk, you can originate a call that has the 2 variables you need with an (basic-authenticated) HTTP request. You will also need some settings and a tiny dialplan. Setting up the SIP account is easier or more difficult, depending on the documentation from the provider. Most of them have detailed documentation for configuring asterisk (not so much so for freeswitch). Keeping the damn thing alive is what's gonna get to you :)
I am developing an iPhone application that allows to basically click through a series of actions. These series are predefined and synced with a common configuration server.
That app might be running on multiple devices at the same time. All devices are assumed to have the same series of actions defined on them. All devices are considered equal, there is not a server and multiple clients or something like that.
(Only) one of these devices is used by a person at any given time, it is however possible that the person switches to a different device at any given time. All "passive" devices need to be synchronized with the active one, so that they display the same action.
The whole thing should happen as automatically as possible. No selection of devices, configuration, all devices in the same network take part in the same series of actions.
One additional requirement is that a device could join during a presentation (a series of actions) and needs to jump to the currently active action.
Right now, I see two options to implement the networking/communication part of that:
Bonjour. I have implemented a working prototype that can automatically connect with one (1) other device in the network and communicate with that. I am not sure at this point how much additional work the "multiple devices" requirement is. Would I have to open a set of connections for every device and manually send the sync events to all of them? Is there a better way or does bonjour provide anything to help me with that? What does Bonjour provide given that I want to communicate with every device in the network anyway?
Multicast with AsyncUdpSocket. Simply define a port and send multicast sync events out to that port. I guess the main issue compared to using bonjour with tcp would be that the connection is not safe and packets could be lost. This is however in a private, protected wlan network with low traffic if that would really be an issue. Are there other disadvantages that I'm not seeing? Because that sounds like a relatively easy option at this point...
Which one would you suggest? Or is there another, better alternative that I'm not thinking of?
You should check out GameKit (built in to iOS)--they have a lot of the machinery you need in a convenient package. You can easily discover peers on the network and easily send data back for forth between clients (broadcast or peer to peer)
In my experience Bonjour is perfect for what you want. There's an excellent tutorial with associated source code: Chatty that can be easily modified to suit your purposes.
I hobbled together a distributed message bus for the iphone (no centralized server) that would work great for this. It should be noted that the UI guy made a mess of the code, so thar' be dragons there: https://code.google.com/p/iphonebusmiddleware/
The basic idea is to use bonjour to form a network with leader election. The leader becomes the hub through which all the slaves subscribe to topics of interest. Then any message sent to a given topic is delivered to every node subscribed to said topic. A master disconnection simple means restarting the leader election process.