tcpdump

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  1. DNP 3 protocol - what?

    I think this is getting clearer now. So in terms of the OSI REference model, DNP 3 is an application layer protocol? The meaning of the DNP transport, link layer and application layers, are all of these DNP specific? i.e. not related to the OSI definitions of transport, link layer and application?
  2. DNP 3 protocol - what?

    Thanks MArk, You have been a great help so far... 1. In terms of encapsulation of the DNP 3 protocol on a SCADA system running on a TCP/IP Ethernet network, Does the the DNP 3 packet get placed into the payload of the TCP segment, then into the payload of the IP packet, then into the Ethernet frame.... I thought the DNP 3 protocl exists at the application layer and also link layer, so is there another layer of encapsulation between the IP packet and the Ethernet frame? 2. If the DNP 3 protocol does not know about the raw value and the scaled value, how is this information passed to the MAster station for display? Thanks, again Mark. Regards, tcpdump.
  3. DNP 3 protocol - what?

    A PLC/RTU communicates with a Master station. The PLC, from the 4mA to 20mA signals, converts this to a raw range (say 0 to 10, 000); then to a scaled range (say 0 to 100 %). If the signal is 12mA, this is a raw value of 5,000 and equivalent to 50%. Is the values 5,000 and 50 both passed to the MAster station in the DNP 3.0 protocol????
  4. DNP 3 protocol - what?

    "...DNP has two layers. Well 2.01. It has a link layer and an application layer. It also has a 1 byte 'transport layer.' ..." How can a single protocol have more than one layer? A protocol resides in a layer, such as TCP resides in Transport layer, IP resides in the network layer, ...
  5. Hi, Does anyone know anything about DNP3.0? 1. Is this a protocol as such, like TCP, UDP, IP ... 2. Is it a framework, e.g. like OSI 3. If it is a protocol, does it live in a layer such as network layer etc... From reading the description on dnp.org, it seems like it a protocol that works at many layers... Can anyone find the actual format of the protocols, in terms of headers and payloads. Why does it pass both the raw and engineering range to the Master Station?
  6. Alarm Handling

    Hello all, I had a question for the alarm banner that appears on the top of the operator workstations, typically. I am just trying to get a grasp of whether or not the way alarms are handled are similar across different SCADA systems. We have different buttons/definitions: Accept: alarm has been dealt with, no further action necessary. Acknowledge: operator is aware of the alarm, and is currently investogating. Note: operator is aware of alarm, but will not action now, alarm will 'fleet' reappear in a certain amount of time. Do these definitions make sense to anyone?
  7. I guess I didn't really explain my problem carefully or detailed enough. The mimic developer has very basic functionalities. If I draw say a pump station, with 2 pumps, and then repeat this 50 times, then if I want to make a change to one pump station, I then have to repeat it 50 times as well. The 50 pumps I draw are not 'linked' and changes to one 'template' will not propogate to the other 50 sites. Is there any advice on this matter?
  8. Hello everyone, It's good to be back. I have a bit of a quandry for you. I develop and maintain a large system which has somewhat over 1000 (yes that is right, 1000) different remote locations. This transposes into about 1000 different mimics. Some of these mimics are somewhat similar and template based, but most of them are site specific, or have some sort of site specific attribute about them. The software that I am using, is very limited in terms of object oriented capabilities and propagating changes through a template to all instances. The problem comes to the testing phases, how do you test a mimic? I know we drive a point and see if displayed on the screen. But this is a manual, time consuming and repetitive process. Resources are limited to do this. Is there any advice or guidelines anyone wants to give?
  9. Hi all, I have a question to ask about communications in SCADA systems. Quite often, you will find literature talking about things such as Line and Path, and , module, Channel... Now, when I studied communications subjects as uni, all of these sort of things meant the same. My understanding of these terms are: Module: Plug in board, which you slot into the chassis. Can have analog, digital, input, output channels Channel: These are on the module,it is like the "interface" to the signal, right? Line: The physical infrastructure, e.g. coaxial, twisted pair, optic fibre, radio, etc... that is used to communicate between the PLC and MS. Path: The logical communication link between the PLC and MS. E.g. There can be more than one line for the path, e.g. if you have ethernet, and radio as backup, then there are two lines for the path.... Does everyone agree with my definiitions.....
  10. Raw Range / Engineering Range

    thanks 4 your replies. they were very informative, and explain WHAT is going on, but to some degree they lack as to WHY we have a raw and scaled range. Why not from the 4mA to 20mA signal, we convert to the 0KPa and 100KPa straight away???? This reduces processing time, storage capacity. etc... Now, what is your experience with these kinds of things?? Do your PLCs have both a raw and scaled range for measurements????
  11. Alarm conditions and threholding

    thanks for the information guys, just for your info, the SCADA system I work on, has most of the alarms being PLC generated. The MS which polls for information from the PLCs, can then collect data and then generate its own alarms, on a more systemi basis. For example, if the PLC at the power generator is giving low power alarms, then the MS can then send instruction to the PLC at the motor to stop running so as to preserve back battery power. Does anyone else use a more systemic approach to control, rather than localised and independent PLCs controlling their own domains????
  12. Hello, The PLC I am programming at the moment has a concept of a "raw range" and an "engineering range". How it works is that, the instrument provides a signal of 0mA to 20mA, where 0mA refers to a raw value of 0, whilst 20mA refers to a raw value of 1000. These raw values between (0,1000) are then converted to a value between (0,100) and then both of these values raw and engineering are given to the MS. Why do we bother in having the raw/engineering values?
  13. Hi all, I would like to know something. With the PLC and Master Station, which is more common to determine if a signal is in alarm state? E.g. if pressure is above say 45 Kpa, does the PLC itself determine that it is in alarm, and then either interrupts the MS to notify this or the MS polls PLC to find the alarm condition or Perhaps the PLC captures the pressure, and then at the next poll by the MS, the value of 55Kpa is greater than 45Kpa so it is really the TC that is determining alarm states? All I want to know, is which is more common based on the SCADA systems that you have worked on?
  14. Umm, I meant a bit more low level than elevator, washing machine etc.. e.g. a timer that resets after 10secs a stopwatch, with start, stop, reset, dual time
  15. Hi, Could anyone suggest some basic, simple examples of programs/applications I could develop to start learning about PLC programming? Thanks, tcpdump