Ethernet, Profinet and Profibus

[electricsheep]

Hi. Firstly I realize this may be classified as a homework question, so please move it if necessary.

Problem
For a lab using PLCs, I'm supposed to answer this question: What is the difference between Ethernet, Profibus and Profinet?

My attempt
This is for a control subject, but due to my course structure I may not have done the subjects that contain the prerequisite knowledge. I have searched the web for over 3 hours for information, using anything from Wikipedia to FAQs of Siemens. This is what I have got so far:

Ethernet: a computer networking technology that was originated designed for office use. It features a star topology and uses twisted pair wiring. In industrial automation, it is typically used for communication between PLCs and HMIs.

Profinet: an open standard for industrial Ethernet with adaptations for improved real-time applications. It can directly connect PLCs and IO devices.

Profibus: a fieldbus system for real-time distributed control. It is used for process and field communication in cell networks with few stations and for data communication. It connects PLCs, sensors, actuators and other automation devices.

Further help required
Well, I'm just not happy with what I've got. My explanations of Profinet and Profibus seem almost the same, and neither mention physical differences with Ethernet (such as wiring form, performance parameters and whatever that's applicable). I've also found some contradictions between sites, with some saying that Profinet is Profibus on Ethernet (which I don't really understand), and others saying that Profinet is a total revolution from Ethernet and so on.

If anyone can fill in the gaps, correct my mistakes and/or give me pointers on where I can find more detailed and reliable information, I would be very grateful.

 

[berkeman]

I think your question is okay here in the EE forum. It's advanced enough and specialized enough that this is probably the right place to be getting some help.

Unfortunately, I'm not able to be of much help in answering your question, because I don't work with the standards that you mention. I'd ask, though, whether any of them are multidrop, or are they all point-to-point? Certainly Ethernet as it is commonly used is point-to-point, but I don't know about the others.

Also, in optimizing network throughput, you will do things with addressing overhead and packet size. Are there differences in that between these threee standards?

 

[CarlHenning]

Resources for PROFIBUS and PROFINET

PROFIBUS and PROFINET are open standards developed and supported by PI (PROFIBUS and PROFINET International). You can find overview brochures at http://www.profibus.com/pall/meta/downloads/ .

In North America the technologies are supported by PTO (www.us.profibus.com)[/url], one of 25 regional associations making up PI. For PROFINET, I recommend the PROFINET Story at http://www.us.profibus.com/resources.aspx?pagetype=sue. In addition, PTO offers free one-day training classes around North America; a schedule, details, and registration at http://us.profibus.com/training.aspx?pagetype=oneday.

Carl Henning
Deputy Director
PTO

 

[electricsheep]

Heh, thanks Carl and berkeman. After more hours of research and learning about some basics, here's my refined version that I will present to my lab demonstrators tomorrow, if they ask for it. I've tried to focus on comparing and contrasting the three rather than talking them in general.

Ethernet is a family of computer networking technologies for LANs. It is not suited to real-time applications as collisions are resolved using the random wait time algorithm.

Profinet is an Ethernet-based open standard iwth adaptations for real-time applications. It is an advanced communication system, linking control systems in industrial automation.

Profibus is a multi-master/slave communication system that links the devices inside each control system. It has a much slower data rate than Profinet as it is a fieldbus only.

* * *

There it is, the fruit of over 4 hours of research. Probably still not correct/complete.

Most useful websites:
http://www.anybus.com/technologies/profibus.shtml"
http://www.anybus.com/technologies/profinet.shtml"
and Wikipedia, of course.

 

[CarlHenning]

Good summaries. HMS, the creators of Anybus, are PTO members and their PROFIBUS and PROFINET pages are excellent. The Wikipedia articles are a little sparse. I’ll have to add updating them to my to-do list.

Carl
www.PROFIblog.com