Controlnet vs. EthernetIP

arekk

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Aug 2007
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Hi.

This question is for communication experts who are experienced in controlnet and ethernetIP.
Did anyone check which one of this nets is really faster. I know that few will teake it as a stupid question because ethernet is 100Mb/s and controlnet is only 5Mb/s, but the size frame and the way of communication does matters.
 
Hello,
If you use a switched network and so do not have collisions on the ethernet and for the same ammount of data traffic ethernet IP will definilely be faster.
 
I cannot remeber exact calculations, but as I know, for small amount of information the ControlNet is faster and of course determinstic
 
arekk said:
Hi.

This question is for communication experts who are experienced in controlnet and ethernetIP.
Did anyone check which one of this nets is really faster. I know that few will teake it as a stupid question because ethernet is 100Mb/s and controlnet is only 5Mb/s, but the size frame and the way of communication does matters.

Are you asking about control of I/O or to pass messages? I would take Controlnet anyday over Ethernet I/P to control I/O.
 
arekk said:
Hi.

This question is for communication experts who are experienced in controlnet and ethernetIP.
Did anyone check which one of this nets is really faster. I know that few will teake it as a stupid question because ethernet is 100Mb/s and controlnet is only 5Mb/s, but the size frame and the way of communication does matters.

Before even thinking about answering that, I want to ask why you need to know?

If you've used one or both, have you discovered a bottleneck? Actually having troubles related to speed?

If not, sounds like an attempt at premature optimization, which is wrong 99.99999% of the time.

For my money? ControlNet for all I/O, Drives, Devices, and Ethernet for all HMI's and Enterprise communications.
 
rdrast said:
Before even thinking about answering that, I want to ask why you need to know?

If you've used one or both, have you discovered a bottleneck? Actually having troubles related to speed?

If not, sounds like an attempt at premature optimization, which is wrong 99.99999% of the time.

For my money? ControlNet for all I/O, Drives, Devices, and Ethernet for all HMI's and Enterprise communications.

I asked this question because my boss claims that ethernet is the fastest net and the most relible and so on and he isn't satisfied with our net He would like to all PLC's connected via ethernet. Our PLC's are connected via controlnet but we have 4 ethernet gateways. It is hard to argue with your own boss
 
The main difference, ControlNet has a guaranteed repeat speed (providing you have not set the updates too low) whilst ethernet speed can/will change.

If your network is only your own PLC's, then it may indeed be faster, but if its a company network and/or higher systems are connected with a lot of data being transferred, then the speed maybe adversley affected.

ControlNet will always try to achieve the programmed rate, whilst ethernet will do it when it can.

Its usually good practice to keep low level interfaces separate using ControlNet/Ptrofibus etc is the best way to achieve this.
 
arekk said:
I asked this question because my boss claims that ethernet is the fastest net and the most relible and so on and he isn't satisfied with our net He would like to all PLC's connected via ethernet. Our PLC's are connected via controlnet but we have 4 ethernet gateways. It is hard to argue with your own boss

Okay, that helps.
For I/O, and devices, it's still very hard to beat ControlNet, even though it is technically a 5 mbps network. If you are loading it down on a single machine so drastically, that you can't keep your RPI below 20 msec or so, you can always another ControNet card. For example, even though it isn't needed, I usually use one ControlNet card for all I/O to slave racks, and a second one dedicated only to Drives.

For supervisory access (remote monitoring and programming, or HMI's) I stick to Ethernet. Also, in some very limited cases, where I have no choice (such as inter-PLC communications), I'll MSG over Ethernet, but it isn't my choice, and I don't do that for critical applications.

For the same I/O count, the speed of either will be similar, even if Ethernet is running at 100mbps, as the CPU still has to deal with everything coming into it, and will be scan-time limited. One big drawback for Ethernet, it it is relatively easy to crash, if you have a network that people can add/remove/modify devices without careful supervision. Another, is there is a tendancy to use extremely sub-par Ethernet cables, switches, and routers, because they are so cheap. The local office supply store's Ethernet switch is NOT A GOOD CHOICE in an industrial enviornment.

Once you start moving to proper, hardened, managed switches, and high quality patch panels, the Ethernet cost goes up drastically.

I also hate the idea of the IT department messing with my control networks. ControlNet prevents that.
 

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