OMG, that was awesome! I don't think it can be described better than this. Greatly appreciated Daba.
Now I have a few more questions.
1- my understanding is that EN2T module has more CIP connections than ENBT. If we have two separate networks with the same controller but one of them with EN2T and the other one with ENBT, the limiting factor is the number of controller' CIP connections. If so, why we ever use EN2T which I think is more expensive than ENBT? The extra CIP connections that it has can not be used because controller have less CIP connections.
2- is CIP connection used for all kinds of communication such as program download/upload, set point change, etc.?
3- each controller or bridge has limited number of CIP and TCP. What does TCP connection do? If we use one CIP, does that mean we use one TCP as well?
4- controller or switch has one or more Ethernet ports. Does the number of RJ45 port show the available number of TCP connections?
Thank you once again for your wonderful support.
Thank you for your kind words.
In order....
1. Most times people use two (or more) Ethernet bridge modules in a controller chassis to physically segregate the networks. One for I/O another for HMI/SCADA/SQL/Programming etc. Often the corporate network is used for SCADA/SQL/Programming, and corporate IT like to keep the amount of traffic on the network as small as possible. But mostly the better reasoning is that you don't want the corporate network traffic eating the available bandwidth for real-time I/O.
Remember that Ethernet is not a "deterministic" network, meaning that you cannot guarantee that data will be transferred at a specific rate, although since 100Mb network speeds it becomes less of an issue.
ControlNet
is deterministic, containing a portion of the cyclic "NUT" (Network Update Time), where specific data transfers were "scheduled". I/O data was transferred in the same order every NUT, so you would get a constant update rate for any specific data. All ControlNet devices needed to follow this schedule, so all had the same "hymn-sheet" or "Keeper". This is why when you made any changes to the I/O, you had to "re-schedule" the network, which you don't have to do with EtherNet.
The EN2T not only gives you more connections than the ENBT, but is also a faster module, and everyone likes faster things, don't they ?
2. CIP (Common Industrial Protocol) is used for everything - it is the
protocol that is layered into the OSI ethernet model, which makes it become EtherNet/IP. In this case, the /IP does not stand for "Internet Protocol", but "Industrial Protocol" - I wish they had called if "Control Protocol" (/CP), which would have removed many people's confusion.
TCP (Transmission Control Protocol) is a layer below CIP, and is the protocol that deals with the actual transmission and reception of packets of data over ethernet.
Yes, CIP is used for everything, I/O and Produced/Consumed tag data transfer, explicit MSGing, Program Upload/Download, Programming Software access, HMI access, SCADA access, and so on....
If the device you are trying to talk to doesn't speak CIP, you have to use plain vanilla data blocks, which will go via TCP.
3. Yes, I believe that to be correct, but am happy to be corrected.
4. No, the number of RJ45 ports on a controller or switch has no relationship to the number of CIP or TCP connections available. The limiting factor will always be the finite number of connections supported by both the end-to-end modules, AND any communication bridge module interposed.
If you want to delve into any statistics, or as an aid in diagnostics, remember that each ENxT module has in-built web pages, where you can view the total number of connections and TCP connections in use by the module (amongst a ton of other info). Just type the IP address of the ENxT module into a browser's address bar.