Automation World has an interesting article in the February issue and online: “Ethernet Protocols’ Flexibility A Boost For Manufacturing.” It manages to mention five different Industrial Ethernet protocols but then goes on to focus on PROFINET and Ethernet/IP. This is a sensible focus since PROFINET and Ethernet/IP are the market leaders. A recent study showed the market roughly equally divided between PROFINET, Ethernet/IP and “other” (see “Industrial Ethernet Market Shares”).
Some of the points made in the article warrant expansion:
The concept of multitasking is an important one for Industrial Ethernet. The main point here is that Ethernet inherently allows multiple protocols to run at the same time over the same wire… and through the same switches and other infrastructure equipment. An Industrial Ethernet infrastructure in your plant will happily support PROFINET, Modbus TCP, web servers/browsers, email, and Ethernet diagnostic protocols (more on those later) AT THE SAME TIME. It will also support Ethernet/IP at the same time provided managed switches with IGMP Snooping are used to limit Ethernet/IP’s multicasts to only the appropriate devices. (IGMP stands for Internet Group Management Protocol.) In contrast to Ethernet/IP, PROFINET unicasts its data only between the communicating devices. EtherCAT can not use the same infrastructure since it requires a closed network with EtherCAT as the only protocol.
Just because you can do a thing does not mean you should do a thing. This applies when sharing the infrastructure! You don’t necessarily want to allow everything to share; partitioning the network architecture is sensible to keep traffic limited to where it’s needed. There is no substitute for doing actual engineering, as I always say.
Connection to legacy buses
Alluded to once in the article, this is an important benefit at which PROFINET excels. To protect the investment of users of PROFIBUS, PROFINET uses an ingenious method to integrate the world’s most popular fieldbus: a proxy. Similar to a gateway in that it connects disparate protocols, it differs because the proxy is specified in the PROFINET spec. This technique worked so well for the largest installed fieldbus base, PROFIBUS, that the number two fieldbus, Interbus, decided to use PROFINET instead of developing their own Industrial Ethernet. Actually, the technique worked so well, that the organization supporting PROFINET also specified proxies for DeviceNet and many other legacy buses, too.
Why would you choose an Industrial Ethernet over a legacy fieldbus? Bandwidth is certainly one benefit. But multiple protocols on the same network, leveraging IT tools, accessing a web server in the device, and increased address space are also important. (One little nit to pick in the article: PROFIBUS runs at speeds up to 12Mbaud, not 5 as the article says.)
Leveraging standard Ethernet tools
The article explains how LLDP and SNMP can be used with Industrial Ethernet in general and PROFINET in particular.
LLDP is Link Layer Discovery Protocol. From Wikipedia: “The Link Layer Discovery Protocol (LLDP) is a vendor-neutral Data Link Layer protocol used by network devices for advertising of their identity, capabilities, and interconnections on a IEEE 802 LAN network.” With PROFINET it allows topology to be discovered and devices to be replaced without using configuration tools. No laptop needed!
SNMP is Simple Network Management Protocol. There’s more about SNMP and PROFINET in a previous blog post, “Needed – a Diagnostic Tool for Idiots.”
A major benefit to OEMs is the ability to access their machines in the field remotely – service calls are expensive. One way that can be done is to VPN (Virtual Private Network) in to the web servers in Ethernet devices like switches and PLCs.
When slip rings are too error prone, when festooned communication cables wear out too soon, when automated guided vehicles roam free, wireless is a better choice. More on wireless in our “Industrial Wireless Networking” webinar.
For even more about PROFINET, come to one of our 10 free PROFINET training classes.