Ethernet is a widely used communication technology that allows devices to communicate with each other over a local area network (LAN). Two main Ethernet-based protocols are used in industrial automation systems: Ethernet TCP/IP and Ethernet/IP. This article will discuss the difference between the two protocols and when they are most applicable.
Let’s start with an overview of Ethernet TCP/IP. Ethernet TCP/IP is a term often used to refer to the general Ethernet we use every day and the protocol stack it uses. It is the primary protocol used when exchanging data over the internet. To understand this, we can look at the OSI model.
The OSI model is used as the framework for exchanging data between devices. In the OSI model, Ethernet TCP/IP is the lower layer of the OSI model. Ethernet describes the bottom two layers, the Physical and Data Link layer. IP, or Internet Protocol, is the 3rd layer, known as the Network layer. TCP, or Transmission Control Protocol, is the 4th Transport layer.
Ethernet TCP/IP is the foundation of the internet as it is the set of protocols that allows two devices to talk to each other over a network and exchange data. What they do with this data falls on the upper layers of the OSI model, the Session, Presentation, and Application layers. In these layers your pc’s software typically gets more involved. This is also where Ethernet/IP comes into play.
Ethernet/IP written out is Ethernet Industrial Protocol. It is the Industrial protocol where the Common Industrial Protocol, CIP, is implemented over Ethernet. The ODVA defines CIP and specifies the upper layers in the OSI model. Ethernet/IP is the adaptation of CIP to Ethernet. There are other adaptations as well; for example, CIP for CAN is known as DeviceNet. The Ethernet/IP specification defines how CIP fits into Ethernet. This covers additional CIP objects down to what LEDs and behavior are required. One key part of the specification is the encapsulation layer. This adds to the UDP and TCP protocols that allow CIP messages to work on any TCP/IP network—allowing the lower layers to be swapped out. This will enable devices such as the Anybus AWB2030 to work with an Ethernet/IP device and connect with a wireless connection.
In the graphic below you can see the OSI model names on the left and the parts that relate to Ethernet IP in the middle. The section in blue is defined by the CIP spec while the parts in green while used by Ethernet/IP are not developed by the ODVA.
Ethernet/IP utilizes the Physical, Transport, and Data Link Layers in Ethernet TCP/IP. Separating these protocols from the Ethernet/IP Specification allows other governing bodies, such as the Institute of Electronic Engineers (IEEE) and the Internet Engineering Task Force (IETF), to manage these specifications. It also allows for interoperability among devices.
Many other industrial protocols use TCP/IP as well. Modbus TCP is one of the simpler protocols. It takes a Modbus RTU message and wraps it up in a TCP packet. The Modbus message is the user data in packet.
While Profinet uses Ethernet as its underlying network technology, it uses TCP/IP for non-critical data such as parameter data, configuration or diagnostic. It does not rely on the CP/IP for the transmission of process data.
Instead, Profinet uses a specialized protocol called the Real-time Protocol (RTP) for transmitting time-critical process data. RTP operates at the data link layer of the Open Systems Interconnection (OSI) model, which is one layer below the transport layer where TCP/IP serves. This allows Profinet to bypass the overhead and potential latency introduced by TCP/IP and provide a faster and more reliable communication channel for processing data.
EtherCAT is an example of a industrial network that does not use the TCP/IP stack by default. It does still use the physical and data link layers of the OSI model. The TCP/IP can be added with EOE which inserts the TCP/IP into EtherCAT frames.
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THE DIFFERENCE BETWEEN ETHERNET TCP/IP AND ETHERNET/IP
So, what is the difference between Ethernet TCP/IP and Ethernet/IP? Ethernet/IP is a protocol defined by the ODVA for exchanging CIP data over an ethernet network. Ethernet TCP/IP is a collection of protocols for connecting two devices over the internet.
Ethernet/IP utilizes standard Ethernet 10Mbps to 100 Mbps infrastructure, you also see this with Network switches being updated without gigabit switches. For example, the bottom physical layer is often swapped from a copper twisted pair for Wi-Fi or Fiber. The top layers typically change depending on what is being done, such as browsing the web with HTTP or transferring files with FTP. Ethernet TCP/IP this is where Ethernet/IP comes into play.
The main difference between Ethernet TCP/IP and Ethernet/IP is the purpose for which they were designed. Ethernet TCP/IP is a general-purpose networking protocol used in many applications, while Ethernet/IP is designed specifically for industrial automation systems. Ethernet/IP includes essential features for industrial applications, such as real-time communication, device discovery, and explicit messaging, which are not available in Ethernet TCP/IP.