A newly released study by ARC Advisory Group, the leading analyst firm covering automation and enterprise software, shows Modbus TCP as the world's leading industrial Ethernet protocol, in terms of units shipped in 2004. Modbus TCP is the Ethernet variant of the ubiquitous Modbus protocol introduced in 1979. The protocol was recently accepted by the IEC as a Publicly Available Specification.

This standing for Modbus TCP is particularly significant given the current and projected growth of Ethernet in industrial applications. According to ARC Advisory Group, "the worldwide market for Industrial Ethernet is expected to grow at a Compounded Annual Growth Rate (CAGR) of 51.4% over the next five years. The market totaled 840 thousand units in 2004 and is forecasted to total just over 6.7 million units in 2009."

Ken Crater, president of Modbus-IDA, the suppliers' and users' association, cites the familiarity and ease of application of Modbus TCP, along with the protocol's openness, as reasons for its current success in the marketplace. According to Crater, "the proliferation of Modbus TCP is related to the open posture we have adopted for the protocol. The Modbus specification may be freely downloaded on the web, and there is widespread familiarity with its application due in part to the number of open-source implementations of the protocol that are available today."

Crater indicates that simplicity of implementation is an important factor: "Absent a compelling business need to the contrary, straightforward protocols such as Modbus TCP are easier and faster to code, apply, and troubleshoot than more complex protocols. This reduces cost and helps companies move more quickly in their markets."

As is often the case, however, success may, in fact, be the primary reason for success. The serial versions of the Modbus protocol have long enjoyed a position of market leadership, and a number of gateway products exist that can bridge between the serial and Ethernet variants of the protocol. The availability of hundreds of compatible products, combined with legacy installations of the serial protocol, has doubtless contributed substantially to the rapid acceptance of Modbus TCP.