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Industrial Ethernet is the name given to the use of the Ethernet
protocol in an industrial environment, for automation and production
machine control.
Until recently, a PLC (Programmable logic controller) would communicate
with a slave machine using one of several possible open or proprietary
protocols, such as Modbus, Sinec H1, Profibus, CANopen, DeviceNet or
FOUNDATION Fieldbus. However, there is now increasing interest in the
use of Ethernet as the link-layer protocol, with one of the above
protocols as the application-layer (see OSI model).
Some of the advantages are:
Increased speed, up from 9.6 kbit/s with RS232 to 1 Gbit/s with IEEE 802
over Cat5e/Cat6 cables or optical fiber
Increased overall performance
Increased distance
Ability to use standard access points, routers, switches, hubs, cables
and optical fiber, which are immensely cheaper than the equivalent
serial-port devices
Ability to have more than two nodes on link, which was possible with
RS485 but not with RS232
Peer-to-peer architectures may replace master-slave ones
Better interoperability
The difficulties of using industrial Ethernet are:
Migrating existing systems to a new protocol (however many adapters are
available)
Real-time uses may suffer for protocols using TCP (but some use UDP and
layer 2 protocols for this reason)
Managing a whole TCP/IP stack is more complex than just receiving serial
data Ethernet is a family of frame-based computer
networking technologies for local area networks (LANs). The name comes
from the physical concept of the ether. It defines a number of wiring
and signaling standards for the physical layer, through means of network
access at the Media Access Control (MAC)/Data Link Layer, and a common
addressing format.
Ethernet is standardized as IEEE 802.3. The combination of the twisted
pair versions of Ethernet for connecting end systems to the network,
along with the fiber optic versions for site backbones, is the most
widespread wired LAN technology. It has been in use from the 1990s to
the present, largely replacing competing LAN standards such as token
ring, FDDI, and ARCNET. In recent years, Wi-Fi, the wireless LAN
standardized by IEEE 802.11, is prevalent in home and small office
networks and augmenting Ethernet in larger installations
Ethernet was originally developed at Xerox PARC in 1973–1975.[1] Robert
Metcalfe and David Boggs wrote and presented their "Draft Ethernet
Overview" before March 1974. In March 1974, R.Z. Bachrach wrote a memo
to Metcalfe and Boggs and their management, stating that "technically or
conceptually there is nothing new in your proposal" and that "analysis
would show that your system would be a failure." This analysis was
flawed in that it ignored the "channel capture effect", though this was
not understood until 1994. In 1975, Xerox filed a patent application
listing Metcalfe and Boggs, plus Chuck Thacker and Butler Lampson, as
inventors (U.S. Patent 4,063,220 : Multipoint data communication system
with collision detection). In 1976, after the system was deployed at
PARC, Metcalfe and Boggs published a seminal paper.[2]
The experimental Ethernet described in that paper ran at 3 Mbit/s, and
had 8-bit destination and source address fields, so Ethernet addresses
were not the global addresses they are today. By software convention,
the 16 bits after the destination and source address fields were a
packet type field, but, as the paper says, "different protocols use
disjoint sets of packet types", so those were packet types within a
given protocol, rather than the packet type in current Ethernet which
specifies the protocol being used.
Metcalfe left Xerox in 1979 to promote the use of personal computers and
local area networks (LANs), forming 3Com. He convinced DEC, Intel, and
Xerox to work together to promote Ethernet as a standard, the so-called
"DIX" standard, for "Digital/Intel/Xerox"; it standardized the 10
megabits/second Ethernet, with 48-bit destination and source addresses
and a global 16-bit type field. The standard was first published on
September 30, 1980. It competed with two largely proprietary systems,
token ring and ARCNET, but those soon found themselves buried under a
tidal wave of Ethernet products. In the process, 3Com became a major
company.
Twisted-pair Ethernet systems have been developed since the mid-80s,
beginning with StarLAN, but becoming widely known with 10BASE-T. These
systems replaced the coaxial cable on which early Ethernets were
deployed with a system of hubs linked with unshielded twisted pair
(UTP), ultimately replacing the CSMA/CD scheme in favor of a switched
full duplex system offering higher performance.
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