Industrial Ethernet

INTRODUCTION

• During the mid-seventies, Xerox Corporation (Palo Alto) developed the Ethernet network concept, based on work done by researchers at the University of Hawaii.
• The University’s ALOHA network was setup using radio broadcasts to connect sites on the islands. This was colloquially known as their ‘Ethernet’ since it used the ‘ether’ as the transmission medium and created a network between the sites.

The philosophy:

• Any station wanting to broadcast would do so immediately.
• The receiving station then had a responsibility to acknowledge the message, advising the original transmitting station of a successful reception of the original message.
• This primitive system did not rely on any detection of collisions (two radio stations transmitting at the same time) but depended on an acknowledgment within a predefined time.
• The initial Xerox system was so successful that it was soon applied to other sites, typically connecting office equipment to shared resources such as printers and large computers acting as repositories of large databases.
• In 1983, the IEEE issued the 802.3 standard for carrier sense multiple access/collision detect (CSMA/CD) LANs based on the Ethernet standard.

By: Mr. Suthagar S / AP / ECE/ Kongu Engineering College

A Perspective of IEEE 802 Standards in Network Communication

Logical

Link

Control

(LLC)

Media

Access

Control

(MAC)

802.2

802.3

802.4

802.5

802.12

802.1 applies

to both.

By: Mr. Suthagar S / AP / ECE/ Kongu Engineering College

By: Mr. Suthagar S / AP / ECE/ Kongu Engineering College

Industrial Ethernet

By: Mr. Suthagar S / AP / ECE/ Kongu Engineering College

Industrial Ethernet

INTRODUCTION

Early Ethernet (of the 10 mbps variety):

• It uses the CSMA/CD access method.
• This gives a system that can operate with little delay, if lightly loaded, but access to the medium can become very slow if the network is heavily loaded.
• Ethernet network interface cards are relatively cheap and produced in vast quantities.
• Ethernet has, in fact, become the most widely used networking standard.
• However, because of its probabilistic access mechanism, there is no guarantee of message transfer and messages cannot be prioritized.

Modern Ethernet systems (10 gigabit Ethernet):

• It is commercially available since the middle of 2002.
• Ethernet has also been modified for industrial use and as such, has made vast inroads into the process control environment.

By: Mr. Suthagar S / AP / ECE/ Kongu Engineering College

Industrial Ethernet

10 Mbps Ethernet

• The IEEE 802.3 standard (also known as ISO 8802.3) defines a range of media types that can be used for a network based on this standard such as coaxial cable, twisted pair cable and fiber optic cable.

It supports various cable media and transmission rates at 10 Mbps, such as:

• 10Base2 – thin wire coaxial cable (6.3 mm/0.25 inch diameter), 10 Mbps baseband operation, bus topology.

​

• 10Base5 – thick wire coaxial cable (13 mm/0.5 inch diameter), 10 Mbps baseband operation, bus topology.

​

• 10BaseT – unscreened twisted pair cable (0.4 to 0.6 mm conductor diameter), 10 Mbps baseband operation, hub topology.

​

• 10BaseF – optical fiber cables, 10 Mbps, 10 Mbps baseband operation, point-to-point topology.

By: Mr. Suthagar S / AP / ECE/ Kongu Engineering College

Industrial Ethernet

10 Mbps Ethernet

10Base5:

• This is the original coaxial cable system and is also called ‘thicknet’.
• The coaxial cable (50-ohm characteristic impedance) is yellow or orange in color.
• The naming convention for 10Base5 means 10 Mbps, baseband signaling on a cable that will support 500-meter (1640 feet) segment lengths.
• The cable is difficult to work with, and cannot normally be taken to the node directly.
• Instead, it is laid in a cabling tray and the transceiver electronics (medium attachment unit or MAU) are installed directly on the cable.
• From there, an intermediate cable, known as an attachment unit interface (AUI) cable is used to connect to the NIC.
• This cable can be a maximum of 50 meters (164 feet) long, compensating for the lack of flexibility of placement of the coaxial cable.
• The AUI cable consists of five individually shielded pairs – two each (control and data) for both transmit and receive, plus one for power.

​

By: Mr. Suthagar S / AP / ECE/ Kongu Engineering College

Industrial Ethernet

10 Mbps Ethernet

10Base5:

• Cutting the cable and inserting N connectors and a coaxial T or more commonly by using a ‘bee sting’ or ‘vampire’ tap can make the MAU connection to the cable.
• The vampire tap is a mechanical connection that clamps directly over the cable.
• Electrical connection is made via a probe that connects to the center conductor and sharp teeth that physically puncture the cable sheath to connect to the braid.
• The location of the connection is important to avoid multiple electrical reflections on the cable, and the cable is marked every 2.5 meters (8 feet) with a black or brown ring to indicate where a tap should be placed.
• Fan-out boxes can be used if there are a number of nodes for connection, allowing a single tap to feed each node as though it was individually connected.

​

By: Mr. Suthagar S / AP / ECE/ Kongu Engineering College

�Industrial Ethernet� 10Base5 Ethernet component

By: Mr. Suthagar S / AP / ECE/ Kongu Engineering College

Industrial Ethernet

10 Mbps Ethernet

10Base5:

• The connection at either end of the AUI cable is made through a 25-pin D connector with a slide latch, often called a DIX connector after the original consortium.

There are certain requirements if this cable architecture is used in a network. These include:

• Segments must be less than 500 meters (1640 feet) in length to avoid signal attenuation problems.

• Not more than 100 taps on each segment.

• Taps must be placed at integer multiples of 2.5 meters (8 feet).

• The cable must be terminated with a 50-ohm terminator at each end.

• It must not be bent at a radius exceeding 25.4 cm or 10 inches.

• One end of the cable shield must be earthed.

By: Mr. Suthagar S / AP / ECE/ Kongu Engineering College

�Industrial Ethernet� 10Base5 Ethernet segment

By: Mr. Suthagar S / AP / ECE/ Kongu Engineering College

Industrial Ethernet

10 Mbps Ethernet

10Base5:

• Note that when MAU and AUI cable are used, the on board transceiver on the NIC is

not used.

• Rather, there is a transceiver in the MAU and this is fed with power from the NIC via the AUI cable.
• Since the transceiver is remote from the NIC, the node needs to be aware that the termination can detect collisions if they occur.
• A signal quality error (SQE), or heartbeat test function in the MAU performs this confirmation.
• The SQE signal is sent from the MAU to the node on detecting a collision on the bus.
• However, on completion of every frame transmission by the MAU, the SQE signal is asserted to ensure that the circuitry remains active, and that collisions can be detected.
• The SQE pulses occur during the 96-bit inter-frame gap between packets but they are recognized by the NIC and are not confused with a collision.
• Not all components support SQE test and mixing those that do with those that do not or could not cause problems.
• If, for example, an MAU is connected to a repeater, the SQE function on that MAU needs to be turned off.
• If not, the repeater will mistakenly see the SQE signal as a collision, and respond with a jam signal.
• This is not easily detectable and can radically slow down a network.

By: Mr. Suthagar S / AP / ECE/ Kongu Engineering College

Industrial Ethernet

10 Mbps Ethernet

10Base2:

• The other type of coax-based Ethernet network is 10Base2, often referred to as ‘thinnet’ or ‘thinwire Ethernet’.
• It uses type RG-58 A/U or C/U cable with a 50-ohm characteristic impedance and 5 mm diameter.
• The cable is normally connected to the NICs in the nodes by means of a BNC T-piece connector.

Connectivity requirements include:

• It must be terminated at each end with a 50-ohm terminator

• The maximum length of a cable segment is 185 meters (600 feet) and not 200 meters (650 feet)

• Not more than 30 transceivers can be connected to any one segment

• There must be a minimum spacing of 0.5 meters (1.6 feet) between nodes

• It may not be used as a link segment between two ‘thicknet’ segments

• The minimum bend radius is 5 cm (2 inches)

• The maximum distance between the medium and the transceiver is 4 inches; this is taken up by the dimensions of the T connector and the pc board tracks, which means that no drop cable may be used – the BNC T-piece has to be located on the front panel of the nic.

By: Mr. Suthagar S / AP / ECE/ Kongu Engineering College

�Industrial Ethernet� 10Base2 Ethernet segment

By: Mr. Suthagar S / AP / ECE/ Kongu Engineering College

Industrial Ethernet

10 Mbps Ethernet

10BaseT:

• 10BaseT uses AWG24 unshielded twisted pair (UTP) cable for connection to the node.
• The physical topology of the standard is a star, with nodes connected to a hub.
• The cable can be category 3 (Cat3) UTP, although that does not support the faster versions of
• Ethernet.

The node cable (hub to node):

• Has a maximum length of 100 meters (328 feet),

• Consists of four pairs of which only two pairs are used (one for receive and one for transmit) and

• Is connected via RJ-45 plugs.

​

• The hub can be considered as a bus internally (any signal input on a given port are reflected as outputs on all other ports), and so the topology is a logical bus topology although it physically resembles a star (hub) topology.
• The following figure shows schematically how the hub interconnects the 10BaseT nodes.
• Collisions are detected by the NIC and so the hub must retransmit an input signal on all output pairs, so that each NIC can also receive its own transmitted signal.
• The electronics in the hub must ensure that the stronger retransmitted signal does not interfere with the weaker input signal.
• The effect is known as far end cross-talk (FEXT), and it is handled by special adaptive cross-talk echo cancellation circuits.

By: Mr. Suthagar S / AP / ECE/ Kongu Engineering College

�Industrial Ethernet� 10Base2 Ethernet segment

By: Mr. Suthagar S / AP / ECE/ Kongu Engineering College

Industrial Ethernet

10 Mbps Ethernet

10BaseF: (10BaseFL, 10BaseFP & 10BaseFB)

10BaseFL

• The fiber link segment standard is basically a 2 km (1.2 miles) upgrade to the existing fiber optic inter repeater link (FOIRL) standard.
• The original FOIRL as specified in the 802.3 standard was limited to a 1-km (0.6-mile) fiber link between two repeaters, with a maximum length of 2.5-km (1.5 miles) if there are five segments in the link.
• Note that this is a link between two repeaters in a network, and cannot have any nodes connected to it.

By: Mr. Suthagar S / AP / ECE/ Kongu Engineering College

�Industrial Ethernet� 10BaseFL Ethernet segment

By: Mr. Suthagar S / AP / ECE/ Kongu Engineering College

�Industrial Ethernet� IEEE 802.3 MAC frameformat

By: Mr. Suthagar S / AP / ECE/ Kongu Engineering College

�Industrial Ethernet� Differernce between 802.3 and Ethernet V2

By: Mr. Suthagar S / AP / ECE/ Kongu Engineering College