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Daanet’s DaaPedia knowledgebase focuses on Industrial Ethernet

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article image Industrial Ethernet

Daanet ’s DaaPedia knowledgebase provides more information on Industrial Ethernet. There is an unmistakable trend towards the adoption of Ethernet as the preferred industrial network. Ethernet is adopted widely by vendors, and the traditional devices such as PLCs, HMIs and computers are being joined by IO, voice, video and smart sensors.

Ethernet is a field rich in jargon however, and here we address the 5 most frequently asked questions regarding Industrial Ethernet, with reference to the Hirschmann range of Industrial Ethernet network components.

What is Industrial Ethernet?

Ethernet is a data communications method using specified media, electrical signals, addressing and data packet structure. It has long been used in the commercial sector for office networks.

Industrial Ethernet recognises that the environment of factories, transport routes (particularly tunnels), and other infrastructure (airports, water treatment etc) introduces challenges for which commercially rated equipment is just not suited.

Extremes of temperature (as well as changing temperature), vibration, shock, EMI and even dirt and moisture are all hazards requiring hardened network components for reliable network performance. The network topology too is different, with the industrial network characterised by a number of switches distributed around the plant being close to the end devices.

By comparison, office networks tend to have banks of centralised switches in air-conditioned rooms and long individual cables to every user node. This structure is typically repeated on every level of the building.

Consequently, an industrial network should be designed by someone specialising in industrial not commercial networks who understands the differences, including the different levels of performance required in a production environment where even very short network outages can have significant impacts.

Hub / Switch / Router / Repeater / Transceiver– what is the difference?

As a general rule, network needs are met by a switch. As well as full-duplex capability (each port can speak and listen at the same time) and their provision of multiple network ports, switches actively control the delivery of data in an optimised manner through their learned address table.

This implies a message received on any port is retransmitted only to the correct destination port. Switches such as Hirschmann’s compact OpenRail series can provide up to 24 ports including fibre in a single switch, with features such as Gigabit uplink, HiPER-Ring redundancy, port mirroring (for data frame diagnosis) and dual power supplies.

Hubs, also called repeaters, operate strictly in half-duplex, and retransmit every data message to every port. These limitations can reduce network performance compared to a switch, and hubs are rarely used.

The performance of an existing network carrying more than a light loading could be improved significantly by the replacement of hubs with switches. Routers are higher level devices, used to separate large networks into smaller ones (subnets), or to provide an interface between different networks.

This enhances network performance by segregating traffic (especially broadcasts and multicasts), and providing more flexibility in network address allocations. Configuration of a router generally requires more specialised knowledge, however many networks have no need for a router at all.

For example, a factory with a number of interconnected PLCs and computers, with no need for connection to the internet or the office network will likely need only a few switches. Hirschmann have two router products, the rack mounted MACH4000, and the modular PowerMICE.

Hardware Firewalls like the Hirschmann Eagle mGuard are effectively two port routers, one port for the trusted side and one port for the untrusted side. Transceivers are a special case where the media changes; for example, copper to fibre, or where the standard changes; for example, from Ethernet to DeviceNet.

What is the difference between a managed switch and an unmanaged switch?

Managed switches provide a range of user-configurable features to add control and security to your network. Port security (to dedicate a port’s use), Quality of Service (QoS) to prioritise say a voice port over a programming port on a fully loaded network, and redundancy are some examples of these features.

Unmanaged switches such as the Hirschmann SPIDER range provide automatic configuration to correctly accommodate duplex, data rate and cable connection for most instances, and for the end point of a network in a switchboard, this is often sufficient.

For networks supporting important production requirements, a managed switch is recommended for its ability to provide better data contouring, and for the enhanced diagnostics capability to reduce downtime.

What media should be used?

Copper cable has a maximum segment length between devices of just 100m. Any longer segment will almost definitely require a fibre optic cable for reliable performance. Generally, Category 5 UTP (Unshielded Twisted Pair) is accepted as a reliable choice in copper, and this will support Gigabit Ethernet.

Shielded Twisted Pair is gaining use, and should be considered in a high EMI environment. (The choice of switch should not be overlooked in such surroundings, the Hirschmann MACH1000 is one of the range of switches with approvals in place recognising its extreme tolerance to EMI/RFI).

Fibre Optic cable is immune to EMI/RFI and is categorised as multi-mode or single-mode, the latter providing higher segment length capability. Cable sizes also have a few variances, and choices relate to the cable length and data rate required.

There are numerous fibre optic connectors available, Hirschmann limit their use to only two; the MICE family use SC type, while the plug-in SFP modules use LC type connectors.

Which cable to use, straight or cross-over?

It generally doesn’t matter that which cable should be used. Most switches feature an auto-crossing feature to adapt to the cable installed.

Before this feature was common, a straight cable was required between a switch (or router) and a host (say a PC), and a cross-over cable was used for uplink connections (that is, between switches).

One exception to this rule is some ring redundancy networks (such as Hirschmann HiPER-Ring) which if built from copper, requires the use of cross-over cables (as well as auto-negotiation disabled).

How to differentiate between a straight and cross-over cable?

Hold the two ends of the cables with the conductors vertical. The conductor colours are visible through the transparent shell; a straight cable has the same connections at each end, while the cross-over cable is different each end.

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