Communication in the industrial and utility sectors has evolved substantially over the last couple years, due mostly to the proliferation of Ethernet as the technology of choice for communication networks. In this editorial we will look at the evolution of different mediums for communications.
Before the use of Ethernet in the industrial and utility sectors, serial communications was the technology of choice for allowing devices to talk to one another. Although being a stable and easy to use communications method, serial does have disadvantages when used in these environments. The first and most serious disadvantage is the distance limitations involved with serial. Serial runs can extend up to 1.2 km depending on the protocol, cables, equipment and environment, however even these distances often prove too short for some applications. Also the greater the distance of the cable run, the more affected by EMI the link will become and the slower the data rates will drop. Serial does not provide the ability to create a communications network as such, not when compared to a technology such as Ethernet. Serial does not lend itself well to expansion, in that for any new device added requires cable to be laid as well as new connectors to be soldered. Also a new device added to a serial link will be placed on the end of the link in series (Thus the name serial), whilst with Ethernet a device can be plugged in at any port that it can reach and is not being used (Parallel). These cables need to then be integrated with the original cable run, compared to Ethernet where we simply need a cable with a crimped connector to plug into an Ethernet switch. Also serial cannot reach the data rates obtainable through Ethernet. Serial can only reach data rates of up to about 2Mbps (Depending on distance, cabling, equipment, protocols etc.), while Ethernet allows speeds of 10/100Mbps up to 1/10Gbps. Finally serial is highly susceptible to EMI (Electro Magnetic Interference) which can delay or corrupt data travelling on the serial links.
And so enters Ethernet. When Ethernet first came about, co-axial cabling was still used, however it has long since evolved past that point. These days the basic cabling used for Ethernet networks is Cat5/e/Cat6 cabling. Also commonly known as UTP (Unshielded Twisted Pair), STP (Shielded Twisted Pair), FTP (Foiled Twisted Pair) this cabling contains 4 pairs of wires twisted together. This twisting helps combat EMI interference, as the twisted pairs help to cancel out the interference on their counterpart. STP and FTP are both the same as UTP, however they have increased shielding to provide higher resistance to EMI.
Cat5e stands for Category 5 Enhanced cable, this defines the make up of the cable, specifically the twists as well as what Ethernet speeds it is meant for. Cat5e is supposed to be used for speeds of 10/100Mbps (Cat5 was originally for 10Mbps, but generally Cat5e is now used for both). Cat6 cabling is meant for use for speeds of 1/10Gbps. The reason for this is that Cat6 cabling has a very specific number of twists per length, and provides the correct medium for the higher data rates as well as being able to handle the higher frequency of signals travelling on the cable. These cables are commonly collectively referred to as copper cabling.
There are pros and cons to using copper cabling. The pros include ease of use and installation, as copper cabling is flexible and can be bent and handled a lot more roughly than fibre cabling. Also connectors for copper cabling are simply crimped on (Although Cat6 does require some specialised equipment when crimping due to the specificity of the number of twists per length) rather than needing soldering equipment (For serial etc) or fibre splicing machines and clean environments (For fibre optic). Copper cabling is also cheap when compared to fibre optic cabling. However, copper cabling is highly susceptible to EMI, and in areas with large machinery or medium to high voltages it can often not be feasible to use copper cabling. Finally copper cabling is limited to maximum runs of up to 100m, meaning that for longer distances more Ethernet hardware will be required.
The next option, especially in high EMI environments and/or for longer distances, is to use Fibre Optic cabling. There are two basic types of fibre optics, multimode and singlemode. Multimode cabling has a larger inner core (50 micrometers) whilst singlemode has a much thinner inner core (9 micrometers). Singlemode, with its thinner inner core, uses only a single, straight beam of light, whilst multimode can handle multiple beams. However multimode suffers more inner refraction, which in turn means that it cannot reach the distance of singlemode cabling. Multimode cabling, when used for 100Mbps Ethernet has a maximum distance of 3km, whilst singlemode allows distances of up to 90kms or even higher. When used for 1000Mbps multimode imposes a maximum distance of 500m whilst singlemode can be used for up to 70 km or higher depending on the cabling, number of splices etc. So why not use singlemode all the time? The answer is that multimode is cheaper than singlemode cabling, and even more so for the hardware needed to inject the data onto the cable (Switches, routers, etc.). The thinner inner core in singlemode requires more precise equipment; for manufacturing the fibre, as well as for splicing connectors and the equipment used to inject the data (light) onto the fibre which all adds to the cost when using singlemode fibre over multimode. Singlemode requires the use of lasers, whilst multimode can use either lasers or the cheaper LEDs for this task. Another pro to using fibre optic cabling is it is completely immune to EMI, as it uses light rather than electrical signals like copper cabling.
Fibre optic cabling is also very fragile, and cannot be bent past a certain radius (Dependant on the fibre being used and the protective covering) else the inner core can snap. Specially shielded fibre optic cable can be used for certain applications, but the shielding adds cost to the fibre, as well as making it a lot less flexible and harder to work with when installing cables.
Occasionally it is required to connect a remote device to the Ethernet network, however in these cases using fibre can often prove unfeasible due to the costs involved or available cable routes. In these cases there are other options available. Staying with the topic of physical mediums, the next choice would be to use a technology called EoVDSL (Ethernet over VDSL). This technology allows the use of single pair cabling (Such as standard telephone lines) to send Ethernet over distances of up to 4km with data-rates of up to 40 Mbps. EoVDSL has similar pros and cons to using standard copper cabling, such as cheap pricing (In fact it is even cheaper than using standard copper cabling), flexibility and ease of installation, but also a high sensitivity to EMI.
There are some cases however when physical cabling is not the most feasible options, due to factors such as the existing architecture, cost of installing the cabling etc. In these cases we can also look at using a wireless system instead. 3 basic catagories of wireless are covered here, ranging from 802.11 (Commonly know as WiFi), 802.16e (Known as WiMAX) or cellular/3G connections.
802.11 wireless is the most commonly used wireless technology. Using the correct hardware and antennas, links of up to 3km or more can be achieved. However these links require Line of Sight (An unobstructed view between antennas) and over this distance data rates will often need to be slowed down to provide a stable link. 802.11 is also susceptible to EMI as well as areas with large machinery or many buildings around, as these can cause the wireless signals to disperse or reflect back on themselves causing degradation of the signal. 802.11 uses public frequencies, meaning there is no need to license the frequencies being used. The pro to this is ease of use and less costly, however the cons include susceptibility to interference caused by other surrounding wireless links. Under good conditions 802.11 can reach data-rates of up to 54 Mbps or higher depending on the protocol being used; however this is dependant on many of the factors already discussed.
The next wireless option to look at would be 802.16e, or WiMAX. WiMAX has some key differences that set it apart from WiFi, one of the greatest of which is the distances achievable. WiMAX can create wireless coverage zones of up to 12km radius or more, and does not require line of sight like standard WiFi. However WiMAX cannot achieve the speeds that WiFi can, with a maximum data rate of around 40Mbps (dependant on surrounding factors). WiMAX also requires special licenses to use a frequency block in a given geographical location. This adds to the cost and complexity involved when setting up a wireless system using WiMAX, however the pro of using a licensed frequency block is that outside interference from other wireless systems is not a concern, and security is greatly increased by the fact that the frequency is not a public access frequency.
Finally, in cases where 802.11 or 802.16e are unfeasible due to factors such as cost, distance, terrain, existing architecture etc. a cellular link can be used instead to provide access to the Ethernet network. A cellular link would typically be used for remote access for simple functions with small data requirements, such as starting/stopping a pump at a remote overflow dam. Although data rates for a 3G connection will generally be lower than that provided by a standard wireless link, generally a high data rate will not be needed. 3G connections can be set up in any area that has cellular signal, and are generally easy to commission and maintain, however they are overall not as reliable as a 802.11/16e link due to the fact that a third party (The ISP being used) being in control. For instance if your service provider shuts down the nearby tower for maintenance the 3G link could be down the whole time they are working on the tower. 3G hardware and sim cards’ costs are generally not overly high, however a monthly running fee will be imposed due to the constant use of the link, which will be dependant on the amount of data traversing the link.
So as we can see the available Ethernet mediums have evolved to a point where a suitable solution can be found for almost any scenario. This is why initial planning of the installation of an Ethernet network (or expansions to an existing network) is so critical, including selecting the correct medium for the application. Gone are the days of serial-only communications when options were limited. However with all the new options a greater understanding of Ethernet and its use is required, as well as more in depth planning taking into account locations, budgets, environment, throughput and device availability requirements, expandability etc.
For any questions, or help and advice on planning, expanding, configuring or maintaining a critical Ethernet network, please contact H3iSquared.
Tim Craven
H3iSquared
Tel: +27 (0)11 454 6025
Email: info@h3isquared.com
Website: www.h3isquared.com