Wireless Communications in the Oil & Gas Sector

By Joaquin Segl, ENCOM Wireless Data Solutions Inc.

Part I: Ethernet

Most of us can appreciate the correlation between knowledge and success. The ability to become well-informed enables us to make stronger decisions. It can then be inferred that increasing the rate in which we receive information will lead to improvements in production. In the Oil and Gas sector, more than ever, we see the urgency of being able to remotely control and monitor our sites. The question then arises? How do can we improve communication to remote sites? Is it true that more throughputs will equal less time? Is Ethernet really the magic cure-all communication protocol? The purpose of this article is to show the myths, truths, advantages and disadvantages of both Ethernet and Serial communications and to illustrate the most effective way of implementing them.

Ethernet History

While the Ethernet terminology has permeated almost all areas of industry, we have barely scratched the surface of what this particular communication protocol is or how it works. Let's start from the beginning:

Ethernet is a frame-based computer networking technology for local area networks (LANs). The name comes from the physical concept of ether. Ethernet is based on the idea of peers on the network sending messages in what was essentially a radio system, captive inside a common wire or channel, sometimes referred to as the ether, (which is an oblique reference to the luminiferous aether through which 19th century physicists incorrectly theorized that electromagnetic radiation traveled).

In 1973, at Xerox Corporation's Palo Alto Research Center (more commonly known as PARC), researcher Bob Metcalfe designed and tested the first Ethernet network while working on a way to link Xerox's "Alto" computer to a printer; Metcalfe developed the physical method of cabling that connected devices on the Ethernet as well as the standards that governed communication on the cable. Ethernet has since become the most popular and most widely deployed network technology in the world. Many of the issues involved with Ethernet are common to many network technologies, and understanding how Ethernet addressed these issues can provide a foundation that will improve your understanding of networking in general. The basic mechanics of operation for every Ethernet network today stem from Metcalfe's original design; according to this model, communications are shared by all devices on the network over a single cable. Once a device is attached to this cable, it has the ability to communicate with any other attached device. This allows the network to expand to accommodate new devices without requiring any modification to those devices already on the network. This flexibility and connectivity is what makes Ethernet so appealing.

Ethernet Basics

Ethernet was conceived as a local area technology, with networks traditionally operating within a single building, connecting devices in close proximity. At most, Ethernet devices could have only a few hundred feet of cable between them, making it impractical to connect geographically dispersed locations. However, modern technological advancements, especially in the radio communication technology (which over the last five decades has converted itself into an extremely secure, reliable and flexible mean of communication), have increase these distances considerably, allowing Ethernet networks to span several miles. The applications of the Ethernet are endless; Interconnect projects, video monitoring, mobile connectivity and mesh-networking are now made easy by having such wireless devices connected to the Fiber-optic backbone at a fraction of the cost.

Protocols and terminology

In networking, the term protocol refers to a set of rules that govern communications. Protocols are to computers what language is to humans. Since this article is in English, to understand it you must be able to read English. Similarly, for two devices on a network to successfully communicate, they must both understand the same protocols. Ethernet follows a simple set of rules that govern its basic operation. To better understand these rules, it is important to understand the basics of Ethernet terminology.

• Segment - We refer to a single shared medium as an Ethernet segment.
• Node - Devices that attach to that segment are stations or nodes.
• Medium - Ethernet devices attach to a common medium that provides a path along which the electronic signals will travel. Historically, this medium has been coaxial copper cable, but today it is more commonly a twisted pair or fiber optic cabling or a radio device able to interpret these signals.
• Frame - The nodes communicate in short messages called frames, which are variably sized chunks of information.

Frames are analogous to sentences in human language. In English, there are rules for constructing sentences in English: We know that each sentence must contain a subject and a predicate. The Ethernet protocol specifies a set of rules for constructing frames. There are explicit minimum and maximum lengths for frames, and a set of required pieces of information that must appear in the frame. Each frame must include, for example, both a destination address and a source address, which identify the recipient and the sender of the message. The address uniquely identifies the node, just as a name identifies a particular person. No two Ethernet devices should ever have the same address.

Since all communications happen on the same wire, any information sent by one computer is received by all, even if that information was intended for just one destination. This "one speaks, all listen" property is a security weakness of shared-medium Ethernet, since a node on an Ethernet network can eavesdrop on all traffic on the wire if it so chooses. This works something like a dinner party, where all the guests talk to each other through a common medium (the air). Before speaking, each guest politely waits for the current guest to finish. If two guests start speaking at the same time, both stop and wait for short, random periods of time (measured in microseconds). The hope is that by each choosing a random period of time, both guests will not choose the same time to try to speak again, thus avoiding another collision. Exponentially increasing back-off times (determined using the truncated binary exponential backoff algorithm) are used when there is more than one failed attempt to transmit. The use of a single cable also means that the bandwidth is shared, so that network traffic can slow to a crawl when, for example, the network and nodes restart after a power failure, so if we follow the "party" analogy, it would be like having all guests at the table talking at the same time to a single person; after a few seconds he would be unable to handle all the information coming at him. This also brings another limitation of Ethernet networks: Attach too many devices to one shared segment and contention for the medium will increase. Every device may have to wait an inordinately long time before getting a chance to transmit. All this limitations forced Engineers to develop a number of network devices that alleviate these difficulties. Many of these devices are not specific to Ethernet, but play roles in other network technologies as well.

Repeaters, Bridges, Switches and Routers
As Ethernet grew, the Ethernet hub was developed to make the network more reliable and the cables easier to connect. As we mentioned before, for signal degradation and timing reasons, Ethernet segments have a restricted size which depends on the medium used. For example, 10BASE5 coax cables have a maximum length of 1,640 feet. A greater length can be obtained by using a wired Ethernet repeater, which takes the signal from one Ethernet cable and repeats it onto another cable. Other alternative would be to use of a wireless device functioning as a link to other segments in the network, effectively extending the reach of the network in areas where the topography makes it impossible or too expensive to connect. This will also alleviate the problem of cable breakage (when an Ethernet coax segment breaks, all devices on that segment are unable to communicate).

Ethernet networks faced congestion problems as they increased in size. If a large number of stations connected to the same segment and each generated a sizable amount of traffic, many stations may attempt to transmit whenever there was an opportunity. Under these circumstances, collisions would become more frequent and could begin to choke out successful transmissions, which could take inordinately large amounts of time to complete. One way to reduce congestion would be to split a single segment into multiple segments, thus creating multiple collision domains. This solution creates a different problem, as now these now separate segments are not able to share information with each other!

To alleviate problems with segmentation, Ethernet networks implemented bridges. Bridges connect two or more network segments, increasing the network diameter as a repeater does, but bridges also help regulate traffic. They can send and receive transmissions just like any other node, but they do not work the same as a normal node; one goal of the bridge is to reduce unnecessary traffic on both segments. It does this by examining the destination address of the frame before deciding how to handle it. By forwarding packets, the bridge allows any of the devices in the network to communicate. Additionally, by filtering packets when appropriate, the bridge makes it possible for station A to transmit to station B at the same time that station C transmits to station D, allowing two conversations to occur simultaneously!

Switches are the modern counterparts of bridges, functionally equivalent but offering a dedicated segment for every node on the network. Switched networks replace the shared medium of legacy Ethernet with a dedicated segment for each station. These segments connect to a switch, which acts much like an Ethernet bridge, but can connect many of these single station segments. Some switches today can support hundreds of dedicated segments. Since the only devices on the segments are the switch and the end station, the switch picks up every transmission before it reaches another node. The switch then forwards the frame over the appropriate segment, just like a bridge, but since any segment contains only a single node, the frame only reaches the intended recipient. This allows many conversations to occur simultaneously on a switched network.

Bridges can reduce congestion by allowing multiple conversations to occur on different segments simultaneously, but they have their limits in segmenting traffic as well. An important characteristic of bridges is that they forward Ethernet broadcasts to all connected segments. This behavior is necessary, as Ethernet broadcasts are destined for every node on the network, but it can pose problems for bridged networks that grow too large. When a large number of stations broadcast on a bridged network, congestion can be as bad as if all those devices were on a single segment.

Routers are advanced networking components that can divide a single network into two logically separate networks. While Ethernet broadcasts cross bridges in their search to find every node on the network, they do not cross routers, because the router forms a logical boundary for the network, (think of them as Gatekeepers), routers operate based on protocols that are independent of the specific networking technology. This allows them to easily interconnect various network technologies, both local and wide area, and has led to their widespread deployment. 

Today, Serial and the Ethernet worlds have begun to merge, it's a trend that is unlikely to stop because of the ever increasing demand for a more flexible, faster and bigger way to transport the data, that means that the Ethernet protocol is here to stay.

Wired and wireless Networks

Once we established what the Ethernet protocol is and how it works, the next question that comes to mind is where and how do we implement it? The oil & gas industry can benefit from the use of Ethernet communications in many applications like video monitoring, or when there's a need to implement a wide area network that requires a bigger throughput, or when is necessary to provide mobile connectivity to a service truck in the field. The possibilities are infinite! Wireless technologies are gaining ground fast. Both wired and wireless can claim advantages over the other, both represent viable options; let's take a closer look.

What is wireless networking?

Generally, wireless networks use the electromagnetic spectrum (radio, micro and light waves) to send data across long distances. Wireless networks carry that data from transmitters and receivers (Or, in the most advanced equipment from Transceivers) or field devices. The advantage of wireless networking is readily apparent; wireless networks are not confined to the locations of wired data jacks accessible by an underground fiber optic cable and we all know how time-consuming and expensive this process is. After hardware installation, the remaining steps in configuring either wired or wireless LANs do not differ much. Both rely on standard Internet Protocol and network operating system configuration options. From a user's perspective, wireless connections are not particularly different from any other network connection: your video cameras, and other devices all work as you would expect. But radio waves have some unexpected properties compared to Ethernet cable. For example, it's very easy to see the path that an Ethernet cable takes: locate the plug sticking out of your central computer, follow the cable to the other end and you've found it! You can also be confident that running many Ethernet cables alongside each other won't cause many problems, since the cables effectively keep their signals contained within the wire itself. But how do you know where the waves emanating from your wireless devices are going? What happens when these waves bounce off of objects in the field like buildings in an outdoor link? How can several wireless radios be used in the same area without interfering with each other? In order to build stable high and low-speed wireless links, it is important to understand how radio waves behave in the real world; many articles have been written on the subject so we won't list them here, instead let's highlight the most useful rules of thumb to plan a wireless network (WAN):

• The lower the frequency, the further it goes.
• The lower the frequency, the better it travels through and around things.
• The higher the frequency, the more data it can transport.

These three rules, simplified as they may be, are rather easy to understand and should serve us as a guide when selecting the type of wireless technology for our specific applications. The most commonly used frequencies used are the 900 MHz, the 2.4 GHz and the 5.8 GHz bands. The key to select a band (and a radio) is to follow the aforementioned rules of thumb. For example, let's suppose that we want to interconnect serial devices (RS232, RS2485, FSK copper, etc.) that are miles apart in a location with adverse climate conditions like rain or dense foliage. For this particular example we would need a radio system capable to transmit the furthest without compromising communications in the network. A quality radio in the 900 MHZ frequency, (specifically one using FHSS technology), should be able to handle the job easily.

Now, let's suppose that what we have is an Ethernet-enabled video camera with PTZ functionality transmitting full motion video and what we want to do is transmit that data to the nearest fiber node in the system. In this particular case, a 2.4 GHz or a 5.8GHz radio will be suitable for the job due to the fact that those frequencies can carry more data, but need a true Line of Sight in order to communicate without problems.

But what if I have the same video camera and because of geographical constrains I have to transmit the data to a location miles away? In this particular scenario we have the needs for both a high throughput and a long range link. Luckily for us, today's market offers radio modems that will operate in the 900 MHz band and will offer a higher processing power that, if not as big as their counterparts in the 2.4 and 5.8 bands, is more than enough to allow the full motion video and PTZ functionalities to work for us.

Summary

Ethernet and serial communications will likely coexist in the oil and gas sector for the foreseen future, both technologies will allow legacy serial devices to communicate with Ethernet products with ease. Wireless technologies have advanced to the point where we must consider them extremely secure, reliable and flexible enough to handle any application. With these options, anybody can take advantage of remote monitoring and control without sacrificing functionality.

Joaquin Segl is ENCOM Wireless Data Solution's General Manager and can be reached at joaquins@enconwireless.com or at 1800-617-3487

References

• www.encomwireless.com
• Metcalfe, Robert M. and Boggs, David R. (July 1976). "Ethernet: Distributed Packet Switching for Local Computer Networks". Communications of the ACM 19 (5): 395-405. - the original Metcalfe and Boggs paper on Ethernet
• Digital Equipment Corporation, Intel Corporation, Xerox Corporation (September, 1980). "The Ethernet: A Local Area Network". - Version 1.0 of the DIX specification
• Boggs, David R. and Mogul, Jeffrey C. and Kent, Christopher A. (1988). "Measured capacity of an Ethernet: myths and reality". SIGCOMM88 - Symposium proceedings on Communications architectures and protocols, 222-234. - on the issue of Ethernet bandwidth collapse (Full text from DEC research)
• IEEE 802.3 2002 standard
• Don Provan (1993-09-17). "Ethernet Framing". comp.sys.novell.

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