Fiber Optic Communications for the Premises
1.1 The Fundamental Problem of Communications
The subject of interest in this book is premises data communications using fiber optic cable as the transmission medium. This is at once a very specific yet very extensive topic. It is an important topic both within the context of data communications today and into the future. All, or almost all, aspects of this subject will be explored. However, it seems rather forbidding just to jump into this topic.
Rather, it is more appropriate to take a step back to the very beginning and talk about the nature of communications first. This will allow some needed terminology to be introduced. It will also lead us in a natural way to the subject of fiber optic cable as a transmission medium and to why it is attractive for premises data links.
Of course, the reader, well versed in data communications, may choose to skip past this introduction and suffer no real penalty.
The subject of communications really begins with the situation shown in Figure 1-1. Here is an entity called the Source and one called the User- located remotely from the Source. The Source generates Information and the User desires to learn what this Information is.
Figure 1-1: Source, User pair with information
Examples of this situation are everywhere prevalent. However, our attention will only be focused on the case illustrated in Figure 1-2 where the Information is a sequence of binary digits, 0's and 1's, bits. Information in this case is termed data. Information of this type is generally associated with computers, computing type devices and peripherals-equipment shown in Figure 1-3. Limiting Information to data presents no real limitation. Voice, images, indeed most other types of Information can be processed to look like data by carrying sampling and Analog-to-Digital conversion.
Figure 1-2: Representations of information
Figure 1-3: Examples of sources and users generating/desiring "data"
It is absolutely impossible in the real world for the User to obtain the Information without the chance of error. These may be caused by a variety of deleterious effects that shall be discussed in the sequel.
This means that the User wanting to learn the Information- the binary sequence- must be content in learning it to within a given fidelity. The fidelity measure usually employed is the Bit Error Rate (BER). This is just the probability that a specific generated binary digit at the Source, a bit, is received in error, opposite to what it is, at the User.
There are some real questions as to how appropriate this fidelity measure is in certain applications. Nonetheless, it is so widely employed in practice, at this point, that further discussion is not warranted.
The question then arises as to how to send the binary data stream from Source to User. A Transmission Medium is employed to transport the Information from Source to User. What is a Transmission Medium?
A Transmission Medium is some physical entity. As shown in Figure 1-4 it is located between the Source and the User and it is accessible to both. The Transmission Medium has a set of properties described by physical parameters. The set of properties exists in a quiescent state. However, at least one of these properties can be stressed or disturbed at the Source end. This is accomplished by somehow imparting energy in order to stress the property. This disturbance does not stay still, but affects the parts of the Transmission Medium around it. This disturbance then travels from the Source end to the User end. Consequently, energy imparted in creating the disturbance is thereby transferred from the Source end to the User end. Finally, this disturbance or stressed property, can be sensed at the User end. It can be measured.
Figure 1-4: Source, transmission medium, user
This propagation of a disturbance by the Transmission Medium is illustrated in Figure 1-5.
What are examples of transmission media? As with types of Information there are many.
Figure 1-5: Disturbance traveling in transmission medium
The Transmission Medium could be air with the stressed property being the air pressure sound waves. The Transmission Medium could be an electromagnetic field set up in space by the current put on an antenna, a radio or wireless system. The Transmission Medium could be a pair of electrical conductors with the stressed property being the potential difference (the voltage) between the conductors, an electrical transmission line. The Transmission Medium could be a sheet of writing paper with the stressed property being the light-dark pattern on the paper, a letter. The Transmission Medium could be a cylindrical glass tube with the stressed property being the intensity of light in the tube, a fiber optic cable.
The Source can have a disturbance to the Transmission medium generated in sympathy to the Information, that is, generate a disturbance which varies in time exactly as the Information. This encoded disturbance will then propagate to the User. The User can then sense the disturbance and decide the identity of the Information that it represents. The process of the Source generating a disturbance in sympathy with the Information and launching it into the Transmission Medium is referred to as modulation and transmission. The process of the User sensing the received disturbance and deciding what Information it represents is referred to as reception and demodulation. The device that carries out modulation and transmission will be called in this work the Transmitter. The device that carries out reception and demodulation will be called the Receiver.
The entire situation with data communications then devolves to the model illustrated in Figure 1-6. Here the Source is generating bits as Information. The User wants to learn the identity of this Information, these bits. The entities used to get the Information from the Source to User are the Transmitter, the Transmission Medium and the Receiver. The fundamental problem of communications is to choose the terminal equipment, the Transmitter and Receiver and to choose the Transmission Medium so as to satisfy the requirements for a given Source-User pair.
Figure 1-6: The model which represents the fundamental problem of communications
The fundamental problem of communications is a design problem. The combination of Transmitter, Transmission Medium and Receiver is termed the communication link. Because of the limitation placed on the Information to be a sequence of bits this combination is generally referred to as a data link. The disturbance launched into the Transmission Medium by the Transmitter is usually referred to as the input data signal. The resulting disturbance at the Receiver is termed the output data signal. In the context of our discussion the fundamental problem of communications is to design a data link appropriate for connecting a given Source-User pair.
There is no fail safe cookbook way to solve this design problem and come up with the best unique solution. While there is science here there is also art. There are always alternative solutions, each with a particular twist. The twist provides some additional attractive feature to the solution. However, the feature is really peripheral to Source-User requirements.
Most exercises in obtaining the design solution usually begin with choosing a Transmission Medium to meet the general requirements of the Source-User pair. That is, the data link design process pivots on choosing the Transmission Medium. Every Transmission Medium has constraints on its operation, on its performance. It is these constraints that really decide which Transmission Medium will be employed for the data link design. It will be worthwhile discussing these constraints.
1.2 The Transmission Medium- Attenuation Constraints
Have a Transmitter launch a disturbance into a Transmission Medium. Provide an input data signal to a Transmission Medium. As it propagates down the Transmission Medium to the Receiver its amplitude will decrease, getting weaker and weaker. The disturbance, the input data signal, is said to suffer attenuation. The situation is exactly as shown in Figure 1-7.
One immediate question that can be raised is why does attenuation occur? There are several reasons. It will be worthwhile pointing out and describing two of them; spatial dispersion and loss due to heat.
Spatial dispersion can best be considered by revisiting Figure 1-7. This illustrates a one-dimensional propagation of the disturbance. However, often this disturbance may propagate in two or even three dimensions. The User/Receiver may be located in a small solid angle relative to the Source/Transmitter. The received disturbance, the output data signal, appears attenuated relative to the transmitted disturbance because in fact, it represents only a small fraction of the overall energy imparted in the disturbance when it was launched. This is exactly the situation with free space propagation of waves through an electromagnetic field transmission medium. For example, this occurs in any sort of radio transmission.
Figure 1-7: Input data signal attenuating as it propagates down a transmission medium
As for loss due to heat, this refers to the basic interaction of the disturbance with the material from which the Transmission Medium is comprised. As the disturbance propagates, a portion of the energy is transferred into the Transmission Medium and heats it. For a mechanical analogy to this consider rolling a ball down a cement lane. The ball is the disturbance launched into the lane that represents the Transmission Medium. As the ball rolls along it encounters friction. It loses part of its kinetic energy to heating the cement lane. The ball begins to slow down. The disturbance gets attenuated. This is the situation with using the potential difference between a pair of electrical conductors as the Transmission Medium.
Attenuation increases with the distance through the Transmission Medium. In fact, the amplitude attenuation is measured in dB/km. As propagation continues attenuation increases. Ultimately, the propagating signal is attenuated until it is at some minimal, detectable, level. That is, the signal is attenuated until it can just be sensed by the Receiver- in the presence of whatever interference is expected. The distance at which the signal reaches this minimal level could be quite significant. The Transmission Medium has to be able to deliver at least the minimal detectable level of output signal to the Receiver by the User. If it can not, communications between Source and User really can not take place.
There are some tricks to getting around this. Suppose the disturbance has been attenuated to the minimal detectable level yet it has still not arrived at the Receiver/User. The output signal at this location can then be regenerated. The signal can be boosted back up to its original energy level. It can be repeated and then continue to propagate on its way to the Receiver/User. This is shown in Figure 1-8.
Figure 1-8: Regenerating and repeating an attenuated signal in order to reach the user
Nonetheless, the attenuation characteristics are an item of significant consequence. The Transmission Medium selected in the design must have its attenuation characteristics matched to the Source-User separation. The lower the attenuation in dB/km the greater advantage a Transmission Medium has.
1.3 The Transmission Medium - Interference Constraints
Have a Transmitter launch a disturbance into a Transmission Medium. Provide an input data signal to a Transmission Medium. As it propagates down the Transmission Medium it will encounter all sorts of deleterious effects which are termed noise or interference. In the simplest example, that of one person speaking to another person, what we refer to as noise really is what we commonly understand noise to be.
What is noise/interference? It is some extraneous signal that is usually generated outside of the Transmission Medium. Somehow it gets inside of the Transmission Medium. It realizes its effect usually by adding itself to the propagating signal. Though, sometimes it may multiply the propagating signal. The term noise is generally used when this extraneous signal appears to have random amplitude parameters- like background static in AM radio. The term interference is used when this extraneous signal has a more deterministic structure-like 60-cycle hum on a TV set.
In any case, when the Receiver obtains the output signal it must make its decision about what Information it represents in the presence of this noise/interference. It must demodulate the output signal in the presence of noise/interference.
Noise/interference may originate from a variety of sources. Noise/interference may come from the signals generated by equipment located near the transmitter/transmission medium/receiver. This may be equipment that has nothing at all to do with the data link. Such equipment may be motors or air conditioners or automated tools. Noise/interference may come from atmospheric effects. It may arise from using multiple electrical grounds. Noise/interference may be generated by active circuitry in the transmitter and/or receiver. It may come from the operation of other data links.
In obtaining the design solution noise/interference makes its effect best known through the Bit Error Rate (BER). The level of noise/interference drives the BER. Of course, this can be countered by having the Transmitter inject a stronger input signal. It can be countered by having the Receiver be able to detect lower minimal level output signals. But, this comes with greater expense. It does not hide the fact that there is concern with noise/interference because of its impact on the BER.
The susceptibility to noise/interference varies from Transmission Medium to Transmission Medium. Consequently, during the design process attention has to be paid to the Source-User pair. Attention has to be directed to the application underlying the communication needed by this pair and to the BER required by this application.
The Transmission Medium must then be picked that has a noise/interference level capable of delivering the required BER.
1.4 The Transmission Medium- Bandwidth Constraints
Go back and consider the model illustrated in Figure 1-6. Suppose the input signal that the Transmitter sends into the Transmission Medium is the simple cosinusoidal signal of amplitude '1' at frequency 'fo' Hz. The output signal response to this at the Receiver is designated 'T (fo).' Now consider the cosinusoidal test input signal frequency, fo to be varied from 0 Hz on up to ¥. The resulting output signal as a function of frequency is T (fo) or suppressing the subscript- it is T (f). This is referred to as the transfer function of the Transmission Medium. Generally, the ordinate target value 'T (f)' for a given frequency 'f' is referred to as the transfer function gain- actually it is a loss- and is expressed logarithmically in dB relative to the amplitude '1' of the input signal.
One example transfer function is illustrated in Figure 1-9. This is merely an example transfer function. It is not to be understood as to be typical in any sense. It is just an example. However, it does illustrate a feature that is common in the transfer function of any Transmission Medium that can actually be obtained in the real, physical, world. The transfer function rolls off with frequency. The transfer function shown here oscillates, but the maximum value of its oscillation becomes less and less. Yet, the transfer function itself never really rolls off and becomes dead flat zero beyond a certain frequency. This roll off with frequency means that the Transmission Medium attenuates the cosinusoidal signals of the higher frequencies that are given to it as inputs. The energy of these higher frequency signals is somehow lost, usually as heat, in traversing the Transmission Medium. The greater the distance through the Transmission Medium, the more high frequency signals get attenuated. This is a consequence of the greater interaction between the propagating signals and the material comprising the Transmission Medium.
Figure 1-9: Example transfer function of a transmission medium
This roll off feature of the transfer function is present in every Transmission Medium regardless of how it is derived. It is present in sound waves. It is present in conductors. It is present in fiber optic cables. It is present in a phonograph record or tape. It is even present in a sheet of writing paper.
The transfer function shown rolls off with frequency. However, most of its activity, most of its area, most of its mass, most of its spread, seems to be below a certain given frequency. In this example it looks like the frequency 'F.' The frequency spread of the transfer function is referred to as its bandwidth. Of course, from what was mentioned above bandwidth decreases with the propagation distance through the Transmission Medium.
Because frequency spread is very subjective the measure of bandwidth is also subjective. When you are discussing communications with someone and they mention bandwidth it isn't such a bad idea to ask exactly how they are defining it. There is a definition in the Glossary in the back of this book. However, it is only one such definition. There are many. For example, there is the 3 dB bandwidth, mean square bandwidth, first lobe bandwidth, brick wall bandwidth and on and on. In a study carried out seventeen years ago the author easily identified over twenty-five separate definitions of bandwidth. All have validity. Whether one is meaningful or not depends upon the context, actually the application, in which it is being used. One definition may be appropriate for describing satellite communication links and another more appropriate for an FCC official considering the request for a broadcast AM radio license.
In any case, a Transmission Medium has a transfer function and the frequency spread of this transfer function is measured by the bandwidth. The bandwidth parameter has implications with respect to the performance of the data link being designed.
In order to see this consider the illustration shown in Figure 1-10. Here the Source is generating data, '0's and '1's every T seconds. Let T= 1/R, in which case the Source is generating data at R bits per second of BPS. To send this data to the User the Transmitter is generating either a positive or negative impulse every T seconds. What is an impulse? It is an infinitesimally narrow pulse, but it is infinitely high so that it has energy of '1.'
Now what comes out at the Receiver in response to the positive impulse sent at time zero to represent the binary data bit '1.' An example result is illustrated in Figure 1-11. Notice that this response out of the Transmission Medium to the input impulse is a pulse spread out in time with its center at t seconds where t is not equal to 0 seconds. This output is only an example. It can not even be called typical. However, it does indicate a property that is typical of all output signals received from the Transmission Medium. The time spreading of the output pulse is this common property. It is called time dispersion. It is a result of the finite bandwidth of the Transmission Medium. To be exact, it is due to the fact that the transfer function of the Transmission Medium- and any Transmission Medium- attenuates the higher signals.
Figure 1-10: Binary data from source represented by impulse train put into transmission medium by transmitter.
Impulses are T seconds apart.
Look closely at the output signal pulse shown in Figure 1-11. Because it is spread in time it is going to interfere with the output pulses due to input data signals which will come after it. These are not shown in the illustration, but the implication should be clear. Likewise, these subsequent data signals will generate output pulses that will also be spread in time. Each will also interfere with the pulses coming after it and also coming before it. This type of interference is called intersymbol interference. It is not just a consequence of the input signals being impulses. An input signal, of finite duration, and of any shape will generate an output signal with time dispersion.
As the data rate from the Source increases the intersymbol interference problem gets worse and worse. Output pulses with time dispersion get squeezed next to one another. The growing level of intersymbol interference makes it harder and harder for the Receiver to demodulate these signals.
To some extent the intersymbol interference can be undone by sophisticated signal processing in the Receiver. This usually goes under the name of equalization. However, in many cases equalization still can not deliver the data from the Receiver with the BER required by the Source-User pair. In other cases, the data being generated by the Source, say R BPS, is so high that an equalizer can not be obtained fast enough to keep up with the output signals.
Figure 1-11: Input signal is positive impulse. Resulting output signal shows time dispersion
In considering the data link design task the first line of defense against time dispersion and intersymbol interference lies in the proper selection of the Transmission Medium. The larger the bandwidth of the Transmission Medium the fewer high frequency components will be attenuated during propagation and the smaller the time dispersion. As a result, there will be less interference between different output pulses. Make no mistake. Intersymbol interference will not disappear. It is just that it will be lessened and made more tolerable as the bandwidth gets larger. In particular, to lessen intersymbol interference the bandwidth of the Transmission Medium must get larger in relation to the Source's generated bit rate, R BPS.
The Transmission Medium must be selected to accommodate the bit rate generated by the Source. This is a critical step in the data link design effort. The Transmission Medium must have sufficient bandwidth so that it will generate tolerable intersymbol interference at the Receiver. This means selecting a Transmission Medium that has a bandwidth that is some multiple of the bit rate, R. A number of rules of thumb are often used to do this. However, they are too specific and not worth discussing at this point especially since the measure of bandwidth is subjective.
The important point is that as the data rate requirement, R, goes up, this limits the selection of Transmission Medium candidates. It limits the selection to those with bandwidths matched to it.
The information technology explosion in the world has made this selection task ever more challenging. Continuously, PCs are becoming more powerful. More complex applications programs can be run and are finding their way into easily usable software. As a result, the Source bit rate requirement is growing at an order of magnitude every few years. To put this in perspective, consider that just ten years ago a Transmission Medium would be quite acceptable if it had a bandwidth matched to a Source bit rate of 9,600 BPS. This Source bit rate was typical of that generated by most data equipment applications. Today with the growing demand for video services and the plethora of graphics in computer applications the demand more often than not is for a Transmission Medium with a bandwidth matched to Source bit rates well upwards of 1 MBPS, possibly 1 GBPS.
1.5 the Transmission Medium - Cost Constraints
You may be able to find the ideal Transmission Medium relative to attenuation, interference and bandwidth. But, you still may not be able to select it as part of the solution to the data link design problem. Why? It simply costs too much. The expense that it presents is beyond the budget allowed for the Source-User communications.
This isn't anything new or revolutionary. Money doesn't drive the world. But, it sure has a tremendous influence on the ultimate choice of solution to any problem based in technology. This was true one hundred years ago and true today.
1.6 Attractiveness of Fiber Optic Cable As A Premises Transmission Medium
Considering this discussion of the constraints on the Transmission Medium we are naturally led to fiber optic cable as an attractive choice for the data link design. Why? When compared with other candidates for the Transmission Medium commonly employed today, there is no comparison when it comes to attenuation, interference and bandwidth.
Illustrations can tell the story best here.
Take a look at Figure 1-12 first. This shows the attenuation of several candidates for the Transmission Medium. All are based on electromagnetic technology and all are in common use today. In other words none are laboratory curiosity items. Attenuation in dB/km is shown as a function of frequency. Here frequency would more or less refer to the data rate from the Source or equivalently the signaling rate from the Transmitter. Attenuation of an electromagnetic Transmission Medium increases with frequency due to effects on an atomic level, which are well beyond this discussion. The attenuation curves of different Transmission Medium candidates are shown as shaded strips because the exact attenuation tends to vary from sample to sample as well as manufacturer to manufacturer. However, the general trend can easily be grasped. The attenuation of the two fiber optic cable types, multi-mode and single mode, are much, much, less than the other candidates. What is more their dependence upon frequency is even flat over quite a large range. This makes designing data links with them simpler. You need not be concerned with the change in attenuation every time you decide to tweak the data rate.
To be absolutely clear the fiber optic cable attenuation shown in this figure is for fiber optic cable fabricated totally from glass (silica). That is, it has a glass core and glass cladding. There is also fiber optic cable fabricated totally from plastic and fiber optic cable having a glass-silica core with a plastic cladding (PCS- Plastic Clad Silica). It is the pure glass- silica based fiber optic cable that has the low attenuation properties. The plastic based fiber optic cable has much higher attenuation, well above coaxial cable. But, it does have some attractive features that will be discussed in a later chapter.
Figure 1-12: Attenuation versus frequency (Courtesy of Siecor Corporation)
You get the idea. When it comes to considering the attenuation issue then fiber optic cable is the unchallenged selection for the Transmission Medium.
Fiber optic cable is fabricated from glass or plastic. Because of the nature of this material it allows signals transmitted through fiber optic cable to be immune from electromagnetic based forms of noise and interference. This includes power transients that may arise from
lightning strikes. It includes noise arising from ground loops. In fact, fiber optic cable provides nearly perfect isolation between multiple grounds. Noise can still affect a fiber optic data link; especially, if it is generated in the receiver or transmitter electronic circuitry. However, the effect of noise and interference originating outside the link is far less than with competing choices for the Transmission Medium, candidates like shielded or unshielded twisted pair cable or coaxial cable or free space microwave radio.
Take a look at Figure 1-13. This illustrates the variation of the bandwidth of fiber optic cable with its length. Remember bandwidth goes down with increasing length. But, that is not the concern here. Notice that at up to 4 km the bandwidth is always above 10 MHz. This implies that a fiber optic link can support data rates of many 10's of MBPS over these distances. This can be done without having to have the Transmitter resort to any sophisticated bandwidth efficient modulation schemes. Of course, people talk about fiber optic cable being able to support Giga Bits Per Second (1 Billion Bits Per Second - GBPS) and even Tera Bits Per Second (1 Trillion Bits Per Second). But, remember this depends upon distance and may often require multiple repeaters.
Figure 1-13: Bandwidth of fiber optic cable vs. length (from Fiber Optic Communications, Joseph C. Palais)
To put this in perspective, unshielded twisted pair copper cable over this distance can support 0-to-100 MBPS. Coaxial cable this distance can support about 20 MBPS. When it comes to the bandwidth issue fiber optic cable is the unquestioned most attractive candidate for the Transmission Medium.
Fiber optic cable is the unchallenged winner in the Transmission Medium sweepstakes when it comes to attenuation, interference and bandwidth. It even has some additional features that are attractive in comparing it to other candidates mentioned. It is the most secure. Tampering with fiber optic with transmissions through fiber optic cable is very difficult to do. It can be detected far more easily than with the other metallic based candidates for Transmission Medium let alone free space propagation candidates. The small size of fiber optic cables allows it to be placed in ducting that is too small for metallic cable. This allows room for substantial growth in capacity if needed. It's easier to put more fiber optic cables in the same duct. This is brought out in the photograph provided in Figure 1-14. Finally, fiber optic cables do not conduct electricity- they are glass or plastic therefore safer. They are particularly suitable for use in areas that might have spark or electrical hazard restrictions. This is especially true of places that may endanger the well being of a technician working with a long segment of metallic cable instead of a fiber.
Figure 1-14: Size comparison: coaxial cable and fiber optic cable (Courtesy of AT&T Archives)
Undoubtedly now you are saying So fiber optic cable is the winner when it comes to attenuation, interference and bandwidth. But, doesn't high cost throw it out? Isn't it very expensive and wasn't this the ultimate driver for the Transmission Medium selection?
It is true when comparing fiber optic cable to other candidates it is not as attractive from a cost point of view. However, the situation is getting better year by year. In particular take a look at Figure1-15. This illustrates the cost trends for different candidates for the Transmission Medium. Cost trends are graphed for the period 1990 through 1995. Notice the decrease for fiber optic cable. In the years since it has decreased even further. Of course, this is for glass based fiber optic cable. Plastic fiber optic cable has a much lower cost. In any case from a cost point of view fiber optic cable is and will probably continue to be more expensive than the cheapest, voice grade, unshielded twisted pair cable. However, its cost is merging with the other candidates. Certainly, the really minor cost disadvantage is greatly outweighed with the significant performance advantages.
Figure 1-15: Cost trends of common transmission media
Putting this altogether there is no argument. Fiber optic cable should be the Transmission Medium of choice when considering data links in new facilities where no other Transmission Medium candidate exists.
There is and will continue to be tremendous activity with respect to carrying out data communications in the wide area network or long haul environment. This is the environment of the long distance carrier, the Telephone Company.
However, there is even greater activity with respect to the implementation of data links in the premises or local area environment. This is the environment of the office building, Small Office Home Office (SOHO), the factory and the campus. As PC's have proliferated throughout all premise type facilities the need for data communications links has followed. Installation of premises data links be they point-to-point, multi-point, part of a Local Area Network (LAN) or whatever is a major agenda item for many business concerns. The case has been made above for fiber optic cable being the Transmission Medium of choice for these links. This is why it is the subject of interest in this book.
This book has been written so that each chapter stands on its own. There is no need to read the chapters in order. There may be occasionally cross-references from one chapter to another. However, the information can easily be gleaned without going back to the very beginning.
A brief summary of the sequel is as follows:
Chapter 2 - A careful review is given to the details of a fiber optic data link for the premise environment. The possibilities for and properties of fiber optic cable are discussed. Candidates for the Transmitter and Receiver are considered. Connectors and splices are introduced. The performance of the data link is analyzed with a careful look at the loss budget.
Chapter 3 - Consideration is given to exploiting the large bandwidth presented by fiber optic cable to support the data communications of multiple users - multiple Source - User pairs. That is, how to carve out multiple fiber optic data links from a single fiber optic cable in the premises environment. This is accomplished by multiplexing. Both Time Division Multiplexing (TDM) and Wavelength Division Multiplexing (WDM) are discussed.
Chapter 4 - Discussion focuses on the Local Area Network (LAN). Fiber optic data links are joined with LAN's. Using LAN architectures carries out a great deal of premise data communication. The delay properties of fiber optic cable can be exploited to extend the distance coverage of a LAN. A fiber optic data link can be used to connect remote stations to a LAN hub. Stations that may be too far from a LAN to be connected by a copper cable may possibly be joined by a fiber optic data link.
Chapter 5 - The manufacturing environment is considered. In particular the environment presented by heavy industry that always has a plethora of high (electric) powered tools in use. The manufacturing environment presents a situation where premises data communications may have to be carried out with intense noise and interference present. The interference protection properties of a fiber optic data link are considered in this environment. In particular, consideration is given to the types of data links and networking architectures generally found in the manufacturing environment. The discussion centers on how these links and architectures can exploit the interference protection properties of a fiber optic data link.
Chapter 6 - Discussion centers on fiber optic products that can be used to serve serial data communications.
Chapter 7 - Standards that cover the use of fiber optic data links within premises networks are enumerated. Organization from which they can be ordered, in full, are provided.
Chapter 8 - A glossary that covers the subject of fiber optic data communications. It provides terminology specifically covered within this book. However, it goes further and provides terminology that may not be used here but may be encountered within a broader view of the interest area or within communications in general.