WiMax Operator's Manual

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CHAPTER 7 ■ SERVICE DEPLOYMENTS OVER PUBLIC WIRELESS MANS 169 puts one in a position of trading capacity off against presentation quality. Moreover, heavily compressed signals are highly intolerant of data loss because they have already been robbed of the redundancy to compensate for it. Compression buys the network operator something, but, as the saying goes, there is no free lunch. Compression is a vast subject, much too vast to treat with any thoroughness here, but most compression techniques fall into a few basic categories. The simplest seek to remove redundant information in a signal and only register changes from one sample to the next. More sophisticated techniques use what are known as codecs, which are idealized models appropriate to a given type of information such as representations of the human voice or a physical depiction of the human form. The information that is to be conveyed is compared to the model, and only what is unique to the individual message is transmitted. Still other compression techniques are based on underlying regularities in the forms of the entities depicted in the data or on perceptual codecs, where features that ordinarily would go unnoticed by a human observer will not be transmitted. Whatever the individual compression technique, all such techniques fit into two overarching categories: lossless compression and lossy compression. In the former, the original message can be reconstructed perfectly even though not all the information in it is actually transmitted, and in lossless transmission a recognizable facsimile is created at the receive end that does not contain all of the original information. The widely used MPEG compression schemes for audio and video are good examples of lossy compression depending upon perceptual codecs. They produce perfectly recognizable sounds and images, but, depending on the compression ratio (that is, the ratio of data removed to data preserved), they may degrade image and sound quality. The compression techniques in common use for audio and video today have grown very sophisticated, and at moderate compression ratios (say, five to one), they are well nigh undetectable by most viewers and listeners. And, inasmuch as this is true, they leverage existing bandwidth effectively. A telephone call that would require 64Kbps can be made with 8 or even 4 kilobits with little loss of fidelity. A high-definition television signal with several times the information per frame as a traditional National Television Standard Committee (NTSC) analog signal can yet be squeezed into a 6MHz NTSC channel while yielding a much more detailed image. Compression is built into many Web tools used today such as real-time video and audio players and is not generally used as an overall strategy on the part of the network operator, though numerous product offerings are available for that purpose. The problem with using them is that they have to be enabled in every customer terminal that is to receive a compressed signal, so the logistics of using compression tends to be challenging. Nevertheless, I expect compression to assume greater importance over time. The routing protocol used end to end will also have a considerable bearing on latency and jitter and hence on QoS. Again, this will primarily concern the operator or operators of the backbone, not the metro operator. Frequently, a message will pass through more than one long-haul network in traversing a great distance. Unfortunately, since many long-haul operators jealously guard routing information within their own networks and do not make it available to other network operators, a router in one network attempting to plot a route across intervening networks to a final destination may simply lack the information to make optimal choices with predictably unfortunate consequences in regard to QoS. To some extent servicelevel agreements between and among long-haul providers can obviate such difficulties, but often the party seeking to maintain QoS by this means will have to pay dearly to do so. Finally, I should mention the methods for supporting QoS that use proprietary route analysis techniques but do not depend on special arrangements with long-haul service providers.
170 CHAPTER 7 ■ SERVICE DEPLOYMENTS OVER PUBLIC WIRELESS MANS A specialized ISP called InterNAP claims to support QoS over the public Internet by such means if the customer utilizes an InterNAP facility to gain access to the backbone. Where QoS Matters Most While QoS is vitally important in any IP multimedia application, only two such applications have found much of a market to date. Those two are IP telephony and conferencing. Fortuitously, considerable overlap exists between the tools, both hardware and software, required for either application. In the future, perhaps in the not-too-distant future, other applications demanding stringent QoS will become routine, and the QoS required to enable top-flight videoconferencing, an application that is already in some demand, should suffice for nearly anything else. Enabling IP Telephony Because telephony is the value add that, apart from VPNs, appears to be most salable today, and because the technology behind it is quite complex, I am devoting an entire section to it. IP telephony properly refers to a whole category of technologies, some complementary and some mutually exclusive. Simply stated, there are a number of different ways to do IP telephony. The end result may appear to be a single application to the end user, but the underlying mechanisms are many and diverse. Any discussion of IP telephony should perhaps begin with some consideration of the rationale for doing it in the first place, and that largely has to do with using fewer network resources per call and building and operating a network for much less than would be the case with a circuit voice implementation. IP telephony network elements cost a fraction as much as traditional circuit switches with a similar port count and also require much less maintenance and manual configuration to operate. An IP telephone service can be operated with fewer staff members than a traditional circuit service—though how many fewer is a matter of debate— which is why few new telephone service providers are buying class 5 switches anymore. Furthermore, since the bandwidth required per call is much less for IP services, the network operator can use available bandwidth for provisioning higher-value data services or simply build less capacity into the network in the first place. In a wireless broadband network, where augmenting capacity generally means increasing the number of costly base stations, anything that increases network efficiency is a godsend, and thus Voice-over IP (VoIP) is incontestably preferable to circuit. All of this being the case, one is moved to ask why IP networks are still relatively little used in transmitting telephone calls. Why is it that more than 90 percent of residential calls made in the United States are still transmitted over inefficient circuit networks? This is for several reasons. First, by most estimates, IP telephone equipment has only recently reached the level of maturity where many carriers would want to rely on it. Second, IP backbones that could support the QoS necessary for IP voice have not been pervasive until now. Third, the price of circuit services has continued to decline, resulting in singular lack of urgency among subscribers to migrate to IP voice. Finally, the services themselves may be viewed as a somewhat inelegant overlay upon a network never intended to support them. Moreover, they have involved a multitude of palliatives and makeshifts that even today do not offer the full functionality of the mature PSTN. It does not help matters that these makeshifts and palliatives do not represent any unified approach to the problem.
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WiMax Operator’s Manual Building
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This book is dedicated to my wife.
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Contents About the Author . . . . .
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■CONTENTS ix Performing Site Surv
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■CONTENTS xi Cyberwarfare . . . .
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About the Technical Reviewer ■ROB
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Introduction Broadband wireless has
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CHAPTER 1 ■ ■ ■ Wireless Broa
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CHAPTER 1 ■ WIRELESS BROADBAND AN
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34 CHAPTER 3 ■ STRATEGIC PLANNING
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64 CHAPTER 4 ■ SETTING UP PHYSICA
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100 CHAPTER 4 ■ SETTING UP PHYSIC
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102 CHAPTER 5 ■ STRATEGIES FOR SU
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Page 152 and 153: CHAPTER 6 ■ ■ ■ Beyond Access
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Page 162 and 163: Figure 6-4. Wireless public network
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Page 168 and 169: Beyond the Central Office CHAPTER 6
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Page 199 and 200: 178 CHAPTER 8 ■ NETWORK MANAGEMEN
Page 208 and 209: CHAPTER 9 ■ ■ ■ Network Secur
Page 210 and 211: CHAPTER 9 ■ NETWORK SECURITY 189
Page 216 and 217: Index ■Numbers 2.4GHz to 928MHz b
Page 218 and 219: asic access and best-effort deliver
Page 220 and 221: ■D dark fiber, features of, 75-76
Page 222 and 223: harmonics, impact on AC power, 188
Page 224 and 225: challenges to, 85-86 and NLOS, 121
Page 226 and 227: PONs (passive optical networks), fe
Page 228 and 229: signal diversity, providing with ad
Page 230 and 231: ■V VDSL and entertainment service
Page 233: forums.apress.com FOR PROFESSIONALS
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