WiMax Operator's Manual

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CHAPTER 4 ■ SETTING UP PHYSICAL INFRASTRUCTURE 93 support are invaluable. One wants to choose a manufacturer who will take an active part in at least the early stages of the installation and that can provide support if difficulties arise later. Obviously, to fill such a role, the manufacturer must avoid bankruptcy, and the large number of business failures among broadband radio manufacturers should incline network operators to scrutinize the stability of the vendor closely. Unfortunately, the solidity of the manufacturer does not necessarily correlate with the quality or performance of the equipment, so one must look at the vendor’s business practices as much as at its products. All RF equipment should be thoroughly measured as to compliance with performance specifications and then used in actual links to determine performance in actual field conditions. During such evaluation, pilot links should not be operated as commercial services. It is entirely illegitimate to do product testing at the customer’s expense, and the ill will that can result from such a practice can subsequently jeopardize the prospects of the wireless service. Field testing of equipment in semipermanent links should be designed to expose the equipment to as variable an environment as possible in order to assess the effects of high levels of interference, severe multipath, network congestion, large obstructions, and so on. The key attribute of carrier-grade equipment is consistency of performance. Be wary of claims of such capabilities being made available in a later product iteration, especially if the development of that capability is likely to challenge the resources of the manufacturer. Look to easy upgrade paths when considering equipment. Will a particular network element be able to grow with the network, and, if so, what is the cost of expanding port counts or adding new types of services? Never assume full interoperability based on a company’s professed adherence to a standard, even with certification. Always determine interoperability based on actual field trials, and never purchase equipment that is to interoperate with existing infrastructure absent such a determination. If equipment is to reside outdoors, make certain it is rugged and complies with industry standards for weather resistance. In the past, many manufacturers have paid insufficient attention to the design of the case, and the equipment has underperformed as a result. Finally, contact every relevant manufacturer, at least at the inception of the network, and invite competitive bids. Few wireless broadband operators have sufficient sales that they can afford not to be accommodating in respect to price. Wireless broadband today is a buyer’s market. Service-Related Specifics The correct equipment choice for network operators is equipment that best supports their service offerings. Chapter 6 explains in detail how equipment supports services and indicates the equipment complement required for various offerings. The 802.16 standard provides a full feature set that will enable a considerable range of service offerings, but for services such as streaming multimedia, conferencing, and voice telephony, special provisions not present in every system will be necessary. Do not assume that any given piece of equipment can be juryrigged to provide every conceivable service. One should also make certain that the radios are provided with all necessary interfaces for other types of networks with which the broadband wireless network might communicate. Many, though not all, radios have fiber interfaces, for instance, and if fiber is to be used for
94 CHAPTER 4 ■ SETTING UP PHYSICAL INFRASTRUCTURE backhaul, better to have interfaces in place rather than having to set up outboard optoelectronic converters. Another technical consideration is the number of RF ports on the base station controller. If the operator wants to operate on multiple bands, that many RF ports will be required. Routing and switching requirements should also be determined before any equipment contracts are signed. It is certainly possible to use a base station controller with an outboard router or switch, but it is generally a lot cheaper to buy an integrated network element that does it all. Lastly, investigate how the component’s element management system will fit in with the overall operations support systems (OSS) software suite utilized in the network. Few startups or competitive service providers can command deep expertise in network management software, and if off-the-shelf programs can be bolted together and made to work reasonably well, that is desired. What one wants to avoid is having to hire consultants and trying to harmonize the software for a single element with an overall system with which it is fundamentally incompatible. Integrating Wireless with Wireline Infrastructure Wireless infrastructure should always be regarded as an option, not as a cause to pursue. Sometimes it is a good option, sometimes it is not, and sometimes the best choice that a network operator can make is to put wireless links in some parts of the network but not in others. But be aware that when some portion of the network is wireless and some part wireline, integration problems may occur. One fact cannot be emphasized enough in this regard, namely, that all the commonly used networking protocols, including SONET/SDH, Ethernet, IP, MPLS, RPR, frame relay, and ATM, were devised for use over wireline networks—networks where high availability was a given. In fact, most of the more recent protocols were explicitly designed for use over optical fiber where packet loss may be presumed to be negligible. None of these protocols work well over wireless airlinks in native form, and wireless standards such as 802.11 and 802.16 all incorporate invisible layers of middleware that adapt the wireline protocol to the exigencies of the RF environment. When a network operator attempts to use a standards-based airlink to carry a protocol for which no appropriate middleware is present, performance is apt to be degraded, or the link may even fail altogether. An example would be attempting to carry SONET or ATM traffic over an 802.11 link. Both standards happen to lack mechanisms for retransmission, and both depend upon precise clocks to coordinate data flows. Furthermore, ATM has procedures for negotiating sessions that depend on the maintenance of precise timing and are intolerant of interruptions in the signal. Obviously, these protocols will not function correctly over an intermittent airlink absent appropriate middleware, and in the case of SONET, the restoration mechanism may even be invoked. Further problems may be anticipated when a multiservice switching platform sits at the core of the network in question and that platform has proprietary enhancements placed on top of the familiar transport protocols. One simply has no way of knowing how the middleware in the 802.16 airlink will cope with those ancillary protocols, but because they have been designed around a fiber connection, the likelihood is that problems will arise. The 802.16 standard generally supports IP, Ethernet, and ATM. No support is specified for frame relay, MPLS, RSVP, DiffServ, resilient packet ring (RPR), DOCSIS, MPEG video, or any IP
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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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14 CHAPTER 2 ■ ARCHITECTING THE N
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34 CHAPTER 3 ■ STRATEGIC PLANNING
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CHAPTER 6 ■ BEYOND ACCESS 143 sto
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Specialized Content Distribution Pl
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Beyond the Central Office CHAPTER 6
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CHAPTER 6 ■ BEYOND ACCESS 149 out
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CHAPTER 6 ■ BEYOND ACCESS 151 som
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CHAPTER 7 ■ ■ ■ Service Deplo
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CHAPTER 7 ■ SERVICE DEPLOYMENTS O
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178 CHAPTER 8 ■ NETWORK MANAGEMEN
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CHAPTER 9 ■ ■ ■ Network Secur
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CHAPTER 9 ■ NETWORK SECURITY 189
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Index ■Numbers 2.4GHz to 928MHz b
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asic access and best-effort deliver
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■D dark fiber, features of, 75-76
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harmonics, impact on AC power, 188
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challenges to, 85-86 and NLOS, 121
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PONs (passive optical networks), fe
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signal diversity, providing with ad
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■V VDSL and entertainment service
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