WiMax Operator's Manual

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CHAPTER 3 ■ STRATEGIC PLANNING OF SPECTRUM AND SERVICES 59 represent choke points for the extension of Ethernet LANs since Ethernet throughputs are minimally 10Mbps rather than 1.5Mbps. Higher-burst speeds are not possible over T1 connections as is the case with many of the newer packet services, and the circuits themselves must be manually provisioned, at least on the older synchronous optical network (SONET) equipment still used by most carriers to anchor their T1 lines. Regarding the relationship between T1s and SONET, a T1 connection occurs over twistedpair copper. The copper pairs themselves terminate at either a central office, more commonly called a central exchange outside the United States, or at a digital loop carrier (DLC), an aggregation device generally placed outdoors in a hardened enclosure. The digital loop carrier itself will normally have a fiber-optic interface through which it will communicate via fiber with a central office. SONET as a standard relates to the fiber portion of the local telecommunications plant only, and SONET itself is a set of protocols and standards pertaining to the assignment of network traffic to circuits and to the restoration of the network in the event of either a failure of one of its nodes or a break in the fiber. Incidentally, SONET networks are usually set up as point-to-consecutive-point sequences of nodes that together form a closed ring. SONET supports T1 data services as well as circuit voice services, but T1s existed long before the SONET standard was promulgated. What SONET really has going for it is redundant fiber paths and very fast restoration of service (less than 50 milliseconds) in the event of a fiber break. T1s themselves are not similarly redundant, but the fact that the core network is so reliable lends a high degree of reliability to T1 services as well. Where it is lacking is in flexibility and bandwidth efficiency. Interestingly, the newer next-generation SONET does permit the aggregation of T1s to afford the users’ higher speed, but relatively little next-generation SONET is in place in the networks as yet. Also, most installed SONET gear does not permit the rapid provisioning and activation of T1 lines. Finally, SONET does not offer inherent support for user subgroups, VPNs, transparent LANs, or other specialized service offerings. All of this discussion of SONET is not intended as digression. It is very much to the point because the equivalent of a SONET-based T1 is what the first millimeter microwave carriers tried to provide. This was extremely misguided insofar as millimeter microwave has the bandwidth and the flexibility to offer flexible, rapidly provisionable fast packet services that form a real alternative to SONET. The central problem facing the millimeter microwave pioneers was that T1 emulation did not play upon the real strengths of millimeter microwave and in fact resulted in an offering that was inferior to a real T1. The first generation point-to-multipoint wireless networks lacked restoration mechanisms when airlinks failed and generally offered availability levels that were at least an order of magnitude worse than those of the wireline incumbents. One equipment manufacturer, the now-defunct Triton Network, did in fact architect a SONET-like radio ring network with built-in restoration mechanisms, but the system was not widely used. T1 emulation in my estimation is a poor strategy and one almost certain to fail, espe- cially if it is embedded within a larger strategy of price competition, as was commonly the case among the first LMDS providers in the United States that tended to price their 1.5Mbps services at about 30 percent below the going rates for T1s in their markets. Telco incumbents can easily drop prices temporarily to fend off interlopers, and they do so. Since they are in a far better position to sustain losses to secure market share than are startups, they generally succeed. So if offering T1 surrogates is not the answer, what is? Currently the best strategy in competing for business data customers is to offer highly flexible packet services.
60 CHAPTER 3 ■ STRATEGIC PLANNING OF SPECTRUM AND SERVICES Packet-Based Services: A Business with Potential As with lower microwave, the network operator has a choice between IP and Ethernet. The 802.16 protocol is built around IP, and IP is better suited for supporting quality of service, service differentiation, and service-level agreements. On the other hand, Ethernet is the protocol used in most internal enterprise LANs today and may be delivered over low-cost interfaces. Some wireless base station equipment has the ability to support both protocols in the last mile, and for certain operators that may make the most sense. IP and Ethernet are highly compatible, and Ethernet streams are easily transported over IP networks with little overhead or wasted capacity, but the network operator is still left with the choice of whether to opt for IP or Ethernet VPNs and of what type of packet telephony standards will be supported. Thus, choosing to support one protocol to the exclusion of the other on the access level imposes certain constraints on the network operator and the subscriber. My belief is that IP is better suited to service creation than is Ethernet but that Ethernet is better suited to service delivery—in other words, delivery of an IP stream over an Ethernet interface appears to make the most sense at this time in terms of both versatility and cost effectiveness. Whatever packet protocol is ultimately employed to manage the link between the base station and subscriber premises, the network operator should strive to differentiate the basic access service from T1 by the following means: The service velocity should be far higher than is the case for T1; that is, the operator should be able to provision the service rapidly, preferably within hours of an order being placed. T1 services typically involve a lengthy provisioning process often extending over several weeks. Providers of such services are highly vulnerable to competition on that account. Ideally, the service should lend itself to self-provisioning in the case of changes of service. If the subscriber wants to lease additional bandwidth for a short period of time to meet special needs, then the operator should permit this through a secure Web site with automatic billing processes registering the event. The service should allow for the leasing of fairly fine increments of bandwidth. In a SONET network the service is generally sold in extremely coarse increments, with DS3 (45Mbps) representing the next level of service above T1. Surveys indicate that most small- and medium-business users are interested in services with throughput rates from 2 to 10 megabits per second—faster than T1 but significantly slower than DS3. Finally, the service provider should offer the same kind of options that have been traditional in ATM networks, including committed bit rates, bandwidth reservation where appropriate, and burstable rates where requirements for high bit rates are intermittent. Guarantees regarding jitter and latency are also desirable service offerings, particularly where the network must support conferencing and multimedia or a high degree of real-time interactivity. These are areas where circuit services such as T1 excel since circuits are by their very nature highly predictable, but such benefits are, in large measure, obtainable through some of the newer IP ancillary protocols such as DiffServ, RSVP, and MPLS as well as through specific QoS provisions within the 802.16 standard. Chapter 7 covers QoS in greater depth.
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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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Page 85 and 86: 64 CHAPTER 4 ■ SETTING UP PHYSICA
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Page 123 and 124: 102 CHAPTER 5 ■ STRATEGIES FOR SU
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110 CHAPTER 5 ■ STRATEGIES FOR SU
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CHAPTER 6 ■ ■ ■ Beyond Access
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CHAPTER 6 ■ BEYOND ACCESS 133 Rou
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CHAPTER 6 ■ BEYOND ACCESS 135 (Qo
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CHAPTER 6 ■ BEYOND ACCESS 137 The
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CHAPTER 6 ■ BEYOND ACCESS 139 ins
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Figure 6-4. Wireless public network
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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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