WiMax Operator's Manual

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CHAPTER 2 ■ ARCHITECTING THE NETWORK TO FIT THE BUSINESS MODEL 15 consistently higher throughput speed. T1s are also difficult and expensive to provision, and provisioning times are commonly measured in weeks. Finally, T1 speeds are a poor match for 10 base T Ethernet, and attempts to extend an enterprise Ethernet over a T1 link will noticeably degrade network performance. Because it is circuit based and reserves bandwidth for each session, T1 offers extremely consistent performance regardless of network loading. Maximum throughput speeds are maintained at all times, and latency, jitter, and error rates are well controlled. Were the bandwidth greater, T1s would be ideal for high-fidelity multimedia, but, as is, 1.5Mbps is marginal in that regard. T1/E1 is legacy access technology. The basic standards were developed in the 1960s, and the SONET and SDH optical equipment supporting massive T1/E1 deployments dates back 20 years. In terms of performance level, T1/E1 is essentially fixed, a fact that will put it at an increasing disadvantage to newer technologies, including broadband wireless. Also, the infrastructure for these circuit-based access networks is expensive to build, but, since most of it has already been constructed, it is by now fully amortized. I do not expect a lot of new copper to be built except in developing countries, and so the last-mile access for T1/E1 must be considered a fixed asset at this time. But, somewhat surprisingly, the sales of SONET and SDH equipment for the metro core have been increasing rapidly through the late 1990s and the opening years of this century, and they are not expected to peak until 2007. Therefore, SONET and the T1 service offerings it supports will be around for alongtime. Prices in the past for T1s were more than $1,000 per month, but they have dropped somewhat, and they are now about $300 to $400 in the United States, though prices vary by region and by individual metropolitan market. Compared to newer access technologies, T1 does not appear to represent a bargain, but it is all that is available in many locales. Moreover, the incumbent carriers that provision most T1 connections are in no hurry to see it supplanted because it has become an extremely lucrative cash cow. Because of the apparently disadvantageous pricing, T1 services may appear to be vulnerable to competition, but thus far they have held their own in the marketplace. Ethernet and IP services, whether wireless or wireline, will probably supplant circuit-based T1 in time, but as long as the incumbent telcos enjoy a near monopoly in the local marketplace and are prepared to ward off competition by extremely aggressive pricing and denial of central office facilities to competitors, the T1 business will survive. I suspect that T1 connections will still account for a considerable percentage of all business data links at the end of this decade. Frame Relay Frame relay is a packet-based protocol developed during the early 1990s for use over fiberoptic networks (see Figure 2-1). Frame relay permits reservation of bandwidth and enables tiered service offerings, but it is not capable of supporting quality-of-service (QoS) guarantees for multimedia, as does ATM, or some of the ancillary protocols associated with IP, such as Multiprotocol Label Switching (MPLS), Reservation Protocol (RSVP), and DiffServ. Also, frame relay does not permit momentary bursting to higher throughput rates or self-provisioning. Frame relay is rarely used to deliver multimedia and other applications demanding stringent traffic shaping, and it is never used to deliver residential service. Usually, frame relay is employed to connect multiple remote locations in an enterprise to its headquarters, and connections over thousands of miles are entirely feasible. Frame relay switches or frame relay
16 CHAPTER 2 ■ ARCHITECTING THE NETWORK TO FIT THE BUSINESS MODEL access devices (FRADs) are usually accessed from an office terminal via a T1 connection, though other physical media may be employed, including wireless broadband. Frame relay transmissions over long distances, commonly referred to collectively as the frame relay cloud, invariably travel over fiber and are usually encapsulated within ATM transmissions. Figure 2-1. A relay network Frame relay services are largely the province of incumbent local phone companies or long-distance service providers. Throughputs vary but are commonly slower than a megabit per second—medium speed rather than high speed. As is the case with T1, frame relay is a legacy technology, standards have not been subject to amendment for years, and not much development work is being done with frame relay devices. The performance of frame relay is not going to improve substantially in all likelihood. Pricing is in the T1 range, with higher prices for higher throughput rates and special value-added services such as Voice-over Frame Relay (VoFR). Also, provisioning of multiple remote locations can be prohibitively expensive with conventional frame relay equipment because the networks do not scale well, and this may limit the popularity of frame relay in the future. Frame relay does not directly compete with wireless broadband in the metro, and thus targeting existing customers for the service makes little sense. Frame relay will continue to lose ground to enhanced metro Ethernet and IP services. DSL DSL is arguably the strongest competitor to 802.16 wireless among broadband access technologies. DSL comes in many variants, including asymmetric DSL (ADSL), symmetric DSL (SDSL), G.lite, single-pair high-speed DSL (SHDSL), and very high data rate DSL (VDSL). The distinguishing features of the various substandards are not particularly germane to this discussion and have to do with the speed of the connection and the apportionment of available spectrum upstream and downstream. DSL utilizes digital signal processing and power amplification to extend the frequency range of ordinary twisted-pair copper lines that were originally designed to carry 56-kilobit voice signals and nothing faster. Aggressive signal processing applied to uncorroded copper can best this nominal limit by orders of magnitude. Commercially available systems can now achieve speeds in excess of 100 kilobits per second over distances of a couple of thousand feet,
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Page 4: This book is dedicated to my wife.
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Page 10 and 11: ■CONTENTS ix Performing Site Surv
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Page 16: About the Technical Reviewer ■ROB
Page 20 and 21: Introduction Broadband wireless has
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102 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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Figure 6-4. Wireless public network
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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 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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