WiMax Operator's Manual

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CHAPTER 4 ■ SETTING UP PHYSICAL INFRASTRUCTURE 75 Circuit Fiber Connections: SONET/SDH: Circuit time intervals are all multiples of the basic 56 kilobit per second (Kbps) voice channel. The chief service offering within SONET networks is the T1 at approximately 1.5Mbps, and the equivalent SDH offering is the E1 at approximately 2Mbps. As indicated earlier, multiple T1/E1 services may be supported by some of the newer SONET equipment platforms, but most carriers have not installed such equipment and will not provide fine increments of bandwidth. In the United States the next level up from the T1 is the DS3 at 45Mbps, and the next increment above that is the OC-3 at 155Mbps. Someone desiring a 20Mbps or 100Mbps backhaul is simply out of luck. Of course, one can always choose to lease more capacity than is absolutely needed, but the pricing of DS3s and OC-3s is steep—thousands of dollars a month for the former and well into the five figures for the latter. For a startup wireless broadband network attempting to build a business, such large-capacity circuit backhaul connections are a heavy burden, a burden made heavier by the fact that they are quite inefficient for the transport of packet traffic and carry a great deal of network overhead. Packet Fiber: Metro Ethernet or IP: Another option for backhaul is a direct packet connection using either the Ethernet or IP protocol. Fast packet services over fiber have been offered by a number of startups such as Cogent and Yipes in the United States and more recently by some of the incumbents. Quite a number of carriers are now offering such services in East Asia as well, particularly in mainland China, Hong Kong, and Taiwan. Certainly in the case of the startups, the pricing has been far more attractive than is the case for circuit services with monthly fees as low as $1,000 for a 100Mbps burstable connection, but in most cases such services are not delivered with rigid service-level agreements in respect to jitter, latency, minimum throughput, bandwidth reservation, and so forth. Direct IP services better support quality of service than do pure Ethernet services, which is something to consider when evaluating fast packet backhaul providers. Where available, packet services over fiber are often preferred to circuit connections strictly on the basis of price, but the problem is that they are not too generally available, and in nearly all cases they are offered by entities that would prefer to have the customers whose transmissions are being backhauled. Then, too, fiber-based access services are expensive to provision, and the provider of metro Ethernet or direct IP-based services may simply not be able to lay fiber to the building being served by the broadband wireless operator. Dark Fiber: Another option, sometimes present and often not, is the lease of so-called dark fiber from a public utility or public transit system. Gas and electrical utilities, and, to a lesser extent, transit districts and railroads, own extensive amounts of optical fiber that they use for monitoring purposes and internal communications. Such private fiber networks are generally grossly underutilized—largely dark in the parlance of the telecommunications industry—and the owners are often amenable to leasing capacity, in which case the lessee may be assigned an individual wavelength or an IP address. Since utilities are not primarily in the business of selling fiber capacity and do not regard such networks as major profit centers, they can often be persuaded to lease capacity at reasonable rates. Be forewarned, however, that using leased dark fiber for backhaul or for any other purpose is a different proposition than purchasing a T1 or fast packet service from an optical services provider. Public utilities often do nothing other than provide access to an optical pipe. They do not provide termination or optical conversion equipment, and they offer no guarantees in respect to network redundancy or
76 CHAPTER 4 ■ SETTING UP PHYSICAL INFRASTRUCTURE provisions for restoration. Consequently, by accepting such an arrangement, broadband wireless operators are in effect becoming optical carriers as well as wireless access providers since the burden of operating and maintaining the optical portion of the network will fall squarely on their shoulders. Stranded Fiber Assets: Yet another possibility is securing what are known as stranded fiber assets. During the late 1990s and the beginning of this decade, a tremendous amount of fiber was laid, particularly in the United States, on both the local level and between cities. Such overcapacity led to falling prices for leased fiber and a wave of bankruptcies among owners of fiber infrastructure. Quite a bit of fiber laid by bankrupt companies is now available for resale from fiber brokers such as Fiberloops, often at extremely low prices. Such stranded assets can be an enormous bargain for the startup broadband access provider, but their usefulness is subject to several qualifications. Usually the optical fiber that was installed did not form a comprehensive or pervasive network but more commonly took the form of a core ring that served to anchor what are known as laterals, fiber runs to individual buildings. Laterals, the access portion of a fiber network, are by far the sparsest fiber deployments and reach less than 10 percent of business locations in the United States. From any given base station a fiber lateral may simply be unavailable. One can, of course, situate one’s base stations with a view to exploiting extant fiber resources, if one can determine their whereabouts. A number of consultancies such as the aforementioned Fiberloops and TeleGeography offer databases of fiber resources, but no one pretends that any such database is exhaustive. Because fiber is an inherently valuable resource in and of itself, requires no licensing, and has proven itself to be long lasting and reliable, and thus far has supported steady increases in throughput speeds through upgrades and improvements in the terminal devices, acquiring fiber is generally a wise decision. But unless the fiber extends the entire distance between the points to be linked, it is fairly useless for backhaul. The network operator who can obtain only some portion of the fiber required to complete a backhaul connection may choose to construct the remaining portion required. This is not an operation to be undertaken lightly and in most cases will be prohibitively expensive. Trenching costs for fiber builds can run as high as several hundred thousand dollars a mile in a large metropolitan area and several tens of thousands in more rural areas. In some cases fiber may be hung from utility poles or even snaked through sewer or gas lines, both installation methods being roughly half the cost of trenching. Still, installation in the best of circumstances is seldom cheap and, moreover, usually entails a long and involved permitting process. Fiber builds are also time consuming as a rule. Other Physical Media for Backhaul While fiber is certainly the preferred medium for backhaul in respect to speed and availability, it is far from the only option, and frequently it is far from the most cost effective. Free-Space Optics for Backhaul A further possibility is obtaining a fraction of the fiber needed on a lease or ownership basis and utilizing free-space optics to provide fill-in. One manufacturer, LightPointe, makes a freespace optical system where the transceiver can link fiber sections transparently with no need for optical-electronic-optical (OEO) conversion, always an expensive proposition.
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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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126 CHAPTER 5 ■ STRATEGIES FOR SU
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128 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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