WiMax Operator's Manual

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CHAPTER 4 ■ SETTING UP PHYSICAL INFRASTRUCTURE 85 infrastructure equipment to a handful of service providers, providing some commercial field experience, but the Finnish company has since ceased production of the radios. Finally, several service providers have set up wholly proprietary mesh architectures of which the nowdefunct Metricom Ricochet network with more than 30,000 subscribers was by far the largest. Whether these constitute real proof of concept is debatable because none of the service providers has survived. Mesh Networks: The Counterarguments While freely acknowledging the revolutionary potential of the mesh, you will see the following challenges facing those who utilize mesh architectures in full-scale metro deployments: Developing routing algorithms that maximize network efficiency and minimize congestion, unacceptable latencies, and “router flaps” where highly inefficient routing paths are inadvertently selected: Packet routers function imperfectly in public networks today and do not provide the same kind of wholly predictable network performance as do traditional circuit switches. Indeed, popular protocols for improving router predictability, such as Multiprotocol Label Switching (MPLS), DiffServ, and Reservation Protocol (RSVP), make the operation of the router notably more switchlike and set up fixed paths through the Internet that essentially ignore the basic mesh structure formed by the crossconnections among the major peering points. Securing the network against hacks and malicious code: If the basic neurons of the network are exposed, which they certainly are in any peer-to-peer arrangement, then it is difficult to protect the core management software. Advocates of grid computing have been preoccupied with network security, and rightly so, but really satisfactory solutions have not been developed to date. Essentially closed systems such as class 5 circuit telephone switches, ATM switches, and optical switches have generally been highly resistant to intrusion and compromise whereas IP routers are almost routinely subject to successful attacks. There are those who argue that nonhierarchical systems will be more resistant to attacks, and the effects of such attacks will be localized rather than catastrophic, but an absolutely convincing case has yet to be made for this position. Minimizing hops: The longer the chain of wireless routers going back to the Internet access point, the less bandwidth available to any given node for transmitting its own data, and this constraint ultimately limits the size of a mesh network. If a mesh network grows sufficiently large, nodes on the periphery will have to go through multiple intervening nodes, which severely limits throughput for any one node. This deficiency is exacerbated by the inability of most radios to transmit while they are receiving. Developing standards: Single-vendor solutions are the norm in mesh networking today, a state of affairs that, ironically, militates against the kind of pervasive deployments mesh advocates envision. Currently little comprehensive standards work is under way in the area of wireless meshes, and no major telecommunications infrastructure manufacturer is directly involved in mesh projects. Providing a strong first-mover advantage and a real ownership of the network for the network operator initiating the mesh: If the intelligence is in the subscriber terminal, there is really nothing to stop subscribers from forming loose cooperatives and dispensing
86 CHAPTER 4 ■ SETTING UP PHYSICAL INFRASTRUCTURE with the middle man, so to speak, or else reducing the middle man to a role of simply negotiating and maintaining a link with an Internet Point of Presence. Mesh equipment, inasmuch as it is nonhierarchical and self-organizing, inherently favors ad hoc, cooperative associations of nodes, and some of the vendors have acknowledged as much. It is rather difficult to ascertain what the precise role of the network operator would be in a truly self-organizing mesh other than serving as a sole conduit for a monopoly infrastructure product, and I cannot see anyone fulfilling such a role indefinitely. It well may be the case that a mesh of meshes on a national scale is infeasible and that local meshes simply cannot coalesce into an all-encompassing canopy, but if they can and do, the function of the service provider must change radically. Technology pundit George Gilder speculated on the properties that a nationwide fiber-based mesh network might exhibit in his book Life After Television (W. W. Norton & Company, 1994), and he assumed that the service provider’s role would consist merely of owning and maintaining the actual fiber plant, but in a wireless mesh there are no actual links to own. The service provider’s place in such a scheme is obviously at issue. A final challenge is the attitude of entrenched wireline incumbents in the event that wireless meshes begin to win acceptance. One could foresee such incumbents seeking some sort of legislative or regulatory relief to preserve the de facto monopoly they enjoy today. And in the United States one could easily see them prevailing against the interests of the public. All of this does not preclude a network operator soliciting a bid or a proposal from a wireless mesh manufacturer. All of the claims made by such manufacturers may yet be realized, and meshes may eventually become the norm rather than the exception. I think, however, that meshes, because they are relatively untried, represent a higher risk option than more traditional architectures. Performing Site Surveys and Determining Link Budgets A site survey is simply a determination of the extent of the interference levels in the frequencies of interest and of the severity of obstructions and multipath at the precise locations in which one wants to install terminals. Such a survey enables the network operator to determine if unacceptable amounts of interference are present at various locales such that adequate signal quality cannot be obtained, as well as the extent to which blockages restrict blanket coverage in a given area. Ideally, the site survey should be an ongoing process and should encompass every link in the network. In practice, something considerably less extensive will be performed because of the prohibitive cost of deploying technicians at every location. Site surveys are performed manually and painstakingly by taking innumerable measurements with a radio spectrum analyzer and eventually with an actual radio transceiver. It is grunt work, but a certain minimum surveying is required for informed network planning. It is also one of the first steps a network operator should take, and if unlicensed spectrum is to be utilized, it should be perhaps the second step after a determination has been made as to what spectrum is available. In theory, a site survey should encompass every location where either an access point or a subscriber terminal may be situated, but of course the time and expense required to achieve that theoretical ideal are enormous in the case of a large metropolitan network. Therefore,
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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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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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