WiMax Operator's Manual

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CHAPTER 7 ■ SERVICE DEPLOYMENTS OVER PUBLIC WIRELESS MANS 161 interface between the subscriber and service provider terminals, IPLS is easier to implement than VPLS, but, for this type of VPN to be set up, subscribers must have routers of their own. Incidentally, IPLS solutions are not standards based as yet. MPLS switching, which seems to represent the more current approach, provides network operators with a number of possibilities in regard to VPNs. They can utilize ATM or frame relay virtual circuits over MPLS-switched label paths, which is a fairly simple procedure but does not scale well. Alternatively, they can utilize the Martini draft extensions of MPLS that have not yet been fully standardized by the Internet Engineering Task Force (IETF) but are supported by many MPLS switches today. This approach does in fact scale well. Yet another approach is the Kompella layer 2 VPN. This is simpler to administer for the network operator than Martini draft, and it is highly scalable. Layer 3–Based VPNs In terms of standards-based solutions, VPNs based on layer 3 are further advanced than their layer 2 counterparts. This being the case, equipment choices will be more varied and protocols will be more stable. Two such layer 3-based approaches are extant today: RFC2547 and virtual routing. RFC2547, also known as Border Gateway Protocol (BGP) over MPLS, is probably the most commonly used service provider VPN technology today. (BGP is a frequently used routing protocol across the public Internet that has been long standardized.) Plain-vanilla BGP will not do, however, because of its inability to handle overlapping addresses, so a route distinguisher extension is required. In this scheme, a separate MPLS label will be associated with each VPN, and BGP will be used to advertise the label to each intermediate node encompassed by the route. Virtual routing is somewhat different in that a separate routing announcement disseminates information on each routing path associated with each VPN, but in RFC2547 a single announcement is made. Virtual routing is more difficult to administer than RFC2547 because of its obviously much greater complexity and is less used in the industry. Its chief advantage is the extreme isolation that it provides for individual traffic streams and its extensive support for fine gradations of QoS as applied to many individual transmissions within the VPN. Tunneling Protocols Setting up and maintaining tunnels is separate from the routing and switching functions that direct information into those tunnels. As you have seen previously, tunneling generally involves adding a header to a packet that will define the tunnel, but this is not the case with all protocols. In the case of MPLS, a tunnel can also be defined with a switching label, avoiding the use of any ancillary protocol. Those protocols used specifically for tunneling include IPsec, Layer 2 Tunneling Protocol (L2TP), IP in IP, and Generic Routing Encapsulation (GRE). IPsec is basically an encryption protocol that segregates streams by applying separate encryption codes to them. It lacks flexibility compared with some of the other tunneling protocols but can be combined with most of them to redress that deficiency. L2TP is designed to tunnel layer 2 information across a layer 3 network. It is often employed in switched VPNs. IP over IP is little used today and can be passed over. GRE, which serves the same purpose (namely, to define IP tunnels over a pure IP network), is much more flexible and contains IP
162 CHAPTER 7 ■ SERVICE DEPLOYMENTS OVER PUBLIC WIRELESS MANS extensions that allow the network operator to make do with a relatively small number of IP addresses and to multiplex tunnels. Applications Requiring Quality of Service This section concerns value-added services that are relatively intolerant of variations in throughput rate and availability. For the most part, they involve multimedia such as voice or video, but they may also encompass real-time scientific computing, gaming, white boarding, voice-over business presentations, distance learning, financial reporting, and indeed any application that is both data intensive and dependent on an orderly and predictable succession of data. Applications will definitely figure more prominently in the future, but the speed with which they will be adopted cannot be predicted. In the late 1980s and early 1990s, many industry analysts assumed that multimedia and “virtual reality” interactivity would typify network applications by the turn of the century, which, of course, was not the case. Web-based multimedia, such as it is, has consisted, for the most part, of short video clips of poor to middling quality, some real-time audio in the form of private conferencing or Internet radio, and an abundance of simple animation made possible through Java applets. Why has Web-based multimedia been so slow in arriving? Answering that question conclusively would require a depth of analysis far beyond the scope of this book. What I can say is that such applications have yet to reveal compelling advantages over more traditional broadcast and circuit-based multimedia in any but a few areas. To cite just a couple of examples, Internet radio and television are qualitatively inferior to standard analog radio and television and have foundered badly on that account, and they are difficult to deliver over conventional domestic and portable entertainment systems. Furthermore, Internet radio is currently infeasible in the mobile environment where most radio listening occurs. Web-based multimedia simply cannot compete effectively with the older circuit-based content delivery systems, and they will not be able to do so until the underlying technology improves significantly. Indeed, only in the areas of conferencing, distance learning, and gaming do the interactive dimension afforded by two-way broadband confer a decisive advantage, and it is precisely these applications that show the most promise of attracting substantial numbers of subscribers in the midterm. QoS is a rather imprecise term, particularly when applied to packet networks. Preeminently, QoS is an end result, one that can be achieved through a number of different transport technologies. Generally, the term refers to conditions within the network that will support the delivery of time-sensitive or low-redundancy services with minimal perceptible degradation. More particularly, QoS encompasses the following: control of throughput rate, specifically the minimum rate; control of overall delay or latency; control of packet-to-packet delay, known as jitter; and control of packet loss or bit error rate. Some would also include availability and the likelihood of call or session blockage as well as subjective impressions of presentation quality—the latter constituting an especially important issue when the network operator is utilizing data compression technologies. I will present each of these attributes in turn in reference to the various services that a broadband wireless operator is apt to offer.
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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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64 CHAPTER 4 ■ SETTING UP PHYSICA
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100 CHAPTER 4 ■ SETTING UP PHYSIC
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102 CHAPTER 5 ■ STRATEGIES FOR SU
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Page 152 and 153: CHAPTER 6 ■ ■ ■ Beyond Access
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Page 162 and 163: Figure 6-4. Wireless public network
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Page 168 and 169: Beyond the Central Office CHAPTER 6
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Page 210 and 211: CHAPTER 9 ■ NETWORK SECURITY 189
Page 216 and 217: Index ■Numbers 2.4GHz to 928MHz b
Page 218 and 219: asic access and best-effort deliver
Page 220 and 221: ■D dark fiber, features of, 75-76
Page 222 and 223: harmonics, impact on AC power, 188
Page 224 and 225: challenges to, 85-86 and NLOS, 121
Page 226 and 227: PONs (passive optical networks), fe
Page 228 and 229: signal diversity, providing with ad
Page 230 and 231: ■V VDSL and entertainment service
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