WiMax Operator's Manual

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CHAPTER 7 ■ SERVICE DEPLOYMENTS OVER PUBLIC WIRELESS MANS 167 protocol because it merely signals the requirements for various traffic flows. Incidentally, RSVP requests must reach every router or switch in every conceivable signal path the packet may take, so it tends not to scale well over distance. RSVP does not employ extra headers or labels, but it frames its requests for bandwidth within the normal IP header in the form of priority bits. IntServ, DiffServ, and IP Precedence IntServ stands for integrated services and was a protocol developed by the IETF in the 1990s. It is little used today, and I will pass over it here. DiffServ, which is widely used today, performs a somewhat different function than RSVP; it provides a classification scheme for various streams rather than requesting bandwidth along a data path. DiffServe, as well as RSVP, requires that priority bits be assigned to the packet header to establish the priority of that packet in terms of the queue it will occupy and the order in which it will be transmitted relative to packets of other priorities occupying other queues. Such queuing will take place at switches rather than routers, whether MPLS switches (increasingly the case today), ATM switches, or metro Ethernet switches. As is the case with RSVP, all relevant network elements must be enabled for DiffServ, or QoS will not be maintained across the network. IP Precedence fulfills a similar function to DiffServ, but the latter is much more widely deployed today. IP Precedence, unfortunately, is not consistently implemented from one vendor to another and thus is of limited usefulness in real-world networks. RTP and RTSP Real Time Protocol (RTP) and Real Time Streaming Protocol (RTSP) are more specialized than the other protocols covered thus far, being designed primarily to support audio and video streaming. RTP, which has somewhat broader application than RTSP, is used for a number of real-time applications, including but not limited to audio and video. RTSP is used mainly in multicast or media-on-demand applications and in IP telephony as well. RTP is a transport protocol, and RTSP, as the name implies, is as streaming protocol used for transient singlesession multimedia presentations rather than the transfer of storable multimedia files. RTSP is designed specifically to work in a client-server environment. MPLS MPLS is a switching protocol that supports QoS by permitting the setup of label-switched paths for traffic of similar characteristics. It is not, as I have seen, intended primarily for QoS but rather for effective network management. Queuing Techniques That Support QoS In addition to the previous protocols, which primarily involve signaling, a number of protocols promote QoS by managing the relationship between and among queues assigned to different classes of traffic. These include strict priority queuing, round-robin queuing, fair queuing, weighted fair queuing, adaptive scheduling, and so on. The first requires the complete emptying of the highest-priority queue before the switch proceeds to that which is next in priority, and the others strive to provide some degree of equity to lower-priority streams. No such protocol can be said to be perfect, and network operators will have to determine which will best satisfy their customers in aggregate. Normally these queuing protocols will not be the province
168 CHAPTER 7 ■ SERVICE DEPLOYMENTS OVER PUBLIC WIRELESS MANS of the broadband wireless access provider but of the owner of backbone fiber and/or Internet access points. Furthermore, several protocols exist for managing connections end to end across the backbone, including Resource Allocation Protocol (RAP) and the aforementioned RSVP. Although the signals may originate in the metro, the actual resource allocation will take place on the backbone. Making Sense of QoS Protocols QoS protocols, as previously mentioned, are often used in multiples. RSVP and DiffServ, for instance, are often used in conjunction with MPLS to support a wide variety of applications. Other protocols may be used more selectively; for example, RSTP would be used for streaming video but not for voice telephony. Given the proliferation of protocols and the complexity of their interactions, engineering an end-to-end IP network for QoS is not an easy task, and it is in fact nearly impossible where protocols are not carried consistently across the network. Unfortunately, configuring intervening switches and routers is generally out of the hands of the local access provider. With content demanding very stringent QoS such as high-definition video or Super Audio Compact Disc (SACD)–quality audio, delivery over a multimode network may simply be infeasible, and if the source is geographically remote, the local access provider may choose to utilize a satellite service to transmit the content in one hop to the local network where it can be cached on a server until needed. It can then be transmitted over a short distance where QoS is entirely under the access provider’s control. Other Methods for Supporting QoS I should not leave the subject of QoS without mentioning a long-standing argument as to the need of special protocols for supporting it over packet networks. Some in fact would contend that QoS can be achieved through other means and that special reservation and prioritization protocols are not the answer because of the difficulty of implementing them across heterogeneous networks. The simplest technique for getting around reservation requirements is to undersubscribe available bandwidth. If everyone on a network enjoys, say, a median throughput rate of 50Mbps, QoS is likely to be satisfactory for almost any application absent any additional provisions for ensuring QoS. And indeed some in the industry have suggested that as network throughputs inch ever upward, the need for special QoS protocols will disappear over time. Given enough bandwidth, surely such representations are correct, but for now bandwidth is still expensive, particularly in metropolitan networks, and with some services such as lifeline telephony or backup storage, the user cannot tolerate momentary suspensions of service, however infrequent. For such services a reservation of bandwidth simply has to be in place against every contingency. Another way to attempt to get around the need for reservation is to create a sort of arti- ficial bandwidth by means of data compression technologies. Compression algorithms reduce the bandwidth required for any given application, often dramatically, and 50-to-1 reductions in the amounts of data required to transmit a signal are commonplace today. In practical terms this may approximate a 50-fold increase in bandwidth, though in reality matters are not so simple. Compression almost always introduces appreciable latency in a transmission, which
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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 199 and 200: 178 CHAPTER 8 ■ NETWORK MANAGEMEN
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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
Page 233: forums.apress.com FOR PROFESSIONALS
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