WiMax Operator's Manual

More documents

Recommendations

Info

CHAPTER 4 ■ SETTING UP PHYSICAL INFRASTRUCTURE 73 In a mesh, no real distinction exists between a base station and subscriber premises terminal. Instead of each subscriber terminal transmitting back to a base station, which itself would define a cell, mesh terminals transmit to one another, passing the signal along until it arrives at its final destination at the central office. Each terminal will normally be endowed with some intelligence and will include a small router and/or switch for determining which adjacent node in the network will be selected as the intermediate destination for a message. The terminal will be able to choose among all the other subscriber terminals within reach and will normally compute a path that is least congested. If one of the terminals is malfunctioning, the transmitting terminal will simply route around it. A wireless mesh is a form of peer-to-peer network, but the peering takes place on the physical layer as well as layers two and three of the network stack. In effect, the mesh provides its own backhaul. To paraphrase George Orwell, in a mesh all nodes are equal, but one node is more equal than the others, and that is known as the seed. The seed is the first node installed and communicates directly with the central office equipment and through it with the PSTN and the public Internet. In networks where subscribers are few and scattered, more than one seed may be required. The Internet itself takes the form of a logical mesh and stands as the prime exemplar of the robustness and essential soundness of the mesh concept; reflecting on the explosive growth of the Internet, some equipment developers familiar with its history have assumed a certain inevitability to the mesh concept in the wireless domain as well. And perhaps such inevitability is real. Still, mesh equipment to date has achieved little success in the marketplace, and most of the more than 20 manufacturers that have developed it have been forced to shut their doors. I suspect that price has been the major issue. Putting a router or switch at every terminal cannot but increase the cost the subscriber premises package, though it should make for a lessexpensive central office installation. Against that price must be weighed the price of backhaul, which of course is highly variable. If backhaul providers are determined to gouge the wireless broadband operator, then opting for a mesh configuration is a counter move. But one should remember that there are other ways to implement wireless backhaul where the wireless broadband operator still retains ownership of the backhaul channel, so the mesh must not be regarded as the sole solution. Ring architectures, the second means of eliminating the backhaul, are equivalent to daisy chains or buses. Each node connects to two other nodes, and the whole assemblage forms a closed ring. Rings tend to be impractical when a large number of subscriber nodes are involved and are much less robust than meshes; on the other hand, they require less network intelligence. Nevertheless, they are similarly expensive to implement because of the presence of routers, switches, or add-drop multiplexers in the subscriber terminals. Much of the point-to-point microwave equipment designed for mobile backhaul supports pointto-consecutive-point architectures as well, and one should opt for this approach when purchasing equipment. Fiber-Optic Backhaul: The Gold Standard If the price is right, fiber backhaul is preferable to all other methods. Fiber links offer higher throughput speeds than any competing access technology and extremely high availability. All fiber links are not equal, however, and, moreover, the fiber link should always be considered in the context of overall metro core network, of which the fiber itself comprises the lowest layer.
74 CHAPTER 4 ■ SETTING UP PHYSICAL INFRASTRUCTURE Fiber-optic networks in the broadest sense may be divided into two categories: active and passive. Active networks employ optoelectronic elements that on-load and off-load traffic and direct it along the network paths, as well as amplifying and conditioning the signals to extend distance and reduce error rates. Passive networks are much simpler and employ passive optical splitters to direct the signal along parallel optical paths, generally not exceeding 32 because each split halves optical power in the resulting pathways. PONS Core optical networks in metropolitan settings are almost exclusively active today. Passive optical networks (PONs) are mainly used as an access technology, though PON manufacturers have been trying to promote them for backhaul for years. PONs carry much lower equipment costs than traditional active optical networks, and they offer aggregate throughput speeds in the low gigabits per second with the possibility of much higher speeds through a technique known as wave division multiplexing. For a wireless broadband operator able to obtain “dark fiber,” explained in detail shortly, a PON provisioned by the broadband operator may constitute an attractive option for backhaul. As is, the number of firms offering PON backhaul anywhere in the world probably does not exceed 20. Figure 4-2 shows a passive optical network. Figure 4-2. A passive optical network, courtesy of Optical Solutions Active Fiber Connections Active optical networks are based largely on synchronous optical network (SONET) and synchronous digital hierarchy (SDH), which means that available bandwidth is apportioned in temporal channels taking the form of fixed time slots. Such networks are inefficient in their use of network resources, and the services running over them are generally expensive, but reliability is high. Packet services, which are just beginning to challenge circuit in the marketplace, are generally less reliable but less expensive per a given throughput speed.
Page 2 and 3:
WiMax Operator’s Manual Building
Page 4:
This book is dedicated to my wife.
Page 8 and 9:
Contents About the Author . . . . .
Page 10 and 11:
■CONTENTS ix Performing Site Surv
Page 12:
■CONTENTS xi Cyberwarfare . . . .
Page 16:
About the Technical Reviewer ■ROB
Page 20 and 21:
Introduction Broadband wireless has
Page 22 and 23:
CHAPTER 1 ■ ■ ■ Wireless Broa
Page 24 and 25:
CHAPTER 1 ■ WIRELESS BROADBAND AN
Page 26 and 27:
Page 28 and 29:
Page 30 and 31:
Page 32:
Page 35 and 36:
14 CHAPTER 2 ■ ARCHITECTING THE N
Page 37 and 38:
Page 39 and 40:
Page 41 and 42:
Page 43 and 44: 22 CHAPTER 2 ■ ARCHITECTING THE N
Page 55 and 56: 34 CHAPTER 3 ■ STRATEGIC PLANNING
Page 85 and 86: 64 CHAPTER 4 ■ SETTING UP PHYSICA
Page 93: 72 CHAPTER 4 ■ SETTING UP PHYSICA
Page 121 and 122: 100 CHAPTER 4 ■ SETTING UP PHYSIC
Page 123 and 124: 102 CHAPTER 5 ■ STRATEGIES FOR SU
Page 145 and 146:
124 CHAPTER 5 ■ STRATEGIES FOR SU
Page 147 and 148:
Page 149 and 150:
Page 152 and 153:
CHAPTER 6 ■ ■ ■ Beyond Access
Page 154 and 155:
CHAPTER 6 ■ BEYOND ACCESS 133 Rou
Page 156 and 157:
CHAPTER 6 ■ BEYOND ACCESS 135 (Qo
Page 158 and 159:
CHAPTER 6 ■ BEYOND ACCESS 137 The
Page 160 and 161:
CHAPTER 6 ■ BEYOND ACCESS 139 ins
Page 162 and 163:
Figure 6-4. Wireless public network
Page 164 and 165:
CHAPTER 6 ■ BEYOND ACCESS 143 sto
Page 166 and 167:
Specialized Content Distribution Pl
Page 168 and 169:
Beyond the Central Office CHAPTER 6
Page 170 and 171:
CHAPTER 6 ■ BEYOND ACCESS 149 out
Page 172 and 173:
CHAPTER 6 ■ BEYOND ACCESS 151 som
Page 174 and 175:
CHAPTER 7 ■ ■ ■ Service Deplo
Page 176 and 177:
CHAPTER 7 ■ SERVICE DEPLOYMENTS O
Page 178 and 179:
Page 180 and 181:
Page 182 and 183:
Page 184 and 185:
Page 186 and 187:
Page 188 and 189:
Page 190 and 191:
Page 192 and 193:
Page 194 and 195:
Page 196:
Page 199 and 200:
178 CHAPTER 8 ■ NETWORK MANAGEMEN
Page 201 and 202:
Page 203 and 204:
Page 205 and 206:
Page 208 and 209:
CHAPTER 9 ■ ■ ■ Network Secur
Page 210 and 211:
CHAPTER 9 ■ NETWORK SECURITY 189
Page 212 and 213:
Page 214 and 215:
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
show all

WiMax Operator's Manual

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?