WiMax Operator's Manual

More documents

Recommendations

Info

CHAPTER 7 ■ SERVICE DEPLOYMENTS OVER PUBLIC WIRELESS MANS 159 Subscriber-administered VPNs are quite common among large enterprise customers who generally have in their employ experienced LAN managers, and for some organizations these privately operated VPNs are entirely satisfactory. But where an enterprise manager must connect with widely scattered remote locations, and especially where specific amounts of bandwidth and stringent constraints on delay are demanded, then a private implementation is unlikely to prove wholly satisfactory. Therefore, wireless broadband operators should not rule out even the largest organizations as candidates for managed VPN services. Switched VPNs The second type of VPN, that defined by layer 2 switching, takes a number of forms based on both the protocols utilized and the setup methodology. Such layer 2 VPNs can be established over pure circuit networks or over packet networks that employ switches rather than routers. Both approaches have their respective advantages and disadvantages. Pure Circuit-Switched VPNs I can dismiss in a few words pure circuit services. It is perfectly possible to create a VPN by concatenating T1 connections over distance, and such “nailed-up” VPNs were commonplace in the 1980s and early 1990s before telcos offered packet services. These TDM circuit-based VPNs provide a high degree of privacy and availability but are prohibitively expensive to set up on a large scale and, since the introduction of so-called fast packet services, have fallen into general disuse. In theory, a broadband wireless operator could set up a circuit-based VPN for a customer by allocating an entire channel to that customer and then arranging with a local and/or long-distance telco for the provision of a circuit connectivity through to the endpoint of the VPN, but this does not represent a service model with much potential for the future. Switched Fast Packet VPNs During the middle and late 1990s, VPNs utilizing frame relay and/or ATM connections—what have come to become known as fast packet connections, though ATM is not really packet based—became popular, and they are still present in the marketplace today, particularly deployments where frame relay traffic is encapsulated within an ATM overlay. Such VPNs are also known as virtual private wire services (VPWSs) because the connections themselves are treated as if they are hardwire circuit connections rather than virtual circuits—that is, fixed allocations of bandwidth set up by the ATM and frame relay protocols. In terms of ensuring privacy and high availability, there is nothing wrong with frame relay VPNs, but the speeds supported by frame relay service providers have been unimpressive, and the efficiency and robustness of frame relay networks are inferior to that of Multiprotocol Label Switching (MPLS)–enabled IP networks that offer similar benefits. Frame relay, because of a relative lack of redundancy and error correction mechanisms, is not well suited to the wireless realm and has seldom been employed in wireless broadband networks. However, as indicated in Chapter 1, the 802.16 standard does support ATM. In theory, an ATM-based VPN service offering is perfectly possible within a broadband wireless network, but it squanders precious bandwidth. Furthermore, in the case of remote locations outside of the wireless operator’s own service area, it compels the operator to purchase expensive end-to-end ATM connections through the backbone from long-distance service providers.
160 CHAPTER 7 ■ SERVICE DEPLOYMENTS OVER PUBLIC WIRELESS MANS Switched Packet VPNs Packet streams can be either switched or routed, and the distinction is important, both generally and in regard to VPNs. Routers direct packet traffic one packet at a time and thus can send individual packets within the same transmission over diverse routes according to momentary fluctuations in network congestion and availability. Switches, on the other hand, establish a single physical path for the stream, and each packet follows that path regardless of network conditions. Thus, switches are relatively dumb compared to routers. Discussions of circuit switching of packet traffic tend to give rise to some confusion, so I will attempt to clarify the issues. In a pure circuit connection, such as that afforded by SONET, only one transmission will occupy any particular path. In a circuit-switched packet network, all packets in the same transmission will follow the same path as well, but they will not have that path for their exclusive use, as is the case with a switched circuit network. In a sense, the circuit-switched path approach may be seen as a kind of compromise between packet routing and pure circuit switching. Because multiple streams are contending for bandwidth within a single path, the efficiency of the network is higher than is case for circuit; however, network availability is lower. At the same time, the intelligence required of the network node is less than for a routed packet network. Two particular switching protocols are employed within VPNs, Ethernet switching and MPLS, and sometimes both are used together. In both cases, and in routed VPNs as well, a technique known as tunneling is used to set up the VPN. A tunnel is a means of transmitting data across a network from one point to another as though the two points were directly connected. The tunnel is established simply by providing the packets with an extra address header that is attached to the front of the packet. Any intermediate node in the network that has been enabled to support a VPN will pass the packet based on the forwarding instructions in the extra header without examining anything else in the packet. Incidentally, tunnels need not be restricted to one user. In certain tunneling protocols, several VPNs may be multiplexed within a single tunnel, though the privacy of the different users will be maintained. In simple tunneling only the address is being used to ensure privacy. Each device attached to the network is being asked in effect not to read the packet and to pass it on. Thus, the privacy within such a virtual private network is conditional, and for subscribers whose transmissions are highly confidential—and that includes most subscribers to business-class data services— something more is needed, namely, encryption of the data stream. Several methods exist for actually executing a packet-switched VPN across a network. Those methods fall into two subsets, one utilizing an Ethernet switch and the other an MPLS switch, both located at the service provider’s central office. The first of the switched Ethernet approaches you shall consider is a virtual private LAN service (VPLS). Here the enterprise LAN extends to the edge of the service provider network, and the provider network assumes the function of an Ethernet switch to connect all the individual remote locations into a single logical-switched Ethernet. Customer premise equipment performs no traffic direction function in regard to the VPN. The service provider handles all that. Closely related to the VPLS is the IPLS (which stands for IP-only LAN-like service). Here IP rather than Ethernet traffic emanates from the subscriber premises, but that traffic is switched rather than routed by the service provider. Inasmuch as 802.16 is based on an IP
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:
Page 45 and 46:
Page 47 and 48:
Page 49 and 50:
Page 51 and 52:
Page 53 and 54:
Page 55 and 56:
34 CHAPTER 3 ■ STRATEGIC PLANNING
Page 57 and 58:
Page 59 and 60:
Page 61 and 62:
Page 63 and 64:
Page 65 and 66:
Page 67 and 68:
Page 69 and 70:
Page 71 and 72:
Page 73 and 74:
Page 75 and 76:
Page 77 and 78:
Page 79 and 80:
Page 81 and 82:
Page 83 and 84:
Page 85 and 86:
64 CHAPTER 4 ■ SETTING UP PHYSICA
Page 87 and 88:
Page 89 and 90:
Page 91 and 92:
Page 93 and 94:
Page 95 and 96:
Page 97 and 98:
Page 99 and 100:
Page 101 and 102:
Page 103 and 104:
Page 105 and 106:
Page 107 and 108:
Page 109 and 110:
Page 111 and 112:
Page 113 and 114:
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
100 CHAPTER 4 ■ SETTING UP PHYSIC
Page 123 and 124:
102 CHAPTER 5 ■ STRATEGIES FOR SU
Page 125 and 126:
Page 127 and 128:
Page 129 and 130: 108 CHAPTER 5 ■ STRATEGIES FOR SU
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 196: CHAPTER 7 ■ SERVICE DEPLOYMENTS O
Page 199 and 200: 178 CHAPTER 8 ■ NETWORK MANAGEMEN
Page 208 and 209: CHAPTER 9 ■ ■ ■ Network Secur
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
show all

WiMax Operator's Manual

Create successful ePaper yourself

Delete template?

Save as template?