【資料名稱】：Wi-Fi Telephony Challenges and Solutions

【資料作者】：Praphul Chandra and Lide

【資料日期】：Copyright © 2007,

【資料語言】：英文

【資料格式】：PDF

【資料目錄和簡介】：

Wi-Fi Telephony Challenges and Solutions for Voice over WLANs
Contents
Acknowledgments .............................................................................................. xii
Acronyms ......................................................................................................... xiii
About the Authors ..............................................................................................xx
Chapter 1: The Telephony World ...........................................................................1
1.1 The Basics ....................................................................................................................1
1.1.1 The Evolution of the Telephone Network ........................................................2
1.2 Digitizing Speech .........................................................................................................3
1.3 PSTN Architecture .......................................................................................................6
1.4 Signaling .......................................................................................................................7
1.4.1 Signaling in the Local Loop .............................................................................7
1.4.2 Signaling in the Network ..................................................................................9
1.4.3 SS7 .................................................................................................................10
1.4.4 Call-Setup .......................................................................................................11
1.5 Voice and Wireless Networks .....................................................................................13
1.5.1 First-Generation Wireless Networks ..............................................................13
1.5.2 Second-GenerationWireless Networks ..........................................................14
1.5.3 Third-GenerationWireless Networks .............................................................20
1.6 Summary ....................................................................................................................22
Chapter 2: The Data World ................................................................................23
2.1 Introduction ................................................................................................................23
2.2 Brief History ...............................................................................................................23
2.3 The OSI Seven-Layer Model ......................................................................................24
2.4 The IP Protocol ...........................................................................................................28
2.5 The TCP/IP Transport Layer ......................................................................................32
2.5.1 Transmission Control Protocol (TCP) ............................................................32
2.5.2 User Datagram Protocol (UDP) .....................................................................38
2.6 Other TCP/IP-Based Protocols ...................................................................................38
2.7 Conclusion ..................................................................................................................41
References .........................................................................................................................41
Chapter 3: Voice over IP .....................................................................................43
3.1 Introduction ................................................................................................................43
3.1.1 Motivation for VoIP ........................................................................................44
Contents
viii
3.1.2 Challenges in VoIP .........................................................................................45
3.2 Putting Voice Over Internet ........................................................................................47
3.3 VoIP Architectures ......................................................................................................50
3.4 Signaling Protocols .....................................................................................................52
3.4.1 Media Gateway Control Protocol ...................................................................53
3.4.2 Megaco/H248 .................................................................................................62
3.4.3 H323 ...............................................................................................................63
3.4.4 Session Initiation Protocol (SIP) ....................................................................66
3.5 Voice-over-IP Media ...................................................................................................74
3.6 The Overall Picture .....................................................................................................76
References .........................................................................................................................77
Chapter 4: Wireless Local Area Networks ............................................................79
4.1 Introduction ................................................................................................................79
4.2 The Alphabet Soup .....................................................................................................80
4.3 Network Architecture .................................................................................................82
4.3.1 Connection Setup ...........................................................................................84
4.4 802.11 Framing ..........................................................................................................86
4.4.1 Frame Control ................................................................................................86
4.4.2 Duration/ID ....................................................................................................89
4.4.3 Addresses ........................................................................................................89
4.4.4 Sequence Control ...........................................................................................90
4.4.5 Frame Body ....................................................................................................90
4.4.6 Frame Check Sequence (FCS) .......................................................................91
4.5 Accessing the Medium ...............................................................................................91
4.5.1 CSMA-CD ......................................................................................................92
4.5.2 Wireless Media Access Challenges ................................................................92
4.5.3 Positive ACK ..................................................................................................95
4.5.4 NAV ................................................................................................................95
4.5.5 CSMA-CA ......................................................................................................95
4.5.6 Inter-Frame Spacing (IFS) ..............................................................................97
4.5.7 RTS-CTS ........................................................................................................98
4.6 802.11 PHY ................................................................................................................99
4.6.1 PLCP Framing ..............................................................................................100
4.6.2 Transmission Rate .........................................................................................103
4.6.3 Nonoverlapping Channels ............................................................................104
4.6.4 Power Consumption .....................................................................................106
4.7 Power Save in 802.11 ...............................................................................................106
4.8 Conclusion ................................................................................................................108
Chapter 5: VoWLAN Challenges .......................................................................109
5.1 Introduction ..............................................................................................................109
5.2 VoWLAN ..................................................................................................................109
5.3 System Capacity and QoS ........................................................................................110
5.3.1 Packet Sizes ..................................................................................................111
Contents
ix
5.3.2 Packetization Overheads ..............................................................................112
5.3.3 DCF Overheads ............................................................................................113
5.3.4 Transmission Rate ........................................................................................114
5.3.5 Inherent Fairness Among All Nodes ............................................................116
5.3.6 Analysis ........................................................................................................118
5.4 PCF ...........................................................................................................................119
5.5 Admission Control ....................................................................................................120
5.6 Security .....................................................................................................................121
5.7 Power Save ...............................................................................................................121
5.8 Roaming/Handoffs in 802.11 ...................................................................................122
5.9 Summary ..................................................................................................................124
Chapter 6: QoS and System Capacity .................................................................125
6.1 Introduction ..............................................................................................................125
6.2 802.11e, WME and “Vanilla” WLANs ....................................................................126
6.3 Traffi c Categories .....................................................................................................128
6.4 Transmission Opportunity ........................................................................................129
6.5 EDCF ........................................................................................................................131
6.6 HCF ..........................................................................................................................135
6.7 Voice Data Coexistence ............................................................................................137
6.8 Achieving QoS for VoWLAN ...................................................................................137
6.8.1 Wireless LAN ...............................................................................................138
6.8.2 Wired LAN ...................................................................................................138
6.8.3 IP Network ...................................................................................................139
6.8.4 LAN-only QoS .............................................................................................140
6.9 System Capacity .......................................................................................................140
6.10 Admission Control ..................................................................................................143
6.10.1 Traffi c Categories and Admission Control .................................................145
6.10.2 Handling Rejected TSPECs........................................................................145
6.10.3 Some Issues With TSPECs .........................................................................146
6.11 Summary ................................................................................................................146
Chapter 7: Security ..........................................................................................147
7.1 Introduction ..............................................................................................................147
7.2 Key Establishment in 802.11 ....................................................................................148
7.2.1 What’s Wrong? .............................................................................................148
7.3 Anonymity in 802.11 ................................................................................................149
7.4 Authentication in 802.11 ..........................................................................................150
7.4.1 Open System Authentication ........................................................................152
7.4.2 Shared Key Authentication ...........................................................................152
7.4.3 Authentication and Handoffs ........................................................................154
7.4.4 What’s Wrong with 802.11 Authentication? ................................................155
7.5 Confi dentiality in 802.11 ..........................................................................................156
7.5.1 What’s Wrong with WEP? ...........................................................................157
7.6 Data Integrity in 802.11 ............................................................................................159
Contents
x
7.7 Loopholes in 802.11 Security ...................................................................................162
7.8 WPA ..........................................................................................................................163
7.8.1 Key Establishment ........................................................................................164
7.8.2 Authentication ..............................................................................................168
7.8.3 Confi dentiality ..............................................................................................171
7.8.4 Integrity ........................................................................................................172
7.8.5 The Overall Picture: Confi dentiality + Integrity ..........................................174
7.8.6 How WPA Fixes WEP Loopholes ................................................................174
7.9 WPA2 (802.11i) ........................................................................................................175
7.9.1 Key Establishment ........................................................................................176
7.9.2 Authentication ..............................................................................................176
7.9.3 Confi dentiality ..............................................................................................176
7.9.4 Integrity ........................................................................................................178
7.9.5 The Overall Picture: Confi dentiality + Integrity ..........................................179
7.10 Beyond 802.11 Security .........................................................................................182
7.10.1 IPsec: Security at Layer 3 ...........................................................................183
7.10.2 TLS: Security at Layer 4 ............................................................................187
7.10.3 SRTP ...........................................................................................................190
7.11 Conclusion ...............................................................................................................192
Chapter 8: Roaming .........................................................................................193
8.1 The Need for Roaming .............................................................................................193
8.2 Types of Roaming .....................................................................................................194
8.3 Roaming Issues .........................................................................................................195
8.3.1 Basic 802.11 Roaming Support ....................................................................195
8.4 Roaming and Voice ...................................................................................................197
8.5 Preparing to Roam: Scanning ...................................................................................199
8.5.1 Scanning Types .............................................................................................200
8.5.2 Scanning Strategies ......................................................................................203
8.5.3 Other Site-Table Management Techniques ..................................................204
8.6 When to Roam ..........................................................................................................205
8.7 Where to Roam .........................................................................................................206
8.8 Reauthentication Delays ...........................................................................................207
8.9 Inter-ESS Roaming ...................................................................................................208
8.10 Future Enhancements .............................................................................................210
8.10.1 802.11k .......................................................................................................210
8.10.2 802.11r ........................................................................................................211
8.11 Conclusion ..............................................................................................................212
Chapter 9: Power Management .........................................................................213
9.1 The Need for Power Management ............................................................................213
9.2 Underlying Philosophy of Power Management .......................................................213
9.3 Designing for Power Management ...........................................................................215
9.3.1 Power-Aware System Design .......................................................................216
9.4 Implementing Power Management ...........................................................................222
Contents
xi
9.4.1 WLAN Subsystem ........................................................................................222
9.4.2 LCD and Backlight .......................................................................................229
9.4.3 Host Processor ..............................................................................................230
9.4.4 DSP and Analog Codec ................................................................................230
9.4.5 Memory ........................................................................................................231
9.4.6 Other Peripherals ..........................................................................................231
9.5 An Operational Perspective ......................................................................................232
9.5.1 Maximizing Talk Time .................................................................................232
9.5.2 Maximizing Standby Time ...........................................................................234
9.6 Summary ..................................................................................................................234
Chapter 10: Voice over Wi-Fi and Other Wireless Technologies ............................235
10.1 Introduction ............................................................................................................235
10.2 Ongoing 802.11 Standard Work .............................................................................235
10.2.1 802.11n .......................................................................................................238
10.2.2 802.11p .......................................................................................................239
10.2.3 802.11s .......................................................................................................239
10.2.4 802.11t ........................................................................................................240
10.2.5 802.11u .......................................................................................................240
10.3 Wi-Fi and Cellular Networks ..................................................................................241
10.3.1 Dual-Mode Issues .......................................................................................242
10.3.2 Convergence Strategies ..............................................................................243
10.4 WiMax ....................................................................................................................251
10.5 VoWi-Fi and Bluetooth ...........................................................................................252
10.6 VoWi-Fi and DECT ................................................................................................256
10.7 VoWi-Fi and Other Ongoing 802.x Wireless Projects ............................................258
10.7.1 802.20 .........................................................................................................258
10.7.2 802.21 .........................................................................................................258
10.7.3 802.22 .........................................................................................................259
10.8 Conclusion ..............................................................................................................260
References .......................................................................................................................260
Index ..............................................................................................................261