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Versions: 00 01 02 03 04 RFC 5412

Control and Provisioning of                                   P. Calhoun
Wireless Access Points Working                                 B. O'Hara
Group                                                            R. Suri
Internet-Draft                                             N. Cam Winget
Intended status: Informational                       Cisco Systems, Inc.
Expires: September 3, 2007                                      S. Kelly
                                                 Facetime Communications
                                                             M. Williams
                                                             Nokia, Inc.
                                                                S. Hares
                                              Nexthop Technologies, Inc.
                                                           March 2, 2007


                   Light Weight Access Point Protocol
                    draft-ohara-capwap-lwapp-04.txt

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   By submitting this Internet-Draft, each author represents that any
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Copyright Notice

   Copyright (C) The IETF Trust (2007).






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Abstract

   In the recent years, there has been a shift in wireless LAN product
   architectures from autonomous access points to centralized control of
   light weight access points.  The general goal has been to move most
   of the traditional wireless functionality such as access control
   (user authentication and authorization), mobility and radio
   management out of the access point into a centralized controller.

   The IETF's CAPWAP WG has identified that a standards based protocol
   is necessary between a wireless Access Controller and Wireless
   Termination Points (the latter are also commonly referred to as Light
   Weight Access Points).  This specification defines the Light Weight
   Access Point Protocol (LWAPP), which addresses the CAPWAP's protocol
   requirements.  Although the LWAPP protocol is designed to be flexible
   enough to be used for a variety of wireless technologies, this
   specific document describes the base protocol, and an extension that
   allows it to be used with the IEEE's 802.11 wireless LAN protocol.

































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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   8
     1.1.   Conventions used in this document  . . . . . . . . . . .   9
   2.  Protocol Overview . . . . . . . . . . . . . . . . . . . . . .  10
     2.1.   Wireless Binding Definition  . . . . . . . . . . . . . .  11
     2.2.   LWAPP State Machine Definition . . . . . . . . . . . . .  12
   3.  LWAPP Transport Layers  . . . . . . . . . . . . . . . . . . .  21
     3.1.   LWAPP Transport Header . . . . . . . . . . . . . . . . .  21
       3.1.1.   VER Field  . . . . . . . . . . . . . . . . . . . . .  21
       3.1.2.   RID Field  . . . . . . . . . . . . . . . . . . . . .  21
       3.1.3.   C Bit  . . . . . . . . . . . . . . . . . . . . . . .  21
       3.1.4.   F Bit  . . . . . . . . . . . . . . . . . . . . . . .  21
       3.1.5.   L Bit  . . . . . . . . . . . . . . . . . . . . . . .  22
       3.1.6.   Fragment ID  . . . . . . . . . . . . . . . . . . . .  22
       3.1.7.   Length . . . . . . . . . . . . . . . . . . . . . . .  22
       3.1.8.   Status and WLANS . . . . . . . . . . . . . . . . . .  22
       3.1.9.   Payload  . . . . . . . . . . . . . . . . . . . . . .  22
     3.2.   Using IEEE 802.3 MAC as LWAPP transport  . . . . . . . .  22
       3.2.1.   Framing  . . . . . . . . . . . . . . . . . . . . . .  23
       3.2.2.   AC Discovery . . . . . . . . . . . . . . . . . . . .  23
       3.2.3.   LWAPP Message Header format over IEEE 802.3 MAC
                transport  . . . . . . . . . . . . . . . . . . . . .  23
       3.2.4.   Fragmentation/Reassembly . . . . . . . . . . . . . .  23
       3.2.5.   Multiplexing . . . . . . . . . . . . . . . . . . . .  24
     3.3.   Using IP/UDP as LWAPP transport  . . . . . . . . . . . .  24
       3.3.1.   Framing  . . . . . . . . . . . . . . . . . . . . . .  24
       3.3.2.   AC Discovery . . . . . . . . . . . . . . . . . . . .  24
       3.3.3.   LWAPP Message Header format over IP/UDP transport  .  25
       3.3.4.   Fragmentation/Reassembly for IPv4  . . . . . . . . .  26
       3.3.5.   Fragmentation/Reassembly for IPv6  . . . . . . . . .  26
       3.3.6.   Multiplexing . . . . . . . . . . . . . . . . . . . .  26
   4.  LWAPP Packet Definitions  . . . . . . . . . . . . . . . . . .  27
     4.1.   LWAPP Data Messages  . . . . . . . . . . . . . . . . . .  27
     4.2.   LWAPP Control Messages Overview  . . . . . . . . . . . .  27
       4.2.1.   Control Message Format . . . . . . . . . . . . . . .  28
       4.2.2.   Message Element Format . . . . . . . . . . . . . . .  30
       4.2.3.   Quality of Service . . . . . . . . . . . . . . . . .  31
   5.  LWAPP Discovery Operations  . . . . . . . . . . . . . . . . .  32
     5.1.   Discovery Request  . . . . . . . . . . . . . . . . . . .  32
       5.1.1.   Discovery Type . . . . . . . . . . . . . . . . . . .  33
       5.1.2.   WTP Descriptor . . . . . . . . . . . . . . . . . . .  33
       5.1.3.   WTP Radio Information  . . . . . . . . . . . . . . .  34
     5.2.   Discovery Response . . . . . . . . . . . . . . . . . . .  35
       5.2.1.   AC Address . . . . . . . . . . . . . . . . . . . . .  35
       5.2.2.   AC Descriptor  . . . . . . . . . . . . . . . . . . .  36
       5.2.3.   AC Name  . . . . . . . . . . . . . . . . . . . . . .  37
       5.2.4.   WTP Manager Control IPv4 Address . . . . . . . . . .  37



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       5.2.5.   WTP Manager Control IPv6 Address . . . . . . . . . .  38
     5.3.   Primary Discovery Request  . . . . . . . . . . . . . . .  38
       5.3.1.   Discovery Type . . . . . . . . . . . . . . . . . . .  39
       5.3.2.   WTP Descriptor . . . . . . . . . . . . . . . . . . .  39
       5.3.3.   WTP Radio Information  . . . . . . . . . . . . . . .  39
     5.4.   Primary Discovery Response . . . . . . . . . . . . . . .  39
       5.4.1.   AC Descriptor  . . . . . . . . . . . . . . . . . . .  39
       5.4.2.   AC Name  . . . . . . . . . . . . . . . . . . . . . .  39
       5.4.3.   WTP Manager Control IPv4 Address . . . . . . . . . .  40
       5.4.4.   WTP Manager Control IPv6 Address . . . . . . . . . .  40
   6.  Control Channel Management  . . . . . . . . . . . . . . . . .  41
     6.1.   Join Request . . . . . . . . . . . . . . . . . . . . . .  41
       6.1.1.   WTP Descriptor . . . . . . . . . . . . . . . . . . .  42
       6.1.2.   AC Address . . . . . . . . . . . . . . . . . . . . .  42
       6.1.3.   WTP Name . . . . . . . . . . . . . . . . . . . . . .  42
       6.1.4.   Location Data  . . . . . . . . . . . . . . . . . . .  42
       6.1.5.   WTP Radio Information  . . . . . . . . . . . . . . .  43
       6.1.6.   Certificate  . . . . . . . . . . . . . . . . . . . .  43
       6.1.7.   Session ID . . . . . . . . . . . . . . . . . . . . .  43
       6.1.8.   Test . . . . . . . . . . . . . . . . . . . . . . . .  44
       6.1.9.   XNonce . . . . . . . . . . . . . . . . . . . . . . .  44
     6.2.   Join Response  . . . . . . . . . . . . . . . . . . . . .  44
       6.2.1.   Result Code  . . . . . . . . . . . . . . . . . . . .  45
       6.2.2.   Status . . . . . . . . . . . . . . . . . . . . . . .  45
       6.2.3.   Certificate  . . . . . . . . . . . . . . . . . . . .  46
       6.2.4.   WTP Manager Data IPv4 Address  . . . . . . . . . . .  46
       6.2.5.   WTP Manager Data IPv6 Address  . . . . . . . . . . .  47
       6.2.6.   AC IPv4 List . . . . . . . . . . . . . . . . . . . .  47
       6.2.7.   AC IPv6 List . . . . . . . . . . . . . . . . . . . .  48
       6.2.8.   ANonce . . . . . . . . . . . . . . . . . . . . . . .  48
       6.2.9.   PSK-MIC  . . . . . . . . . . . . . . . . . . . . . .  49
     6.3.   Join ACK . . . . . . . . . . . . . . . . . . . . . . . .  50
       6.3.1.   Session ID . . . . . . . . . . . . . . . . . . . . .  50
       6.3.2.   WNonce . . . . . . . . . . . . . . . . . . . . . . .  50
       6.3.3.   PSK-MIC  . . . . . . . . . . . . . . . . . . . . . .  51
     6.4.   Join Confirm . . . . . . . . . . . . . . . . . . . . . .  51
       6.4.1.   Session ID . . . . . . . . . . . . . . . . . . . . .  51
       6.4.2.   PSK-MIC  . . . . . . . . . . . . . . . . . . . . . .  51
     6.5.   Echo Request . . . . . . . . . . . . . . . . . . . . . .  51
     6.6.   Echo Response  . . . . . . . . . . . . . . . . . . . . .  52
     6.7.   Key Update Request . . . . . . . . . . . . . . . . . . .  52
       6.7.1.   Session ID . . . . . . . . . . . . . . . . . . . . .  52
       6.7.2.   XNonce . . . . . . . . . . . . . . . . . . . . . . .  52
     6.8.   Key Update Response  . . . . . . . . . . . . . . . . . .  52
       6.8.1.   Session ID . . . . . . . . . . . . . . . . . . . . .  53
       6.8.2.   ANonce . . . . . . . . . . . . . . . . . . . . . . .  53
       6.8.3.   PSK-MIC  . . . . . . . . . . . . . . . . . . . . . .  53
     6.9.   Key Update ACK . . . . . . . . . . . . . . . . . . . . .  53



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       6.9.1.   WNonce . . . . . . . . . . . . . . . . . . . . . . .  53
       6.9.2.   PSK-MIC  . . . . . . . . . . . . . . . . . . . . . .  53
     6.10.  Key Update Confirm . . . . . . . . . . . . . . . . . . .  53
       6.10.1.  PSK-MIC  . . . . . . . . . . . . . . . . . . . . . .  54
     6.11.  Key Update Trigger . . . . . . . . . . . . . . . . . . .  54
       6.11.1.  Session ID . . . . . . . . . . . . . . . . . . . . .  54
   7.  WTP Configuration Management  . . . . . . . . . . . . . . . .  55
     7.1.   Configuration Consistency  . . . . . . . . . . . . . . .  55
     7.2.   Configure Request  . . . . . . . . . . . . . . . . . . .  56
       7.2.1.   Administrative State . . . . . . . . . . . . . . . .  56
       7.2.2.   AC Name  . . . . . . . . . . . . . . . . . . . . . .  57
       7.2.3.   AC Name with Index . . . . . . . . . . . . . . . . .  57
       7.2.4.   WTP Board Data . . . . . . . . . . . . . . . . . . .  57
       7.2.5.   Statistics Timer . . . . . . . . . . . . . . . . . .  58
       7.2.6.   WTP Static IP Address Information  . . . . . . . . .  59
       7.2.7.   WTP Reboot Statistics  . . . . . . . . . . . . . . .  59
     7.3.   Configure Response . . . . . . . . . . . . . . . . . . .  60
       7.3.1.   Decryption Error Report Period . . . . . . . . . . .  61
       7.3.2.   Change State Event . . . . . . . . . . . . . . . . .  61
       7.3.3.   LWAPP Timers . . . . . . . . . . . . . . . . . . . .  62
       7.3.4.   AC IPv4 List . . . . . . . . . . . . . . . . . . . .  62
       7.3.5.   AC IPv6 List . . . . . . . . . . . . . . . . . . . .  62
       7.3.6.   WTP Fallback . . . . . . . . . . . . . . . . . . . .  63
       7.3.7.   Idle Timeout . . . . . . . . . . . . . . . . . . . .  63
     7.4.   Configuration Update Request . . . . . . . . . . . . . .  63
       7.4.1.   WTP Name . . . . . . . . . . . . . . . . . . . . . .  64
       7.4.2.   Change State Event . . . . . . . . . . . . . . . . .  64
       7.4.3.   Administrative State . . . . . . . . . . . . . . . .  64
       7.4.4.   Statistics Timer . . . . . . . . . . . . . . . . . .  64
       7.4.5.   Location Data  . . . . . . . . . . . . . . . . . . .  64
       7.4.6.   Decryption Error Report Period . . . . . . . . . . .  64
       7.4.7.   AC IPv4 List . . . . . . . . . . . . . . . . . . . .  64
       7.4.8.   AC IPv6 List . . . . . . . . . . . . . . . . . . . .  64
       7.4.9.   Add Blacklist Entry  . . . . . . . . . . . . . . . .  64
       7.4.10.  Delete Blacklist Entry . . . . . . . . . . . . . . .  65
       7.4.11.  Add Static Blacklist Entry . . . . . . . . . . . . .  66
       7.4.12.  Delete Static Blacklist Entry  . . . . . . . . . . .  66
       7.4.13.  LWAPP Timers . . . . . . . . . . . . . . . . . . . .  67
       7.4.14.  AC Name with Index . . . . . . . . . . . . . . . . .  67
       7.4.15.  WTP Fallback . . . . . . . . . . . . . . . . . . . .  67
       7.4.16.  Idle Timeout . . . . . . . . . . . . . . . . . . . .  67
     7.5.   Configuration Update Response  . . . . . . . . . . . . .  67
       7.5.1.   Result Code  . . . . . . . . . . . . . . . . . . . .  67
     7.6.   Change State Event Request . . . . . . . . . . . . . . .  67
       7.6.1.   Change State Event . . . . . . . . . . . . . . . . .  68
     7.7.   Change State Event Response  . . . . . . . . . . . . . .  68
     7.8.   Clear Config Indication  . . . . . . . . . . . . . . . .  68
   8.  Device Management Operations  . . . . . . . . . . . . . . . .  69



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     8.1.   Image Data Request . . . . . . . . . . . . . . . . . . .  69
       8.1.1.   Image Download . . . . . . . . . . . . . . . . . . .  69
       8.1.2.   Image Data . . . . . . . . . . . . . . . . . . . . .  69
     8.2.   Image Data Response  . . . . . . . . . . . . . . . . . .  70
     8.3.   Reset Request  . . . . . . . . . . . . . . . . . . . . .  70
     8.4.   Reset Response . . . . . . . . . . . . . . . . . . . . .  70
     8.5.   WTP Event Request  . . . . . . . . . . . . . . . . . . .  71
       8.5.1.   Decryption Error Report  . . . . . . . . . . . . . .  71
       8.5.2.   Duplicate IPv4 Address . . . . . . . . . . . . . . .  71
       8.5.3.   Duplicate IPv6 Address . . . . . . . . . . . . . . .  72
     8.6.   WTP Event Response . . . . . . . . . . . . . . . . . . .  73
     8.7.   Data Transfer Request  . . . . . . . . . . . . . . . . .  73
       8.7.1.   Data Transfer Mode . . . . . . . . . . . . . . . . .  73
       8.7.2.   Data Transfer Data . . . . . . . . . . . . . . . . .  74
     8.8.   Data Transfer Response . . . . . . . . . . . . . . . . .  74
   9.  Mobile Session Management . . . . . . . . . . . . . . . . . .  75
     9.1.   Mobile Config Request  . . . . . . . . . . . . . . . . .  75
       9.1.1.   Delete Mobile  . . . . . . . . . . . . . . . . . . .  75
     9.2.   Mobile Config Response . . . . . . . . . . . . . . . . .  76
       9.2.1.   Result Code  . . . . . . . . . . . . . . . . . . . .  76
   10. LWAPP Security  . . . . . . . . . . . . . . . . . . . . . . .  77
     10.1.  Securing WTP-AC communications . . . . . . . . . . . . .  77
     10.2.  LWAPP Frame Encryption . . . . . . . . . . . . . . . . .  78
     10.3.  Authenticated Key Exchange . . . . . . . . . . . . . . .  78
       10.3.1.  Terminology  . . . . . . . . . . . . . . . . . . . .  79
       10.3.2.  Initial Key Generation . . . . . . . . . . . . . . .  80
       10.3.3.  Refreshing Cryptographic Keys  . . . . . . . . . . .  84
     10.4.  Certificate Usage  . . . . . . . . . . . . . . . . . . .  85
   11. IEEE 802.11 Binding . . . . . . . . . . . . . . . . . . . . .  86
     11.1.  Division of labor  . . . . . . . . . . . . . . . . . . .  86
       11.1.1.  Split MAC  . . . . . . . . . . . . . . . . . . . . .  86
       11.1.2.  Local MAC  . . . . . . . . . . . . . . . . . . . . .  88
     11.2.  Roaming Behavior and 802.11 security . . . . . . . . . .  91
     11.3.  Transport specific bindings  . . . . . . . . . . . . . .  92
       11.3.1.  Status and WLANS field . . . . . . . . . . . . . . .  92
     11.4.  BSSID to WLAN ID Mapping . . . . . . . . . . . . . . . .  93
     11.5.  Quality of Service . . . . . . . . . . . . . . . . . . .  93
     11.6.  Data Message bindings  . . . . . . . . . . . . . . . . .  93
     11.7.  Control Message bindings . . . . . . . . . . . . . . . .  93
       11.7.1.  Mobile Config Request  . . . . . . . . . . . . . . .  94
       11.7.2.  WTP Event Request  . . . . . . . . . . . . . . . . . 100
     11.8.  802.11 Control Messages  . . . . . . . . . . . . . . . . 102
       11.8.1.  IEEE 802.11 WLAN Config Request  . . . . . . . . . . 102
       11.8.2.  IEEE 802.11 WLAN Config Response . . . . . . . . . . 107
       11.8.3.  IEEE 802.11 WTP Event  . . . . . . . . . . . . . . . 107
     11.9.  Message Element Bindings . . . . . . . . . . . . . . . . 109
       11.9.1.  IEEE 802.11 WTP WLAN Radio Configuration . . . . . . 109
       11.9.2.  IEEE 802.11 Rate Set . . . . . . . . . . . . . . . . 111



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       11.9.3.  IEEE 802.11 Multi-domain Capability  . . . . . . . . 111
       11.9.4.  IEEE 802.11 MAC Operation  . . . . . . . . . . . . . 112
       11.9.5.  IEEE 802.11 Tx Power . . . . . . . . . . . . . . . . 114
       11.9.6.  IEEE 802.11 Tx Power Level . . . . . . . . . . . . . 114
       11.9.7.  IEEE 802.11 Direct Sequence Control  . . . . . . . . 115
       11.9.8.  IEEE 802.11 OFDM Control . . . . . . . . . . . . . . 116
       11.9.9.  IEEE 802.11 Antenna  . . . . . . . . . . . . . . . . 117
       11.9.10. IEEE 802.11 Supported Rates  . . . . . . . . . . . . 118
       11.9.11. IEEE 802.11 CFP Status . . . . . . . . . . . . . . . 118
       11.9.12. IEEE 802.11 WTP Mode and Type  . . . . . . . . . . . 119
       11.9.13. IEEE 802.11 Broadcast Probe Mode . . . . . . . . . . 119
       11.9.14. IEEE 802.11 WTP Quality of Service . . . . . . . . . 120
       11.9.15. IEEE 802.11 MIC Error Report From Mobile . . . . . . 121
     11.10. IEEE 802.11 Message Element Values . . . . . . . . . . . 122
   12. LWAPP Protocol Timers . . . . . . . . . . . . . . . . . . . . 123
     12.1.  MaxDiscoveryInterval . . . . . . . . . . . . . . . . . . 123
     12.2.  SilentInterval . . . . . . . . . . . . . . . . . . . . . 123
     12.3.  NeighborDeadInterval . . . . . . . . . . . . . . . . . . 123
     12.4.  EchoInterval . . . . . . . . . . . . . . . . . . . . . . 123
     12.5.  DiscoveryInterval  . . . . . . . . . . . . . . . . . . . 123
     12.6.  RetransmitInterval . . . . . . . . . . . . . . . . . . . 123
     12.7.  ResponseTimeout  . . . . . . . . . . . . . . . . . . . . 124
     12.8.  KeyLifetime  . . . . . . . . . . . . . . . . . . . . . . 124
   13. LWAPP Protocol Variables  . . . . . . . . . . . . . . . . . . 125
     13.1.  MaxDiscoveries . . . . . . . . . . . . . . . . . . . . . 125
     13.2.  DiscoveryCount . . . . . . . . . . . . . . . . . . . . . 125
     13.3.  RetransmitCount  . . . . . . . . . . . . . . . . . . . . 125
     13.4.  MaxRetransmit  . . . . . . . . . . . . . . . . . . . . . 125
   14. NAT Considerations  . . . . . . . . . . . . . . . . . . . . . 126
   15. Security Considerations . . . . . . . . . . . . . . . . . . . 128
     15.1.  Certificate based Session Key establishment  . . . . . . 129
     15.2.  PSK based Session Key establishment  . . . . . . . . . . 129
   16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 130
   17. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . 131
   18. IPR Statement . . . . . . . . . . . . . . . . . . . . . . . . 132
   19. References  . . . . . . . . . . . . . . . . . . . . . . . . . 133
     19.1.  Normative References . . . . . . . . . . . . . . . . . . 133
     19.2.  Informational References . . . . . . . . . . . . . . . . 134
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . 135
   Intellectual Property and Copyright Statements  . . . . . . . . . 137











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1.  Introduction

   Unlike wired network elements, Wireless Termination Points (WTPs)
   require a set of dynamic management and control functions related to
   their primary task of connecting the wireless and wired mediums.
   Today, protocols for managing WTPs are either manual static
   configuration via HTTP, proprietary Layer 2 specific or non-existent
   (if the WTPs are self-contained).  The emergence of simple 802.11
   WTPs that are managed by a WLAN appliance or switch (also known as an
   Access Controller, or AC) suggests that having a standardized,
   interoperable protocol could radically simplify the deployment and
   management of wireless networks.  In many cases the overall control
   and management functions themselves are generic and could apply to an
   AP for any wireless Layer 2 protocol.  Being independent of specific
   wireless Layer 2 technologies, such a protocol could better support
   interoperability between Layer 2 devices and enable smoother
   intertechnology handovers.

   The details of how these functions would be implemented are dependent
   on the particular Layer 2 wireless technology.  Such a protocol would
   need provisions for binding to specific technologies.

   LWAPP assumes a network configuration that consists of multiple WTPs
   communicating either via layer 2 (MAC) or layer 3 (IP) to an AC.  The
   WTPs can be considered as remote RF interfaces, being controlled by
   the AC.  The AC forwards all L2 frames it wants to transmit to an WTP
   via the LWAPP protocol.  Packets from mobile nodes are forwarded by
   the WTP to the AC, also via this protocol.  Figure 1 illustrates this
   arrangement as applied to an IEEE 802.11 binding.

              +-+          802.11frames          +-+
              | |--------------------------------| |
              | |              +-+               | |
              | |--------------| |---------------| |
              | |  802.11 PHY/ | |     LWAPP     | |
              | | MAC sublayer | |               | |
              +-+              +-+               +-+
              STA              WTP                AC

                       Figure 1: LWAPP Architecture

   Security is another aspect of Wireless Termination Point management
   that is not well served by existing solutions.  Provisioning WTPs
   with security credentials, and managing which WTPs are authorized to
   provide service are today handled by proprietary solutions.  Allowing
   these functions to be performed from a centralized AC in an
   interoperable fashion increases managability and allows network
   operators to more tightly control their wireless network



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   infrastructure.

   This document describes the Light Weight Access Point Protocol
   (LWAPP), allowing an AC to manage a collection of WTPs.  The protocol
   is defined to be independent of Layer 2 technology, but an 802.11
   binding is provided for use in growing 802.11 wireless LAN networks.

   Goals

   The following are goals for this protocol:

   1. Centralization of the bridging, forwarding, authentication and
      policy enforcement functions for a wireless network.  Optionally,
      the AC may also provide centralized encryption of user traffic.
      This will permit reduced cost and higher efficiency when applying
      the capabilities of network processing silicon to the wireless
      network, as it has already been applied to wired LANs.

   2. Permit shifting of the higher level protocol processing burden
      away from the WTP.  This leaves the computing resource of the WTP
      to the timing critical applications of wireless control and
      access.  This makes the most efficient use of the computing power
      available in WTPs that are the subject of severe cost pressure.

   3. Providing a generic encapsulation and transport mechanism, the
      protocol may be applied to other access point type in the future
      by adding the binding.

   The LWAPP protocol concerns itself solely with the interface between
   the WTP and the AC.  Inter-AC, or mobile to AC communication is
   strictly outside the scope of this document.

1.1.  Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [1].














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2.  Protocol Overview

   LWAPP is a generic protocol defining how Wireless Termination Points
   communicate with Access Controllers.  Wireless Termination Points and
   Access Controllers may communicate either by means of Layer 2
   protocols or by means of a routed IP network.

   LWAPP messages and procedures defined in this document apply to both
   types of transports unless specified otherwise.  Transport
   independence is achieved by defining formats for both MAC level and
   IP level transport (see Section 3).  Also defined are framing,
   fragmentation/reassembly, and multiplexing services to LWAPP for each
   transport type.

   The LWAPP Transport layer carries two types of payload.  LWAPP Data
   Messages are forwarded wireless frames.  LWAPP Control Messages are
   management messages exchanged between an WTP and an AC.  The LWAPP
   transport header defines the "C-bit", which is used to distinguish
   data and control traffic.  When used over IP, the LWAPP data and
   control traffic are also sent over separate UDP ports.  Since both
   data and control frames can exceed PMTU, the payload of an LWAPP data
   or control message can be fragmented.  The fragmentation behavior is
   highly dependent upon the lower layer transport and is defined in
   Section 3.

   The Light Weight Access Protocol (LWAPP) begins with a discovery
   phase.  The WTPs send a Discovery Request frame, causing any Access
   Controller (AC) , receiving that frame to respond with a Discovery
   Response.  From the Discovery Responses received, an WTP will select
   an AC with which to associate, using the Join Request and Join
   Response.  The Join Request also provides an MTU discovery mechanism,
   to determine whether there is support for the transport of large
   frames between the WTP and it's AC.  If support for large frames is
   not present, the LWAPP frames will be fragmented to the maximum
   length discovered to be supported by the network.

   Once the WTP and the AC have joined, a configuration exchange is
   accomplished that will cause both devices to agree on version
   information.  During this exchange the WTP may receive provisioning
   settings.  For the 802.11 binding, this information would typically
   include a name (802.11 Service Set Identifier, SSID), and security
   parameters, the data rates to be advertised as well as the radio
   channel (channels, if the WTP is capable of operating more than one
   802.11 MAC and PHY simultaneously) to be used.  Finally, the WTPs are
   enabled for operation.

   When the WTP and AC have completed the version and provision exchange
   and the WTP is enabled, the LWAPP encapsulates the wireless frames



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   sent between them.  LWAPP will fragment its packets, if the size of
   the encapsulated wireless user data (Data) or protocol control
   (Management) frames causes the resultant LWAPP packet to exceed the
   MTU supported between the WTP and AC.  Fragmented LWAPP packets are
   reassembled to reconstitute the original encapsulated payload.

   In addition to the functions thus far described, LWAPP also provides
   for the delivery of commands from the AC to the WTP for the
   management of devices that are communicating with the WTP.  This may
   include the creation of local data structures in the WTP for the
   managed devices and the collection of statistical information about
   the communication between the WTP and the 802.11 devices.  LWAPP
   provides the ability for the AC to obtain any statistical information
   collected by the WTP.

   LWAPP also provides for a keep alive feature that preserves the
   communication channel between the WTP and AC.  If the AC fails to
   appear alive, the WTP will try to discover a new AC to communicate
   through.

   This Document uses terminology defined in [5]

2.1.  Wireless Binding Definition

   This draft standard specifies a protocol independent of a specific
   wireless access point radio technology.  Elements of the protocol are
   designed to accommodate specific needs of each wireless technology in
   a standard way.  Implementation of this standard for a particular
   wireless technology must follow the binding requirements defined for
   that technology.  This specification includes a binding for the IEEE
   802.11 (see Section 11).

   When defining a binding for other technologies, the authors MUST
   include any necessary definitions for technology-specific messages
   and all technology-specific message elements for those messages.  At
   a minimum, a binding MUST provide the definition for a binding-
   specific Statistics message element, which is carried in the WTP
   Event Request message, and Add Mobile message element, which is
   carried in the Mobile Configure Request.  If any technology specific
   message elements are required for any of the existing LWAPP messages
   defined in this specification, they MUST also be defined in the
   technology binding document.

   The naming of binding-specific message elements MUST begin with the
   name of the technology type, e.g., the binding for IEEE 802.11,
   provided in this standard, begins with "IEEE 802.11"."





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2.2.  LWAPP State Machine Definition

   The following state diagram represents the lifecycle of an WTP-AC
   session:


      /-------------\
      |             v
      |       +------------+
      |      C|    Idle    |<-----------------------------------\
      |       +------------+<-----------------------\           |
      |        ^    |a    ^                         |           |
      |        |    |     \----\                    |           |
      |        |    |          |                 +------------+ |
      |        |    |          |          -------| Key Confirm| |
      |        |    |          |        w/       +------------+ |
      |        |    |          |        |           ^           |
      |        |    |          |t       V           |5          |
      |        |    |        +-----------+       +------------+ |
      |       /     |       C|    Run    |       | Key Update | |
      |     /       |       r+-----------+------>+------------+ |
      |    /        |              ^    |s      u        x|     |
      |   |         v              |    |                 |     |
      |   |   +--------------+     |    |                 v     |y
      |   |  C|  Discovery   |    q|    \--------------->+-------+
      |   |  b+--------------+    +-------------+        | Reset |
      |   |     |d     f|  ^      |  Configure  |------->+-------+
      |   |     |       |  |      +-------------+p           ^
      |   |e    v       |  |              ^                  |
      |  +---------+    v  |i            2|                  |
      | C| Sulking |   +------------+    +--------------+    |
      |  +---------+  C|    Join    |--->| Join-Confirm |    |
      |               g+------------+z   +--------------+    |
      |                   |h      m|        3|       |4      |
      |                   |        |         |       v       |o
      |\                  |        |         |     +------------+
       \\-----------------/         \--------+---->| Image Data |C
        \------------------------------------/     +------------+n

                       Figure 2: LWAPP State Machine

   The LWAPP state machine, depicted above, is used by both the AC and
   the WTP.  For every state defined, only certain messages are
   permitted to be sent and received.  In all of the LWAPP control
   messages defined in this document, the state for which each command
   is valid is specified.

   Note that in the state diagram figure above, the 'C' character is



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   used to represent a condition that causes the state to remain the
   same.

   The following text discusses the various state transitions, and the
   events that cause them.

   Idle to Discovery (a):  This is the initialization state.

      WTP:  The WTP enters the Discovery state prior to transmitting the
         first Discovery Request (see Section 5.1).  Upon entering this
         state, the WTP sets the DiscoveryInterval timer (see
         Section 12).  The WTP resets the DiscoveryCount counter to zero
         (0) (see Section 13).  The WTP also clears all information from
         ACs (e.g., AC Addresses) it may have received during a previous
         Discovery phase.

      AC:  The AC does not need to maintain state information for the
         WTP upon reception of the Discovery Request, but it MUST
         respond with a Discovery Response (see Section 5.2).

   Discovery to Discovery (b):  This is the state the WTP uses to
      determine which AC it wishes to connect to.

      WTP:  This event occurs when the DiscoveryInterval timer expires.
         The WTP transmits a Discovery Request to every AC which the WTP
         hasn't received a response to.  For every transition to this
         event, the WTP increments DisoveryCount counter.  See
         Section 5.1) for more information on how the WTP knows which
         ACs it should transmit the Discovery Requests to.  The WTP
         restarts the DiscoveryInterval timer.

      AC:  This is a noop.

   Discovery to Sulking (d):  This state occurs on a WTP when Discovery
      or connectivity to the AC fails.

      WTP:  The WTP enters this state when the DiscoveryInterval timer
         expires and the DiscoveryCount variable is equal to the
         MaxDiscoveries variable (see Section 13).  Upon entering this
         state, the WTP will start the SilentInterval timer.  While in
         the Sulking state, all LWAPP messages received are ignored.

      AC:  This is a noop.








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   Sulking to Idle (e):  This state occurs on a WTP when it must restart
      the discovery phase.

      WTP:  The WTP enters this state when the SilentInterval timer (see
         Section 12) expires.

      AC:  This is a noop.

   Discovery to Join (f):  This state is used by the WTP to confirm its
      commitment to an AC that it wishes to be provided service.

      WTP:  The WTP selects the best AC based on the information it
         gathered during the Discovery Phase.  It then transmits a Join
         Request (see Section 6.1 to its preferred AC.  The WTP starts
         the WaitJoin Timer (see Section 12).

      AC:  The AC enters this state for the given WTP upon reception of
         a Join Request.  The AC processes the request and responds with
         a Join Response.

   Join to Join (g):  This state transition occurs during the join
      phase.

      WTP:  The WTP enters this state when the WaitJoin timer expires,
         and the underlying transport requires LWAPP MTU detection
         Section 3).

      AC:  This state occurs when the AC receives a retransmission of a
         Join Request.  The WTP processes the request and responds with
         the Join Response..

   Join to Idle (h):  This state is used when the join process failed.

      WTP:  This state transition occurs if the WTP is configured to use
         PSK security and receives a Join Response that includes an
         invalid PSK-MIC message element.

      AC:  The AC enters this state when it transmits an unsuccessful
         Join Response.

   Join to Discovery (i):  This state is used when the join process
      failed.

      WTP:  The WTP enters this state when it receives an unsuccessful
         Join Response.  Upon entering this state, the WTP sets the
         DiscoveryInterval timer (see Section 12).  The WTP resets the
         DiscoveryCount counter to zero (0) (see Section 13).  This
         state transition may also occur if the PSK-MIC (see



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         Section 6.2.9) message element is invalid.

      AC:  This state transition is invalid.

   Join to Join-Confirm (z):  This state is used to provide key
      confirmation during the join process.

      WTP:  This state is entered when the WTP receives a Join Response.
         In the event that certificate based security is utilized, this
         transition will occur if the Certificate message element is
         present and valid in the Join Response.  For pre-shared key
         security, the Join Response must include a valud and
         authenticated PSK-MIC message element.  The WTP MUST respond
         with a Join ACK, which is used to provide key confirmation.

      AC:  The AC enters this state when it receives a valid Join ACK.
         For certificate based security, the Join ACK MUST include a
         valid and authenticated xxxx message element.  For pre-shared
         key security, the message must include a valid PSK-MIC message
         element.  The AC MUST respond with a Join Confirm message,
         which includes the Session Key message element.

   Join-Confirm to Idle (3):  This state is used when the join process
      failed.

      WTP:  This state transition occurs when the WTP receives an
         invalid Join Confirm.

      AC:  The AC enters this state when it receives an invalid Join
         ACK.

   Join-Confirm to Configure (2):  This state is used by the WTP and the
      AC to exchange configuration information.

      WTP:  The WTP enters this state when it receives a successful Join
         Confirm, and determines that its version number and the version
         number advertised by the AC are the same.  The WTP transmits
         the Configure Request (see Section 7.2) message to the AC with
         a snapshot of its current configuration.  The WTP also starts
         the ResponseTimeout timer (see Section 12).

      AC:  This state transition occurs when the AC receives the
         Configure Request from the WTP.  The AC must transmit a
         Configure Response (see Section 7.3) to the WTP, and may
         include specific message elements to override the WTP's
         configuration.





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   Join-Confirm to Image Data (4):  This state is used by the WTP and
      the AC to download executable firmware.

      WTP:  The WTP enters this state when it receives a successful Join
         Confirm, and determines that its version number and the version
         number advertised by the AC are different.  The WTP transmits
         the Image Data Request (see Section 8.1) message requesting
         that the AC's latest firmware be initiated.

      AC:  This state transition occurs when the AC receives the Image
         Data Request from the WTP.  The AC must transmit a Image Data
         Response (see Section 8.2) to the WTP, which includes a portion
         of the firmware.

   Image Data to Image Data (n):  This state is used by WTP and the AC
      during the firmware download phase.

      WTP:  The WTP enters this state when it receives a Image Data
         Response that indicates that the AC has more data to send.

      AC:  This state transition occurs when the AC receives the Image
         Data Request from the WTP while already in this state, and it
         detects that the firmware download has not completed.

   Image Data to Reset (o):  This state is used when the firmware
      download is completed.

      WTP:  The WTP enters this state when it receives a Image Data
         Response that indicates that the AC has no more data to send,
         or if the underlying LWAPP transport indicates a link failure.
         At this point, the WTP reboots itself.

      AC:  This state transition occurs when the AC receives the Image
         Data Request from the WTP while already in this state, and it
         detects that the firmware download has completed, or if the
         underlying LWAPP transport indicates a link failure.  Note that
         the AC itself does not reset, but it places the specific WTPs
         context it is communicating with in the reset state, meaning
         that it clears all state associated with the WTP.

   Configure to Reset (p):  This state transition occurs if the
      Configure phase fails.

      WTP:  The WTP enters this state when the reliable transport fails
         to deliver the Configure Request, or if the ResponseTimeout
         Timer (see Section 12)expires.





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      AC:  This state transition occurs if the AC is unable to transmit
         the Configure Response to a specific WTP.  Note that the AC
         itself does not reset, but it places the specific WTPs context
         it is communicating with in the reset state, meaning that it
         clears all state associated with the WTP.

   Configure to Run (q):  This state transition occurs when the WTP and
      AC enters their normal state of operation.

      WTP:  The WTP enters this state when it receives a successful
         Configure Response from the AC.  The WTP initializes the
         HeartBeat Timer (see Section 12), and transmits the Change
         State Event Request message (see Section 7.6).

      AC:  This state transition occurs when the AC receives the Change
         State Event Request (see Section 7.6) from the WTP.  The AC
         responds with a Change State Event Response (see Section 7.7)
         message.  The AC must start the Session ID and Neighbor Dead
         timers (see Section 12).

   Run to Run (r):  This is the normal state of operation.

      WTP:  This is the WTP's normal state of operation, and there are
         many events that cause this to occur:

         Configuration Update:  The WTP receives a Configuration Update
            Request (see Section 7.4).  The WTP MUST respond with a
            Configuration Update Response (see Section 7.5).

         Change State Event:  The WTP receives a Change State Event
            Response, or determines that it must initiate a Change State
            Event Request, as a result of a failure or change in the
            state of a radio.

         Echo Request:  The WTP receives an Echo Request message
            Section 6.5), which it MUST respond with an Echo Response
            (see Section 6.6).

         Clear Config Indication:  The WTP receives a Clear Config
            Indication message Section 7.8).  The WTP MUST reset its
            configuration back to manufacturer defaults.

         WTP Event:  The WTP generates a WTP Event Request to send
            information to the AC Section 8.5).  The WTP receives a WTP
            Event Response from the AC Section 8.6).






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         Data Transfer:  The WTP generates a Data Transfer Request to
            the AC Section 8.7).  The WTP receives a Data Transfer
            Response from the AC Section 8.8).

         WLAN Config Request:  The WTP receives an WLAN Config Request
            message Section 11.8.1), which it MUST respond with an WLAN
            Config Response (see Section 11.8.2).

         Mobile Config Request:  The WTP receives an Mobile Config
            Request message Section 9.1), which it MUST respond with an
            Mobile Config Response (see Section 9.2).

      AC:  This is the AC's normal state of operation, and there are
         many events that cause this to occur:

         Configuration Update:  The AC sends a Configuration Update
            Request (see Section 7.4) to the WTP to update its
            configuration.  The AC receives a Configuration Update
            Response (see Section 7.5) from the WTP.

         Change State Event:  The AC receives a Change State Event
            Request (see Section 7.6), which it MUST respond to with the
            Change State Event Response (see Section 7.7).

         Echo:  The AC sends an Echo Request message Section 6.5) or
            receives the associated Echo Response (see Section 6.6) from
            the WTP.

         Clear Config Indication:  The AC sends a Clear Config
            Indication message Section 7.8).

         WLAN Config:  The AC sends an WLAN Config Request message
            Section 11.8.1) or receives the associated WLAN Config
            Response (see Section 11.8.2) from the WTP.

         Mobile Config:  The AC sends an Mobile Config Request message
            Section 9.1) or receives the associated Mobile Config
            Response (see Section 9.2) from the WTP.

         Data Transfer:  The AC receives a Data Transfer Request from
            the AC (see Section 8.7) and MUST generate the associated
            Data Transfer Response message (see Section 8.8).

         WTP Event:  The AC receives a WTP Event Request from the AC
            (see Section 8.5) and MUST generate the associated WTP Event
            Response message (see Section 8.6).





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   Run to Reset (s):  This event occurs when the AC wishes for the WTP
      to reboot.

      WTP:  The WTP enters this state when it receives a Reset Request
         (see Section 8.3).  It must respond with a Reset Response (see
         Section 8.4), and once the reliable transport acknowledgement
         has been received, it must reboot itself.

      AC:  This state transition occurs either through some
         administrative action, or via some internal event on the AC
         that causes it to request that the WTP disconnect.  Note that
         the AC itself does not reset, but it places the specific WTPs
         context it is communicating with in the reset state.

   Run to Idle (t):  This event occurs when an error occurs in the
      communication between the WTP and the AC.

      WTP:  The WTP enters this state when the underlying reliable
         transport in unable to transmit a message within the
         RetransmitInterval timer (see Section 12), and the maximum
         number of RetransmitCount counter has reached the MaxRetransmit
         variable (see Section 13).

      AC:  The AC enters this state when the underlying reliable
         transport in unable to transmit a message within the
         RetransmitInterval timer (see Section 12), and the maximum
         number of RetransmitCount counter has reached the MaxRetransmit
         variable (see Section 13).

   Run to Key Update (u):  This event occurs when the WTP and the AC are
      to exchange new keying material, with which it must use to protect
      all future messages.

      WTP:  This state transition occurs when the KeyLifetime timer
         expires (see Section 12).

      AC:  The WTP enters this state when it receives a Key Update
         Request (see Section 6.7).

   Key Update to Key Confirm (w):  This event occurs during the rekey
      phase and is used to complete the loop.

      WTP:  This state transition occurs when the WTP receives the Key
         Update Response.  The WTP MUST only accept the message if it is
         authentic.  The WTP responds to this response with a Key Update
         ACK.





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      AC:  The AC enters this state when it receives an authenticated
         Key Update ACK message.

   Key Confirm to Run (5):  This event occurs when the rekey exchange
      phase is completed.

      WTP:  This state transition occurs when the WTP receives the Key
         Update Confirm.  The newly derived encryption key and IV must
         be plumbed into the crypto module after validating the
         message's authentication.

      AC:  The AC enters this state when it transmits the Key Update
         Confirm message.  The newly derived encryption key and IV must
         be plumbed into the crypto module after transmitting a Key
         Update Confirm message.

   Key Update to Reset (x):  This event occurs when the key exchange
      phase times out.

      WTP:  This state transition occurs when the WTP does not receive a
         Key Update Response from the AC.

      AC:  The AC enters this state when it is unable to process a Key
         Update Request.

   Reset to Idle (y):  This event occurs when the state machine is
      restarted.

      WTP:  The WTP reboots itself.  After reboot the WTP will start its
         LWAPP state machine in the Idle state.

      AC:  The AC clears out any state associated with the WTP.  The AC
         generally does this as a result of the reliable link layer
         timing out.

















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3.  LWAPP Transport Layers

   The LWAPP protocol can operate at layer 2 or 3.  For layer 2 support,
   the LWAPP messages are carried in a native Ethernet frame.  As such,
   the protocol is not routable and depends upon layer 2 connectivity
   between the WTP and the AC.  Layer 3 support is provided by
   encapsulating the LWAPP messages within UDP.

3.1.  LWAPP Transport Header

   All LWAPP protocol packets are encapsulated using a common header
   format, regardless of the transport used to carry the frames.
   However, certain flags are not applicable for a given transport, and
   it is therefore necessary to refer to the specific transport section
   in order to determine which flags are valid.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |VER| RID |C|F|L|    Frag ID    |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Status/WLANs         |   Payload...  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.1.1.  VER Field

   A 2 bit field which contains the version of LWAPP used in this
   packet.  The value for this draft is 0.

3.1.2.  RID Field

   A 3 bit field which contains the Radio ID number for this packet.
   WTPs with multiple radios but a single MAC Address use this field to
   indicate which radio is associated with the packet.

3.1.3.  C Bit

   The Control Message 'C' bit indicates whether this packet carries a
   data or control message.  When this bit is zero (0), the packet
   carries an LWAPP data message in the payload (see Section 4.1).  When
   this bit is one (1), the packet carries an LWAPP control message as
   defined in section Section 4.2 for consumption by the addressed
   destination.

3.1.4.  F Bit

   The Fragment 'F' bit indicates whether this packet is a fragment.
   When this bit is one (1), the packet is a fragment and MUST be



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   combined with the other corresponding fragments to reassemble the
   complete information exchanged between the WTP and AC.

3.1.5.  L Bit

   The Not Last 'L' bit is valid only if the 'F' bit is set and
   indicates whether the packet contains the last fragment of a
   fragmented exchange between WTP and AC.  When this bit is 1, the
   packet is not the last fragment.  When this bit is 0, the packet is
   the last fragment.

3.1.6.  Fragment ID

   An 8 bit field whose value is assigned to each group of fragments
   making up a complete set.  The fragment ID space is managed
   individually for every WTP/AC pair.  The value of Fragment ID is
   incremented with each new set of fragments.  The Fragment ID wraps to
   zero after the maximum value has been used to identify a set of
   fragments.  LWAPP only supports up to 2 fragments per frame.

3.1.7.  Length

   The 16 bit length field contains the number of bytes in the Payload.
   The field is encoded as an unsigned number.  If the LWAPP packet is
   encrypted, the length field includes the AES-CCM MIC (see
   Section 10.2 for more information).

3.1.8.  Status and WLANS

   The interpretation of this 16 bit field is binding specific.  Refer
   to the transport portion of the binding for a wireless technology for
   the specification.

3.1.9.  Payload

   This field contains the header for an LWAPP Data Message or LWAPP
   Control Message, followed by the data associated with that message.

3.2.  Using IEEE 802.3 MAC as LWAPP transport

   This section describes how the LWAPP protocol is provided over native
   ethernet frames.  An LWAPP packet is formed from the MAC frame header
   followed by the LWAPP message header.  The following figure provides
   an example of the frame formats used when LWAPP is used over the IEEE
   802.3 transport.






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       Layer 2 LWAPP Data Frame
       +------------