Network Working Group P. Calhoun Internet-Draft B. O'Hara Expires: August 5, 2005 Airespace S. Kelly Facetime Communications R. Suri Airespace M. Williams Nokia, Inc. S. Hares Nexthop Technologies, Inc. Feb 2005 Light Weight Access Point Protocol (LWAPP) draft-ohara-capwap-lwapp-01.txt Status of this Memo This document is an Internet-Draft and is subject to all provisions of Section 3 of RFC 3667. By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she become aware will be disclosed, in accordance with RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 5, 2005. Copyright Notice Copyright (C) The Internet Society (2005). Calhoun, et al. Expires August 5, 2005 [Page 1] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 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. Calhoun, et al. Expires August 5, 2005 [Page 2] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 7 1.1 Conventions used in this document . . . . . . . . . . . 8 2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . 9 2.1 Wireless Binding Definition . . . . . . . . . . . . . . 11 2.2 LWAPP State Machine Definition . . . . . . . . . . . . . 11 3. LWAPP Transport Layers . . . . . . . . . . . . . . . . . . . 18 3.1 LWAPP Transport Header . . . . . . . . . . . . . . . . . 18 3.1.1 VER Field . . . . . . . . . . . . . . . . . . . . . 18 3.1.2 RID Field . . . . . . . . . . . . . . . . . . . . . 18 3.1.3 C Bit . . . . . . . . . . . . . . . . . . . . . . . 18 3.1.4 F Bit . . . . . . . . . . . . . . . . . . . . . . . 18 3.1.5 L Bit . . . . . . . . . . . . . . . . . . . . . . . 19 3.1.6 Fragment ID . . . . . . . . . . . . . . . . . . . . 19 3.1.7 Length . . . . . . . . . . . . . . . . . . . . . . . 19 3.1.8 Status and WLANS . . . . . . . . . . . . . . . . . . 19 3.1.9 Payload . . . . . . . . . . . . . . . . . . . . . . 19 3.2 Using IEEE 802.3 MAC as LWAPP transport . . . . . . . . 19 3.2.1 Framing . . . . . . . . . . . . . . . . . . . . . . 19 3.2.2 AC Discovery . . . . . . . . . . . . . . . . . . . . 20 3.2.3 LWAPP Message Header format over IEEE 802.3 MAC transport . . . . . . . . . . . . . . . . . . . . . 20 3.2.4 Fragmentation/Reassembly . . . . . . . . . . . . . . 20 3.2.5 Multiplexing . . . . . . . . . . . . . . . . . . . . 20 3.3 Using IPv4/UDP as LWAPP transport . . . . . . . . . . . 20 3.3.1 Framing . . . . . . . . . . . . . . . . . . . . . . 20 3.3.2 AC Discovery . . . . . . . . . . . . . . . . . . . . 21 3.3.3 LWAPP Message Header format over IPv4/UDP transport 21 3.3.4 Fragmentation/Reassembly . . . . . . . . . . . . . . 22 3.3.5 Multiplexing . . . . . . . . . . . . . . . . . . . . 22 4. LWAPP Packet Definitions . . . . . . . . . . . . . . . . . . 23 4.1 LWAPP Data Messages . . . . . . . . . . . . . . . . . . 23 4.2 LWAPP Control Messages Overview . . . . . . . . . . . . 23 4.2.1 Control Message Format . . . . . . . . . . . . . . . 24 4.2.2 Message Element Format . . . . . . . . . . . . . . . 26 5. LWAPP Discovery Operations . . . . . . . . . . . . . . . . . 28 5.1 Discovery Request . . . . . . . . . . . . . . . . . . . 28 5.1.1 Discovery Type . . . . . . . . . . . . . . . . . . . 29 5.1.2 WTP Descriptor . . . . . . . . . . . . . . . . . . . 29 5.1.3 WTP Radio Information . . . . . . . . . . . . . . . 30 5.2 Discovery Response . . . . . . . . . . . . . . . . . . . 30 5.2.1 AC Descriptor . . . . . . . . . . . . . . . . . . . 31 5.2.2 AC Name . . . . . . . . . . . . . . . . . . . . . . 31 5.2.3 WTP Manager Control IP Address . . . . . . . . . . . 32 5.3 Primary Discovery Request . . . . . . . . . . . . . . . 32 5.3.1 Discovery Type . . . . . . . . . . . . . . . . . . . 33 5.3.2 WTP Descriptor . . . . . . . . . . . . . . . . . . . 33 Calhoun, et al. Expires August 5, 2005 [Page 3] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 5.3.3 WTP Radio Information . . . . . . . . . . . . . . . 33 5.4 Primary Discovery Response . . . . . . . . . . . . . . . 33 5.4.1 AC Descriptor . . . . . . . . . . . . . . . . . . . 33 5.4.2 AC Name . . . . . . . . . . . . . . . . . . . . . . 33 5.4.3 WTP Manager Control IP Address . . . . . . . . . . . 33 6. Control Channel Management . . . . . . . . . . . . . . . . . 35 6.1 Join Request . . . . . . . . . . . . . . . . . . . . . . 35 6.1.1 AC Address . . . . . . . . . . . . . . . . . . . . . 35 6.1.2 WTP Descriptor . . . . . . . . . . . . . . . . . . . 36 6.1.3 WTP Name . . . . . . . . . . . . . . . . . . . . . . 36 6.1.4 Location Data . . . . . . . . . . . . . . . . . . . 36 6.1.5 WTP Radio Information . . . . . . . . . . . . . . . 37 6.1.6 Certificate . . . . . . . . . . . . . . . . . . . . 37 6.1.7 Session ID . . . . . . . . . . . . . . . . . . . . . 37 6.1.8 Test . . . . . . . . . . . . . . . . . . . . . . . . 37 6.2 Join Response . . . . . . . . . . . . . . . . . . . . . 38 6.2.1 Result Code . . . . . . . . . . . . . . . . . . . . 38 6.2.2 Status . . . . . . . . . . . . . . . . . . . . . . . 39 6.2.3 Certificate . . . . . . . . . . . . . . . . . . . . 39 6.2.4 Session Key . . . . . . . . . . . . . . . . . . . . 39 6.2.5 WTP Manager Data IP Address . . . . . . . . . . . . 40 6.3 Echo Request . . . . . . . . . . . . . . . . . . . . . . 40 6.4 Echo Response . . . . . . . . . . . . . . . . . . . . . 40 6.5 Key Update Request . . . . . . . . . . . . . . . . . . . 41 6.5.1 Session ID . . . . . . . . . . . . . . . . . . . . . 41 6.6 Key Update Response . . . . . . . . . . . . . . . . . . 41 6.6.1 Session Key . . . . . . . . . . . . . . . . . . . . 42 6.7 Key Update Trigger . . . . . . . . . . . . . . . . . . . 42 6.7.1 Session ID . . . . . . . . . . . . . . . . . . . . . 42 7. WTP Configuration Management . . . . . . . . . . . . . . . . 43 7.1 Configure Request . . . . . . . . . . . . . . . . . . . 43 7.1.1 Administrative State . . . . . . . . . . . . . . . . 43 7.1.2 AC Name . . . . . . . . . . . . . . . . . . . . . . 44 7.1.3 AC Name with Index . . . . . . . . . . . . . . . . . 44 7.1.4 WTP Board Data . . . . . . . . . . . . . . . . . . . 44 7.1.5 Statistics Timer . . . . . . . . . . . . . . . . . . 45 7.1.6 WTP Static IP Address Information . . . . . . . . . 45 7.1.7 WTP Reboot Statistics . . . . . . . . . . . . . . . 46 7.2 Configure Response . . . . . . . . . . . . . . . . . . . 46 7.2.1 Decryption Error Report Period . . . . . . . . . . . 47 7.2.2 Change State Event . . . . . . . . . . . . . . . . . 47 7.2.3 LWAPP Timers . . . . . . . . . . . . . . . . . . . . 48 7.2.4 AC List . . . . . . . . . . . . . . . . . . . . . . 48 7.2.5 WTP Fallback . . . . . . . . . . . . . . . . . . . . 48 7.2.6 Idle Timeout . . . . . . . . . . . . . . . . . . . . 49 7.3 Configuration Update Request . . . . . . . . . . . . . . 49 7.3.1 WTP Name . . . . . . . . . . . . . . . . . . . . . . 49 7.3.2 Change State Event . . . . . . . . . . . . . . . . . 50 Calhoun, et al. Expires August 5, 2005 [Page 4] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 7.3.3 Administrative State . . . . . . . . . . . . . . . . 50 7.3.4 Statistics Timer . . . . . . . . . . . . . . . . . . 50 7.3.5 Location Data . . . . . . . . . . . . . . . . . . . 50 7.3.6 Decryption Error Report Period . . . . . . . . . . . 50 7.3.7 AC List . . . . . . . . . . . . . . . . . . . . . . 50 7.3.8 Add Blacklist Entry . . . . . . . . . . . . . . . . 50 7.3.9 Delete Blacklist Entry . . . . . . . . . . . . . . . 51 7.3.10 Add Static Blacklist Entry . . . . . . . . . . . . . 51 7.3.11 Delete Static Blacklist Entry . . . . . . . . . . . 52 7.3.12 LWAPP Timers . . . . . . . . . . . . . . . . . . . . 52 7.3.13 AC Name with Index . . . . . . . . . . . . . . . . . 52 7.3.14 WTP Fallback . . . . . . . . . . . . . . . . . . . . 52 7.3.15 Idle Timeout . . . . . . . . . . . . . . . . . . . . 52 7.4 Configuration Update Response . . . . . . . . . . . . . 52 7.4.1 Result Code . . . . . . . . . . . . . . . . . . . . 53 7.5 Change State Event Request . . . . . . . . . . . . . . . 53 7.5.1 Change State Event . . . . . . . . . . . . . . . . . 53 7.6 Change State Event Response . . . . . . . . . . . . . . 53 7.7 Clear Config Indication . . . . . . . . . . . . . . . . 54 8. Device Management Operations . . . . . . . . . . . . . . . . 55 8.1 Image Data Request . . . . . . . . . . . . . . . . . . . 55 8.1.1 Image Download . . . . . . . . . . . . . . . . . . . 55 8.1.2 Image Data . . . . . . . . . . . . . . . . . . . . . 55 8.2 Image Data Response . . . . . . . . . . . . . . . . . . 56 8.3 Reset Request . . . . . . . . . . . . . . . . . . . . . 56 8.4 Reset Response . . . . . . . . . . . . . . . . . . . . . 56 8.5 WTP Event Request . . . . . . . . . . . . . . . . . . . 56 8.5.1 Decryption Error Report . . . . . . . . . . . . . . 57 8.5.2 Duplicate IP Address . . . . . . . . . . . . . . . . 57 8.6 WTP Event Response . . . . . . . . . . . . . . . . . . . 58 8.7 Data Transfer Request . . . . . . . . . . . . . . . . . 58 8.7.1 Data Transfer Mode . . . . . . . . . . . . . . . . . 58 8.7.2 Data Transfer Data . . . . . . . . . . . . . . . . . 59 8.8 Data Transfer Response . . . . . . . . . . . . . . . . . 59 9. Mobile Session Management . . . . . . . . . . . . . . . . . 60 9.1 Mobile Config Request . . . . . . . . . . . . . . . . . 60 9.1.1 Delete Mobile . . . . . . . . . . . . . . . . . . . 60 9.2 Mobile Config Response . . . . . . . . . . . . . . . . . 61 9.2.1 Result Code . . . . . . . . . . . . . . . . . . . . 61 10. Session Key Generation . . . . . . . . . . . . . . . . . . 62 10.1 Securing WTP-AC communications . . . . . . . . . . . . . 62 10.2 LWAPP Frame Encryption . . . . . . . . . . . . . . . . . 63 10.3 Authenticated Key Exchange . . . . . . . . . . . . . . . 63 10.4 Refreshing Cryptographic Keys . . . . . . . . . . . . . 65 11. IEEE 802.11 Binding . . . . . . . . . . . . . . . . . . . 67 11.1 Transport specific bindings . . . . . . . . . . . . . . 67 11.1.1 Status and WLANS field . . . . . . . . . . . . . . . 67 11.2 Data Message bindings . . . . . . . . . . . . . . . . . 68 Calhoun, et al. Expires August 5, 2005 [Page 5] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 11.3 Control Message bindings . . . . . . . . . . . . . . . . 68 11.3.1 Mobile Config Request . . . . . . . . . . . . . . . 68 11.3.2 WTP Event Request . . . . . . . . . . . . . . . . . 72 11.4 802.11 Control Messages . . . . . . . . . . . . . . . . 74 11.4.1 IEEE 802.11 WLAN Config Request . . . . . . . . . . 74 11.4.2 IEEE 802.11 WLAN Config Response . . . . . . . . . . 78 11.4.3 IEEE 802.11 WTP Event . . . . . . . . . . . . . . . 78 11.5 Message Element Bindings . . . . . . . . . . . . . . . . 79 11.5.1 IEEE 802.11 WTP WLAN Radio Configuration . . . . . . 80 11.5.2 IEEE 802.11 Rate Set . . . . . . . . . . . . . . . . 81 11.5.3 IEEE 802.11 Multi-domain Capability . . . . . . . . 82 11.5.4 IEEE 802.11 MAC Operation . . . . . . . . . . . . . 82 11.5.5 IEEE 802.11 Tx Power . . . . . . . . . . . . . . . . 84 11.5.6 IEEE 802.11 Tx Power Level . . . . . . . . . . . . . 84 11.5.7 IEEE 802.11 Direct Sequence Control . . . . . . . . 84 11.5.8 IEEE 802.11 OFDM Control . . . . . . . . . . . . . . 85 11.5.9 IEEE 802.11 Antenna . . . . . . . . . . . . . . . . 86 11.5.10 IEEE 802.11 Supported Rates . . . . . . . . . . . 86 11.5.11 IEEE 802.11 CFP Status . . . . . . . . . . . . . . 87 11.5.12 IEEE 802.11 WTP Mode and Type . . . . . . . . . . 87 11.5.13 IEEE 802.11 Broadcast Probe Mode . . . . . . . . . 88 11.5.14 IEEE 802.11 WTP Quality of Service . . . . . . . . 88 11.5.15 IEEE 802.11 MIC Error Report From Mobile . . . . . 89 11.6 IEEE 802.11 Message Element Values . . . . . . . . . . . 90 12. LWAPP Protocol Timers . . . . . . . . . . . . . . . . . . 91 12.1 MaxDiscoveryInterval . . . . . . . . . . . . . . . . . . 91 12.2 SilentInterval . . . . . . . . . . . . . . . . . . . . . 91 12.3 NeighborDeadInterval . . . . . . . . . . . . . . . . . . 91 12.4 EchoInterval . . . . . . . . . . . . . . . . . . . . . . 91 12.5 DiscoveryInterval . . . . . . . . . . . . . . . . . . . 91 12.6 RetransmitInterval . . . . . . . . . . . . . . . . . . . 91 12.7 ResponseTimeout . . . . . . . . . . . . . . . . . . . . 92 12.8 KeyLifetime . . . . . . . . . . . . . . . . . . . . . . 92 13. LWAPP Protocol Variables . . . . . . . . . . . . . . . . . 93 13.1 MaxDiscoveries . . . . . . . . . . . . . . . . . . . . . 93 13.2 DiscoveryCount . . . . . . . . . . . . . . . . . . . . . 93 13.3 RetransmitCount . . . . . . . . . . . . . . . . . . . . 93 13.4 MaxRetransmit . . . . . . . . . . . . . . . . . . . . . 93 14. Security Considerations . . . . . . . . . . . . . . . . . 94 15. IANA Considerations . . . . . . . . . . . . . . . . . . . 95 16. IPR Statement . . . . . . . . . . . . . . . . . . . . . . 96 17. References . . . . . . . . . . . . . . . . . . . . . . . . 97 17.1 Normative References . . . . . . . . . . . . . . . . . . 97 17.2 Informational References . . . . . . . . . . . . . . . . 97 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 98 Intellectual Property and Copyright Statements . . . . . . . 100 Calhoun, et al. Expires August 5, 2005 [Page 6] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 1. Introduction Unlike wired network elements, Wireless Termination Points (WTPs) require a set of management and control functions related to their primary task of connecting the wireless and wired mediums. Today, protocols for managing WTPs are either 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 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 WTP 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 infrastructure. Calhoun, et al. Expires August 5, 2005 [Page 7] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 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 protocols in the future by adding the binding. The LWAPP protocol concerns itself solely on 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]. Calhoun, et al. Expires August 5, 2005 [Page 8] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 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 is 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. Layer 2 LWAPP Data Frame +-----------------------------------------------------------+ | MAC Header | LWAPP Header [C=0] | Forwarded Data ... | +-----------------------------------------------------------+ Layer 3 LWAPP Data Frame +--------------------------------------------+ | MAC Header | IP | UDP | LWAPP Header [C=0] | +--------------------------------------------+ |Forwarded Data ... | +-------------------+ Layer 2 LWAPP Control Frame +---------------------------------------------------+ | MAC Header | LWAPP Header [C=1] | Control Message | +---------------------------------------------------+ | Message Elements ... | +----------------------+ Layer 3 LWAPP Control Frame +--------------------------------------------+ | MAC Header | IP | UDP | LWAPP Header [C=1] | +--------------------------------------------+ Calhoun, et al. Expires August 5, 2005 [Page 9] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 | Control Message | Message Elements ... | +-----------------+----------------------+ 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 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] Calhoun, et al. Expires August 5, 2005 [Page 10] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 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 bindings 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 definition of 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"." 2.2 LWAPP State Machine Definition The following state diagram represents the lifecycle of an WTP-AC session: Calhoun, et al. Expires August 5, 2005 [Page 11] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 /-------------\ | v | +------+ | C| Idle |<-------------------------------------\ | +------+<--------------------------\ | | ^ | ^ | | | | | \---------------\ | | | | | | | | | / | +---------+-->+------------+ | | / | C| Run | | Key Update | | | / | +---------+<--+------------+ | | / v | ^ | | | | | +-----------+ | | | v | | | C| Discovery |<--------/ | \------------>+-------+ | | +-----------+ +-----------+ | Reset | | | | \ ^ /-->| Configure |------->+-------+ | | v \ \ / +-----------+ ^ | +---------+ v \ / | | C| Sulking | +------+ | | +---------+ C| Join |----------------------\ | | +------+ v | \ | +------------+ \-----------------/ C| Image Data | +------------+ Figure 3: 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 specification, the specific state for which they are valid is specified. Note that in the state diagram figure above, the 'C' character is 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: 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. Calhoun, et al. Expires August 5, 2005 [Page 12] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 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: 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: 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. Sulking to Idle: 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: 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 WTP processes the request and responds with a Join Response. Join to Join: This state transition 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: This state is used when the join process failed. WTP: This state transition is invalid. AC: The AC enters this state when it transmits an unsuccessful Join Response. Calhoun, et al. Expires August 5, 2005 [Page 13] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 Join to Discovery: 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). AC: This state transition is invalid. Join to Configure: 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 Response, 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 7.1) 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 transition occurs when the AC receives the Configure Request from the WTP. The AC must transmit a Configure Response (see Section 7.2) to the WTP, and may include specific message elements to override the WTP's configuration. Join to Image Data: 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 Response, 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 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: 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 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: 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 Calhoun, et al. Expires August 5, 2005 [Page 14] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 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: 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. AC: This state transition occurs if the AC is unable to transmit the Configure Response. 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: 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 7.5). AC: This state transition occurs when the AC receives the Change State Event Request (see Section 7.5) from the WTP. The AC responds with a Change State Event Response (see Section 7.6) message. The AC must start the Session ID and Neighbor Dead timers (see Section 12). Run to Run: 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 7.3). The WTP MUST respond with a Configuration Update Response (see Section 7.4). 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 6.3), which it MUST respond with an Echo Response (see Section 6.4). Clear Config Indication: The WTP receives a Clear Config Indication message Section 7.7). 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). 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). Calhoun, et al. Expires August 5, 2005 [Page 15] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 WLAN Config Request: The WTP receives an WLAN Config Request message Section 11.4.1), which it MUST respond with an WLAN Config Response (see Section 11.4.2). 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 7.3) to the AP to update its configuration. The AC receives a Configuration Update Response (see Section 7.4) from the WTP. Change State Event: The AC receives a Change State Event Request (see Section 7.5), which it MUST respond to with the Change State Event Response (see Section 7.6). Echo: The AC sends an Echo Request message Section 6.3) or receives the associated Echo Response (see Section 6.4) from the WTP. Clear Config Indication: The AC sends a Clear Config Indication message Section 7.7). WLAN Config: The AC sends an WLAN Config Request message Section 11.4.1) or receives the associated WLAN Config Response (see Section 11.4.2) 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). Run to Reset: This event occurs when the AC wishes for the WTP re 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: This event occurs when an error occurs in the communication between the WTP and the AC. Calhoun, et al. Expires August 5, 2005 [Page 16] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 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: 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 6.5). It must create new keying material and include it in the Key Update Response (see Section 6.6). Key Update to Run: This event occurs when the key exchange phase is completed. WTP: This state transition occurs when the AC receives the Key Update Response. The WTP must plumb the new keys in its crypto module, allowing it to communicate with the AC using the new key. AC: The WTP enters this state when it transmits the Key Update Response message. The key is then plumbed into its crypto module, allowing it to communicate with the WTP using the new key. Calhoun, et al. Expires August 5, 2005 [Page 17] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 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 C bit indicates whether this packet carries a data message or a control message. When this bit is 0, the packet carries an LWAPP data message in the payload. When this bit is 1, the packet carries an LWAPP control messwage as defined in section 4 for consumption by the addressed destination. 3.1.4 F Bit The F bit indicates whether this packet is a fragment. When this bit is 1, the packet is a fragment and MUST be combined with the other Calhoun, et al. Expires August 5, 2005 [Page 18] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 corresponding fragments to reassemble the complete information exchanged between the WTP and AC. 3.1.5 L Bit The 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 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. 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. 3.2.1 Framing Source Address A MAC address belonging to the interface from which this message is sent. If multiple source addresses are configured on an interface, then the one chosen is implementation dependent. Calhoun, et al. Expires August 5, 2005 [Page 19] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 Destination Address A MAC address belonging to the interface to which this message is to be sent. This destination address MAY be either an individual address or a multicast address, if more than one destination interface is intended. Ethertype The Ethertype field is set to 0x88bb. 3.2.2 AC Discovery When run over IEEE 802.3, LWAPP messages are distributed to a specific MAC level broadcast domain. The AC discovery mechanism used with this transport is for an WTP to transmit a Discovery Request message to a broadcast destination MAC address. The ACs will receive this message and reply based on their policy. 3.2.3 LWAPP Message Header format over IEEE 802.3 MAC transport All of the fields described in Section 3.1 are used when LWAPP uses the IEEE 802.3 MAC transport. 3.2.4 Fragmentation/Reassembly Fragmentation at the MAC layer is managed using the F,L and Frag ID fields of the LWAPP message header. The LWAPP protocol only allows a single packet to be fragmented into 2, which is sufficient for a frame that exceeds MTU due to LWAPP encapsulation. When used with layer 2 (Ethernet) transport, both fragments MUST include the LWAPP header. 3.2.5 Multiplexing LWAPP control messages and data messages are distinguished by the C Bit in the LWAPP message header. 3.3 Using IPv4/UDP as LWAPP transport This section defines how LWAPP makes use of IPV4/UDP transport between the WTP and the AC. When this transport is used, the MAC layer is controlled by the IPv4 stack, and there are therefore no special MAC layer requirements. 3.3.1 Framing Communication between WTP and AC is established according to the Calhoun, et al. Expires August 5, 2005 [Page 20] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 standard UDP client/server model. The connection is initiated by the WTP (client) to the well-known UDP port of the AC (server) used for control messages. This UDP port number of the AC is 12222 for LWAPP data and 12223 for LWAPP control frames. 3.3.2 AC Discovery When LWAPP is run over routed IPv4 networks, the WTP and the AC do not need to reside in the same IP subnet (broadcast domain). However, in the event the peers reside on separate subnets, there must exist a mechanism for the WTP to discover the AC. As the WTP attempts to establish communication with the AC, it sends the Discovery Request message and receives the corresponding response message from the AC. The WTP must send the Discovery Request message to either the limited broadcast IP address (255.255.255.255), a well known multicast address or to the unicast IP address of the AC. Upon receipt of the message, the AC issues a Discovery Response message to the unicast IP address of the WTP, regardless of whether Discovery Request was sent as a broadcast, multicast or unicast message. Whether the WTP uses a limited IP broadcast, multicast or unicast IP address is implementation dependent. In order for a WTP to transmit a Discovery Request to a unicast address, the WTP must first obtain the IP address of the AC. Any static configuration of an AC's IP address on the WTP non-volatile storage is implementation dependent. However, additional dynamic schemes are possible, for example: DHCP: A comma delimited ASCII encoded list of AC IP addresses is embedded inside a DHCP vendor specific option 43 extension. An example of the actual format of the vendor specific payload is of the form "LWAPP=10.1.1.1, 10.1.1.2". DNS: The DNS name "LWAPP-AC-Address" MAY be resolvable to or more AC addresses 3.3.3 LWAPP Message Header format over IPv4/UDP transport All of the fields described in Section 3.1 are used when LWAPP uses the IPv4/UDP transport, with the following exceptions: 3.3.3.1 F Bit This flag field is not used with this transport, and MUST be set to zero. Calhoun, et al. Expires August 5, 2005 [Page 21] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 3.3.3.2 L Bit This flag field is not used with this transport, and MUST be set to zero. 3.3.3.3 Frag ID This field is not used with this transport, and MUST be set to zero. 3.3.4 Fragmentation/Reassembly When LWAPP is implemented at L3, the transport layer uses IP fragmentation to fragment and reassemble LWAPP messages that are longer than MTU size used by either WTP or AC. The details of IP fragmentation are covered in [8]. When used with the IP transport, only the first fragment would include the LWAPP header [ed: IP fragmentation may raise security concerns and bring additional configuration requirements for certain firewalls and NATs. One alternative is to re-use the layer 2 (application layer) fragmentation reassembly. Comments are welcomed.] 3.3.5 Multiplexing LWAPP messages convey control information between WTP and AC, as well as binding specific data frames or binding specific management frames. As such, LWAPP messages need to be multiplexed in the transport sub-layer and be delivered to the proper software entities in the endpoints of the protocol. However, the 'C' bit is still used to differentiate between data and control frames. In case of Layer 3 connection, multiplexing is achieved by use of different UDP ports for control and data packets (see Section 3.3.1. As part of Join procedure, the WTP and AC may negotiate different IP Addresses for data or control messages. The IP Address returned in the AP Manager Control IP Address message element is used to inform the WTP with the IP address to which it must sent all control frames. The AP Manager Data IP Address message element MAY be present only if the AC has a different IP Address which the WTP is to use to send its data LWAPP frames. In the event the WTP and AC are separated by a NAT, with the WTP using private IP address space, it is the responsibility of the NAT to manage appropriate UDP port mapping. Calhoun, et al. Expires August 5, 2005 [Page 22] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 4. LWAPP Packet Definitions This section contains the packet types and format. The LWAPP protocol is designed to be transport agnostic by specifying packet formats for both MAC frames and IP packets. An LWAPP packet consists of an LWAPP Transport Layer packet header followed by an LWAPP message. Transport details can be found in Section 3. 4.1 LWAPP Data Messages An LWAPP data message is a forwarded wireless frame. When forwarding wireless frames, the sender simply encapsulates the wireless frame in an LWAPP data packet, using the appropriate transport rules defined in section Section 3. In the event that the encapsulated frame would exceed the transport layer's MTU, the sender is responsible for the fragmentation of the frame, as specified in the transport specific section of Section 3. The actual format of the encapsulated LWAPP data frame is subject to the rules defined under the specific wireless technology binding. 4.2 LWAPP Control Messages Overview The LWAPP Control protocol provides a control channel between the WTP and the AC. The control channel is the series of control messages between the WTP and AC, associated with a session ID and key. Control messages are divided into the following distinct message types: Discovery: LWAPP Discovery messages are used to identify potential ACs, their load and capabilities. Control Channel Management: Messages that fall within this classification are used for the discovery of ACs by the WTPs as well as the establishment and maintenance of an LWAPP control channel. WTP Configuration: The WTP Configuration messages are used by the AC to push a specific configuration to the WTPs it has a control channel with. Messages that deal with the retrieval of statistics from the WTP also fall in this category. Mobile Session Management: Mobile session management messages are used by the AC to push specific mobile policies to the WTP. Firmware Management: Messages in this category are used by the AC to push a new firmware image down to the WTP. Control Channel, WTP Configuration and Mobile Session Management MUST be implemented. Firmware Management MAY be implemented. Calhoun, et al. Expires August 5, 2005 [Page 23] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 In addition, technology specific bindings may introduce new control channel commands that depart from the above list. 4.2.1 Control Message Format All LWAPP control messages are sent encapsulated within the LWAPP header (see Section 3.1). Immediately following the header, is the LWAPP control header, which has the following format: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message Type | Seq Num | Msg Element Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Session ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Msg Element [0..N] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4.2.1.1 Message Type The Message Type field identifies the function of the LWAPP control message. The valid values for Message Type are the following: Calhoun, et al. Expires August 5, 2005 [Page 24] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 Description Value Discovery Request 1 Discovery Response 2 Join Request 3 Join Response 4 Unused 5-9 Configure Request 10 Configure Response 11 Configuration Update Request 12 Configuration Update Response 13 WTP Event Request 14 WTP Event Response 15 Change State Event Request 16 Change State Event Response 17 Unused 18-21 Echo Request 22 Echo Response 23 Image Data Request 24 Image Data Response 25 Reset Request 26 Reset Response 27 Unused 28-29 Key Update Request 30 Key Update Response 31 Primary Discovery Request 32 Primary Discovery Response 33 Data Transfer Request 34 Data Transfer Response 35 Clear Config Indication 36 WLAN Config Request 37 WLAN Config Response 38 Mobile Config Request 39 Mobile Config Response 40 4.2.1.2 Sequence Number The Sequence Number Field is an identifier value to match request/response packet exchanges. When an LWAPP packet with a request message type is received, the value of the sequence number field is copied into the corresponding response packet. When an LWAPP control frame is sent, its internal sequence number counter is monotonically incremented, ensuring that no two requests pending have the same sequence number. This field will wrap back to zero. Calhoun, et al. Expires August 5, 2005 [Page 25] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 4.2.1.3 Message Element Length The Length field indicates the number of bytes following the Session ID field. 4.2.1.4 Session ID The Session ID is a 32-bit unsigned integer that is used to identify the security context for encrypted exchanges between the WTP and the AC. Note that a Session ID is a random value that MUST be unique between a given AC and any of the WTP it may be communicating with. 4.2.1.5 Message Element[0..N] The message element(s) carry the information pertinent to each of the control message types. Every control message in this specification specifies which message elements are permitted. 4.2.2 Message Element Format The message element is used to carry information pertinent to a control message. Every message element is identified by the Type field, whose numbering space is managed via IANA (see Section 15). The total length of the message elements is indicated in the Message Element Length field. All of the message element definitions in this document use a diagram similar to the one below in order to depict its format. Note that in order to simplify this specification, these diagrams do not include the header fields (Type and Length). However, in every message element description, the header's fields values will be defined. Note that additional message elements may be defined in separate IETF documents. The format of a message element uses the TLV format shown here: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Value ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Where Type (8 bit) identifies the character of the information carried in the Value field and Length (16 bits) indicates the number of bytes in the Value field. Calhoun, et al. Expires August 5, 2005 [Page 26] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 4.2.2.1 Generic Message Elements This section includes message elements that are not bound to a specific control message. 4.2.2.1.1 Vendor Specific The Vendor Specific Payload is used to communicate vendor specific information between the WTP and the AC. The value contains the following format: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Vendor Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Element ID | Value... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 104 for Vendor Specific Length: >= 7 Vendor Identifier: A 32-bit value containing the IANA assigned "SMI Network Management Private Enterprise Codes" [9] Element ID: A 16-bit Element Idenfier which is managed by the vendor. Value: The value associated with the vendor specific element. Calhoun, et al. Expires August 5, 2005 [Page 27] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 5. LWAPP Discovery Operations The Discovery messages are used by an WTP to determine which ACs are available to provide service, as well as the capabilities and load of the ACs. 5.1 Discovery Request The Discovery Request is used by the WTP to automatically discover potential ACs available in the network. An WTP must transmit this command even if it has a statically configured AC, as it is a required step in the LWAPP state machine. Discovery Requests MUST be sent by an WTP in the Discover state after waiting for a random delay less than MaxDiscoveryInterval, after an WTP first comes up or is (re)initialized. An WTP MUST send no more than a maximum of MaxDiscoveries discoveries, waiting for a random delay less than MaxDiscoveryInterval between each successive discovery. This is to prevent an explosion of WTP Discoveries. An example of this occurring would be when many WTPs are powered on at the same time. Discovery requests MUST be sent by an WTP when no echo responses are received for NeighborDeadInterval and the WTP returns to the Idle state. Discovery requests are sent after NeighborDeadInterval, they MUST be sent after waiting for a random delay less than MaxDiscoveryInterval. An WTP MAY send up to a maximum of MaxDiscoveries discoveries, waiting for a random delay less than MaxDiscoveryInterval between each successive discovery. If a discovery response is not received after sending the maximum number of discovery requests, the WTP enters the Sulking state and MUST wait for an interval equal to SilentInterval before sending further discovery requests. The Discovery Request message may be sent as a unicast, broadcast or multicast message. Upon receiving a discovery request, the AC will respond with a Discovery Response sent to the address in the source address of the received discovery request. The following subsections define the message elements that MUST be included in this LWAPP operation. Calhoun, et al. Expires August 5, 2005 [Page 28] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 5.1.1 Discovery Type The Discovery message element is used to configure an WTP to operate in a specific mode. 0 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | Discovery Type| +-+-+-+-+-+-+-+-+ Type: 58 for Discovery Type Length: 1 Discovery Type: An 8-bit value indicating how the AC was discovered. The following values are supported: 0 - Broadcast 1 - Configured 5.1.2 WTP Descriptor The WTP descriptor message element is used by the WTP to communicate it's current hardware/firmware configuration. The value contains the following fields. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Hardware Version | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Software Version | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Boot Version | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Max Radios | Radios in use | Encryption Capabilities | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 3 for WTP Descriptor Length: 16 Hardware Version: A 32-bit integer representing the WTP's hardware version number Software Version: A 32-bit integer representing the WTP's Firmware version number Boot Version: A 32-bit integer representing the WTP's boot loader's version number Max Radios: An 8-bit value representing the number of radios (where each radio is identified via the RID field) supported by the WTP Calhoun, et al. Expires August 5, 2005 [Page 29] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 Radios in use: An 8-bit value representing the number of radios present in the WTP Encryption Capabilities: This 16-bit field is used by the WTP to communicate it's capabilities to the AC. Since most WTPs support link layer encryption, the AC may make use of these services. There are binding dependent encryption capabilites. An WTP that does not have any encryption capabilities would set this field to zero (0). Refer to the specific binding for the specification. 5.1.3 WTP Radio Information The WTP radios information message element is used to communicate the radio information in a specific slot. The Discovery Request MUST include one such message element per radio in the WTP. The Radio-Type field is used by the AC in order to determine which technology specific binding is to be used with the WTP. The value contains two fields, as shown. 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Radio ID | Radio Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 4 for WTP Radio Information Length: 2 Radio ID: The Radio Identifier, typically refers to some interface index on the WTP Radio Type: The type of radio present. The following values are supported 1 - 802.11bg: An 802.11bg radio. 2 - 802.11a: An 802.11a radio. 3 - 802.16: An 802.16 radio. 4 - Ultra Wideband: An UWB radio. 7 - all: Used to specify all radios in the WTP. 5.2 Discovery Response The Discovery Response is a mechanism by which an AC advertises its services to requesting WTPs. Discovery Responses are sent by an AC after receiving a Discovery Request. When an WTP receives a Discovery Response, it MUST wait for an interval not less than DiscoveryInterval for receipt of additional Discovery Responses. After the DiscoveryInterval elapses, the WTP Calhoun, et al. Expires August 5, 2005 [Page 30] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 enters the Joining state and will select one of the ACs that sent a Discovery Response and send a Join Request to that AC. The following subsections define the message elements that MUST be included in this LWAPP operation. 5.2.1 AC Descriptor The AC payload message element is used by the AC to communicate it's current state. The value contains the following fields. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Hardware Version ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | HW Ver | Software Version ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SW Ver | Stations | Limit | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Limit | Radios | Max Radio | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Max Radio | +-+-+-+-+-+-+-+-+ Type: 6 for AC Descriptor Length: 17 Reserved: MUST be set to zero Hardware Version: A 32-bit integer representing the AC's hardware version number Software Version: A 32-bit integer representing the AC's Firmware version number Stations: A 16-bit integer representing number of mobile stations currently associated with the AC Limit: A 16-bit integer representing the maximum number of stations supported by the AC Radios: A 16-bit integer representing the number of WTPs currently attached to the AC Max Radio: A 16-bit integer representing the maximum number of WTPs supported by the AC 5.2.2 AC Name The AC name message element contains an ASCII representation of the AC's identity. The value is a variable length byte string. The string is NOT zero terminated. Calhoun, et al. Expires August 5, 2005 [Page 31] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 0 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | Name ... +-+-+-+-+-+-+-+-+ Type: 31 for AC Name Length: > 0 Name: A variable length ASCII string containing the AC's name 5.2.3 WTP Manager Control IP Address The WTP Manager Control IP Address message element is sent by the AC to the WTP during the discovery process and is used by the AC to provide the interfaces available on the AC, and their current load. This message elemenet is useful for the WTP to perform load balancing across multiple interfaces. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IP Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | WTP Count | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 99 for WTP Manager Control IP Address Length: 6 IP Address: The IP Address of an interface. WTP Count: The number of WTPs currently connected to the interface. 5.3 Primary Discovery Request The Primary Discovery Request is sent by the WTP in order to determine whether its preferred (or primary) AC is available. Primary Discovery Request are sent by an WTP when it has a primary AC configured, and is connected to another AC. This generally occurs as a result of a failover, and is used by the WTP as a means to discover when its primary AC becomes available. As a consequence, this message is only sent by a WTP when it is in the Run state. The frequency of the Primary Discovery Requests should be no more often than the sending of the Echo Request message. Upon receiving a discovery request, the AC will respond with a Primary Discovery Response sent to the address in the source address of the received Primary Discovery Request. Calhoun, et al. Expires August 5, 2005 [Page 32] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 The following subsections define the message elements that MUST be included in this LWAPP operation. 5.3.1 Discovery Type The Discovery Type message element is defined in section Section 5.1.1. 5.3.2 WTP Descriptor The WTP Descriptor message element is defined in section Section 5.1.2. 5.3.3 WTP Radio Information An WTP Radio Information message element must be present for every radio in the WTP. This message element is defined in section Section 5.1.3. 5.4 Primary Discovery Response The Primary Discovery Response is a mechanism by which an AC advertises its availability and services to requesting WTPs that are configured to have the AC as its primary AC. Primary Discovery Responses are sent by an AC after receiving a Primary Discovery Request. When an WTP receives a Primary Discovery Response, it may opt to establish an LWAPP connection to its primary AC, based on the configuration of the WTP Fallback Status message element on the WTP. The following subsections define the message elements that MUST be included in this LWAPP operation. 5.4.1 AC Descriptor The Discovery Type message element is defined in section Section 5.2.1. 5.4.2 AC Name The AC Name message element is defined in section Section 5.2.2. 5.4.3 WTP Manager Control IP Address An WTP Radio Information message element must be present for every radio in the WTP. This message element is defined in section Calhoun, et al. Expires August 5, 2005 [Page 33] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 Section 5.2.3. Calhoun, et al. Expires August 5, 2005 [Page 34] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 6. Control Channel Management The Control Channel Management messages are used by the WTP and AC to create and maintain a channel of communication on which various other commands may be transmitted, such as configuration, firmware update, etc. 6.1 Join Request The Join Request is used by an WTP to inform an AC that it wishes to provide services through it. Join Requests are sent by an WTP in the Joining state after receiving one or more Discovery Responses. The Join Request is also used as an MTU discovery mechanism by the WTP. The WTP issues a Join Request with a Test message element, bringing the total size of the message to exceed MTU. If the transport used does not provide MTU path discovery, the initial Join Request is padded with the Test message element to 1596 bytes. If a Join Response is received, the WTP can forward frames without requiring any fragmentation. If no Join Response is received, it issues a second Join Request padded with the Test payload to a total of 1500 bytes. The WTP continues to cycle from large (1596) to small (1500) packets until a Join Response has been received, or until both packets sizes have been retransmitted 3 times. If the Join Response is not received after the maximum number of retransmissions, the WTP MUST abandon the AC and restart the discovery phase. When an AC receives a Join Request it will respond with a Join Response. The AC validates the certificate found in the request. If valid, the AC generates a session key which will be used to secure the control frames it exchanges with the WTP. When the AC issues the Join Response, the AC creates a context for the session with the WTP. Details on the key generation is found in Section 10. The following subsections define the message elements that MUST be included in this LWAPP operation. 6.1.1 AC Address The AC address message element is used to communicate the identity of the AC. The value contains two fields, as shown. Calhoun, et al. Expires August 5, 2005 [Page 35] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | MAC Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MAC Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 2 for AC Address Length: 7 Reserved: MUST be set to zero Mac Address: The MAC Address of the AC 6.1.2 WTP Descriptor The WTP Descriptor message element is defined in section Section 5.1.2. 6.1.3 WTP Name The WTP name message element value is a variable length byte string. The string is NOT zero terminated. 0 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | Name ... +-+-+-+-+-+-+-+-+ Type: 5 for WTP Name Length: > 0 Name: A non zero terminated string containing the WTP's name. 6.1.4 Location Data The location data message element is a variable length byte string containing user defined location information (e.g. "Next to Fridge"). The string is NOT zero terminated. 0 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | Location ... +-+-+-+-+-+-+-+-+ Calhoun, et al. Expires August 5, 2005 [Page 36] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 Type: 35 for Location Data Length: > 0 Location: A non zero terminated string containing the WTP's location. 6.1.5 WTP Radio Information An WTP Radio Information message element must be present for every radio in the WTP. This message element is defined in section Section 5.1.3. 6.1.6 Certificate The certificate message element value is a byte string containing a DER-encoded x.509v3 certificate. 0 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | Certificate... +-+-+-+-+-+-+-+-+ Type: 44 for Certificate Length: > 0 Certificate: A non zero terminated string containing the device's certificate. 6.1.7 Session ID The session ID message element value contains a randomly generated [4] unsigned 32-bit integer. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Session ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 45 for Session ID Length: 4 Session ID: 32 bit random session identifier. 6.1.8 Test The test message element is used as padding to perform MTU discovery, and MAY contain any value, of any length. Calhoun, et al. Expires August 5, 2005 [Page 37] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 0 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | Padding ... +-+-+-+-+-+-+-+-+ Type: 18 for Test Length: > 0 Padding: A variable length pad. 6.2 Join Response The Join Response is sent by the AC to indicate to an WTP whether it is capable and willing to provide service to it. Join Responses are sent by the AC after receiving a Join Request. Once the Join Response has been sent, the heartbeat timer is initiated for the session to EchoInterval. Expiration of the timer will result in deletion of the AC-WTP session. The timer is refreshed upon receipt of the Echo Request. When an WTP receives a Join Response it enters the Joined state and initiates either a Configure Request or Image Data to the AC to which it is now joined. Upon entering the Joined state, the WTP begins timing an interval equal to NeighborDeadInterval. Expiration of the timer will result in the transmission of the Echo Request. The following subsections define the message elements that MUST be included in this LWAPP operation. 6.2.1 Result Code The Result Code message element value is a 32-bit integer value, indicating the result of the request operation corresponding to the sequence number in the message. The Result Code is included in a successful Join Response. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Result Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 2 for Result Code Length: 4 Calhoun, et al. Expires August 5, 2005 [Page 38] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 Result Code: The following values are defined: 0 Success 1 Failure 6.2.2 Status The Status message element is sent by the AC to the WTP in a non-successful Join Response message. This message element is used to indicate the reason for the failure and should only be accompanied with a Result Code message element that indicates a failure. 0 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | Status | +-+-+-+-+-+-+-+-+ Type: 60 for Status Length: 1 Status: The status field indicates the reason for an LWAPP failure. The following values are supported: 1 - Reserved - do not use 2 - Resource Depletion 3 - Unknown Source 4 - Incorrect Data 6.2.3 Certificate The Certificate message element is defined in section Section 6.1.6. 6.2.4 Session Key The Session Key message element is sent by the AC to the WTP and includes the randomly generated session key, which is used to protect the LWAPP control messages. More details are available in Section 10. The value contains the following fields. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Session ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Session Key | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Session Key | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Session Key | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Calhoun, et al. Expires August 5, 2005 [Page 39] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 | Session Key | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 46 for Session Key Length: 20 Session ID: A 32-bit value defined in the session ID above. Session Key: A signed, encrypted 128-bit randomly generated session key. See Section 10 for more information on how this field is created. 6.2.5 WTP Manager Data IP Address The WTP Manager Data IP Address message element is optionally sent by the AC to the WTP during the join phase. If present, the IP Address contained in this message element is the address the WTP is to use when sending any of its LWAPP data frames. Note this message element is only valid when LWAPP uses the IP/UDP layer 3 transport 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IP Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: TBD for WTP Manager Data IP Address Length: 4 IP Address: The IP Address of an interface. 6.3 Echo Request The Echo Request message is a keepalive mechanism for the LWAPP control message. Echo Requests are sent periodically by an WTP in the Run state (see Figure 3) to determine the state of the connection between the WTP and the AC. The Echo Request is sent by the WTP when the Heartbeat timer expires, and it MUST start its NeighborDeadInterval timer. The Echo Request carries no message elements. When an AC receives an Echo Request it responds with an Echo Response. 6.4 Echo Response The Echo Response acknowledges the Echo Request, and are only Calhoun, et al. Expires August 5, 2005 [Page 40] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 accepted while in the Run state (see Figure 3). Echo Responses are sent by an AC after receiving an Echo Request. After transmitting the Echo Response, the AC should reset its Heartbeat timer to expire in the value configured for EchoInterval. If another Echo request is not received by the AC when the timer expires, the AC SHOULD consider the AP to no longer be reachable. The Echo Response carries no message elements. When an WTP receives an Echo Response it stops the NeighborDeadInterval timer, and starts the Heartbeat timer to EchoInterval. If the NeighborDeadInterval timer expires prior to receiving an Echo Response, the WTP enters the Idle state. 6.5 Key Update Request The Key Update Request updates the LWAPP session key used to secure messages between the WTP and the AC. Key Update Requests are sent by an WTP in the Run state to update a session key. The Session ID message element MUST include a new session identifier. When an AC receives a Key Update Request it generates a new key (see Section 10) and responds with a Key Update Response. The following subsections define the message elements that MUST be included in this LWAPP operation. 6.5.1 Session ID The Session ID message element is defined in section Section 6.1.7. 6.6 Key Update Response The Key Update Response updates the LWAPP session key used to secure messages between the WTP and the AC, and acknowledges the Key Update Request. Key Update Responses are sent by a AC after receiving a Key Update Request. The Key Update Responses is secured using public key cryptography. When an WTP receives a Key Update Response it will use the information contained in the Session Key message element to determine Calhoun, et al. Expires August 5, 2005 [Page 41] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 the keying material used to encrypt the LWAPP communications between the WTP and the AC. The following subsections define the message elements that MUST be included in this LWAPP operation. 6.6.1 Session Key The Session Key message element is defined in section Section 6.2.4. 6.7 Key Update Trigger The Key Update Trigger is used by the AC to request that a Key Update Request be initiated by the WTP. Key Update Trigger are sent by an AC in the Run state to inform the WTP to initiate a Key Update Request message. When a WTP receives a Key Update Trigger it generates a key Update Request. The following subsections define the message elements that MUST be included in this LWAPP operation. 6.7.1 Session ID The Session ID message element is defined in section Section 6.1.7. Calhoun, et al. Expires August 5, 2005 [Page 42] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 7. WTP Configuration Management The Wireless Termination Point Configuration messages are used to exchange configuration between the AC and the WTP. 7.1 Configure Request The Configure Request message is sent by an WTP to send its current configuration to its AC. Configure Requests are sent by an WTP after receiving a Join Response, while in the Configure state. The Configure Request carries binding specific message elements. Refer to the appropriate binding for the definition of this structure. When an AC receives a Configure Request it will act upon the content of the packet and respond to the WTP with a Configure Response. The Configure Request includes multiple Administrative State message Elements. There is one such message element for the WTP, and then one per radio in the WTP. The following subsections define the message elements that MUST be included in this LWAPP operation. 7.1.1 Administrative State The administrative event message element is used to communicate the state of a particular radio. The value contains the following fields. 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Radio ID | Admin State | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 27 for Administrative State Length: 2 Radio ID: An 8-bit value representing the radio to configure. The Radio ID field may also include the value of 0xff, which is used to identify the WTP itself. Therefore, if an AC wishes to change the administrative state of an WTP, it would include 0xff in the Radio ID field. Calhoun, et al. Expires August 5, 2005 [Page 43] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 Admin State: An 8-bit value representing the administrative state of the radio. The following values are supported: 1 - Enabled 2 - Disabled 7.1.2 AC Name The AC Name message element is defined in section Section 5.2.2. 7.1.3 AC Name with Index The AC Name with Index message element is sent by the AC to the WTP to configure preferred ACs. The number of instances where this message element would be present is equal to the number of ACs configured on the WTP. 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Index | AC Name... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 90 for AC Name with Index Length: 5 Index: The index of the preferred server (e.g., 1=primary, 2=secondary). AC Name: A variable length ASCII string containing the AC's name. 7.1.4 WTP Board Data The WTP Board Data message element is sent by the WTP to the AC and contains information about the hardware present. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Card ID | Card Revision | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | WTP Model | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | WTP Model | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | WTP Serial Number ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | WTP Options | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Ethernet MAC Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Calhoun, et al. Expires August 5, 2005 [Page 44] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 | Ethernet MAC Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 50 for WTP Board Data Length: 26 Card ID: A hardware identifier. Card Revision: Revision of the card. WTP Model: WTP Model Number. WTP Serial Number: WTP Serial Number. WTP Options: A vendor specific field encoding specific options enabled on the WTP. Ethernet MAC Address: MAC Address of the WTP's Ethernet interface. 7.1.5 Statistics Timer The statistics timer message element value is used by the AC to inform the WTP of the frequency which it expects to receive updated statistics. 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Statistics Timer | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 37 for Statistics Timer Length: 2 Statistics Timer: A 16-bit unsigned integer indicating the time, in seconds 7.1.6 WTP Static IP Address Information The WTP Static IP Address Information message element is used by an AC to configure or clear a previously configured static IP address on an WTP. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IP Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Netmask | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Gateway | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Static | +-+-+-+-+-+-+-+-+ Calhoun, et al. Expires August 5, 2005 [Page 45] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 Type: 82 for WTP Static IP Address Information Length: 13 IP Address: The IP Address to assign to the WTP. Netmask: The IP Netmask. Gateway: The IP address of the gateway. Netmask: The IP Netmask. Static: An 8-bit boolean stating whether the WTP should use a static IP address or not. 7.1.7 WTP Reboot Statistics The WTP Reboot Statistics message element is sent by the WTP to the AC to communicate information about reasons why reboots have occurred. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Crash Count | LWAPP Initiated Count | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link Failure Count | Failure Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 67 for WTP Reboot Statistics Length: 7 Crash Count: The number of reboots that have occurred due to an WTP crash. LWAPP Initiated Count: The number of reboots that have occured at the request of some LWAPP message, such as a change in configuration that required a reboot or an explicit LWAPP reset request. Link Failure Count: The number of times that an LWAPP connection with an AC has failed. Failure Type: The last WTP failure. The following values are supported: 0 - Link Failure 1 - LWAPP Initiated 2 - WTP Crash 7.2 Configure Response The Configure Response message is sent by an AC and provides an opportunity for the AC to override an WTP's requested configuration. Configure Responses are sent by an AC after receiving a Configure Request. The Configure Response carries binding specific message elements. Calhoun, et al. Expires August 5, 2005 [Page 46] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 Refer to the appropriate binding for the definition of this structure. When an WTP receives a Configure Response it acts upon the content of the packet, as appropriate. If the Configure Response message includes a Change State Event message element that causes a change in the operational state of one of the Radio, the WTP will transmit a Change State Event to the AC, as an acknowledgement of the change in state. The following subsections define the message elements that MUST be included in this LWAPP operation. 7.2.1 Decryption Error Report Period The Decryption Error Report Period message element value is used by the AC to inform the WTP how frequently it should send decryption error report messages. 0 1 2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Radio ID | Report Interval | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 38 for Decryption Error Report Period Length: 3 Radio ID: The Radio Identifier, typically refers to some interface index on the WTP Report Interval: A 16-bit unsigned integer indicating the time, in seconds 7.2.2 Change State Event The WTP radios information message element is used to communicate the operational state of a radio. The value contains two fields, as shown. 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Radio ID | State | Cause | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 26 for Change State Event Calhoun, et al. Expires August 5, 2005 [Page 47] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 Length: 3 Radio ID: The Radio Identifier, typically refers to some interface index on the WTP. State: An 8-bit boolean containing the state of the radio. Cause: In the event of a radio being inoperable, the cause field would contain the reason the radio is out of service. 7.2.3 LWAPP Timers The LWAPP Timers message element is used by an AC to configure LWAPP timers on an WTP. 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Discovery | Echo Request | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 68 for LWAPP Timers Length: 2 Discovery: The number of seconds between LWAPP Discovery packets, when the WTP is in the discovery mode. Echo Request: The number of seconds between WTP Echo Request LWAPP messages. 7.2.4 AC List The AC List message element is used to configure an WTP with the latest list of ACs in a cluster. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AC IP Address[] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 59 for AC List Length: >= 4 AC IP Address: An array of 32-bit integers containing an AC's IP Address. 7.2.5 WTP Fallback The WTP Fallback message element is sent by the AC to the WTP to enable or disable automatic LWAPP fallback in the event that an WTP detects its preferred AC, and is not currently connected to it. Calhoun, et al. Expires August 5, 2005 [Page 48] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 0 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | Mode | +-+-+-+-+-+-+-+-+ Type: 91 for WTP Fallback Length: 1 Mode: The 8-bit boolean value indicates the status of automatic LWAPP fallback on the WTP. When enabled, if the WTP detects that its primary AC is available, and it is not connected to it, it SHOULD automatically disconnect from its current AC and reconnect to its primary. If disabled, the WTP will only reconnect to its primary through manual intervention (e.g., through the Reset Request command). 7.2.6 Idle Timeout The Idle Timeout message element is sent by the AC to the WTP to provide it with the idle timeout that it should enforce on its active mobile station entries. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Timeout | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 97 for Idle Timeout Length: 4 Timeout: The current idle timeout to be enforced by the WTP. 7.3 Configuration Update Request Configure Update Requests are sent by the AC to provision the WTP while in the Run state. This is used to modify the configuration of the WTP while it is operational. When an AC receives a Configuration Update Request it will respond with a Configuration Update Response, with the appropriate Result Code. The following subsections define the message elements introduced by this LWAPP operation. 7.3.1 WTP Name The WTP Name message element is defined in section Section 6.1.3. Calhoun, et al. Expires August 5, 2005 [Page 49] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 7.3.2 Change State Event The Change State Event message element is defined in section Section 7.2.2. 7.3.3 Administrative State The Administrative State message element is defined in section Section 7.1.1. 7.3.4 Statistics Timer The Statistics Timer message element is defined in section Section 7.1.5. 7.3.5 Location Data The Location Data message element is defined in section Section 6.1.4. 7.3.6 Decryption Error Report Period The Decryption Error Report Period message element is defined in section Section 7.2.1. 7.3.7 AC List The AC List message element is defined in section Section 7.2.4. 7.3.8 Add Blacklist Entry The Add Blacklist Entry message element is used by an AC to add a blacklist entry on an WTP, ensuring that the WTP no longer provides any service to the MAC addresses provided in the message. The MAC Addresses provided in this message element are not expected to be saved in non-volative memory on the WTP. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Num of Entries| MAC Address[] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MAC Address[] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Calhoun, et al. Expires August 5, 2005 [Page 50] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 Type: 65 for Add Blacklist Entry Length: >= 7 Num of Entries: The number of MAC Addresses in the array. MAC Address: An array of MAC Addresses to add to the blacklist entry. 7.3.9 Delete Blacklist Entry The Delete Blacklist Entry message element is used by an AC to delete a previously added blacklist entry on an WTP, ensuring that the WTP provides service to the MAC addresses provided in the message. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Num of Entries| MAC Address[] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MAC Address[] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 66 for Delete Blacklist Entry Length: >= 7 Num of Entries: The number of MAC Addresses in the array. MAC Address: An array of MAC Addresses to delete from the blacklist entry. 7.3.10 Add Static Blacklist Entry The Add Static Blacklist Entry message element is used by an AC to add a permanent blacklist entry on an WTP, ensuring that the WTP no longer provides any service to the MAC addresses provided in the message. The MAC Addresses provided in this message element are expected to be saved in non-volative memory on the WTP. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Num of Entries| MAC Address[] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MAC Address[] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 70 for Delete Blacklist Entry Length: >= 7 Num of Entries: The number of MAC Addresses in the array. Calhoun, et al. Expires August 5, 2005 [Page 51] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 MAC Address: An array of MAC Addresses to add to the permanent blacklist entry. 7.3.11 Delete Static Blacklist Entry The Delete Static Blacklist Entry message element is used by an AC to delete a previously added static blacklist entry on an WTP, ensuring that the WTP provides service to the MAC addresses provided in the message. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Num of Entries| MAC Address[] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MAC Address[] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 71 for Delete Blacklist Entry Length: >= 7 Num of Entries: The number of MAC Addresses in the array. MAC Address: An array of MAC Addresses to delete from the static blacklist entry. 7.3.12 LWAPP Timers The LWAPP Timers message element is defined in section Section 7.2.3. 7.3.13 AC Name with Index The AC Name with Index message element is defined in section Section 7.1.3. 7.3.14 WTP Fallback The WTP Fallback message element is defined in section Section 7.2.5. 7.3.15 Idle Timeout The Idle Timeout message element is defined in section Section 7.2.6. 7.4 Configuration Update Response The Configuration Update Response is the acknowledgement message for the Configuration Update Request. Configuration Update Responses are sent by an WTP after receiving a Configuration Update Request. Calhoun, et al. Expires August 5, 2005 [Page 52] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 When an AC receives a Configure Update Response the result code indicates if the WTP successfully accepted the configuration. The following subsections define the message elements that must be present in this LWAPP operation. 7.4.1 Result Code The Result Code message element is defined in section Section 6.2.1. 7.5 Change State Event Request The Change State Event is used by the WTP to inform the AC of a change in the operational state. The Change State Event message is sent by the WTP when it receives a Configuration Response that includes a Change State Event message element. It is also sent in the event that the WTP detects an operational failure with a radio. The Change State Event may be sent in either the Configure or Run state (see Figure 3. When an AC receives a Change State Event it will respond with a Change State Event Response and make any necessary modifications to internal WTP data structures. The following subsections define the message elements that must be present in this LWAPP operation. 7.5.1 Change State Event The Change State Event message element is defined in section Section 7.2.2. 7.6 Change State Event Response The Change State Event Response acknowledges the Change State Event. Change State Event Response are sent by an WTP after receiving a Change State Event. The Change State Event Response carries no message elements. Its purpose is to acknowledge the receipt of the Change State Event. The WTP does not need to perform any special processing of the Change State Event Response message. Calhoun, et al. Expires August 5, 2005 [Page 53] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 7.7 Clear Config Indication The Clear Config Indication is used to reset an WTP's configuration. The Clear Config Indication is sent by an AC to request that an WTP reset its configuration to manufacturing defaults. The Clear Config Indication message is sent while in the Run LWAPP state. The Reset Request carries no message elements. When an WTP receives a Clear Config Indication it will reset its configuration to manufacturing defaults. Calhoun, et al. Expires August 5, 2005 [Page 54] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 8. Device Management Operations This section defines LWAPP operations responsible for debugging, gathering statistics, logging, and firmware management. 8.1 Image Data Request The Image Data Request is used to update firmware on the WTP. This message and its companion response are used by the AC to ensure that the image being run on each WTP is appropriate. Image Data Requests are exchanged between the WTP and the AC to download a new program image to an WTP. When an WTP or AC receives an Image Data Request it will respond with a Image Data Response. The format of the Image Data and Image Download message elements are described in the following subsections. 8.1.1 Image Download The image download message element is sent by the WTP to the AC and contains the image filename. The value is a variable length byte string. The string is NOT zero terminated. 8.1.2 Image Data The image data message element is present when sent by the AC and contains the following fields. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode | Checksum | Image Data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Image Data ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 33 for Image Data Length: >= 5 Opcode: An 8-bit value representing the transfer opcode. The following values are supported: 3 - Image data is included 5 - An error occurred. Transfer is aborted Calhoun, et al. Expires August 5, 2005 [Page 55] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 Checksum: A 16-bit value containing a checksum of the image data that follows Image Data: The Image Data field contains 1024 characters, unless the payload being sent is the last one (end of file) 8.2 Image Data Response The Image Data Response acknowledges the Image Data Request. An Image Data Responses is sent in response to an Image Data Request. Its purpose is to acknowledge the receipt of the Image Data Request packet. The Image Data Response carries no message elements. No action is necessary on receipt. 8.3 Reset Request The Reset Request is used to cause an WTP to reboot. Reset Requests are sent by an AC to cause an WTP to reinitialize its operation. The Reset Request carries no message elements. When an WTP receives a Reset Request it will respond with a Reset Response and then reinitialize itself. 8.4 Reset Response The Reset Response acknowledges the Reset Request. Reset Responses are sent by an WTP after receiving a Reset Request. The Reset Response carries no message elements. Its purpose is to acknowledge the receipt of the Reset Request. When an AC receives a Reset Response it is notified that the WTP will now reinitialize its operation. 8.5 WTP Event Request WTP Event Request is used by an WTP to send an information to its AC. These types of events may be periodical, or some asynchronous event on the WTP. For instance, an WTP collects statistics and uses the WTP Event Request to transmit this information to the AC. Calhoun, et al. Expires August 5, 2005 [Page 56] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 When an AC receives a WTP Event Request it will respond with a WTP Event Request. The WTP Event Request message MUST contain one of the following message element described in the next subsections, or a message element that is defined for a specific technology. 8.5.1 Decryption Error Report The Decryption Error Report message element value is used by the WTP to inform the AC of decryption errors that have occured since the last report. 0 1 2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Radio ID |Num Of Entries | Mobile MAC Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Mobile MAC Address[] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 39 for Decryption Error Report Length: >= 8 Radio ID: The Radio Identifier, typically refers to some interface index on the WTP Num Of Entries: An 8-bit unsigned integer indicating the number of mobile MAC addresses. Mobile MAC Address: An array of mobile station MAC addresses that have caused decryption errors. 8.5.2 Duplicate IP Address The Duplicate IP Address message element is used by an WTP to inform an AC that it has detected another host using the same IP address it is currently using. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IP Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MAC Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MAC Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Calhoun, et al. Expires August 5, 2005 [Page 57] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 Type: 77 for Duplicate IP Address Length: 10 IP Address: The IP Address currently used by the WTP. MAC Address: The MAC Address of the offending device. 8.6 WTP Event Response WTP Event Response acknowledges the WTP Event Request. WTP Event Response are sent by an AC after receiving a WTP Event Request. The WTP Event Response carries no message elements. 8.7 Data Transfer Request The Data Transfer Request is used to upload debug information from the WTP to the AC. Data Transfer Requests are sent by the WTP to the AC when it determines that it has important information to send to the AC. For instance, if the WTP detects that its previous reboot was caused by a system crash, it would want to send the crash file to the AC. The remote debugger function in the WTP also uses the data transfer request in order to send console output to the AC for debugging purposes. When an AC receives an Data Transfer Request it will respond with a Data Transfer Response. The AC may log the information received, as it sees fit. The data transfer request message MUST contain ONE of the following message element described in the next subsection. 8.7.1 Data Transfer Mode The Data Transfer Mode message element is used by the AC to request information from the WTP for debugging purposes. 0 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | Data Type | +-+-+-+-+-+-+-+-+ Calhoun, et al. Expires August 5, 2005 [Page 58] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 Type: 52 for Data Transfer Mode Length: 1 Data Type: An 8-bit value the type of information being requested. The following values are supported: 1 - WTP Crash Data 2 - WTP Memory Dump 8.7.2 Data Transfer Data The Data Transfer Data message element is used by the WTP to provide information to the AC for debugging purposes. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Data Type | Data Length | Data .... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 53 for Data Transfer Data Length: >= 3 Data Type: An 8-bit value the type of information being sent. The following values are supported: 1 - WTP Crash Data 2 - WTP Memory Dump Data Length: Length of data field. Data: Debug information. 8.8 Data Transfer Response The Data Transfer Response acknowledges the Data Transfer Request. An Data Transfer Response is sent in response to an Data Transfer Request. Its purpose is to acknowledge the receipt of the Data Transfer Request packet. The Data Transfer Response carries no message elements. Upon receipt of a Data Transfer Response, the WTP transmits more information, if any is available. Calhoun, et al. Expires August 5, 2005 [Page 59] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 9. Mobile Session Management Messages in this section are used by the AC to create, modify or delete mobile station session state on the WTPs. 9.1 Mobile Config Request The Mobile Config Request message is used to create, modify or delete mobile session state on an WTP. The message is sent by the AC to the WTP, and may contain one or more message elements. The message elements for this LWAPP control message include information that is generally highly technology specific. Therefore, please refer to the appropriate binding section or document for the definitions of the messages elements that may be used in this control message. This section defines the format of the Delete Mobile message element, since it does not contain any technology specific information. 9.1.1 Delete Mobile The Delete Mobile message element is used by the AC to inform an WTP that it should no longer provide service to a particular mobile station. The WTP must terminate service immediately upon receiving this message element. The transmission of a Delete Mobile message element could occur for various reasons, including for administrative reaons, as a result of the fact that the mobile has roamed to another WTP, etc. Once access has been terminated for a given station, any future packets received from the mobile must result in a deauthenticate message, as specified in [6]. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Radio ID | MAC Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MAC Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 30 for Delete Mobile Length: 7 Radio ID: An 8-bit value representing the radio MAC Address: The mobile station's MAC Address Calhoun, et al. Expires August 5, 2005 [Page 60] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 9.2 Mobile Config Response The Mobile Configuration Response is used to acknowledge a previously received Mobile Configuration Request, and includes a Result Code message element which indicates whether an error occured on the WTP. This message requires no special processing, and is only used to acknowledge the Mobile Configuration Request. The data transfer request message MUST contain the message elements described in the next subsection. 9.2.1 Result Code The Result Code message element is defined in section Section 6.2.1. Calhoun, et al. Expires August 5, 2005 [Page 61] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 10. Session Key Generation Note: This version only defines a certificate based mechanism to secure traffic between the WTP and the AC. A shared-secret mechanism will be added in a future version. 10.1 Securing WTP-AC communications While it is generally straightforward to produce network installations in which the communications medium between the WTP and AC is not accessible to the casual user (e.g. these LAN segments are isolated, no RJ45 or other access ports exist between the WTP and the AC), this will not always be the case. Furthermore, a determined attacker may resort to various more sophisticated monitoring and/or access techniques, thereby compromising the integrity of this connection. In general, a certain level of threat on the local (wired) LAN is expected and accepted in most computing environments. That is, it is expected that in order to provide users with an acceptable level of service and maintain reasonable productivity levels, a certain amount of risk must be tolerated. It is generally believed that a certain perimeter is maintained around such LANs, that an attacker must have access to the building(s) in which such LANs exist, and that they must be able to "plug in" to the LAN in order to access the network. With these things in mind, we can begin to assess the general security requirements for AC-WTP communications. While an in-depth security analysis of threats and risks to these communication is beyond the scope of this document, some discussion of the motivation for various security-related design choices is useful. The assumptions driving the security design thus far include the following: o WTP-AC communications take place over a wired connection which may be accessible to a sophisticated attacker o access to this connection is not trivial for an outsider (i.e. someone who does not "belong" in the building) to access o if authentication and/or privacy of end to end traffic for which the WTP and AC are intermediaries is required, this may be provided via IPsec [11]. o privacy and authentication for at least some WTP-AC control traffic is required (e.g. WEP keys for user sessions, passed from AC to WTP) o the AC can be trusted to generate strong cryptographic keys AC-WTP traffic can be considered to consist of two types: data traffic (e.g. to or from an end user), and control traffic which is strictly between the AC and WTP. Since data traffic may be secured Calhoun, et al. Expires August 5, 2005 [Page 62] Internet-Draft Light Weight Access Point Protocol (LWAPP) Feb 2005 using IPsec (or some other end-to-end security mechanism), we confine our solution to control traffic. The resulting security consists of two components: an authenticated key exchange, and control traffic security encapsulation. The security encapsulation is accomplished using AES CCM, described in [3]. This encapsulation provides for strong AES-based authentication and encryption. The exchange of cryptographic keys used for CCM is described below. 10.2 LWAPP Frame Encryption While, the LWAPP protocol uses AES-CCM to encrypt control traffic, it is important to note that not all control frames are encrypted. The LWAPP discovery and join phase are not encrypted. The Discovery messages are sent in the clear since there does not exist a security association between the WTP and the AC during the discovery phase. The Join phase is used to negotiate symmetric session keys (see Section 6.2.4). Once the join phase has been successfully completed, the LWAPP state machine Figure 3 will move to the Configure state, at which time all LWAPP control frames are encrypted using AES-CCM. Encryption of a control message begins at the Message Element field, meaning tha the Msg Type, Seq Num, Msg Element Length and Session ID fields are left intact (see Section 4.2.1). The AES-CCM 12 byte authentication data is appended to the end of the message. The authentication data is calculated from the start of the LWAPP packet, and includes the complete LWAPP header. The AES-CCM block cipher protocol requires an initialization vector. The IV is initialized on both the WTP and the AC to the Session ID, and the IV is monotonically increased for every packet transmitted. Note that the IV is implicit, and is not transmitted in the LWAPP header, and therefore an LWAPP device MUST keep track of bo