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MAC State Generic Convergence Function

MAC State Generic Convergence Function. Authors:. Date: 2007-10-22. Abstract. This presentation describes proposed changes to the 802.11u draft to support the MAC State Generic Convergence Function originally described in 11-07/2488. The text of the full proposal is found in 11-07/2604r1.

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MAC State Generic Convergence Function

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  1. MAC State Generic Convergence Function Authors: Date: 2007-10-22 Matthew Gast, Trapeze Networks

  2. Abstract This presentation describes proposed changes to the 802.11u draft to support the MAC State Generic Convergence Function originally described in 11-07/2488. The text of the full proposal is found in 11-07/2604r1. Matthew Gast, Trapeze Networks

  3. Architectural Overview of Convergence Function Matthew Gast, Trapeze Networks

  4. Architecture Overview: Replacing Figure 5-10 MIH Other higher layers using MAC state information MAC_STATE_CONVERGENCE_SAP MAC State Convergence Function 802.1X MAC_SAP MSCF-SME_SAP MAC MLME SME Mobility Management MLME_SAP PHY_SAP MLME_PLME_SAP Interworking Service Management PLCP sublayer PLME PMD_SAP PLME_SAP PMD sublayer RSNA Key Management Note: The base standard version of this diagram is Figure 5-10 on page 42 of 802.11-2007 Matthew Gast, Trapeze Networks

  5. The Need for a State Machine • MIH events apply to the whole ESS, not individual APs • Events are network-based, so they occur when things happen relative to multiple APs • Is the ESS up or down? • State machine operates on “ESS Links,” which are a new construct defined to support MIH Matthew Gast, Trapeze Networks

  6. Convergence Function State Machine ESS_UP ESS_FAILING ESS_SEARCH ESS_DOWN POWER_OFF Matthew Gast, Trapeze Networks

  7. Link Operations Link_Up Link_Down Link_Going_Down Link_Event_Rollback Link_Detected Link_PDU_Transmit_Status Mobility Operations Link_Handover_Imminent Link_Handover_Complete MAC “API” Link_Event_Subscribe Link_Event_Unsubscribe Link_Capability_Discover Link_Action Link Parameter operations Link_Configure_Thresholds Link_Get_Parameters Link_Parameters_Report Classification of 802.21 Primitives Matthew Gast, Trapeze Networks

  8. Events for Network Operation(corresponding to MIH Link Operations) Supporting the following 802.21 primitives: Link_Up, Link_Down, Link_Going_Down, Link_Event_Rollback, and Link_Detected Matthew Gast, Trapeze Networks

  9. MSGCF-ESS-Link-Up • Corresponding 802.21 primitive: Link_Up • English meaning for 802.11: A network (i.e., a set of APs offering identical data-link services) is now up at layer 2 • 802.11u proposal • Adds timestamp to the MLME-Associate.confirm primitive for time-based filtering • SME mobility manager may also report initial associations, so that indication was added to the SME SAP with the convergence function • Interactions of 802.21 with this event • LINK_TUPLE_ID (Table B4, page 171 of 802.21-D7.1) must be put together by MIH. It contains a link identifier and a link address. Both of these parameters are defined in this CF event • Link_Up has an optional IP_RENEWAL_FLAG that can be set (see 802.21-D7.1 clause 7.3.4). This is supplied by the L2 network, and therefore, will not be present in 802.21 Link_Up messages regarding 802.11 networks • Note: The Link_Up indication in 802.21 has MAC Access Router options which are not supplied on 802.11 interfaces Matthew Gast, Trapeze Networks

  10. MSGCF-ESS-Link-Down • Corresponding 802.21 primitive: Link_Down • English meaning: The 802.11 network has gone down and can no longer send packets • 802.11u draft changes • Added MIB entries to Annex D to describe threshold parameters to be used to declare links down • Method of declaring link down is specific to SME, and may include key expiration or power saving • 802.21 interactions • The MIB can only store one set of parameters; therefore, the MIH function is required to mediate between any applications with conflicting performance thresholds Matthew Gast, Trapeze Networks

  11. MSGCF-ESS-Link-Going-Down • Corresponding 802.21 primitive: Link_Going_Down • English meaning: The 802.11 network has gone down and can no longer send packets • Notes • This specifies the time in time units (TU), which is the native 802.11 “time quantum.” One TU = 1,024 μs = 1.024 msec. • 802.21 said that threshold was configurable, so the desired time threshold is added to the MIB • 802.11u proposal • This event indicates a prediction of link failure • Link quality degradation is no longer a reason for predicted failure, but this event may be simultaneous with a ESS-Link-Threshold-Report event indicating decreasing quality • 802.21 interactions • The MIHF will need to translate 802.11 TUs into other time units • 802.11 can provide parameters for the confidence interval calculation, but not the confidence level itself. This is an open question. • Multiple users may wish for different prediction thresholds, and the MIH function needs to mediate between them • 802.11 future implications • Need ANA management of the values of the reason code in the table Matthew Gast, Trapeze Networks

  12. MSGCF-ESS-Link-Event-Rollback • Corresponding 802.21 primitive: Link_Event_Rollback • English meaning: The 802.11 network has gone down and can no longer send packets • 802.11u draft text simply uses the Event ID to indicate that the previous event is no longer valid Matthew Gast, Trapeze Networks

  13. MSGCF-ESS-Link-Detected • Corresponding 802.21 primitive: Link_Detected • How it works • MLME-SCAN.request primitives are sent to learn about the area networks. These requests may be scheduled by the SME to avoid interrupting service • Networks are stored in the dot11MacStateNetworkDetectedTable. Each entry in this table has a timestamp of when the network was detected, its constituent BSSes, and the MIH capabilities (as defined in Table B4 on page 183 of 802.21-D7.1) • The CF can assemble the Network Identifier from the MLME-SCAN.confirm primitive because it has both the SSID and the Interworking information, and the latter contains the HESSID (as per 11-07/2494) • Notes on 802.11u text • MIH support is inferred from the presence of the GAS Advertising Protocol IDs used in the Interworking information. 802.11u has values for MIH IS (GAS APID #1) and MIH ES/CS (GAS APID #2) • Note for 802.21 • GAS in 802.11u does not provide separate capability information for MIH CS & ES Matthew Gast, Trapeze Networks

  14. Events for Threshold Configuration(corresponding to MIH parameter operations) Supporting the following 802.21 primitives: Link_Configure_Thresholds, Link_Get_Parameters, and Link_Parameters_Report Matthew Gast, Trapeze Networks

  15. MSGCF-Set-ESS-Link-Thresholds • Corresponding 802.21 primitive: Link_Configure_Thresholds • How it works • This provides a “window” to set parameters in the MIB that may be of interest • Provides access to RSSI on both Beacon and Data frames, SNR, frame error rates on both Beacon and Data frames, the BER of the radio channel, the peak operational rate observed, and the throughput of Data frames • 802.21 interaction notes • Any future parameters need to be added to both this primitive and the MIB Matthew Gast, Trapeze Networks

  16. MSGCF-Get-ESS-Link-Parameters • Matching 802.21 primitive: Link_Get_Parameters • Proposal for 802.11u: Simple primitive operation to retrieve relevant information from the MIB Matthew Gast, Trapeze Networks

  17. MSGCF-ESS-Link-Threshold-Report • Matching 802.21 primitive: Link_Parameters_Report • 802.21-D7.1 states that this primitive returns a list of LINK_PARAM_REPORT objects, as defined in table B4 on page 182 • Each LINK_PARAM_REPORT is composed of the link parameter plus the threshold crossing direction (upward or downward) • Proposal for 802.11u • This report contains the set of parameters whose thresholds have been crossed, plus a set of directions (one for each parameter) to indicate whether the threshold was passed as the value was going up or down Matthew Gast, Trapeze Networks

  18. MAC Control Operations(corresponding to MIH “API” primitives) Supporting the following 802.21 primitives: Link_Capability_Discover and Link_Action Matthew Gast, Trapeze Networks

  19. MSGCF-ESS-Link-Capability • Matching 802.21 primitive: Link_Capability_Discover • 802.11 implementation • All events which are supported by the convergence function are available for use • 802.21 Notes • The convergence function can report on its own capabilities, but those must be translated by the MIHF as in Table L2 in 802.21-D7.1. For example, Link_Up in 802.21 is equivalent to Network-Up in 802.11. • MIH events that are always unsupported are the link handover events (Link_Handover_Imminent and Link_Handover_Complete), the link event subscription events (Link_Event_Subscribe and Link_Event_Unsubscribe) • The MIH event Link_Transmit_PDU_Status is always available on 802.11 because it maps directly to a MAC data service primitive that is always supported • Obviously, Get-ESS-Link-Parameters and Set-ESS-Link-Parameters must be supported if the corresponding threshold events are Matthew Gast, Trapeze Networks

  20. MSGCF-ESS-Link-Command • Matching 802.21 primitive: Link_Action • Notes for 802.11u proposal • Maps DISCONNECT action to MLME-Deauthenticate & MLME-Disassociate • Maps LOW_POWER action to MLME-POWERMGT • Maps SCAN to MLME-SCAN • There is no mapping for power up and power down, since those are not defined primitives by 802.11 • DATA_FORWARDING_REQUEST is standard 802.11 behavior, and is not part of this proposal • LINK_RESOURCE_RETAIN is a resource reservation attribute used for future reconnections, which is not a concept implemented by 802.11; therefore, it is not part of this proposal Matthew Gast, Trapeze Networks

  21. Convergence Function MIB Matthew Gast, Trapeze Networks

  22. What needs to be in the MIB? • Configuration table • Indicates frequency of scanning for network detection • Parameters on a per-network basis • Minimum signal strength, error rates, and so on • Error rates may be expressed in scientific/exponential notation, so multiple MIB variables are needed to store such numbers (compare to geospatial entries in existing 802.11u draft) • Network list table • Most SMEs maintain a list of area networks, so this MIB table is a gateway to data already maintained by implementations Matthew Gast, Trapeze Networks

  23. 802.21 Primitives not Implemented by 802.11u CF proposal Discussion of the following 802.21 primitives: Link_Handover_Imminent, Link_Handover_CompleteLink_Event_Subscribe, Link_Event_Unsubscribe Matthew Gast, Trapeze Networks

  24. Link Handover Events • 802.21 primitives: Link_Handover_Imminent and Link_Handover_Complete • These would need to apply to networks of APs • Reporting on intra-ESS transitions is out of scope for 802.21, and would be extremely frequent • No clear use case identified for 802.11 networks • Best example: a network can refrain from sending packets when an inter-ESS transition that disrupts L3 networking is about to occur so that it does not lose packets in transition • It seems more likely that mobility-aware applications will need to be designed to tolerate occasional packet loss and recover accordingly Matthew Gast, Trapeze Networks

  25. Link Event Subscriptions • 802.21 primitives: Link_Event_Subscribe and Link_Event_Unsubscribe • Designed for link layer technologies where there are clear types of native events that map to 802.21 primitives • So a device can say that it supports Link_Up, but not Link_Going_Down • The convergence function maps all 802.21 primitives that make sense for 802.11, so all events that can be supported are supported Matthew Gast, Trapeze Networks

  26. References • 802.11-2007 – the baseline standard • P802.11u-D1.0 – the TGu amendment • 802.21-D7.1 – MIH specification and initial motivation for this idea • 11-07/2488 – the initial high-level proposal for the state convergence function • 11-07/2604 –proposed text for the 802.11 specification, described in this presentation Matthew Gast, Trapeze Networks

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