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MAC State Convergence Function for 802.11 and 802.21 MIH Support

Explore the need for MAC state convergence and a proposed approach to synchronize state information for higher-layer protocols like 802.21 MIH in 802.11 networks. Presentation by Matthew Gast from Trapeze Networks.

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MAC State Convergence Function for 802.11 and 802.21 MIH Support

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  1. MAC State Convergence Function Authors: Date: 2007-09-18 Matthew Gast, Trapeze Networks

  2. Abstract This presentation provides one potential approach for providing 802.21 MIH support in 802.11: • Discussion of required support of 802.21 primitive operations in terms of existing 802.11 primitives and potential new additions, and • Discussion of a “convergence function” that would supply MAC state information to higher layer applications such as 802.21 MIH Matthew Gast, Trapeze Networks

  3. The Problem, In Brief • The 802.11 MAC does not have much state • Example: MIH Link_Up event is the “first” time that a wireless LAN is available • Existing MLME operations are like the “lower” MAC – there is no high-level state, such as the ESSID a STA is associated with • Many higher layer protocols (e.g. 802.21 MIH) need context • Proposal: A “MAC state convergence function” • Snoops on MAC management (MLME) and PHY management (PLME) events, and can retrieve state from station management (SME) • Synthesizes events and state to create new logical operations/indications • Inputs: MLME and PLME events, state information retrieved from SME • Output: Operations and events useful to higher level protocols Matthew Gast, Trapeze Networks

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

  5. Analysis of 802.21 Primitive Operations Matthew Gast, Trapeze Networks

  6. From 802.21-D7.1, Table L2: Link_Event_Subscribe Link_Event_Unsubscribe Link_Configure_Thresholds Link_Up Link_Down Link_Going_Down Link_Event_Rollback Link_Detected Link_Parameters_Report Link_PDU_Transmit_Status Link_Handover_Imminent Link_Handover_Complete Link_Capability_Discover Link_Get_Parameters Link_Action Primitives Required by 802.21 Matthew Gast, Trapeze Networks

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

  8. Link Operations Link_Up Link_Down Link_Going_Down Link_Event_Rollback Link_Detected Link_Parameters_Report Link_PDU_Transmit_Status Matthew Gast, Trapeze Networks

  9. Link_Up • English meaning for 802.11: A network is now up at layer 2 • Technical meaning in terms of 802.11 • (1) the MLME-Associate.confirm with a result code of success for unencrypted networks, or… • (2) the first MLME-Associate.confirm along with an MLME-SetKeys.confirm, both with result codes of success, for encrypted networks • Implications for 802.11u draft • MLME-Reassociate primitives are unimportant because they cannot be “first” • MLME-Associate.confirm primitives may need to be filtered, based on whether associations occur within a “small enough” time window to be considered “first” – perhaps this should be tied to whether a full 802.1X authentication was required? Matthew Gast, Trapeze Networks

  10. Link_Down • English meaning: The 802.11 link has gone down and can no longer send packets • Technical meaning in terms of 802.11 • (1) the STA has received an MLME-Disassociate.indication • (2) the STA has received an MLME-Deauthenticate.indication • (3) frames to the STA are not acknowledged for a “long enough” period of time • Implications for 802.11u draft • The convergence function must access the state of Protected Management Frame MIB entry (dot11RSNAProtectedManagementFramesEnabled) • Need to investigate whether TGw authentication will suppress Disassociate and Deauthenticate primitives. If not, then unauthenticated disconnection attempts or disconnects that fail authentication must be filtered by the convergence function • Different applications may require different link performance metrics for #3, so the convergence function should store the state of metrics that are required to declare a link dead. Defaults may be vendor-specific. Matthew Gast, Trapeze Networks

  11. Link_Going_Down • English meaning: The 802.11 link seems to be getting weaker, and might go down soon. This requires some form of prediction for future link quality. It may also mean an administrative shutdown • Technical meaning in terms of 802.11 • (1) According to indications received with frames, it is possible to predict the link will fail “soon” • (2) This may be received Data frames, or received Beacon frames • Implications for 802.11u draft • This is a new event that will be synthesized by the convergence function • No “best” prediction algorithm can be specified in the standard, and must be vendor-specific logic in the SME • There may be a need to provide configurable thresholds for the predictive algorithm through the SAP with between the CF and SME • An identifier and sequence number are required to support rollback (the next primitive) • RSSI is available for all of the radio PHYs (clauses 14, 15, 17, 18, and 19), but not the IR PHY (clause 16) Matthew Gast, Trapeze Networks

  12. Link_Event_Rollback • English meaning: “Oops! We were wrong about that impending link failure, so never mind.” • Technical meaning • The Link_Going_Down event no longer applies, so it needs to be cancelled • No tie to existing 802.11 primitive operations • Implications for 802.11u draft: • If the previous event is supported, this must also be supported • This event needs a tie to the previous event -- they operate as two sides of the same operation Matthew Gast, Trapeze Networks

  13. Link_Detected • English meaning: A new type of is available for potential use; e.g., we have powered on the 802.11 interface • Implication for 802.11u draft • No other IEEE 802 PHY supports this, so no support is required Matthew Gast, Trapeze Networks

  14. Link_PDU_Transmit_Status • English meaning: Gets the status of a protocol data unit transmission • Technical meaning in terms of 802.11 • Maps to existing MA-UNITDATA.confirm primitive • Implication for 802.11u draft • MA-UNITDATA.confirm results are received by the convergence function and passed up as this event Matthew Gast, Trapeze Networks

  15. Mobility Operations Link_Handover_Imminent Link_Handover_Complete Matthew Gast, Trapeze Networks

  16. Note on MIH “Handover” operations • According to 802.21-D7.1, clause 7.3.11: • “Link_Handover_Imminent is generated when a native link layer handover or switch decision has been made and its execution is imminent …” • Similar definition for handover complete operation in 7.3.12 • This is an L2 event, indicating intra-ESS transitions in 802.11 • This may be an extremely frequent report for 802.11 link layers • Question for 802.21 WG: why is it necessary to report intra-L2 handover, since 802.11 access networks are built with L2 mobility in mind • These events probably do not need support in 802.11 Matthew Gast, Trapeze Networks

  17. Link_Handover_Imminent • English meaning: The non-AP STA is about to try to move to another AP, but has not completed the process • Technical meaning in terms of 802.11 • (1) The non-AP STA has 802.11 authenticated (not 802.1X-authenticated) to a new AP, but has not moved its association. The mobility manager intends to move • (2) The non-AP STA has initiated an 802.11r fast transition; in 802.11r-D7.0, this means that the MLME-RESOURCE_REQUEST.request has been sent, or that the MLME-(RE)ASSOCIATE.request containing the Fast Transition IE has been sent • Implications for 802.11u draft • The “intention to move” can only be determined by the SME. Therefore, this event must be reported by the SME and passed to the convergence function • Or, TGu may choose not to support this, since intra-ESS handover is not an interesting or valuable event from the perspective of L3 mobility Matthew Gast, Trapeze Networks

  18. Link_Handover_Complete • English meaning: The non-AP STA has completed its move to a new AP • Technical meaning in terms of 802.11 • (1) On an unencrypted network, the MLME has received the MLME-ASSOCIATE.confirm primitive • (2) On an encrypted network, the MLME-(RE)ASSOCIATE.confirm primitive has been followed by an MLME-SetKeys.confirm primitive in a “short” period of time • Implications for 802.11u draft • TGu may choose not to support this, since intra-ESS handover is not an interesting or valuable event from the perspective of L3 mobility Matthew Gast, Trapeze Networks

  19. MAC API Operations Link_Event_Subscribe Link_Event_Unsubscribe Link_Capability_Discover Link_Action Matthew Gast, Trapeze Networks

  20. Link_Event_Subscribe • English meaning: MIH has requested to receive events from the lower level that will assist in its own operation • Technical meaning • Not relevant to the proposed 802.11 convergence function. The convergence function would always be available, and thus, there is no need to define a subscription model. • These functions are not defined for other IEEE 802 networks in 802.21-D7.1 Table L2. • Implications for 802.11u draft • None; does not need to be incorporated Matthew Gast, Trapeze Networks

  21. Link_Event_Unsubscribe • English meaning: MIH no longer needs lower level events • Technical meaning • Not relevant to the proposed 802.11 convergence function. The convergence function would always be available, and thus, there is no need to define a subscription model. • These functions are not defined for other IEEE 802 networks in 802.21-D7.1 Table L2. • Implications for 802.11u draft • None; does not need to be incorporated Matthew Gast, Trapeze Networks

  22. Link_Capability_Discover • English meaning: MIH requests a list of supported events • Technical meaning in terms of 802.11 • No primitive currently exists • Implications for 802.11u • Need to define two primitives in the convergence function: a request that comes in from higher layers, and a result that returns supported events Matthew Gast, Trapeze Networks

  23. Link_Action • English meaning: Requests action on a link. Valid actions are listed in Table B4 on 802.21-D7.1, p. 178. • Technical meaning for 802.11 • Disconnect: Deauthenticate/Disassociate peer MAC address (MLME-Deauthentate.request or MLME-Diassociate.request) • Low power: change power save status; in 802.11-2007, this translates to MLME-POWERMGT.request • Power down and power up link: no 802.11 primitives exist • Scan: issue MLME-SCAN.request • LINK_RESOURCE_RETAIN attribute is defined in Table B5 (p 184). It is used to reserve resources for future reconnection, which is not a concept that exists in 802.11 • DATA_FORWARDING_REQUEST attribute asks that buffered data be sent to new point, which is already required by 802.11 • Implications for 802.11u draft • Convergence function would need to map disconnect and low power actions to respective 802.11 primitives Matthew Gast, Trapeze Networks

  24. Link Parameter Operations Link_Configure_Thresholds Link_Get_Parameters Link_Parameters_Report Matthew Gast, Trapeze Networks

  25. What are Link Parameters? • For 802.11 links, 802.21 defines only 2 parameters in Table B2, page 181: • RSSI of the beacon channel • Flag to indicate that no QoS resources are available (i.e., request for capacity denied) • Implications for 802.11u • The 802.11 MAC has no state. The state is stored in the SME, and the convergence function provides a “window” on to that new state that higher layers can access • The 802.21 parameter set is not as rich as the 802.11k framework, which includes noise, received power, signal/noise, antenna indication • TGu may wish to assist 802.21 in incorporating new 802.11k measurement parameters into the draft, along with additional parameters such as frame- or bit-error rates Matthew Gast, Trapeze Networks

  26. Link_Configure_Thresholds • Meaning in English: Sets thresholds for MIH operations so that events will be reported only when they exceed thresholds • Technical meaning for 802.11 • This operation sets a trigger threshold. Even though 802.11k-D8.0 defines triggered reporting, its MLME primitives do not define primitives • Implications for TGu draft • Need to define operations of the converge function to store parameter values (from the SME) • Need to indicate normative behavior of events that are triggered when thresholds are passed; 802.11k revises clause 11.10.7 to create triggered measurement reports, and TGu will need to define something similar in its functional description Matthew Gast, Trapeze Networks

  27. Link_Get_Parameters • English meaning: Retrieve the parameters set by the previous operation so that a higher layer protocol can determine when events will be triggered • Technical meaning • This operation retrieves a trigger threshold set by the previous operation • Implication for 802.11u • Need to define operations of the converge function to retrieve parameter values (from the SME) Matthew Gast, Trapeze Networks

  28. Link_Parameters_Report • English meaning: Link parameters have crossed a specified threshold • Technical meaning in terms of 802.11 • The MLME is stateless, so there is no existing 802.11 primitive. This type of event would have be generated by the SME and passed to the convergence function so it can be made available to higher layers • Implications for TGu draft • Generation of an event triggered by crossing a parameter threshold needs to be defined, perhaps in a similar fashion to 802.11k Matthew Gast, Trapeze Networks

  29. Way Forward Matthew Gast, Trapeze Networks

  30. Next Steps • TGu investigation required • Do MLME events for Deauthentication and Disassociation incorporate TGw protection, or do we need to filter them? • Joint TGu-802.21 technical investigation • Do the intra-L2 handover events need to be supported with an 802.11 link layer? • Is the current parameter list sufficient for 802.11, or should more types of parameters be defined? • Define convergence function for inclusion within TGu draft • Call for ad hoc meeting! Matthew Gast, Trapeze Networks

  31. References • 802.21-D7.1 • 802.11-2007 • 802.11k-D8.0 • 802.11w-D2.3 • 802.11u-D1.0 Matthew Gast, Trapeze Networks

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