MAC State Convergence Function

1
MAC State Convergence Function

• Date 2007-09-18

Authors
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

3
The Problem, In Brief

• The 802.11 MAC is stateless
• 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

4
Architectural Overview
MIH
Other higher layers using MAC state information
MAC_STATE_CONVERGENCE_SAP
MAC State Convergence Function
MSCF-SME_SAP
MAC_SAP
MAC
MLME
SME
Mobility Management
MLME_SAP
PHY_SAP
PHY
PLME
PLME_SAP
Note The base standard version of this diagram
is Figure 5-10 on page 42 of 802.11-2007
5
Analysis of 802.21 Primitive Operations
6
Primitives Required by 802.21

• 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

7
Classification of 802.21 Primitives

• 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

8
Link Operations

• Link_Up
• Link_Down
• Link_Going_Down
• Link_Event_Rollback
• Link_Detected
• Link_Parameters_Report
• Link_PDU_Transmit_Status

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?

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.indi
  cation
• (2) the STA has received an MLME-Deauthenticate.in
  dication
• (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.

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.
• 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)

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

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

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

15
Mobility Operations

• Link_Handover_Imminent
• Link_Handover_Complete

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

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

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

19
MAC API Operations

• Link_Event_Subscribe
• Link_Event_Unsubscribe
• Link_Capability_Discover
• Link_Action

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

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

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

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

24
Link Parameter Operations

• Link_Configure_Thresholds
• Link_Get_Parameters
• Link_Parameters_Report

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

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

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)

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

29
Way Forward
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!

31
References

• 802.21-D7.1
• 802.11-2007
• 802.11k-D8.0
• 802.11w-D2.3
• 802.11u-D1.0