MAC State Generic Convergence Function

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MAC State Generic Convergence Function

• Date 2007-10-22

Authors
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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 11-07/2604.

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Classification of 802.21 Primitives

• 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

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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

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MSGCF-Network-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 requires that the IP_RENEWAL_FLAG be set
  (see 802.21-D7.1 clause 7.3.4). 802.11 has
  information only about layer 2, and therefore,
  this event cannot supply the IP_RENEWAL_FLAG.
• Table B-12, page 193 in 802.21-D7.1 defines
  mobility management protocols. Should an 802.11
  native mobility management protocol be defined?
• Because this event applies to a network of 802.11
  APs, the MIHF should not define access router MAC
  addresses in terms of BSSIDs

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MSGCF-Network-Down

• Corresponding 802.21 primitive Link_Down
• English meaning The 802.11 link 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
• 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

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MSGCF-Network-Going-Down

• Corresponding 802.21 primitive Link_Going_Down
• English meaning The 802.11 link 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
  1,204 µs 1.204 msec.
• 802.21 said that threshold was configurable, so
  the desired time threshold is added to the MIB
• 802.11u proposal
• The predictive algorithm for link quality
  degradation resides in the SME, so an SME
  indication is passed to indicate one type of
  network going down event
• Explicit network down predictions may also occur
  because of MLME events
• The convergence function takes any of these
  inputs as reason to issue this event
• 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

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MSGCF-Network-Event-Rollback

• Corresponding 802.21 primitive
  Link_Event_Rollback
• English meaning The 802.11 link 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

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MSGCF-Network-Detected

• Corresponding 802.21 primitive Link_Detected
• How it works
• CF issues MLME-SCAN.request primitives to learn
  about the area networks
• Networks are stored in the dot11MacStateNetworkDet
  ectedTable. 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
• Timestamps included in the MIB are integers with
  no valid range, following the TSF timer values in
  MLME-SCAN.confirm in 10.3.2.2.2 of 802.11-2007
• 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

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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

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MSGCF-Set-Network-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

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MSGCF-Get-Network-Parameters

• Matching 802.21 primitive Link_Get_Parameters
• Proposal for 802.11u Simple primitive operation
  to retrieve relevant information from the MIB

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MSGCF-Network-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

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MAC Control Operations(corresponding to MIH
API primitives)

• Supporting the following 802.21 primitives
• Link_Capability_Discover and Link_Action

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MSGCF-Network-Capability

• Matching 802.21 primitive Link_Capability_Discove
  r
• 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-Network-Parameters and
  Set-Network-Parameters must be supported if the
  corresponding threshold events are

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MSGCF-Network-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

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Convergence Function MIB
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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

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802.21 Primitives not Implemented by 802.11u CF
proposal

• Discussion of the following 802.21 primitives
• Link_Handover_Imminent, Link_Handover_CompleteLin
  k_Event_Subscribe, Link_Event_Unsubscribe

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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

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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

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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