mac state generic convergence function

October 2007

Matthew Gast, Trapeze Networks

Slide 1

doc.: IEEE 802.11-07/2629r0

Submission

MAC State Generic Convergence FunctionDate: 2007-10-22

Name Affiliations Address Phone email Matthew Gast Trapeze Networks 5753 W. Las Positas Blvd,

Pleasanton, CA 94588 USA 925-474-2273 [email protected]

Authors:

October 2007


Slide 2

doc.: IEEE 802.11-07/2629r0

Submission

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.

October 2007


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doc.: IEEE 802.11-07/2629r0

Submission

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

October 2007


Slide 4

doc.: IEEE 802.11-07/2629r0

Submission

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

October 2007


Slide 5

doc.: IEEE 802.11-07/2629r0

Submission

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

October 2007


Slide 6

doc.: IEEE 802.11-07/2629r0

Submission

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

October 2007


Slide 7

doc.: IEEE 802.11-07/2629r0

Submission

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

October 2007


Slide 8

doc.: IEEE 802.11-07/2629r0

Submission

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

October 2007


Slide 9

doc.: IEEE 802.11-07/2629r0

Submission

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 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– 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

October 2007


Slide 10

doc.: IEEE 802.11-07/2629r0

Submission

Events for Threshold Configuration(corresponding to MIH parameter operations)


Link_Configure_Thresholds, Link_Get_Parameters, and Link_Parameters_Report

October 2007


Slide 11

doc.: IEEE 802.11-07/2629r0

Submission

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

October 2007


Slide 12

doc.: IEEE 802.11-07/2629r0

Submission

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

October 2007


Slide 13

doc.: IEEE 802.11-07/2629r0

Submission

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

October 2007


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doc.: IEEE 802.11-07/2629r0

Submission

MAC Control Operations(corresponding to MIH “API” primitives)


Link_Capability_Discover and Link_Action

October 2007


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doc.: IEEE 802.11-07/2629r0

Submission

MSGCF-Network-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-Network-Parameters and Set-Network-Parameters must be supported if the corresponding threshold events are

October 2007


Slide 16

doc.: IEEE 802.11-07/2629r0

Submission

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

October 2007


Slide 17

doc.: IEEE 802.11-07/2629r0

Submission

Convergence Function MIB

October 2007


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doc.: IEEE 802.11-07/2629r0

Submission

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

October 2007


Slide 19

doc.: IEEE 802.11-07/2629r0

Submission

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

October 2007


Slide 20

doc.: IEEE 802.11-07/2629r0

Submission

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

October 2007


Slide 21

doc.: IEEE 802.11-07/2629r0

Submission

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

October 2007


Slide 22

doc.: IEEE 802.11-07/2629r0

Submission

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

mac state generic convergence function

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