September 2007
doc.: IEEE 802.11-07/2488r2
MAC State Convergence Function
Date: 2007-09-18
Authors:
Name
Matthew Gast
Submission
Affiliations
Address
Trapeze
Networks
5753 W. Las Positas 925-474-2273
Blvd, Pleasanton,
CA 94588
Slide 1
Phone
email
msg@trapezenetworks.co
m
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
Abstract
This presentation provides one potential approach for
providing 802.21 MIH support in 802.11:
(1) Discussion of a “convergence function” that would
supply MAC state information to higher layer
applications such as 802.21 MIH, and
(2) Discussion of required support of 802.21 primitive
operations in terms of existing 802.11 primitives and
potential new additions
Submission
Slide 2
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
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 highlevel 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
Submission
Slide 3
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
Architectural Overview
Other higher layers using
MAC state information
MIH
MAC_STATE_CONVERGENCE_SAP
MAC State
Convergence Function
MAC_SAP
MAC
MSCF-SME_SAP
MLME
Mobility
Management
MLME_SAP
PHY_SAP
SME
PHY
Submission
PLME
PLME_SAP
Interworking
Service
Management
Note: The base standard version of this diagram is Figure 5-10 on page 42 of 802.11-2007
Slide 4
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
Analysis of 802.21 Primitive Operations
Submission
Slide 5
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
Primitives Required by 802.21
• From 802.21-D7.1, Table L2:
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Submission
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–
–
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Link_Event_Subscribe
Link_Event_Unsubscribe
Link_Configure_Thresholds
Link_Up
Link_Down
Link_Going_Down
Link_Event_Rollback
Link_Detected
Link_Parameters_Report
Slide 6
Link_PDU_Transmit_Status
Link_Handover_Imminent
Link_Handover_Complete
Link_Capability_Discover
Link_Get_Parameters
Link_Action
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
Classification of 802.21 Primitives
• Link Operations
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Link_Up
Link_Down
Link_Going_Down
Link_Event_Rollback
Link_Detected
Link_Parameters_Report
Link_PDU_Transmit_Status
• MAC “API”
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–
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Link_Event_Subscribe
Link_Event_Unsubscribe
Link_Capability_Discover
Link_Action
• Link Parameter operations
– Link_Configure_Thresholds
– Link_Get_Parameters
– Link_Parameters_Report
• Mobility Operations
– Link_Handover_Imminent
– Link_Handover_Complete
Submission
Slide 7
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
Notes on Analysis
•
This analysis attempts to:
(1) Describe each 802.21 operation in English words, and
(2) Figure out the closest mapping to existing 802.11 primitive
operations within the MLME or PLME, or, if there is no close
primitive, what we would need to implement within the
convergence function.
•
Unless otherwise specified, the “technical meaning in
terms of 802.11” should be read as a list of alternative
options (“or”) rather than a list of requirements
(“and”)
Submission
Slide 8
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
Link Operations
Link_Up
Link_Down
Link_Going_Down
Link_Event_Rollback
Link_Detected
Link_Parameters_Report
Link_PDU_Transmit_Status
Submission
Slide 9
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
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
• Technical meaning in terms of 802.11
– (1) the first MLME-Associate.confirm with a result code of success for
unencrypted networks, or…
– (2) the first MLME-Associate.confirm along with an MLMESetKeys.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?
Submission
Slide 10
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
The Meaning of Link_Up
• From the 802.21 perspective, the main consumer is applications
that need to know when new application-layer addressing is
necessary
– Application examples: MIP, SIP, etc…
• From the 802.11 perspective, a “link” is the ability to continue to
send frames to the same destination
– On an IP network, the destination of these frames is likely the default IP
router for the subnet
– A single “link” may move from AP to AP without the application being
aware of it
• Conclusion: LinkUp events only need to be generated when an
802.11 STA moves to an AP that does not offer identical service to
its existing AP
– Therefore, the term “network” means a collection of APs that offer
common link-layer attachment
Submission
Slide 11
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
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.
Submission
Slide 12
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
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)
Submission
Slide 13
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
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
Submission
Slide 14
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
Link_Detected
• English meaning: A new link of is available for potential use
– This corresponds to detection of a Beacon frame for a new network, e.g. a
new component of an MLME-SCAN result
– It is not: “we have powered on the 802.11 interface”
• Implication for 802.11u draft
– The convergence function may need to issue period MLME-SCAN
requests to learn about networks in the area, and report new networks as
they appear in the scan result list
– Many areas have lots of 802.11 networks of many different types available
within small areas; it may be prudent to use the TGu network type
classifications to help filter new entries in the scan result list so that only
relevant links are detected
Submission
Slide 15
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
Link_PDU_Transmit_Status
• English meaning: Gets the status of a protocol data unit
transmission
• Technical meaning in terms of 802.11
– If this refers to a frame transmission: Maps to existing MAUNITDATA.confirm primitive
– If it refers to an application layer success indication (e.g. MIH
information services), then this is out of scope for 802.11 because
the 802.11 MAC cannot get access to higher-layer protocol
information
• Implication for 802.11u draft
– MA-UNITDATA.confirm results are received by the convergence
function and passed up as this event
Submission
Slide 16
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
Mobility Operations
Link_Handover_Imminent
Link_Handover_Complete
Submission
Slide 17
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
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 will 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
Submission
Slide 18
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
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 802.11rD7.0, 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
Submission
Slide 19
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
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
Submission
Slide 20
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
Link Handover discussion points
• Purpose of Link Handover, as described in September 19, 2007
joint meeting
– Inform higher layers that there may be interruption in service, causing
packet loss or TCP slow start delays
– 802.11 already handles packet loss on AP-to-AP transition within an ESS
• Frames are buffered during transition
• Frames may be retransmitted rapidly without requiring network- or
application-layer action (link layer retry counters)
• Use cases for handover imminent events from Sep-19-2007 meeting
– Potential use case #1: Use handover imminent events to filter Link_Up to
network purposes within the MIH function
– Potential use case #2: Inter-ESS mobility in combination with higher layer
mobility protocols (e.g. Mobile IP) or other application protocols, so that a
MIH-capable device will hold back on transmissions during the ESS
switch
Submission
Slide 21
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
MAC API Operations
Link_Event_Subscribe
Link_Event_Unsubscribe
Link_Capability_Discover
Link_Action
Submission
Slide 22
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
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
Submission
Slide 23
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
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
Submission
Slide 24
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
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
Submission
Slide 25
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
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 (MLMEDeauthentate.request or MLME-Diassociate.request)
– Low power: change power save status; in 802.11-2007, this translates to MLMEPOWERMGT.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
Submission
Slide 26
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
Link Parameter Operations
Link_Configure_Thresholds
Link_Get_Parameters
Link_Parameters_Report
Submission
Slide 27
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
What are Link Parameters?
• 802.21 defines generic parameters for all links
(LINK_PARAM_GENERAL) in Table B2, page 181:
– Speed, signal strength, SINR (“signal over interference plus noise ratio”),
throughput, and packet Error Rate
• 802.21 defines 2 additional parameters for 802.11 links
(LINK_PARAM_802_11):
– 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 reports, but does not persistently store, many of these
parameters. They are 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
Submission
Slide 28
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
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)
– Intent is to support the entire parameter list required by 802.21
– Need to define 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
Submission
Slide 29
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
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)
Submission
Slide 30
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
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
Submission
Slide 31
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
Way Forward
Submission
Slide 32
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
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!
Submission
Slide 33
Matthew Gast, Trapeze Networks
September 2007
doc.: IEEE 802.11-07/2488r2
References
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802.21-D7.1
802.11-2007
802.11k-D8.0
802.11w-D2.3
802.11u-D1.0
Submission
Slide 34
Matthew Gast, Trapeze Networks