IEEE 802.11-19/1575r0 Multi-Link BA Operation Overview

 
Slide 1
 
Multi-link BA Operation
 
Date:
 2019-08-23
 
Authors:
 
September 2019
 
Matthew Fischer (Broadcom)
 
Multi-Link Operation (MLO) has been discussed as a major 11be
feature for throughput improvement and latency reduction
[1, 2] discusses the synchronized and asynchronized MLO rules
[3, 4] discusses the terminology and architecture
[4] discusses the multi link aggregation
Packet switch, TID mapping, common BA session etc.
This presentation discusses MLO operation that supports the flexibility
of accommodating different implementation architectures
 
September 2019
 
Matthew Fischer (Broadcom)
 
Slide 2
 
Recap of the Current Discussions
 
Assuming that a single TID between two MLO STAs is
split across >1 link
How many BA sessions are negotiated?
 
September 2019
 
Matthew Fischer (Broadcom)
 
Slide 3
 
Common BA Session?
 
Define an architecture that supports the benefits of the MLO operation
while accommodating different implementation choices
TX: Packet flow is split between links somewhere between the MAC SAP
and the WM
RX: Packet flow from different links is merged somewhere between the
antenna and the MAC SAP
Desire a protocol that allows packet flow split location to be an
implementation choice
 
September 2019
 
Matthew Fischer (Broadcom)
 
Slide 4
 
Proposal
 
Low split
 
September 2019
 
Matthew Fischer (Broadcom)
 
Slide 5
 
Low MAC MLLE Link Split
EDCA0
EDCA1
PHY0
PHY1
R
X
DEFRAG
DEAGG
REORDER
EDCA0
EDCA1
PHY0
PHY1
MAC SAP
MAC SAP
 
ADDR_A
 
ADDR_B
 
ADDR_C
 
ADDR_Y
 
ADDR_Z
 
ADDR_X
AMSDU
AMPDU
MACSEQ
FRAG
BACON
BACON
 
TX
 
RX
 
High split
 
September 2019
 
Matthew Fischer (Broadcom)
 
Slide 6
 
High MAC MLLE Link Split
EDCA0
EDCA1
PHY0
PHY1
R
X
DEFRAG
DEAGG
REORDER
EDCA0
EDCA1
PHY0
PHY1
MAC SAP
MAC SAP
 
ADDR_A
 
ADDR_B
 
ADDR_C
 
ADDR_Y
 
ADDR_Z
 
ADDR_X
MACSEQ
R
X
 FIFO
R
X
 FIFO
BACON
BACON
AMSDU
AMPDU
FRAG
AMSDU
AMPDU
FRAG
BACON
BACON
 
TX
 
RX
 
Requires some sequencing information
If the split is above the MPDU, then the sequencing information
needs to be generated on the TX side above the MPDU generation
and carried up to the merge point on the RX side
E.g. sequence value associated with MSDUs
Maintain existing BA for MPDU sequencing
Separate queue management
Single BA or Multiple per-link BA
Single BA might impose minor restrictions
 
September 2019
 
Matthew Fischer (Broadcom)
 
Slide 7
 
High MAC split
 
Requires TX queue sharing
Requires RX queue sharing
Or merge above the RX queue, i.e. asymmetric split between TX
and RX
Single BA
Assuming BA Control above the split
 
September 2019
 
Matthew Fischer (Broadcom)
 
Slide 8
 
Low MAC split
 
The pros and cons of each split point can be debated
But such a debate is best left as an implementation
decision
TGbe protocol definition should support a range of
options
Let the market select the winning implementation choice
 
September 2019
 
Matthew Fischer (Broadcom)
 
Slide 9
 
High vs Low
 
The main requirement of the high MAC split is
sequencing information available at the high end of the
MAC
E.g. per MSDU sequencing information
MSDU sequencing information can be:
In addition to MPDU sequencing
Tightly coupled to MPDU sequencing
 
September 2019
 
Matthew Fischer (Broadcom)
 
Slide 10
 
High MAC Split Requirement
 
Each MSDU could contain its own MSDU sequencing
numbering
GSN = Global Sequence Number
Only needed by high MAC devices
Could be negotiated to be used, only on links that need it
Can be zero-overhead
See next slides
 
September 2019
 
Matthew Fischer (Broadcom)
 
Slide 11
 
Separate MSDU Sequencing
 
Use LLC/SNAP headers to pass the global MSDU sequence number
LLC/SNAP protocol (802.2) is used to encapsulate all MSDUs when forming an 802.11
frame
The SNAP/DSAP and SNAP/SSAP fields are set to 0xAA to create a SNAP header and this
value is not changed while the frame is inside of the 802.11 domain
Proposal: At the TX side, replace SNAP/DSAP and SNAP/SSAP field values 0xAAAA
with the GSN when creating the 802.11 frame from the MSDU and replace the GSN with
0xAAAA when leaving the 802.11 domain (i.e. top of the MLLE at the RX side)
 
 
 
September 2019
 
Matthew Fischer (Broadcom)
 
Slide 12
 
Zero Overhead GSN SNAP
 
GSN uses existing SEQCON Field
i.e. SEQCON of MAC header
Nearly
 transparent vs architectural choices
 
September 2019
 
Matthew Fischer (Broadcom)
 
Slide 13
 
Zero Overhead GSN MACSEQ
FRAG (4)
SEQ (12)
 
Existing SEQ Con field definition:
 
Do we need to repartition the SEQ Control field?
Existing MAC SEQCON Sequence field is 12 bits
New BA limit of 1024 (10 bits)
Only half of SEQ space is usable to avoid ambiguity > vs <
Existing field permits AMSDU aggregation average of 2 MSDU
I.e. MPDU count remains the same if BA limit is increased to 2048
Desire higher average AMSDU aggregation
SEQ 14 bits = BA x 1024 (10 bits), AMSDU x 8 (4 bits)
FRAG 2 bits (Level 3 MAX)
Increase BA Window max to 8192 (8192 MSDU => 1024 MPDU)
New DATA Subtype
 
September 2019
 
Matthew Fischer (Broadcom)
 
Slide 14
 
GSN MACSEQ Field Size
 
Do we need a BA function for the GSN?
In the case of a TX queued MSDU that has a timeout or for some
other reason is deleted from the TX queue, the RX side needs to
move past the GSN hole
In MACSEQ case, this is done by sending a BAR
Need something similar for GSN
If single BA, then no need for GSN BA action, use regular BAR
BAR and BA must be transmitted on the link associated with the
frames of reference
If multiple BA, then need to define at least GSN BAR
GSN ADDBA, GSN DELBA optional
 
September 2019
 
Matthew Fischer (Broadcom)
 
Slide 15
 
GSN BAR
 
If GSN is embedded in MSDU
E.g. GSN in SNAP
GSN use is negotiated
If GSN is embedded in MACSEQCON
No GSN negotiation needed
 
September 2019
 
Matthew Fischer (Broadcom)
 
Slide 16
 
Negotiate use of GSN
 
RSNA using MAC SAP addresses
Generally agreed, not formally agreed
Beacons using LMAC addresses?
Or all Beacons using common TA, but indicating other MAC
addresses within elements in the Beacon?
Data MPDUs use which addresses?
How many BA sessions?
 
September 2019
 
Matthew Fischer (Broadcom)
 
Slide 17
 
RA TA Values and BA Sessions
 
Use MAC SAP address for everything
No need for other addresses
Loss of explicit link differentiate within MPDU
Single BA across links
Multiple BA session is difficult
What about non-MLLE STA?
E.g. non-MLLE 11be and 11ax STA
Scanning Non-MLLE device sees same BSS in Beacons on
multiple link channels
Confusing at best
 
September 2019
 
Matthew Fischer (Broadcom)
 
Slide 18
 
Option 1: 1 Address
 
Use WM Addresses for everything ON THE AIR
Use MAC SAP address for RSNA only:
Perform address substitution for encrypt/decrypt if MLLE device
No substitution if non-MLLE device
BA per link
 
September 2019
 
Matthew Fischer (Broadcom)
 
Slide 19
 
Option 2: Multiple Addresses
 
Use MAC SAP address for MLLE devices
Use WM Addresses for non-MLLE devices
And Beacons, Probe Responses, etc
Loss of explicit link differentiate within MPDU
One BA negotiated per device connection
 
September 2019
 
Matthew Fischer (Broadcom)
 
Slide 20
 
Option 3: Mixed Addresses
 
 
Do you support that
BAR and BA shall be transmitted on the link associated with the
frames of reference?
 
YES
NO
ABS
 
September 2019
 
Matthew Fischer (Broadcom)
 
Slide 21
 
Straw poll 1
 
 
Do you support that
A new DATA Subtype is defined with SEQCON redefined as 2
bits of FRAG and 14 bits of SEQ?
 
YES
NO
ABS
 
September 2019
 
Matthew Fischer (Broadcom)
 
Slide 22
 
Straw poll 2
 
 
Do you support that
A BAR may be aggregated within an AMPDU that includes
DATA Subtypes?
 
YES
NO
ABS
 
September 2019
 
Matthew Fischer (Broadcom)
 
Slide 23
 
Straw poll 3
 
 
Do you support that
There is a negotiation of whether there is one BA session per link
or one BA session, per TID per MLLE pair?
 
YES
NO
ABS
 
September 2019
 
Matthew Fischer (Broadcom)
 
Slide 24
 
Straw poll 4
 
 
1.
https://mentor.ieee.org/802.11/dcn/19/11-19-1116-00-00be-channel-access-in-
multi-band-operation.pptx
2.
https://mentor.ieee.org/802.11/dcn/19/11-19-0821-02-00be-multiple-band-
discussion.pptx
3.
https://mentor.ieee.org/802.11/dcn/19/11-19-0773-02-00be-multi-link-operation-
framework.pptx
4.
https://mentor.ieee.org/802.11/dcn/19/11-19-1082-00-00be-multi-link-operation-
dynamic-tid-transfer.pptx
 
September 2019
 
Matthew Fischer (Broadcom)
 
Slide 25
 
Reference
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doc.: IEEE 802.11-19/1575r0

Matthew Fischer (Broadcom)

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Presentation slides from September 2019 discussing the Multi-Link Operation (MLO) in IEEE 802.11-19/1575r0 standard. The slides cover topics such as the benefits of MLO, synchronized/asynchronized rules, terminology, architecture, and common BA sessions. The proposal aims to define an architecture supporting MLO benefits and implementation choices, including packet flow splitting and merging. Details on low and high MAC MLLE link splits are included, outlining the process of packet flow handling across multiple links.


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  1. doc.: IEEE 802.11-19/1575r0 September 2019 Multi-link BA Operation Date: 2019-08-23 Authors: Name Affiliations Address Phone Email Zhou Lan 250 Innovation Dr, San Jose, CA 95134 zhou.lan@broadcom.com Chunyu Hu Broadcom George Kondylis Peyush Agarwal Matthew Fischer Srinath Puducheri Submission Slide 1 Matthew Fischer (Broadcom)

  2. doc.: IEEE 802.11-19/1575r0 September 2019 Recap of the Current Discussions Multi-Link Operation (MLO) has been discussed as a major 11be feature for throughput improvement and latency reduction [1, 2] discusses the synchronized and asynchronized MLO rules [3, 4] discusses the terminology and architecture [4] discusses the multi link aggregation Packet switch, TID mapping, common BA session etc. This presentation discusses MLO operation that supports the flexibility of accommodating different implementation architectures Submission Slide 2 Matthew Fischer (Broadcom)

  3. doc.: IEEE 802.11-19/1575r0 September 2019 Common BA Session? Assuming that a single TID between two MLO STAs is split across >1 link How many BA sessions are negotiated? MLO Device MAC Addr (M1) MAC-SAP-a MLO Entity STA (MAC/PHY) x STA (MAC/PHY) y WM WM Submission Slide 3 Matthew Fischer (Broadcom)

  4. doc.: IEEE 802.11-19/1575r0 September 2019 Proposal Define an architecture that supports the benefits of the MLO operation while accommodating different implementation choices TX: Packet flow is split between links somewhere between the MAC SAP and the WM RX: Packet flow from different links is merged somewhere between the antenna and the MAC SAP Desire a protocol that allows packet flow split location to be an implementation choice Submission Slide 4 Matthew Fischer (Broadcom)

  5. doc.: IEEE 802.11-19/1575r0 September 2019 Low MAC MLLE Link Split TX RX MAC SAP MAC SAP ADDR_A ADDR_X RX AMSDU DEFRAG DEAGG REORDER MACSEQ AMPDU FRAG BACON BACON ADDR_B EDCA0 EDCA1 ADDR_C ADDR_Y EDCA0 EDCA1 ADDR_Z PHY0 PHY1 PHY0 PHY1 Low split Submission Slide 5 Matthew Fischer (Broadcom)

  6. doc.: IEEE 802.11-19/1575r0 September 2019 High MAC MLLE Link Split TX RX MAC SAP MACSEQ MAC SAP ADDR_A ADDR_X RX DEFRAG DEAGG REORDER AMSDU AMSDU AMPDU FRAG BACON AMPDU FRAG BACON RX FIFO RX FIFO BACON BACON ADDR_B EDCA0 EDCA1 ADDR_C ADDR_Y EDCA0 EDCA1 ADDR_Z PHY0 PHY1 PHY0 PHY1 High split Submission Slide 6 Matthew Fischer (Broadcom)

  7. doc.: IEEE 802.11-19/1575r0 September 2019 High MAC split Requires some sequencing information If the split is above the MPDU, then the sequencing information needs to be generated on the TX side above the MPDU generation and carried up to the merge point on the RX side E.g. sequence value associated with MSDUs Maintain existing BA for MPDU sequencing Separate queue management Single BA or Multiple per-link BA Single BA might impose minor restrictions Submission Slide 7 Matthew Fischer (Broadcom)

  8. doc.: IEEE 802.11-19/1575r0 September 2019 Low MAC split Requires TX queue sharing Requires RX queue sharing Or merge above the RX queue, i.e. asymmetric split between TX and RX Single BA Assuming BA Control above the split Submission Slide 8 Matthew Fischer (Broadcom)

  9. doc.: IEEE 802.11-19/1575r0 September 2019 High vs Low The pros and cons of each split point can be debated But such a debate is best left as an implementation decision TGbe protocol definition should support a range of options Let the market select the winning implementation choice Submission Slide 9 Matthew Fischer (Broadcom)

  10. doc.: IEEE 802.11-19/1575r0 September 2019 High MAC Split Requirement The main requirement of the high MAC split is sequencing information available at the high end of the MAC E.g. per MSDU sequencing information MSDU sequencing information can be: In addition to MPDU sequencing Tightly coupled to MPDU sequencing Submission Slide 10 Matthew Fischer (Broadcom)

  11. doc.: IEEE 802.11-19/1575r0 September 2019 Separate MSDU Sequencing Each MSDU could contain its own MSDU sequencing numbering GSN = Global Sequence Number Only needed by high MAC devices Could be negotiated to be used, only on links that need it Can be zero-overhead See next slides Submission Slide 11 Matthew Fischer (Broadcom)

  12. doc.: IEEE 802.11-19/1575r0 September 2019 Zero Overhead GSN SNAP Use LLC/SNAP headers to pass the global MSDU sequence number LLC/SNAP protocol (802.2) is used to encapsulate all MSDUs when forming an 802.11 frame The SNAP/DSAP and SNAP/SSAP fields are set to 0xAA to create a SNAP header and this value is not changed while the frame is inside of the 802.11 domain Proposal: At the TX side, replace SNAP/DSAP and SNAP/SSAP field values 0xAAAA with the GSN when creating the 802.11 frame from the MSDU and replace the GSN with 0xAAAA when leaving the 802.11 domain (i.e. top of the MLLE at the RX side) 802.11 MAC Header LLC/SNAP Header PHY Preamble Payload FCS SNAP/DSAP 0xAA SNAP/SSAP 0xAA Control 0x03 OUI Protocol ID 0x0800 0x000000 Submission Slide 12 Matthew Fischer (Broadcom)

  13. doc.: IEEE 802.11-19/1575r0 September 2019 Zero Overhead GSN MACSEQ GSN uses existing SEQCON Field i.e. SEQCON of MAC header Nearly transparent vs architectural choices FRAG (4) SEQ (12) Existing SEQ Con field definition: Submission Slide 13 Matthew Fischer (Broadcom)

  14. doc.: IEEE 802.11-19/1575r0 September 2019 GSN MACSEQ Field Size Do we need to repartition the SEQ Control field? Existing MAC SEQCON Sequence field is 12 bits New BA limit of 1024 (10 bits) Only half of SEQ space is usable to avoid ambiguity > vs < Existing field permits AMSDU aggregation average of 2 MSDU I.e. MPDU count remains the same if BA limit is increased to 2048 Desire higher average AMSDU aggregation SEQ 14 bits = BA x 1024 (10 bits), AMSDU x 8 (4 bits) FRAG 2 bits (Level 3 MAX) Increase BA Window max to 8192 (8192 MSDU => 1024 MPDU) New DATA Subtype Submission Slide 14 Matthew Fischer (Broadcom)

  15. doc.: IEEE 802.11-19/1575r0 September 2019 GSN BAR Do we need a BA function for the GSN? In the case of a TX queued MSDU that has a timeout or for some other reason is deleted from the TX queue, the RX side needs to move past the GSN hole In MACSEQ case, this is done by sending a BAR Need something similar for GSN If single BA, then no need for GSN BA action, use regular BAR BAR and BA must be transmitted on the link associated with the frames of reference If multiple BA, then need to define at least GSN BAR GSN ADDBA, GSN DELBA optional Submission Slide 15 Matthew Fischer (Broadcom)

  16. doc.: IEEE 802.11-19/1575r0 September 2019 Negotiate use of GSN If GSN is embedded in MSDU E.g. GSN in SNAP GSN use is negotiated If GSN is embedded in MACSEQCON No GSN negotiation needed Submission Slide 16 Matthew Fischer (Broadcom)

  17. doc.: IEEE 802.11-19/1575r0 September 2019 RA TA Values and BA Sessions RSNA using MAC SAP addresses Generally agreed, not formally agreed Beacons using LMAC addresses? Or all Beacons using common TA, but indicating other MAC addresses within elements in the Beacon? Data MPDUs use which addresses? How many BA sessions? Submission Slide 17 Matthew Fischer (Broadcom)

  18. doc.: IEEE 802.11-19/1575r0 September 2019 Option 1: 1 Address Use MAC SAP address for everything No need for other addresses Loss of explicit link differentiate within MPDU Single BA across links Multiple BA session is difficult What about non-MLLE STA? E.g. non-MLLE 11be and 11ax STA Scanning Non-MLLE device sees same BSS in Beacons on multiple link channels Confusing at best Submission Slide 18 Matthew Fischer (Broadcom)

  19. doc.: IEEE 802.11-19/1575r0 September 2019 Option 2: Multiple Addresses Use WM Addresses for everything ON THE AIR Use MAC SAP address for RSNA only: Perform address substitution for encrypt/decrypt if MLLE device No substitution if non-MLLE device BA per link Submission Slide 19 Matthew Fischer (Broadcom)

  20. doc.: IEEE 802.11-19/1575r0 September 2019 Option 3: Mixed Addresses Use MAC SAP address for MLLE devices Use WM Addresses for non-MLLE devices And Beacons, Probe Responses, etc Loss of explicit link differentiate within MPDU One BA negotiated per device connection Submission Slide 20 Matthew Fischer (Broadcom)

  21. doc.: IEEE 802.11-19/1575r0 September 2019 Straw poll 1 Do you support that BAR and BA shall be transmitted on the link associated with the frames of reference? YES NO ABS Submission Slide 21 Matthew Fischer (Broadcom)

  22. doc.: IEEE 802.11-19/1575r0 September 2019 Straw poll 2 Do you support that A new DATA Subtype is defined with SEQCON redefined as 2 bits of FRAG and 14 bits of SEQ? YES NO ABS Submission Slide 22 Matthew Fischer (Broadcom)

  23. doc.: IEEE 802.11-19/1575r0 September 2019 Straw poll 3 Do you support that A BAR may be aggregated within an AMPDU that includes DATA Subtypes? YES NO ABS Submission Slide 23 Matthew Fischer (Broadcom)

  24. doc.: IEEE 802.11-19/1575r0 September 2019 Straw poll 4 Do you support that There is a negotiation of whether there is one BA session per link or one BA session, per TID per MLLE pair? YES NO ABS Submission Slide 24 Matthew Fischer (Broadcom)

  25. doc.: IEEE 802.11-19/1575r0 September 2019 Reference 1. https://mentor.ieee.org/802.11/dcn/19/11-19-1116-00-00be-channel-access-in- multi-band-operation.pptx 2. https://mentor.ieee.org/802.11/dcn/19/11-19-0821-02-00be-multiple-band- discussion.pptx 3. https://mentor.ieee.org/802.11/dcn/19/11-19-0773-02-00be-multi-link-operation- framework.pptx 4. https://mentor.ieee.org/802.11/dcn/19/11-19-1082-00-00be-multi-link-operation- dynamic-tid-transfer.pptx Submission Slide 25 Matthew Fischer (Broadcom)

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