1. September 2007
doc.: IEEE /2376r0
November 2007
Avoiding Frame Reorder and Recovering Active State in Tunneled Direct Link Setup Protocol (TDLS)
Date:
Authors:
L.Chu Etc.
Steve Emeott, Motorola

2. Frame Reorder when changing Path Between AP path and direct link path
September 2007
doc.: IEEE /2376r0
November 2007
Frame Reorder when changing Path Between AP path and direct link path
Being unable to reuse direct link when recovering from power saving
TDLS Setup and Deletion
Backup Slides
L.Chu Etc.
Steve Emeott, Motorola

3. TDLS may be Used in QBSS 802.11Z PAR November 2007 5.2 Scope:
This amendment defines a new Direct Link Setup (DLS) mechanism to allow operation with non-DLS capable access points and allow stations with an active DLS session to enter power save mode. The scope is specifically limited to modifications related to the DLS mechanism.
5.4 Purpose
This amendment defines a new DLS mechanism which: a) Does not require access point upgrades (i.e. supports DLS operation with the non-DLS capable access points), b) Which supports power save mode (when associated with either DLS or non-DLS capable access points), and c) Continues to allow operation of DLS in the presence of existing DLS
capable access points.
5.5 Need for the project:
The lack of DLS capable access points is a key obstacle to the adoption of DLS. Furthermore, the current DLS mechanism does not support power save mode and it is important to find a power save mechanism that does not require access point upgrade. This amendment will create a new DLS mechanism, which will allow much wider adoption of DLS. This will be increasingly important as IEEE is applied to new market applications, e.g. video streaming.
A QAP may not support optional DLS feature in IEEE Std
So, TDLS may be used in QBSS for direct QSTA communication.
In QBSS, TDLS related frames should select suitable access categories.
AC-based buffers should be considered in defining the protocol.
L.Chu Etc.

4. Problems with One Tx Path Switch Request in [1]
November 2007
Problems with One Tx Path Switch Request in [1]
Before transmitting the first data frame over the direct link, a STA may send a TDLS Tx Path Switch Request (TPSR) indicating a switch to the direct path.
it is not clear how many TPSRs to be transmitted between peer QSTAs and which access category (AC) should be used if QOS frames are used to encapsulate TPSRs between QSTAs.
After recovering from power saving state, a STA may request a peer STA to (re)enable the direct Rx path by sending a TDLS Tx Path Switch Request (TPSR).
it is not clear how many TPSRs to be transmitted between peer QSTAs and which access category should be used if QOS frames are used to encapsulate TPSRs between QSTAs.
QAP 1b
TPSR 1a 2a 2b
TPSP
Direct Link
QSTA1
QSTA2
L.Chu Etc.

5. Problem with One Tx Path Switch Request (Cont’d)
November 2007
Problem with One Tx Path Switch Request (Cont’d)
If one TDLS Tx Path Switch Request (TPSR)/one TDLS TxPath Switch Reply (TPSP) with the highest priority AC (AC_VO) is used, this may not be able to avoid potential reordering of frames between the AP path and the direct link.
After QSTA1 receives AC_VO TPSP, there may be buffered AC VI and AC BE frames in AP with SA=QSTA1 and DA=QSTA2.
. . 2b
AC_VO
. .
TPSP3
AC_VI
. .
TPSR3= TPSR using AC (access category) 3
AC_BE
. .
TPSR3
TPSP3=TPSP using AC 3
AC_BK
TPSR3 1b
QAP 2a 1a
TPSP3
AC_VO==3
AP Path
AC_VI==2
AC_BE==0
AC_BK==1
Direct Link Path
QSTA1
QSTA2
L.Chu Etc.

6. Problem with One Tx Path Switch Request (Cont’d)
November 2007
Problem with One Tx Path Switch Request (Cont’d)
If one TDLS Tx Path Switch Request (TPSR)/one TDLS TxPath Switch Reply (TPSP) with the lowest priority AC (AC-BK) is used, this may not guarantee the QOS of the high priority AC frames.
. .
AC_VO
. .
AC_VI
. .
TPSR1= TPSR using AC 1
AC_BE
. .
TPSP1=TPSP using AC 1
AC_BK 2b
TPSP1
QAP
TPSR1
TPSP1
TPSR1 2a 1b 1a
AP Path
. .
AC_VO
. .
Direct Link Path
QSTA1
QSTA2
AC_VI
. .
AC_BE
. .
Before receiving AC_BK TPSP, QSTA1 has to buffer AC VO and VI frames.
AC_BK
L.Chu Etc.

7. Solution to Frame Reorder
November 2007
Solution to Frame Reorder
Before transmitting the first data frame over the direct link to QSTA2, QSTA1 may send a TDLS Tx Path Switch Request (TPSR) indicating a switch to the direct path in each access category to QSTA2.
After QSTA2 receives a TPSR, it will sends a TPSP to QSTA1 with the same access category as received TPSR.
After QSTA1 receives a TPSP from QSTA2, it will uses direct link path to send the frames to QSTA2 with the same access category as received TPSP.
. .
AC_VO
. .
AC_VI
. .
AC_BE
. .
TPSP[0-3] 2b
AC_BK
TPSR[0-3]
TPSP[0-3] 2a
TPSR[0-3]
QAP 1b
Guaranteeing QOS!
No frame reorder! 1a
AP Path
. .
AC_VO
. .
AC_VI
. .
Direct Link Path
QSTA1
QSTA2
AC_BE
. .
AC_BK
TPSR[0-3]=TPSR0 (TPSR using AC 0), TPSR1, TPSR2, TPSR3
TPSP[0-3]=TPSP0 (TPSP using AC 0), TPSP1, TPSP2, TPSP3
L.Chu Etc.

8. Solution to Frame Reorder (Cont’d)
November 2007
Solution to Frame Reorder (Cont’d)
After recovering from power saving state, QSTA1 may send a TDLS Tx Path Switch Request (TPSR) indicating a switch to the direct path in each access category to QSTA2.
After QSTA2 receives a TPSR, it shall enable the direct Rx path and responds a TPSP to QSTA1 with the same access category as received TPSR.
After QSTA1 receives a TPSP from QSTA2, it will uses direct link path to send the frames to QSTA2 with the same access category as received TPSP.
. .
AC_VO
. .
AC_VI
. .
AC_BE
. .
TPSP[0-3] 2b
AC_BK
TPSR[0-3]
TPSP[0-3] 2a
TPSR[0-3]
QAP 1b
Guaranteeing QOS!
No frame reorder! 1a
. .
AP Path
AC_VO
. .
AC_VI
. .
Direct Link Path
AC_BE
. .
QSTA1
QSTA2
AC_BK
TPSR[0-3]=TPSR0 (TPSR using AC 0), TPSR1, TPSR2, TPSR3
TPSP[0-3]=TPSP0 (TPSP using AC 0), TPSP1, TPSP2, TPSP3
L.Chu Etc.

9. One Rx Path Switch Request
November 2007
One Rx Path Switch Request
A TDLS Rx Path Switch Request (RPSR) is used to switch to AP path from direct path and switch the receiving path to direct path from AP path.
One RPSR is enough since there are no buffered data frames from RPSR source in the AP in these two scenario.
It is not clear which access category should be used if QOS frames are used to encapsulate TPSRs between QSTAs.
Solution:
TDLS Rx Path Switch Request/Response should use access category AC-VO.
QAP
RPSR 1b 1a 2a 2b
RPSP
Direct Link
QSTA1
QSTA2
L.Chu Etc.

10. Frame Reorder when changing Path Between AP path and direct link path
September 2007
doc.: IEEE /2376r0
November 2007
Frame Reorder when changing Path Between AP path and direct link path
Being unable to reuse direct link when recovering from power saving
TDLS Setup and Deletion
Backup Slides
L.Chu Etc.
Steve Emeott, Motorola

11. Problem with Power Saving Recovery in [1]
November 2007
Problem with Power Saving Recovery in [1]
After returning to active state, STA1 may request a peer STA to enable the direct Rx path by sending a TDLS Tx Path Switch Request to peer STA2, indicating a switch to the direct path.
Upon receipt of the TDLS Tx Path Switch Request indicating the direct path, STA2 shall enable the direct Rx path and respond with a TDLS Tx Path Switch Response echoing the switch to the direct path.
This may not be true since STA2 may also be in power saving mode.
QAP 1b 1a
TPSR 2a 2b
TPSP
Direct Link
QSTA1
QSTA2
L.Chu Etc.

12. Solution with Power Saving Recovery
November 2007
Solution with Power Saving Recovery
After returning to active state, QSTA1 may request a peer QSTA to enable the direct Rx path by sending a TDLS Tx Path Switch Request for each access category to peer QSTA2, indicating a switch to the direct path.
Upon receipt of the TDLS Tx Path Switch Request indicating the direct path,
if QSTA2 is in active state, it shall enable the direct Rx path and respond with a TDLS Tx Path Switch Response for each access category echoing the switch to the direct path. After QSTA1 receives a TPSP from QSTA2, it will uses direct link path to send the frames to QSTA2 with the same access category as received TPSP.
if QSTA2 is in power saving state, it shall not reply with a TDLS Tx Path Switch Response. It may also reply with a TDLS Tx Path Switch Response for each request with path=AP path. A reason being in power saving state may be included in the response frame.
L.Chu Etc.

13. Frame Reorder when changing Path Between AP path and direct link path
September 2007
doc.: IEEE /2376r0
November 2007
Frame Reorder when changing Path Between AP path and direct link path
Being unable to reuse direct link when recovering from power saving
TDLS Setup and Deletion
Backup Slides
L.Chu Etc.
Steve Emeott, Motorola

14. Access Category of TDLS Setup and Deletion Messages
November 2007
Access Category of TDLS Setup and Deletion Messages
To setup a direct link, a TDLS Setup Request and a TDLS Setup Response are used.
it is not clear which access category (AC) should be used if QOS frames are used to encapsulate TDLS Setup Request/Response between QSTAs.
To tear down a direct link, a TDLS Teardown Request and a TDLS Teardown Response are used.
it is not clear which access category should be used if QOS frames are used to encapsulate TDLS Teardown Request/Response between QSTAs.
Solutions:
TDLS Setup Request/Response and TDLS Teardown Request/Response should use access category AC-VO.
QAP
TDLS Setup/Teardown Req 1b 1a 2a 2b
TDLS Setup/Teardown Res
Direct Link
QSTA1
QSTA2
L.Chu Etc.

15. TDLS Setup Request/Response Messages
November 2007
TDLS Setup Request/Response Messages
The following fields in Association Request frame body are not necessary in TDLS Setup Request message:
Listen interval, Power Capacity, Support Channels, RSN, QoS Capacity.
The following fields in Association Response frame body are not necessary in TDLS Setup Response message:
Status code, AID, EDCA Parameter Set.
TDLS Setup Request message should be updated:
Delete Association Request frame body,
Add the following fields in TDLS Setup Request message:
Capability, Supported Rates, Extended Supported Rates (Optional), HT Capabilities (Optional), Extended Capabilities (Optional), Vender Specific (Optional).
TDLS Setup Response message should be updated:
Delete Association Response frame body,
Add the following fields in TDLS Setup Response message:
L.Chu Etc.

16. November 2007
Reference
[1] 11-07/2515r7, Tunneled Direct Link Setup (TDLS), Menzo Wentink etc.
L.Chu Etc.

17. Frame Reorder when changing Path Between AP path and direct link path
September 2007
doc.: IEEE /2376r0
November 2007
Frame Reorder when changing Path Between AP path and direct link path
Being unable to reuse direct link when recovering from power saving
TDLS Setup and Deletion
Backup Slides
L.Chu Etc.
Steve Emeott, Motorola

18. TDLS Setup Request/Response Message Formats
November 2007
TDLS Setup Request/Response Message Formats
Order
Information
Notes 1
Link Identifier
The Link Identifier is specified in z1. 2
Association Request frame body
The Association Request frame body is specified in 3
Dialog Token
The Dialog Token contains a unique value for this conversation. 4
RSNIE_I
RSNIE for Initiator STA (optional) 5
SMK Message 1 FTIE
SMK Message 1 FTIE (optional) 6
DH_I
Public value for Initiator STA (optional)
TDLS Setup Request
Order
Information
Notes 1
Link Identifier
The link identifier is specified in z1. 2
Status Code
The Status Code is defined in 3
Association Request frame body
The Association Request frame body is specified in Only present for Status Code 0. 4
Dialog Token
The Dialog Token is copied from the corresponding TDLS Setup Request. 5
RSNIE_P
RSNIE of Peer STA (Optional) 6
SMK Message s FTIE
SMK Message 2 FTIE (Optional) 7
DH_P
Public value for Peer STA (Optional)
TDLS Setup Response
L.Chu Etc.

19. Association Request/Response Frame Body
November 2007
Association Request/Response Frame Body
Order
Information
Notes 1
Capacity 2
Listen Interval 3
SSID 4
Support Rates
Optional 5
Extended Support Rates 6
Power Capacity 7
Supported Channels 8
RSN 9
QoS Capacity
Last
Vendor Specific
Order
Information
Notes 1
Capacity 2
Status Code 3
AID 4
Support Rates
Optional 5
Extended Support Rates 6
EDCA Parameter Set
Last
Vendor Specific
Association Response Frame Body
Association Request Frame Body
L.Chu Etc.