Jiyoung et al.

doc.: IEEE 802.11-07/2797r00

Submission

Oct 2007

Path Selection and Path Switch MechanismPath Selection and Path Switch Mechanism

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Date: 2007-11-13

Name Compay Address Phone E-mail

Jiyoung Huh LG Electronics jyhuh@lge.com

Yongho Seok LG Electronics yhseok@lge.com

Jiyoung et al.

doc.: IEEE 802.11-07/2797r00

Submission

Oct 2007

AbstractAbstract

The direct link assumes that STAs using direct link can use one of AP-Path and DL-Path and the path switch is caused by the link state (e.g., Link RCPI), or PSM.This proposal combines the Link RCPI Request/Report and the Path Switch Request/Response in order to resolve the limitation of the Link RCPI Request/Report and make the Path Selection and Switch more efficient.

Jiyoung et al.

doc.: IEEE 802.11-07/2797r00

Submission

Oct 2007

Path Selection and Switch MechanismPath Selection and Switch Mechanism

• The Path Selection & Switch Mechanism is required for the following:– Entering a power save state– Using the better one of the two paths (i.e, AP-Path or Direct Link)

• The better path is decided based on the quality of the following links– AP-Path Link = Sending STA to AP (a) + AP to Receiving STA

(b)– Direct Link = Sending STA to Receiving STA (c)

※ Each Link state can be known to ending STA of the links

AP

STA1 STA2

Link ①

②

③

④

⑤

⑥

• Two parts are defined for the path selection in TDLS– Radio Measurement (Link RCPI

Request/Report)– Path Switch Mechanism

Jiyoung et al.

doc.: IEEE 802.11-07/2797r00

Submission

Oct 2007

Link RCPI Request/ReportLink RCPI Request/Report

• Link RCPI Request • Link RCPI Report

BSSIDSTA

Address

Octets 6 6

BSSID RCPI1STA

AddressRCPI2

Octets 6 1 6 1

• A STA may transmit a Link RCPI Measurement Request to an (intended) peer STA to obtain an indication of the RCPI values at the peer STA. The Link RCPI measurement request and report are sent to the peer STA directly. The RCPI information may be used to decide whether to switch over to a direct link for communication with the peer STA.

AP

STA1 STA2

Link ①

③

⑤

Jiyoung et al.

doc.: IEEE 802.11-07/2797r00

Submission

Oct 2007

Concern about Link RCPI Request/ReportConcern about Link RCPI Request/Report

• When should STA send the Link RCPI Request?– The link status changes frequently and randomly.– The requesting STA (STA1) never know when the link

status changes.– The only requested STA (STA2) can always know the

link status changes

AP

STA1 STA2Link RCPI Request

Periodically?Randomly?

After receivingseveral NAKs?

Jiyoung et al.

doc.: IEEE 802.11-07/2797r00

Submission

Oct 2007

Path Switch Mechanism (Cont.)Path Switch Mechanism (Cont.)

• Four frames are defined to request path switch and respond to the request in Rx and Tx side and have Link Identifier, Dialog Token, and Path information

• Tx Path Switch Request/Response

– A sending STA sends request to peer STA to switch to Direct Link

– The peer STA SHALL enable the direct link and respond to the request by sending response frame

• Rx Path Switch Request/Response

– A receiving STA sends request to switch to DL or AP-Path

– The Peer STA SHALL use the AP-Path if the request indicates a switch to AP-Path.

– The Peer STA can use the DL or not if the request indicates a switch to DL

Jiyoung et al.

doc.: IEEE 802.11-07/2797r00

Submission

Oct 2007

Concern about Path Switch MechanismConcern about Path Switch Mechanism

APSTA1 STA2

①

③

②

④

⑤

⑥

①: Direct Link③+⑤: AP-Path

There may beseveral reasonsfor the request

There may beseveral reasons

that cannot acceptthe request

Tx Path Switch Response?

Rx Path Switch Response ?

Tx Path Switch Request

Rx Path Switch Request

• The Path Switch Request/Response frame cannot indicate why the path switch is requested and whether the request is acceptable or not

Jiyoung et al.

doc.: IEEE 802.11-07/2797r00

Submission

Oct 2007

SuggestionSuggestion

• A STA that can know the link state requests the path switch including the information such as the reason for the request and, if necessary, link state.

• The STA receiving the request can decide whether the link should be changed or not based on the information included in the request and itself.

Jiyoung et al.

doc.: IEEE 802.11-07/2797r00

Submission

Oct 2007

Tx Path Switch Request/ResponseTx Path Switch Request/Response

APSTA1 STA2

①

③ ⑤

①: Direct Link③+⑤: AP-PathRCPI1: RCPI of ⑤RCPI2: RCPI of ①RCPI3: RCPI of ③

Tx Path Switch Response

RCPI2(Optional)

RCPI1(Optional)

ResultPathDialog Token

Link Identifier

Tx Path Switch Response

Reserved ~3Reject because of Link / state① ⑤2

Accept0

Reject because of entering power save mode1

ExplanationResult

Tx Path Switch Request

RCPI3(Optional)

ReasonPathDialog Token

Link Identifier

Tx Path Switch Request

The state of Link is very good③2Reserved3~

The state of Link is very terrible③1Request for stopping the PS mode0

ExplanationReason

Jiyoung et al.

doc.: IEEE 802.11-07/2797r00

Submission

Oct 2007

Rx Path Switch Request/ResponseRx Path Switch Request/Response

APSTA1 STA2

①

③ ⑤

①: Direct Link③+⑤: AP-PathRCPI1: RCPI of ⑤RCPI2: RCPI of ①RCPI3: RCPI of ③

RCPI2(Optional)

RCPI1(Optional)

ReasonPathDialog Token

Link Identifier

Rx Path Switch Request

Reserved ~3The state of Link is better than ’s⑤ ①2

Request for entering the PS mode0

The state of Link is better than ’s ① ⑤1

ExplanationReason

Rx Path Switch Request

RCPI3(Optional)

ResultPathDialog Token

Link Identifier

Rx Path Switch Response

Reserved2 ~

Accept0

Reject because of Link state③1

ExplanationResult

Rx Path Switch Response

Jiyoung et al.

doc.: IEEE 802.11-07/2797r00

Submission

Oct 2007

ConclusionConclusion

• Link RCPI Request/Report is suggested for the best path selection, but sometimes unnecessary or overhead.

• If Path Switch Request/Response frame includes the link state information instead of Link RCPI Request/Report, unnecessary Link RCPI request/report is not sent and the best path selection is performed more efficiently.

Jiyoung et al.

doc.: IEEE 802.11-07/2797r00

Submission

Oct 2007

Straw PollStraw Poll

• Do you think that suggested path switch request/response can make the path selection and switch more efficient?

– Yes:

– No:

– I don’t know: