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PREQ/PREP Create/Process/Forward. Authors:. Date: 2008-08-05. Path Stability With Rate of Sequence Number Change. Sequence number (SN) is used to avoid path loop in HWMP. Increasing SN by 1 each time a MP sends a PREQ may change the path frequently.

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preq prep create process forward
PREQ/PREP Create/Process/Forward

Authors:

Date: 2008-08-05

L. Chu Etc.

path stability with rate of sequence number change
Path Stability With Rate of Sequence Number Change
  • Sequence number (SN) is used to avoid path loop in HWMP.
  • Increasing SN by 1 each time a MP sends a PREQ may change the path frequently.
  • One solution to maintain path stability in the current draft is to use the same source SN for dot11MeshHWMPnetDiameterTraversalTime.
    • PREQ ID is increased by 1 each time a new PREQ is created.
  • Path instability created by PREP is not considered.

L. Chu Etc.

current preq acceptance criteria
Current PREQ Acceptance Criteria
  • The PREQ element shall not be accepted:
    • The Originator DSN < previous Originator DSN
    • (DSN = previous DSN) AND (updated path metric is worse than previous path metric)
    • (the destination address of the PREQ is neither the recipient MAC address nor a MAC address proxied by the recipient) AND (dot11MeshForwarding is set to 0)
  • PREQ ID is not considered in PREQ acceptance criteria.

L. Chu Etc.

current prep creating criteria
Current PREP Creating Criteria
  • Case A: Original transmission A PREP is transmitted if the MP has received a PREQ fulfilling all of the following conditions:
    • a. One of the following applies:
      • The Destination Address of the PREQ is the same as MAC address of the receiving MP
      • The Destination Address of the PREQ = all 1’s (broadcast) and the PREP flag is set to 1 (”Proactive PREP”)
      • The Destination Address of the PREQ is currently proxied by the MP
    • b. One of the following applies:
      • The Originator DSN of the PREQ (preq.orig_dsn) is greater than the DSN of the last PREQ received from the same originator address (that includes the case that there is no path to the originating MP)
      • The Metric is better than the path selection metric currently associated with the Originator Address and the Originator DSN of the PREQ (preq.orig_dsn) is equal to the DSN of the last PREQ received from the same originator address
  • PREQ ID is not considered in PREP creating criteria.

L. Chu Etc.

wrongly preq discard in intermediate mp
MP1 requests a path to MP5.

x

MPj

MPi

x: Metric between MPi and MPj

S:x P:y

S:1 P:1

S:1 P:1

S:1 P:1

PREQ for MP5 with source SN x and PREQ ID y

S:1 P:2

S:1 P:2

S:x P:y

PREQ for MP6 with source SN x and PREQ ID y

Wrongly PREQ Discard in Intermediate MP
  • MP1 requests a path to MP6.

MP2

MP5

2

1

1

MP1

MP4

MP4 discards PREQ (S:1 P:2) Since bullet 2 in PREQ accepting criteria is true

1

1

1

MP3

MP6

L. Chu Etc.

wrongly preq discard in destination mp

S:1 P:1

S:1 P:1

S:1 P:2

S:1 P:2

x

MPj

MPi

x: Metric between MPi and MPj

S:x P:y

PREQ for STA1 with source SN x and PREQ ID y

S:x P:y

PREQ for STA2 with source SN x and PREQ ID y

PREP for STA1

Wrongly PREQ Discard in Destination MP
  • MP1 requests a path to STA1 associated with MAP4.
  • MP1 requests a path to STA2 associated with MAP4.

MP2

STA1

2

1

MP1

MAP4

MAP4 discards PREQ (S:1 P:2) since the metric is not better than PREQ (S:1 P:1)

1

1

MP3

STA2

L. Chu Etc.

wrongly prep discard in intermediate mp

S:1 P:1

S:1 P:1

S:1 P:1

S:1 P:1

S:1 P:1

S:1 P:1

x

MPj

MPi

x: Metric between MPi and MPj

S:x P:y

PREQ for STA1 with source SN x

S:x P:y

PREQ for STA2 with source SN x

D:1

D:x

PREP for STA1 with destination SN x

D:x

PREP for STA2 with destination SN x

Wrongly PREP Discard in Intermediate MP
  • MP0 requests a path to STA1 associated with MAP5.
  • MP1 requests a path to STA2 associated with MAP5.

MP3

MP1

STA1

1

1

1

MP2

MAP5

1

1

2

MP4

MP0

STA2

L. Chu Etc.

wrongly prep discard in intermediate mp cont d

x

MPj

MPi

x: Metric between MPi and MPj

S:x P:y

PREQ for STA1 with source SN x

S:x P:y

PREQ for STA2 with source SN x

D:1

D:x

PREP for STA1 with destination SN x

D:2

D:x

D:2

D:2

PREP for STA2 with destination SN x

Wrongly PREP Discard in Intermediate MP (Cont’d)
  • MP0 requests a path to STA1 associated with MAP5.
  • MP1 requests a path to STA2 associated with MAP5.

MP1

MP3

STA1

1

1

1

MP2

MAP5

1

1

2

MP0

MP4

STA2

MP2 discards PREP (D:1) since the SN is older

L. Chu Etc.

path instability with prep replying right away

x

MPj

MPi

x: Metric between MPi and MPj

S:x P:y

PREQ for MP5 with source SN x

S:1 P:1

S:1 P:1

S:1 P:1

PREP for MP5 with destination SN x

S:1 P:1

D:1

D:x

Path Instability with PREP Replying Right away
  • MP0 requests a path to MP5.

MP3

MP1

1

1

1

MP2

MP5

1

1

2

MP4

MP0

L. Chu Etc.

path instability with prep replying right away cont d

S:1 P:1

D:1

D:x

D:1

D:2

D:2

D:2

Path Instability with PREP Replying Right away (Cont’d)
  • MP0 requests a path to MP5.

x

MPj

MPi

x: Metric between MPi and MPj

MP3

MP1

S:x P:y

1

PREQ for MP5 with source SN x

1

1

MP2

MP5

PREP for MP5 with destination SN x

1

1

2

MP4

MP0

L. Chu Etc.

preq create process forward procedure refinement
The PREQ element shall not be accepted if any of the following is true:

The Originator DSN < previous Originator DSN

(DSN = previous DSN) AND (PREQ ID of the originator is not the first time to be received) AND (updated path metric is worse than previous path metric)

(the destination address of the PREQ is neither the recipient MAC address nor a MAC address proxied by the recipient) AND (dot11MeshForwarding is set to 0)

Effect of PREQ receipt (Add the following restriction):

The receiving MP shall not update the active forwarding information for the originator if the updated path metric is worse than the previous path metric

PREQ Create/Process/Forward Procedure Refinement

L. Chu Etc.

prep create process forward procedure refinement
The interval between two new PREPs transmitted by a destination MP shall be more than dot11MeshHWMPprepMinInterval (= dot11MeshHWMPpreqMinInterval)

Adding the following new bullet to PREP original transmission Case A’s b:

The Originator DSN of the PREQ (preq.orig_dsn) is equal to the DSN of the last PREQ received from the same originator address AND the PREQ ID of the originator is the first time to be received

PREP Create/Process/Forward Procedure Refinement

L. Chu Etc.

prep create process forward procedure refinement cont d
Further PREP updates (to support the use of the same destination SN for some time):

to use the same destination SN for dot11MeshHWMPnetDiameterTraversalTime.

PREP ID is increased by 1 each time a new PREQ is created.

The PREP element shall not be accepted if any of the following is true:

The DSN < previous DSN

(DSN = previous DSN) AND (PREP ID of the originator is not the first time to be received) AND (updated path metric is worse than previous path metric)

(the destination address of the PREP is neither the recipient MAC address nor a MAC address proxied by the recipient) AND (dot11MeshForwarding is set to 0)

Effect of PREP receipt (Add the following restriction):

The receiving MP shall not update the active forwarding information for the destination if the updated path metric is worse than the previous path metric

PREP Create/Process/Forward Procedure Refinement (Cont’d)

L. Chu Etc.

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