1 / 13

PREQ/PREP Create/Process/Forward

PREQ/PREP Create/Process/Forward. Authors:. Date: 2008-08-14. Path Stability With Rate of Sequence Number (SN) 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.

yannis
Télécharger la présentation

PREQ/PREP Create/Process/Forward

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. PREQ/PREP Create/Process/Forward Authors: Date: 2008-08-14 L. Chu Etc.

  2. Path Stability With Rate of Sequence Number (SN) 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. • Path instability will create MSDU reordering. • Why avoiding path instability is important: • Baseline dot11 standard requires that “There shall be no reordering of unicast MSDUs with the same TID value and addressed to the same destination.” (Section 6.1.3) L. Chu Etc.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. PREP Introduction • PREP follows unicast reverse path from the destination MP to the source MP • A destination does not need to increase its destination sequence number each time it sends a PREP in the current HWMP • An intermediate MP uses the destination sequence number and path metric to decide if the received PREP is discarded • The PREP element shall not be accepted (and shall not be processed as described in 11B.9.6.3.2) if any of the following is true: • The DSN < previous DSN from this originator • The Time to Live is 1 or less • (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) • Different reverse paths from a destination may have same intermediate MPs • these intermediate MPs will decide if the PREPs for different source MPs from the same destination MP are discarded L. Chu Etc.

  9. Destination Sequence Number in 11s Draft • In section 11B.9.4.2, a destination MP increments its sequence number • Immediately before a destination MP originates a PREP in response to a PREQ, it shall update its own sequence number to the maximum of its current sequence number and the destination sequence number in the PREQ. • The intermediate MP may wrongly discard received PREP based on this DSN updating criteria L. Chu Etc.

  10. MP1 request a path to MP5 with DO = 1, DSN=0 S:1 P:1 S:1 P:1 S:1 P:1 D:1 D:x Wrongly PREP Discard in Intermediate MP MP3 discards PREP (D:1) since the SN and path metric are the same. MP1 MP3 1 1 1 MP2 MP5 does not increase its destination SN since DSN in MP5 is 1. MP5 1 1 2 MP4 MP0 x MPj MPi x: Metric between MPi and MPj S:x P:y PREQ for MP5 with source SN x PREP for MP5 with destination SN x L. Chu Etc.

  11. Updated Destination Sequence Number in 11s Draft • A destination MP shall update its sequence number based on the following criteria: • A destination MP shall increment its own sequence number the same as the destination sequence number in the RREQ plus 1 if the destination sequence number in the RREQ is larger than or equal to the sequence number in the destination MP • Otherwise, a destination MP shall not change its sequence number • Intermediate MP may still wrongly discard PREP after this update • Again slide 10 give an example • The further update should be done in intermediate MP: • When an intermediate MP accepts an PREQ, if the destination MP’s SN in the forwarding table of the intermediate MP is larger than the DSN of the destination MP in PREQ, the DSN in PREQ shall be updated to the destination MP’s SN maintained in this intermediate MP L. Chu Etc.

  12. Backup Slides L. Chu Etc.

  13. Destination Sequence Number in AODV • In section 6.1, a destination MP increments its sequence number • Immediately before a destination MP originates a PREP in response to a PREQ, it shall update its own sequence number to the maximum of its current sequence number and the destination sequence number in the PREQ • In section 6.6.1, a destination MP increments its sequence number • If the generating node is the destination itself, it MUST increment its own sequence number by one if the sequence number in the RREQ packet is equal to that incremented value. Otherwise, the destination does not change its sequence number before generating the RREP message • These two criteria are contradictory with each other • The description in section 6.6.1 is very difficult to understand L. Chu Etc.

More Related