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Multiple NAV Protection - Revisited

Multiple NAV Protection - Revisited. Mathilde Benveniste Avaya Labs, Research October 2004. NAV protection. Current NAV protection is not adequate to provide reliable virtual carrier sensing The NAV of a station should be set or reset by considering all stations involved

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Multiple NAV Protection - Revisited

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  1. Multiple NAV Protection - Revisited Mathilde Benveniste Avaya Labs, Research October 2004

  2. NAV protection • Current NAV protection is not adequate to provide reliable virtual carrier sensing • The NAV of a station should be set or reset by considering all stations involved • The NAV rules do not protect QBSS properly when HCCA is used with overlapping BSS • This will be problematic for high-density VoWLAN, encountered in public spaces (hotspots) and the enterprise M. Benveniste -- Avaya Labs, Research

  3. HCF Polling (HCCA) NAV Reset • With HCCA, the HC overrules the NAV values • HC can reset NAV of QSTAs by sending CF-END • HC can reset NAV of QSTAs by sending QoS (+)CF-poll to itself with Dur/ID = 0 • The NAV of a QSTA, S1, may have been set as a result of two NAV setting events: • a poll to a QSTA in the BSS and • a RTS/CTS from a (Q)STA in an adjacent BSS • If QSTA S1 cleared its NAV and transmitted when the HC resets NAVs, there would be a collision M. Benveniste -- Avaya Labs, Research

  4. Proposed Solution • Restore the ability to use multiple NAVs and make it optional • Stations that have not implemented at least 2 NAVs may not reset their NAV when an AP engaged in HCF polling resets the NAV for the BSS M. Benveniste -- Avaya Labs, Research

  5. Motion Move to accept the normative text changes in doc 04/1070r2 • Comment addressed by this motion: 15 (SB 2) M. Benveniste -- Avaya Labs, Research

  6. Sample implementation of multiple NAVs The following is the most conservative implementation of a NAV setting involving 2 NAV values. A simpler implementation would ignore the field DISCARDED.

  7. NAV Problem Solution Define NA: address TXOP holder causing NAV to be set • Keep a set of the n longest NAV values, ANAV. Discard the shorter NAV values. For each NAV retain the NA of the node setting it. • When an HC sets the NAV, the NA is the address of the HC • When the NAV is set through an RTS/CTS, the NA is the address of the station sending the RTS/CTS • In general, a station will refrain from transmitting if a ANAV component >0 • When a component of ANAV expires it becomes 0 • A new NAV is retained among the n ANAV components if it exceeds the length of the shortest NAV retained, which it replaces. • Reset the ANAV component of the source requesting reset. Set a ANAV[NA]=0 when NA coincides with the address of a node responsible for NAV cancellation (i.e. the HC), unless at least one NAV value has been discarded and none of the non-discarded NAV values has since expired M. Benveniste -- Avaya Labs, Research

  8. +3 +1 +1 Time increment Time 1 4 5 Example – 2 NAV values retained in ANAV; NAV cleared Reset NAV NA=XA NAV value=3 NA=XC Time 0: NAV setting requests received from XA, XB, and XC Time 1: Discarded is set to T when ANAV[XB] is discarded Time 4: Discardedis reset to F when ANAV[XC] expires Time 5: XA requests NAV reset 5 time-units later, and the ANAV[XA] is cleared; the station NAV is also cleared as Discardedis F and all other NAV values have expired 10, XA 9, XA 6, XA 0, XA ANAV … 2, XB 3, XC 0, XC Discarded=F Discarded=T Discarded=F Discarded=F 0 M. Benveniste -- Avaya Labs, Research

  9. +3 +1 +1 Time increment Time 1 4 5 Example – 2 NAV values retained in ANAV; NAV not cleared Reset NAV NA=XA NAV value=5 NA=XC Time 0: NAV setting requests received from XA, XB, and XC Time 1: Discarded is set to T when ANAV[XB] is discarded Time 4: Discardedis reset to F when ANAV[XC] expires Time 5: XA requests NAV reset 5 time-units later, and the ANAV[XA] is cleared; the station NAV is notcleared as all other NAV values have not expired 10, XA 9, XA 6, XA 1, XC ANAV … 0, XA 2, XB 5, XC 2, XC Discarded=F Discarded=T Discarded=F Discarded=F 0 M. Benveniste -- Avaya Labs, Research

  10. History of the “NAV Problem” In July 2003 comments to LB 51 raised the following problem: Several sources of NAV setting; the NAV should be set always to the longest value. The problem arises when NAV must be reset because a source requests so. How can we know which source set the NAV in order to cancel it? The Problem was identified initially in 2001 by S. Choi, A. Soomro, and J DelPrado – See 01/272 Comments to LB 51 were addressed by providing a solution, an optional feature, proposed by M. Benveniste - See 03/565r1 Normative text provided by M. Benveniste, M. Sherman, and C. Wright - See 03/594r1 The solution has been present in D5, D6, D7, D8 (SP 1) M. Benveniste -- Avaya Labs, Research

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