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Mesh Deterministic Access (MDA)

Mesh Deterministic Access (MDA). Optional Access Method. Enhanced Distributed Channel Access (EDCA). Mesh Deterministic Access. MDAOP Protocol. MDAOP Operation. Motivation.

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Mesh Deterministic Access (MDA)

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  1. Mesh Deterministic Access(MDA) Optional Access Method

  2. Enhanced Distributed Channel Access (EDCA)

  3. Mesh Deterministic Access

  4. MDAOP Protocol

  5. MDAOP Operation

  6. Motivation • To allow MPs that support this optional access method to access the channel at selected times with lower contention than would otherwise be possible • Standard does not require all MPs to use MDA • MDA can be used by a subset of MPs in a mesh • However, the performance of MDA may be impacted by devices that do not respect MDA reservations

  7. Mesh Deterministic Access Opportunities (MDAOP) • Reserved time periods on the WM

  8. MDAOP information fields • MDAOP Duration: specifies the duration of the MDAOP in multiples of 32 microsec. • MDAOP Periodicity: specifies the number of times the MDAOP is reserved in a DTIM interval • MDAOP offset: the position of the MDAOP beginning form the beginning of the DTIM interval and subsequent intervals

  9. MDAOP • A set of MDAOPs is set up by an MP between itself (the owner) and the addressed MP using an MDAOP setup request • MDAOP Set ID:ID of the requested set of MDAOP, chosen by the owner to uniquely identify the set • The addressed MP returns an MDAOP setup reply

  10. MDAOP Advertisements • Every MP that has MDA active is required to advertise periodically MDAOPs it knows of • including those it learns from other MPs’ advertisements • Advertisements are transmitted in group addressed frames (either Beacons or MDA action frames)

  11. TX-RX Times and Interfering Times • TX-RX times report: • All MDAOP times for which the MP is the transmitter or the receiver • All times (other than MDAOP) that it knows are busy/reserved such that it is either the transmitter or receiver (e.g., HCCA, beacon times) • Interfering times report • All TX-RX times reported by the MP’s neighbor peer MPs such that it is neither the transmitter nor the receiver during those times

  12. Format of the TX-RX Times and Interfering Reports

  13. MDA Access Fraction and Limit • MDA Access Fraction Limit:Limit on the allowed fraction of time of a Mesh DTIM interval that may be reserved for MDAOPs (expressed in units of 1/16) • MDA Access Fraction:Current value of the MDA Access fraction at the MP

  14. Selection of MDAOP Times • To avoid contention, an MP setting up MDAOP times with a neighbor MP must select times that do not overlap with: • Neighborhood MDAOP times: set of MDAOP times already being used in the neighborhood • All the TX-RX times reported by all the MP’s neighbors in their advertisements • Neighbor MP’s MDAOP interfering times: • Interfering Times reported by the neighbor MP

  15. MDA Access Fraction Limit • When setting up a new set of MDAOPs, the MP must verify that the MDA Access Fraction Limit is not exceeded at the MP or any of its neighbors; • if it does, then the setup procedure is suspended • Similar checks regarding overlaps in MDAOPs and MDA Access Fraction Limit are made at the addressed MP • If any of the checks fails, the addressed MP rejects the setup request by indicating an appropriate error code in its reply

  16. Access During MDAOP • If an MP is • owner of an MDAOP • has an MSDU associated with an MDA session to transmit, then it attempts to obtain a TXOP using EDCA contention and backoff parameters corresponding to the Access Category of the MSDU • The attempt is successful if the MP completes a frame exchange with the receiver of the MSDU • If successful, it may transmit until the EDCA TXOP limit is reached (and may attempt to obtain subsequent TXOP if needed) • If unsuccessful, the MP shall perform the backoff procedure

  17. Access During MDAOP • If an MDA supporting MP is not the owner of the MDAOP, • then it shall defer initiating transmissions during the TXOP initiated in the MDAOP. • It may start contending for access to the channel after the conclusion of the TXOP initiated in the current MDAOP

  18. MDAOP Set Teardown • Either the transmitter or the receiver of an MDAOP set may initiate a teardown • Teardown shall be initiated when either the owner or receiver learn of a conflicting MDAOP set from an advertisement by a neighbor with a lower MAC address • Teardown is considered successful by the transmitter or receiver of the MDAOP set if: • Teardown is acked • Maximum retries is reached • Peer MP’s advertisement does not include MDAOP set

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