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Mesh Discovery and Peer Link Management

Mesh Discovery and Peer Link Management. Mesh Discovery. Mesh Discovery. Based on information about MPs referred to as Mesh Profiles comprising: Mesh identifier (Mesh ID) Path Selection protocol identifier Path selection metric identifier

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Mesh Discovery and Peer Link Management

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  1. Mesh Discovery and Peer Link Management

  2. Mesh Discovery

  3. Mesh Discovery • Based on information about MPs referred to as Mesh Profiles comprising: • Mesh identifier (Mesh ID) • Path Selection protocol identifier • Path selection metric identifier • Mesh discovery process requires detection of potential mesh neighbors • Beacons • Active scanning (Probe Requests)

  4. Mesh Identifier (Mesh ID) • Mesh ID is used to identify a mesh network • Given to MPs that may form a mesh network • Matching Mesh ID is necessary for an MP to join a mesh • Installed in MPs by a variety of means beyond the scope of 802.11 • Mesh ID is different from SSID to avoid confusing non-mesh STAs • Beacons sent by MPs contain a wildcard SSID

  5. Candidate Peer MP Discovery • Procedure used to discover candidate peer MPs and their properties • Two cases to consider: • Before an MP is member of a mesh network • After an MP is member of a mesh network • A configured MP has at least one profile • If MP is member of a mesh, exactly one mesh profile is active

  6. MP is already member of a mesh • Neighbor MPs are identified as those MPs having • Mesh ID and Path Selection protocol and metric IDs in Beacons/Probe Responses match the MP’s active mesh profile • Congestion Control Mode ID in Beacons/Probe Responses matches the MP’s active mode • Candidate Peer MPs are neighbors that Accept Peer Links

  7. MP is not member of a mesh • Neighbor MPs are those MPs having • Mesh ID and Path Selection protocol and metric IDs match those in at least one of the MP’s mesh profiles • Congestion Control Mode ID matches one of the MP’s congestion control modes

  8. Mesh Peer Link Management

  9. Mesh Peer Link Management • Protocol used to establish and close Peer Links between candidate peer MPs • Peer link establishment is required prior to the transmission of data or management frames (except for those used in discovery and link management) • An MP may be able to establish many such links with other MPs, up to a maximum

  10. Link Instance and Identification • A link instance is identified by <localMAC, peerMAC, LocalLinkID, peerLinkID> • A LinkID is an integer generated by the MP that allows the MP to uniquely identify a link instance among all its current peer link instances

  11. Mesh Peer Link Management Protocol Interface • SME in MP starts the protocol • Two possibilities • SME instructs MP to passively listen to incoming requests from candidate peer MPs • SME instructs MP to request the establishment of a link instance with a specific candidate peer MP • SME may close an established peer link

  12. Protocol Mechanism • MPs use peer link management frames to manage a link instance: • Peer Link Open Frame • Peer Link Confirm Frame • Peer Link Close Frame • Both MPs must send Open and receive Confirm frames for a link to get established • Protocol uses a Retry Timer and a maximum number of retries for Open frames

  13. Processing Peer Link Management Frames • Open and Confirm frames include • Mesh Configuration Element containing • active path selection protocol and metric IDs • mesh capability field (including accepting peer links and MDA enabled • Peer Link Management Element containing LocalLinkID and PeerLinkID • All are checked for consistency before link is established

  14. Mesh Network Channel Selection

  15. Channel Configurations in a mesh network • A mesh network may include MPs with one or more PHYs and may utilize one or more channels for communication between MPs • Each PHY on an MP operates on one channel at a time, (but the channel may change during the lifetime of the mesh network) • Devices with more than one PHY tune each PHY to a different channel • In its simplest form, a mesh operates only on one channel, and does not require more than one PHY per MP

  16. Mesh with Single Channel Configuration

  17. Mesh Networks with Multiple Channel Configurations

  18. Simple Channel Unification Protocol • Used to select a unified channel for operation in a mesh network with a single channel configuration • Based on a channel precedence criteria • Unified Channel Graph (UCG): A set of MPs that are interconnected to each other via a common WM communication channel

  19. MP Without Neighbors • If an MP is unable to detect neighbor MPs • It may adopt a Mesh ID from one of its profiles, • Select a channel for operation • Select an initial channel precedence value (31 bit random number) • Proceed to the active state

  20. Disjoint Mesh • If an MP discovers that the list of candidate peer MPs spans more than one channel • The MP selects the channel that is indicated by the candidate peer MP that has the numerically highest channel precedence indicator to be the unification channel • If the identified unification channel is different from the current operating channel, the MP shall execute the channel graph switch protocol

  21. Channel Graph Switch Protocol • Allows an MP to initiate switching of a UCG to a new channel • Accommodates the possibility of multiple MPs executing the protocol concurrently by introducing a Mesh Channel Switch timer (MCS timer) • An MP that determines the need to switch channel • Sets the MCS timer to a MCS wait time • Transmits a Mesh Channel Switch Announcement to each neighbor to which a mesh link has been established in the UCG

  22. Mesh Channel Switch Announcement Information Element • Channel Switch Mode: • Indicates restrictions on transmissions until a channel switch. • Mode = 1 implies that addressed MP is advised to transmit no further frames on current channel until the scheduled channel switch

  23. Mesh Channel Switch Announcement Information Element • New Regulatory Class: • Number of the regulatory class after the channel switch • New Channel Number: • Number of the channel to which the MP is moving • New Channel Precedence Indicator: • Channel precedence value of the channel to which the MP is moving • Channel Switch Count: • Time until the MP sending the announcement switches to the new channel • Source Address: • MAC address of the MP that originates the frame

  24. Channel Graph Switch Protocol • An MP receiving a Mesh Channel Switch Announcement with a channel precedence value larger than the current channel precedence value: • Sets MCS timer to the channel switch count value in the announcement • Sends an announcement to each neighbor peer MP to which a mesh link has been established • If an MP receives more than one announcement, it acts on an announcement only if its precedence value is higher than the previously received announcement

  25. Channel Graph Switch Protocol • If an MCS timer has been set on an MP: • The MP shall not originate a new Mesh Channel Switch Announcement frame during the duration of the MCS timer • When the timer expires, the MP should switch its PHY to the candidate channel and update its channel precedence indicator • The channel switch should be scheduled so that all neighbor peer MPs (including MPs in PS mode) have the opportunity to receive an announcement before the channel switch

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