Introduction to mesh functions

4.3.15.5 Introduction to mesh functions
4.3.15.5.1 General

A mesh BSS is formed and operated by the set of services called mesh services. Mesh services are provided
by the following major mesh facilities:
— Mesh discovery
— Mesh peering management
— Mesh security
— Mesh beaconing and synchronization
— Mesh coordination function
— Mesh power management
— Mesh channel switching
— Three address, four address, and extended address frame formats
— Mesh path selection and forwarding
— Interworking with external networks
— Intra-mesh congestion control
— Emergency service support in mesh BSS

4.3.15.5.2 Mesh discovery
A mesh STA performs either active scanning or passive scanning to discover an operating mesh BSS. Each
mesh STA transmits Beacon frames periodically and responds with Probe Response frames when a Probe
Request frame is received, so that neighbor mesh STAs can perform mesh discovery appropriately. The
identification of the mesh BSS is given by the Mesh ID element contained in the Beacon and the Probe
Response frames. The details for the mesh discovery facility are described in 13.2.
4.3.15.5.3 Mesh peering management (MPM)
Within a mesh BSS, direct communication between neighbor mesh STAs is allowed only when they are peer
mesh STAs. After mesh discovery, two neighbor mesh STAs agree to establish a mesh peering to each other,
and, after successfully establishing the mesh peering, they become peer mesh STAs. A mesh STA can
establish a mesh peering with multiple neighbor mesh STAs. The mesh peering management (MPM)
facilitates the mesh peering establishment and closure of the mesh peerings. The details of MPM are
described in 13.3.
4.3.15.5.4 Mesh security
In an MBSS, mesh link security protocols are used to authenticate a pair of mesh STAs and to establish
session keys between them. Mesh authentication protocols establish a shared, common pairwise master key
(PMK), and authenticate a peer mesh STA. The authenticated mesh peering exchange protocol relies on the
existence of the PMK between the two mesh STAs to establish an authenticated peering and derive session
keys. The details of mesh security are described in 11.3, 13.3.3, 13.5, and 13.6.
4.3.15.5.5 Mesh beaconing and synchronization
In order to assist mesh discovery, mesh power management, and synchronization in a mesh BSS, all mesh
STAs periodically transmit Beacon frames. Synchronization in a mesh BSS is maintained by the MBSS’s
active synchronization method. The default synchronization method is the neighbor offset synchronization
method. Mesh beacon collision avoidance (MBCA) mitigates collisions of Beacon frames among hidden
nodes. The details of mesh beaconing and synchronization are described in 13.13.
4.3.15.5.6 Mesh coordination function (MCF)
A mesh STA uses the mesh coordination function (MCF) for channel access. MCF consists of EDCA
(contention-based channel access defined in 9.20.2) and MCCA (controlled channel access defined in
9.20.3). MCCA is a reservation based channel access method and aims to optimize the efficiency of frame
exchanges in a mesh BSS.
4.3.15.5.7 Mesh power management
A mesh STA can manage the activity level of its links per mesh peering. A mesh STA sets the activity level
of each of its mesh peerings to either active mode, light sleep mode, or deep sleep mode. The mesh STA
performs mesh power mode tracking for each of its neighbor peer mesh STAs, and delivers the frames based
on the rules defined in 13.14.
4.3.15.5.8 Mesh channel switching
When a mesh STA switches the operating channel, it uses the channel switch protocol defined in 10.9.8 and
10.10. The channel switch protocol enables the propagation of channel switching messages throughout the
mesh BSS, prior to the channel switch execution.