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WIFI DIRECT

WiFi direct is the WiFi solution for ad hoc networks, It provides a node that plays the role of the Group owner GO and serve the other WiFi capable nodes like an AP in infrastructured mode:

flowchart TD
subgraph net
a((GO))
b((node1))
c((node2))
d((node3))
e((node4))
b-->a
c-->a
d-->a
e-->a
end

There are some limitations:

  • the group owner cannot be changed in a session
  • cross connectivity must pass trough the GO and need to be handled at the network layer (e.g. thorugh NAT)
  • if the GO leaves the group the network is destroyed and need a new creation process

GO DETERMINATION

there are 2 phases for the formation of a WiFi network group:

  • determination of the GO
  • provisioning of the GO

Determination of the group owner can be done by 2 modes:

  • negotiation between devices
  • establish the GO at the application level

GROUP FORMATION

There are three ways to perform group formation:

  • standard p2p devices discovers each other and then determines the group owner

  • autonomous a device create a group and becomes the group owner waiting for

  • persistent a group is marked as persistent using WiFi direct beacon and nodes can exploits invitation to accelerate the group creation process

POWER SAVING

Two ways to implement power saving capabilities

  • opportunistic the GO saves energy when the nodes are sleeping

  • Notice of absence the GO announces time intervals when the nodes are not allowed to communicate in the channel

SECURITY

WiFi direct uses WPS to implement a simple layer of security that has minimum user interaction requirements (ask pin or ask for confirmation)

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