Wi-Fi mode management

A Wi-Fi 802.11 transponder can operate in one of four modes: Access Point (AP), Client, Ad Hoc and Direct:

  • nodes in Ad Hoc mode can only communicate with other nodes in Ad Hoc mode
  • Client nodes can only communicate with one AP node (to which they must first associate)
  • AP nodes can only communicate with all associated Client nodes
  • Client nodes cannot communicate directly with other Client nodes, only via a shared AP node
  • Direct mode operates like an AP with one or more Clients, but any node can rapidly re-negotiate its AP association and switch between Client and AP mode, so it is typically used to establish communicating pairs that can grow to groups

For Serval purposes, Ad Hoc mode is the most flexible, followed by Direct mode. However, these modes are not always available, so it must also be able to work with only AP and Client modes. A problem arises in a mixed area, which contains some Ad Hoc and some AP/Client nodes. To communicate with both, a node must regularly switch between Ad Hoc and Client mode, and associate with an AP every time it enters Client mode. This can take 30 seconds or more, so the decision to switch must be scheduled based on the kind and amount of traffic queued or connection requested.


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