Operational Modes

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Operational Modes

• ITN 220 1 Feb 2007

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Network configurations

• Networks can be configured in the following
  manner
• Point-to-point
• Point-to-multipoint
• Multipoint-to-multipoint

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Point-to-Point

• Simplest to configure
• two nodes
• very simple management

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Point-to-Multipoint

• One-to-many
• Requires management (usually centralized)
• Most common

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Multipoint-to-Multipoint

• Many to many
• Very complex management (or almost none)
• Mesh or ad-hoc

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Radio Modes of Operation

• Wi-Fi Radios can operate in any one of a number
  modes (one at a time)
• Ad-hoc
• Managed (Infrastructure) - Client
• Repeater
• Mesh
• Monitor
• Bridge
• Master Access Point

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Ad-hoc Mode

• Multi-point to multi-point (direct communications
  only)
• No master mode radio (no AP)
• Can communicate directly with any other node
  using the same network name and channel (must be
  within range)

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Master Mode

• AKA Infrastructure mode
• Access Point
• manages a network with a specific SSID and
  channel
• join/no join
• talk/no talk
• Can only communicate with other radios which are
  in managed mode

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Managed Mode

• Client mode
• Associates with one specific AP (Master mode)
• Normally cannot see other clients

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Monitor Mode

• AKA RFMon
• Radio is put into a passive listen (sniffer)
  state
• not to be confused with libpcap tools such as
  tcpdump
• Not available on all cards or via normal drivers
• Useful for troubleshooting or gathering data for
  spectrum management

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Bridge Mode

• Similar to a wired bridge where all LLC (MAC
  addresses included) traffic is repeated between
  the wired and wireless sides of the AP
• MAC addresses
• Broadcast traffic
• Very simple configuration
• Quickly becomes inefficient as nodes are added
• AirFortress

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Mesh Mode

• Similar to ad-hoc mode in that each node can talk
  with each other
• Different in that some sort of routing is used to
  provide a path to invisible nodes or a gateway
• Requires a routing protocol
• Though it normally uses ad-hoc mode, with the
  proper routing protocol, mesh can involve Master,
  Managed, or Bridged devices

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Metrics
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Routing

• Typically
• Point-to-point static
• Point-to-multipoint static or dynamic
• RIP or OSPF
• Mesh
• OLSR
• HSLS
• AODV

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Mesh/Repeater

• Routing allows equipment, intended to be WLAN, to
  become a WWAN
• Not a perfect solution
• suffers from the hidden node problem
• timing issues
• above 15 km too long for normal acknowlegements
  to be received (Atheros allows for timeouts to be
  extended) (Wi-Fi Shootout)

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Hidden Node

• Hidden node problem fixed (partially) via RTS/CTS
• Even better with routing protocols