802.11 WLAN Topologies, Antennas, and Protocols

Posted on Jan 11, 2025 in Electronics

WLAN Topologies

802.11 LAN Topologies:

  • Ad hoc: Direct device-to-device communication.
  • Infrastructure: Uses an Access Point (AP).

Key Terms:

  • BSS: Basic Service Set.
  • IBSS: Independent Basic Service Set (no AP).

Network Setup:

  • Devices communicate without an AP by defining a group name.
  • In infrastructure mode, an AP acts as a bridge connecting wireless clients to a wired network.
  • Wireless clients are also known as stations.
  • An AP is an infrastructure device.
  • The coverage area of a single AP is called a BSA.
  • Multiple APs connected to a common distribution form an extended service area.
  • Clients connect to an SSID to access the LAN via a wireless AP.
  • The service set advertised by an AP is called a BSSID.
  • MBSSIDs indicate multiple MAC addresses on one SSID.

Connecting Isolated Networks:

  • A WGB can connect an isolated wired network to a LAN.
  • Cisco offers AWGB and UWGB wireless bridges.

Extending Range:

  • Repeaters can be used where cable lengths are an issue.
  • Wireless repeaters need a 50% overlap with the AP.

Mesh Networks:

  • Outdoor mesh networks support more than point-to-point topologies.
  • Mesh deployments are appropriate when connectivity is a major concern.

Antenna Fundamentals

Polarization:

  • Types: Vertical, horizontal, circular.
  • Cisco antennas use linear polarization.
  • Magnetic waves are perpendicular (90°) to electric waves.

Diversity:

  • Uses two antennas.
  • Listens to the preamble to choose the better antenna.
  • Antennas should be placed one wavelength apart.
  • Diversity antennas do not cover two areas.

Antenna Families:

  • Omnidirectional and directional.

Antenna Planes:

  • Horizontal plane (H) is also called azimuth.
  • Vertical plane (E) displays coverage from top to bottom.

Specific Antennas:

  • 2.2 dipole antenna: Indoor omnidirectional.
  • Air-Ant3213: Special omnidirectional antenna.
  • Yagi antenna: Warehouse, point-to-point, long hallways.
  • Parabolic dish antenna: Uses a narrow RF path.
  • Polarity can be changed on a parabolic antenna for mounting.
  • Air-ant3213 uses two antennas.

Connectors:

  • Cisco uses N-connector and RP-TNC.

Devices:

  • Attenuator: Lowers energy to the antenna.
  • Amplifier: Increases energy to the antenna.
  • Lightning arrestors are not designed to withstand a full lightning strike.

WLAN Protocol Overview

Standards:

  • IEEE standardizes the 802.11 protocols.

Original 802.11:

  • Maximum data rate: 2 Mbps.
  • RF technologies: FHSS, DSSS.
  • Frequency range: 2.4 GHz.
  • Operates in the ISM bands.

802.11b:

  • Frequency range: 2.4 GHz.
  • 3 non-overlapping channels.
  • Modulation techniques: DBPSK, DQPSK.
  • Coding method: Barker 11.
  • Non-overlapping channels: 1, 6, 11.