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Wireless Service Engineering

Properties of Communication technologies

  • Communication range
    • Lower frequency → less power required to gain longer distance,
  • Latency
  • Data transfer rate
  • Architecture
  • Price for creating network

Wireless LANs

  • IEEE 802.11 family, HiperLAN…
  • IEEE Standards dominant
    • Wi-Fi (Wireless Fidelity)
      • Certified 802.11 standard family compliant product
      • Trademark of Wi-Fi Alliance
    • Supported by most types of devices
      • built-in on most laptops and some PDA's and evenn mobile phone
      • Adding the capability to the device
        • PCMCIA cards
        • CF cards
    • Global standard → same client works everywhere.
    • Core elements of Ethernet present
      • 48-bit MAC
      • Frames delivered based on MAC
      • Additional reliability mechanisms
  • HiperLAN is ETSI standard
    • co-operation on 2.4Ghz spectrum
  • Topology
    • Infrastructure mode/network
      • Terminals connected to access point
    • Peer-to-peer or ad hoc mode or independent network
      • Terminals connected to each other directly
  • Access points
    • Directional or omnidirectional RF
    • range is from tens to hundreds of meters
    • Access points usually have an ethernet connection.
    • Many brands to choose from
      • Lower cost
  • 2.4GHz ISM band (Industrial Scientific Medical) (used by most WLAN standards)
    • Free for using, no regulations
      • Maximum transmission power
    • Creating own network free, no licenses needed
    • No regulation → interference problems
    • s
  • No strong authentication
  • Nominal speed from 1Mb/s to 100Mb/s
  • Power consumption rather high

IEEE 802.11 family

specspeedFrequency
802.11a54Mbps5Ghznon free frequency
802.11b11Mbps2.4GhzWi-FI
802.11g54Mbps2.4Ghzspeed update to b
802.11n100Mbps2.4Ghznext step after g

Connectivity

  • Connection forming between AP and mobile or between several mobiles
    • The desired network is found through scanning
      • SSID is the identifier of network (service set identifier)
      • Active scan
        • Sending probe frame to inform SSID of the network the device wants to join
        • using Broadcast SSID in probe results response from all networks within range
      • Passive scanning
        • Listening communication on each WLAN channel to found out which is used by desired SSID
    • Responses
      • Access points responses to the probes
      • On ad hoc networks station that generated last beacon frame responds
    • After the desired network is found authentication and association is conducted
      • Open system authentication
        • Authentication based on MAC address
      • Shared key authentication
        • WEP must be enabled
  • One access point can serve up to 100 devices
  • Latency
    • from few milliseconds to hundreds of illiseconds
    • Processing the connections increase latency
      • The more there is users the higher the latency
  • Roaming is possible
    • Not always supported
    • Some compatibility issues between different vendors products.

Things to consider

  • Who creates network?
  • How big network is required?
  • What is the cost for upkeeping own network?
  • What kind of billing we can arrange?
  • Rely on TCP/IP?
  • How to conduct service discovery?
    • Dedicated SSID for a device providing certain type of service?
  • How about security?
Last modified: 2013/07/01 14:42