• When computers communicate "via the air waves," and without physical media like wires and cable, the transmission between the computers is considered "wireless." Wireless data transfer is also called "wireless communication."
• Categories of wireless communications:
1. Wireless LAN Communications
2. Wireless Bridging and Internetworking
3. Wireless Mobile Communications
• Mobile communications include any communications over public carrier facilities by way of radio, cellular and satellite stations. Cellular (mobile) telephones use radio frequencies in an overlapping, honeycomb-shaped cellular pattern to provide coverage throughout a region.
• Wireless LAN communications act like radio communications that connect devices within a single office or floor of a building (or within a home). This is done primarily through a wireless router that connects with a wireless access point (WAP). Essentially this router performs much like a modem that can link a LAN together as well as provide a gateway to the Internet.
• Wireless Bridging and Internetworking: Radio or satellite communications can also be used to connect separate buildings in a more complex network. A wireless bridge device can be used to connect wired Ethernet LANs together through a browser based administrative interface.
• Advantages of Radio or Satellite communications to connect buildings:
• Cabling needs are reduced or essentially eliminated
• Connections can be made to remote locations and through environments
• proven too rigorous for physical media (e.g., mountainous, rocky terrain)
• Penetrates through barriers without drilling holes (e.g., radio waves)
• Less expensive that physical media
• Transmits voice, video and data
• Can transmit in analog and digital
• Mobility without restriction by a cable
• Can be “self healing” since the network makes adjustments to find more reliable paths
• Versatility: easier to adapt and expand as needed
• Disadvantages of Radio or Satellite communications to connect buildings:
• Atmospheric interference
• Clear line-of-site needed for infrared wireless connections
• Frequency licensing from the Federal Communications Commission (FCC)
• Requires more security vigilance


• IEEE 802.11 is the wireless standard for peer to peer and for client/server networks.
• Wireless LAN Communications
  
  
  • Most often located within a single office building, and utilize a wireless transceiver (also called access point) in a fixed location.
  • Advantages:
  • Flexibility
  • Mobility
  • No FCC license requirement
  • Disadvantages:
  • Security concerns
  • Lack of complete standardization
• Techniques for wireless transmission:
  
  
  • Infrared transmission system employs light as its media. Infrared light signals fall into the electromagnetic spectrum's TeraHertz (THz) range. Infrared signals are created by a device called a Light Emitting Diode (LED). Infrared is supported at the Physical Layer of the OSI model.
  • Point-to-point communications requires line-of-sight (no obstacles) between the communicating nodes. Point-to-point infrared transmission systems have many advantages. No licenses are required to broadcast an infrared transmission, eavesdropping is extremely difficult, and signals rarely suffer from attenuation.
  • Broadcast transmission systems beam light signals in a less concentrated fashion, spreading them throughout a wider area. Broadcast systems often have several receivers, some of which are mobile and frequently moved

Wireless Bridging and Internetworking

• Generally used for connecting buildings and facilities on campuses, within metropolitan areas or between offices in different planetary locations by satellite.
• Two basic types of microwave transmission systems:
• Terrestrial: used when a local cable network would be too extensive, expensive or impractical.
• Advantages:
• Long distance transmission
• Speedy MHz and GHz transmission
• Flexible analog or digital transmission
• Transmits voice, video, and data
• Avoid most right of way problems
• Disadvantages:
• FCC licensing required
• Performance degraded by weather
• Frequency congestion
• Power lines can interfere
• Flash light pattern transmission
• Satelite: use parabolic antennas, operate on low GHz frequency and rely on line-of-sight (point-to-point) antennas
• Consist of a space component, a signal component, and a ground component.
• Received data is transformed into binary-coded microwaves and transmitted to an orbital satellite
• Ad-Hoc Mode is the simplest Wireless LAN (WLAN) topology. Ad-Hoc Mode does not require an access point, therefore making it possible for two wireless devices to communicate directly with one another, essentially forming a wireless, peer-to-peer network.
• Infrastructure Mode requires a network infrastructure based around Wireless Access Points (WAP).

Wireless Mobil Communications

• Modern cellular networks consist of four major components:
• Mobile Telephone Switching Office (MTSO)
• Cell sites with a controller and transceiver
• System interconnections
• Mobile telephone units

Wireless Network Authentication

• Wired Equivalent Privacy (WEP) - early security standard specified by 802.11
• Types:
• Open System authentication – WLAN client authenticates with Access Point before attempting to associate. This method is best used with networks that need minimal security.
• Shared Key authentication – WEP key is used for authentication before going through a 4 way handshake challenge/response process. Although this may appear to be more secure, it actually leaves open many holes that hackers can exploit relatively easily.
• Weaknesses:
• Initialization Vector (IV) – Most implementations start with an IV of zero and increment it by one for each packet that is sent. On a busy network, all possible IVs are used in about 5 hours, after which the numbers are recycled. The IV is appended to the encrypted packet in clear text. This weakness leaves WEP open to several active and passive attacks.
• Shared-key implementation – A challenge text string is sent in the clear, without encryption.

• WPA-- adopted by the Wi-Fi Alliance as an immediate solution before the full development of the 802.11i standard.
  
  
  • Improvements over WEP:
    
    
    • Mixing function: combines secret root key with initialization vector before passing
    • Sequence counter to guard against repeated attacks
    • Uses 64-bit message integrity check
• WPA2-- fully compliant with 802.11i
  
  
  • Requires Robust Security Network (RSN) that includes two additional protocols:
    
    
    • 4-Way Handshake – used to create a secret Pairwise Transient Key (PTK) that is put through a cryptographic hash function
    • Group Key Handshake – method of updating a Group Temporal Key (GTK) when a device leaves the network or due to expiration of a preset timer
• Standard Hotspots -- a location where Internet access is available via Wi-Fi.
• RADIUS
  
  
  • Functions:
• Authenticate users or devices before granting them access to a network
• Authorize those users or devices for certain network services
• Account for usage of those services