7.1 – Introduction

  • We can identify the following elements in a wireless network:
    • Wireless hosts:
      • It might be a laptop, tablet, smartphone, or desktop machine. The hosts themselves may or may not be mobile.
    • Wireless links:
      • A host connects to a base station or to another wireless host through a wireless communication link.
      • Two key characteristics:
        • Coverage area
        • Link rate
      • Some types of networks are only now being deployed, and some link rates can increase or decrease beyond the values shown depending on distance, channel, conditions, and the number of users in the network.
      • Wireless links are also sometimes used within a network to connect routers, switches, and other network equipment.
    • Base station:
      • A base station has no obvious counterpart in a wired network.
      • A base station is responsible for sending and receiving data to and from a wireless host that is associated with that base station.
      • A base station will often be responsible for coordinating the transmission of multiple wireless hosts with which it is associated.
      • Wireless host is “associated” with a base station means:
        • The host is within the wireless communication distance of the base station
        • The host uses that base station to relay data between it and the larger network.
      • Cell towers in cellular networks and access points in 802.11 wireless LANs are examples of base stations.
      • Hosts associated with a base station are often referred to as a operating in infrastructure mode, sine all traditional network services are provided by the network to which a host is connected via the base station.
      • In Ad hoc networks, wireless hosts have no such infrastructure with which to connect. In the absence of such infrastructure, the hosts themselves must provide for services such as routing, address assignment, DNS-like name translation and more.
      • The process of changing its point of attachment into the larger network when a mobile host moves beyond the range of one base station and into the ranger of another is called handoff.
    • Network infrastructure:
      • The larger network with which a wireless host may wish to communicate.
  • At the highest level we can classify wireless network according to two criteria:
    • whether a packet in the wireless network: Crosses exactly one wireless hop or multiple wireless hops.
    • Whether there is infrastructure such as a base station in the network.
  • Networks:
    • Single-hop, infrastructure-based:
      • Have a base station that is connected to a larger wired network.
      • All communication is between this base station and a wireless host over a single wireless hop.
      • The type you use in a classroom, café, libraries etc.
    • Single-hop, infrastructure-less:
      • No base station that is connected to a wireless network. One of the nodes in this single-hop network may coordinate the transmission of the other nodes.
      • Bluetooth networks and 802.11 networks in ad hoc mode are single-hop, infrastructure-less networks.
    • Multi-hop, infrastructure-based:
      • A base station is present that is wired to the larger network. Some wireless nodes may have to relay their communication through other wireless nodes in order to communicate via the base station.
      • Some wireless sensor networks and so-called wireless mesh networks fall in this category.
    • Multi-hop, infrastructure-less:
      • No base station, and nodes may have to relay messages among several other nodes in order to reach a destination.
        • Nodes may also be mobile, with connectivity changing among nodes.
        • A class of networks known as mobile ad hoc networks (MANETs).
      • If the mobile nodes are vehicles, the network is a vehicular ad hoc network (VANET).

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