6.1 Introduction
1. Terms:
1. Wireless host- Hosts are the end-system devices that run applications. It could be
a laptop, palmtop, PDA, phone, or desktop computer. Wireless hosts may or may
not be mobile.
2. Wireless links- A host connects to a base station or to another wireless host
through wireless links. Different links have different transmission rates and
distances.
3. Base station- 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. Cell towers and access points in 802.11 wireless
LANs are examples of base stations.
4. two wireless operating mode
1. Infrastructure mode- Hosts associated with base stations are in
infrastructure mode. All traditional network services (e.g., address
assignment and routing) are provided by the network to which a host is
connected to through the base station.
2. Ad hoc network- wireless hosts have no infrastructure to connect to, and
must provide services such as routing, address assignment, DNS-like
name translation, and more for themselves.
5. hand-off – This occurs when a mobile user moves out of the range of one base
station and into the range of another. The process by which it changes it’s point
of attachment from one station to another is called a hand-off.
2. What does associate mean in the context of wireless network?
1. The host is within the wireless communication distance of the base station
2. The host uses that base station to relay data between it and the larger networks
3. What are the challenges raised by the mobility characteristic of wireless network?
1. How do you find a host’s current location in a network so that data can be
forwarded to that mobile host?
2. How is addressing performed, given that a host can be in one of many possible
locations?
3. If a host moves during a TCP connection or phone call, how is data routed so that
the connection continues uninterrupted?
4. How wireless network could be classified and the criteria used to classify them?
1. Whether a packet in the wireless network crosses exactly one wireless hop or
multiple wireless hops.
2. Whether there is infrastructure such as a base station in the network.
Single-hop, infrastructure-based: These networks have a base station that is connected to
a larger wired network. Examples are classroom, café, or library wireless networks;
cellular telephonony networks, and 802.16 WiMAX networks.
Single-hop, infrastructure-less: These networks have no base station. Instead, one of he
nodes in the wireless network coordinates the transmissions of the other nodes.
Examples are Bluetooth networks and 802.11 networks in Ad Hoc mode.
Multi-hop, infrastructure-based: A base station is present in these networks and
connected to a larger wired network. However, some wireless nodes have to relay
messages through other wireless nodes in order to reach the base station. Examples are
some wireless sensor networks and so-called wireless mesh networks.
Multi-hop, infrastructure-less: There is not base station present in this network, and
nodes may have to relay messages in order to reach their intended destinations. Nodes
may also be mobile, with connectivity changing among nodes. This class of networks is
know as mobile ad hoc networks (MANETs). If the mobile nodes are vehicles, the
network is a vehicular ad hoc network (VANET).