This chapter is a survey about the wireless technologies that allows us to have self-configured and self-organized networks. This chapter highlights the design factors, architectures, characteristics and the advantages of the self configured networks. Also a comparison between WMN and MANET is presented in this chapter. Application domain of WMN is discussed in the end of the chapter.
2.1 Wireless Networks
One of the most promising and discussed technologies in the past decade is the wireless communication technology which allows each users to utilize devices that enable the access to information at any place any time. These demands make wireless communication networks the best solution for inter connect the devices and people worldwide. Unlike wired communication networks, which are comprised of devices that can communicate through wires, wireless networks are comprised of devices that communicate through media such as infra-red and radio signals. Wireless networks are generally classified into two categories: infrastructure-based and infrastructure less network (ad hoc wireless networks).
Infrastructure-based wireless network consists of base stations system located in expedient places, which provide wireless connectivity coverage to devices within their region. Such devices which provide wireless connectivity are called as access points (AP). Examples of this type are cellular networks and Wireless Local Area Networks (WLANs). A WLAN is a reliable data communication system implemented as an extension to a wired LAN system within a building, a campus or office.
On the other hand, mobile ad hoc wireless networks do not have a pre-established infrastructure scenario. Moreover, mobile nodes connect to each other through automatic configuration when they are in transmission range and keen to forward data for other nodes. In this way, an ad hoc wireless network is fashioned which is both flexible and dominant. Therefore, these capabilities make wireless ad hoc networks appropriate for many applications where one central node may not be well-located, and where minimal configuration and quick deployment is required in crisis situations. Wireless ad hoc networks can be further classified by their application in mobile ad hoc networks, wireless mesh networks and wireless sensor network .
2.2 The IEEE 802.11
In this section I emphasized the basics of the IEEE 802.11 standard that identify the wireless communication. 802.11 specifies the physical and MAC layer adapted to the special needs of wireless networks but offers same interface as the other standards to higher layers to maintain interoperability . Many concepts and definitions are needed in order to better understand the standard. The specifications details can be found in .
2.2.1 IEEE 802.11 Architectures
The IEEE 802.11 architecture comprise of numerous devices and services that interact to provide wireless communication to stations which are any component that uses the functionality of the IEEE 802.11 protocol and connect to the wireless media devices. The IEEE 802.11 standard specifies three primary steps. The first setup is a Basic Service Station (BSS), which is defined as a group of base stations that communicates with each other in a geographical area or cell known as Basic Service Area (BSA). When these base stations can communicate without the need of an infrastructure network, they are called to as an Independent Basic Service Set (IBSS) which is the common name of an ad hoc network in the IEEE 802.11 standard. These stations operate in the ‘ad hoc mode’ because they interact directly with another node in their transmission range.
In comparison, in the ‘infrastructure mode’, a station in a Base Service Station communicates with another through a Base Station (BS) which is also called Access Point (AP) if it is connected to a wired network. The Base service station operating with a Base Station is known as the Infrastructure Basic Service (IBS).
In addition, a different setup known as Extended Service Set (ESS) can be created. In this setup, Base Stations (or APs) provide the integration points for network connectivity in the midst of different BSSs. Thus, a network backbone, also known as distributed system (DS), is formed. The Distributed System is responsible for Media Access level transport of MAC data units, and is implemented independent meaning that the DS could be a wired Local area network (LAN), Metropolitan area network (MAN), or another IEEE 802.11 standard. In the infrastructure mode, a base station needs to join a BSS to communicate with one another. It obtains synchronization information from periodic message from the Base Station. It can either get this information by requesting this from the BS (active probing), or it can wait for the periodic message from the Base Station. Before being able to send and receive data, the station has to go through a validation and association process. The IEEE 802.11 standard do not only defines a Medium Access Control (MAC), but also the interrelated management protocols and services, and the physical layer. Also, important timing intervals are specified by the standard and they are:
‘ Short Inter-frame space (SIFS): It is the shortest time interval. It is used amid a frame and its acknowledgment. It is elongated enough for the sender to relay to the receiver mode.
‘ Slot time (Slot): A modest longer than SIFS, it is the basic time unit for the binary exponential back-off algorithm spell out in the standard.
‘ PCF inter-frame space (PIFS): It is equal to the SIFS along with one Slot. It is used by the Point Coordinator to obtain higher precedence in accessing the medium.
‘ Distributed inter-frame space (DIFS): It is equal to the SIFS along with two Slots. It is used earlier than starting a new transmission.
...(download the rest of the essay above)