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Wireless Communication - WAN
In the field of computers, the wide usage of group connections have become inevitable, which lead to the introduction of LANs (Local Area Networks). These LANs come under the category of small scale networks within a single building or campus.
WANs are Wide Area Networks which cover a wider area such a city, or a limited area greater than LAN. Wireless Personal Area Networks (PANs) are the next step down from WLANs, covering smaller areas with low power transmission, for networking of portable and mobile computing devices such as PCs, Personal Digital Assistants (PDAs).
Fundamentals of WLANs
The technical issues in WLANs must be understood in order to appreciate the difference between wired networks and wireless networks. The use of WLANs and their design goals are then studied. The types of WLANS, their components and their basic functionalities are also detailed.
IEEE 802.11 Standard
This section introduces a prominent standard ion WLANs, the IEEE 802.11 standard. The medium access control (MAC) layer and the physical layer mechanisms are explained. This section also covers some of the optional functionalities such as security and quality of service (QoS).
This section describes another WLAN standard, HIPERLAN standard, which is a European standard based on radio access.
This section deals with the Bluetooth standard, which enables personal devices to communicate with each other in the absence of infrastructure.
While both portable terminals and mobile terminals can move from one place to another, portable terminals are accessed only when they are stationary.
Mobile Terminals (MTs), on the other hand, are more powerful, and can be accessed when they are in motion. WLANs aim to support truly mobile work stations.
Wireless computer networks are capable of offering versatile functionalities. WLANs are very flexible and can be configured in a variety of topologies based on the application. Some possible uses of WLANs are described below.
Users would be able to surf the Internet, check e-mail, and receive Instant Messages on the move.
In areas affected by earthquakes or other disasters, no suitable infrastructure may be available on the site. WLANs are handy in such locations to set up networks on the fly.
There are many historic buildings where there has been a need to set up computer networks. In such places, wiring may not be permitted or the building design may not be conductive to efficient wiring. WLANs are very good solutions in such places.
The following are some of the goals which have to be achieved while designing WLANs −
Operational simplicity − Design of wireless LANS must incorporate features to enable a mobile user to quickly set up and access network services in a simple and efficient manner.
Power efficient operation − The power-constrained nature of mobile computing devices such as laptops and PDAs necessitates the important requirement of WLANs operating with minimal power consumption. Therefore, the design of WLAN must incorporate power-saving features and use appropriate technologies and protocols to achieve this.
License-free operation − One of the major factors that affects the cost of wireless access is the license fee for the spectrum in which a particular wireless access technology operates. Low cost of access is an important aspect for popularizing a WLAN technology. Hence the design of WLAN should consider the parts of the frequency spectrum. For its operation which does not require an explicit
Tolerance to interference − The proliferation of different wireless networking technologies both for civilian and military applications have led to a significant increase in the interference level across the radio spectrum.
The WLAN design should account for this and take appropriate measures by way of selecting technologies and protocols to operate in the presence of interference.
Global Usability − The design of the WLAN, the choice of technology, and the selection of the operating frequency spectrum should take into account the prevailing spectrum restriction in countries across the world. This ensures the acceptability of the technology across the world.
Security − The inherent broadcast nature of wireless medium adds to the requirement of security features to be included in the design of WLAN technology.
Safety requirements − The design of WLAN technology should follow the safety requirements that can be classified into the following.
- Interference to medical and other instrumentation devices.
- Increased power level of transmitters that can lead to health hazards.
A well-designed WLAN should follow the power emission restrictions that are applicable in the given frequency spectrum.
Quality of service requirements − Quality of Service (QoS) refers to the provisioning of designated levels of performance for multimedia traffic. The design of WLAN should take into consideration the possibility of supporting a wide variety of traffic, including multimedia traffic.
Compatibility with other technologies and applications − The interoperability among different LANS is important for efficient communication between hosts operating with different LAN technologies.
Network architecture describes the types of WLANs, the components of a typical WLAN and the services offered by a WLAN.
Infrastructure based versus Ad Hoc LANs
WLANs can be broadly classified into two types, namely Infrastructure networks and Ad hoc LANs, based on the underlying architecture.
Infrastructure networks contain special nodes called Access Points (APs), which are connected via existing networks.
- APs are special in the sense that they can interact with wireless nodes as well as with the existing wired network.
- The other wireless nodes, also known as Mobile stations (STAs), communicate via APs.
- The APs also act as bridges with other networks.
Ad hoc LANs
Ad hoc LANs do not need any fixed infrastructure. These networks can be set up on the fly at any place. Nodes communicate directly with each other for forward messages through other nodes that are directly accessible.