Mobile Computing Unit 2 :: Part 1
Wireless LANs and Application
Early wireless LAN products, introduced in the late 1980s, were marketed as substitutes for traditional wired LANs. A wireless LAN saves the cost of the installation of LAN cabling and eases the task of relocation and other modifications to network structure. In a number of environments, there is a role for the wireless LAN as an alternative to a wired LAN. Examples include buildings with large open areas, such as manufacturing plants, stock exchange trading floors, and warehouses; historical buildings with insufficient twisted pair wiring or where drilling holes for new wiring is prohibited; and small offices where installation and maintenance of wired LANs is not economical. In all of these cases, a wireless LAN provides an effective and more attractive alternative. In most of these cases, an organization will also have a wired LAN to support servers and some stationary workstations. For example, a manufacturing facility typically has an office area that’s separate from the factory floor but that must be linked to it for networking purposes. Therefore, typically, a wireless LAN will be linked into a wired LAN on the same premises. Thus, this application area is referred to as a LAN extension.
A wireless local area network (WLAN) is a wireless distribution method for two or more devices that use highfrequency radio waves and often include an access point to the Internet. A WLAN allows users to move around the coverage area, often a home or small office, while maintaining a network connection.
A WLAN is sometimes call a local area wireless network (LAWN).
In the early 1990s, WLANs were very expensive and were only used when wired connections were strategically impossible. By the late 1990s, most WLAN solutions and proprietary protocols were replaced by IEEE 802.11 standards in various versions (versions “a” through “n”). WLAN prices also began to decrease significantly.
WLAN should not be confused with the Wi-Fi Alliance’s Wi-Fi trademark. Wi-Fi is not a technical term, but is described as a superset of the IEEE 802.11 standard and is sometimes used interchangeably with that standard. However, not every Wi-Fi device actually receives Wi-Fi Alliance certification, although Wi-Fi is used by more than 700 million people through about 750,000 Internet connection hot spots.
Every component that connects to a WLAN is considered a station and falls into one of two categories: access points (APs) and clients. APs transmit and receive radio frequency signals with devices able to receive transmitted signals; they normally function as routers. Clients may include a variety of devices such as desktop computers, workstations, laptop
computers, IP phones and other cell phones and Smartphones. All stations able to communicate with each other are called basic service sets (BSSs), of which there are two types: independent and infrastructure. Independent BSSs (IBSS) exist when two clients communicate without using APs, but cannot connect to any other BSS. Such WLANs are called a peer-to-peer or an ad-hoc WLANs. The second BSS is called an infrastructure BSS. It may communicate with other stations but only in other BSSs and it must use APs.
Different methods and standards of wireless communication have developed across the world, based on various commercially driven requirements. These technologies can roughly be classified into four individual categories, based on their specific application and transmission range. These categories are summarised in the figure below.
A wireless LAN (or WLAN, for wireless local area network, sometimes referred to as LAWN, for local area wireless network) is one in which a mobile user can connect to a local area network (LAN) through a wireless (radio) connection. The IEEE 802.11 group of standards specify the technologies for wireless LANs. 802.11 standards use the Ethernet protocol and CSMA/CA (carrier sense multiple access with collision avoidance) for path sharing and include an encryption method, the Wired Equivalent Privacy algorithm. High-bandwidth allocation for wireless will make possible a relatively low-cost wiring of classrooms in the United States. A similar frequency allocation has been made in Europe. Hospitals and businesses are also expected to install wireless LAN systems where existing LANs are not already in place. Using technology from the Symbionics Networks, Ltd., a wireless LAN adapter can be made to fit on a Personal Computer Memory Card Industry Association (PCMCIA) card for a laptop or notebook computer.
Infrared Vs Radio Transmission:-
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- An ad-hoc network is a local area network (LAN) that is built spontaneously as devices connect. Instead of relying on a base station to coordinate the flow of messages to each node in the network, the individual network nodes forward packets to and from each other. In Latin, ad hoc literally means “for this,” meaning “for this special purpose” and also, by extension, improvised or impromptu.
- In the Windows operating system, ad-hoc is a communication mode (setting) that allows computers to directly communicate with each other without a router.
Wireless application protocol (WAP) is a communications protocol that is used for wireless data access through most mobile wireless networks. WAP enhances wireless specification interoperability and facilitates instant connectivity between interactive wireless devices (such as mobile phones) and the Internet.
WAP functions in an open application environment and may be created on any type of OS. Mobile users prefer WAP because of its ability to efficiently deliver electronic information.
The WAP cascading style sheet (CSS) is a mobile rendering of the World Wide Web that allows developers to format screen sizes for mobile device adaptability. Reformatting is not required when using WAP CSS content, which controls page layout compatibility with a variety of mobile device display screens.
The core interface of WAP architecture is the WAP datagram protocol, which manages the transmission layer protocols of Internet models and facilitates operations between mobile wireless networks and platforms, independent of upper layer protocols. The transport layer deals with physical network issues, allowing wireless global operations to readily access wireless gateways. A WAP gateway is a server that facilitates wireless network access.
The WAP Forum, now known as the Open Mobile Alliance (OMA), provides WAP tool testing, specification development and support for all mobile services.
Mac Issues Wireless LAN:-
Mobile IP is an Internet Engineering Task Force (IETF) standard communications protocol that is designed to allow mobile device users to move from one network to another while maintaining their permanent IP address. Defined in Request for Comments (RFC) 2002, Mobile IP is an enhancement of the Internet Protocol (IP) that adds mechanisms for forwarding Internet traffic to mobile devices (known as mobile nodes) when they are connecting through other than their home network.
In traditional IP routing, IP addresses represent a topology. Routing mechanisms rely on the assumption that each network node will always have the same point of attachment to the Internet, and that each node’s IP address identifies the network link where it is connected. Core Internet routers look at the IP address prefix, which identifies a device’s network. At the network level, routers look at the next few bits to identify the appropriate subnet. Finally, at the subnet level, routers look at the bits identifying a particular device. In this routing scheme, if you disconnect a mobile device from the Internet and want to reconnect through a different subnet, you have to configure the device with a new IP address, and the appropriate netmask and default router. Otherwise, routing protocols have no means of delivering packets because the device’s IP address doesn’t contain the necessary information about the current point of attachment to the Internet.
All the variations of Mobile IP assign each mobile node a permanent home address on its home network and a care-of address that identifies the current location of the device within a network and its subnets. Each time a user moves the device to a different network, it acquires a new care-of address. A mobility agent on the home network associates each permanent address with its care-of address. The mobile node sends the home agent a binding update each time it changes its care-of address using Internet Control Message Protocol (ICMP). In Mobile IPv4, traffic for the mobile node is sent to the home network but is intercepted by the home agent and forwarded via tunneling mechanisms to the appropriate care-of address. Foreign agents on the visited network help to forward datagrams. Mobile IPv6 was developed to minimize the necessity for tunneling and to include mechanisms that make foreign agents unnecessary.
Enhancements to the Mobile IP standard, such as Mobile IPv6 and Hierarchical Mobile IPv6 (HMIPv6), were developed to advance mobile communications by making the processes involved less cumbersome. Although the North American mobile trend is not moving as quickly as some other markets, the growing adoption of mobile communications elsewhere is likely to drive acceptance globally. According to a Gartner Group report, by 2004 40% of all business-tobusiness (B2B) transactions outside of North America will be initiated by mobile devices.