High-Speed Wireless ATM and LANsby Benny Bing
Understand the technological issues associated with wireless local area networks (WLANs) as a means of providing cable-free data access, easy upgrading and flexible reconfiguration compared to the extensive multimedia and intensive application support provided by terrestrial and satellite asynchronous transfer mode (ATM) networks using this new resource. You see
Understand the technological issues associated with wireless local area networks (WLANs) as a means of providing cable-free data access, easy upgrading and flexible reconfiguration compared to the extensive multimedia and intensive application support provided by terrestrial and satellite asynchronous transfer mode (ATM) networks using this new resource. You see the benefits and the issues related to developing wireless ATM and get a comprehensive overview of both WLAN and WATM technologies, as well as their global standards, performance evaluations of the two network options, and the pros and cons of each, written by an acknowledged expert in the fields of wireless communications and high-speed networking.
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3.5.7 Mobile Internet support
The World Wide Web (WWW) is perhaps the largest source of distributed information. The network that drives the Web is the Internet. While the size of the Internet has been increasing at a rapid rate, the use of the Web has grown at an explosive pace. With the advent of dynamic content (e.g., HTML, CGI, XML) and executable content (e.g., Java), the Web is poised to play a central role in the process of making information ubiquitously accessible. The Internet runs on internetworking devices called routers that forward network layer Internet Protocol (IP) packets among networks with different link layers. Managing the network layer is much more flexible than the link layer since network administrators can assign structured IP addresses as opposed to unstructured MAC (link layer) addresses. However, mobile computing poses a problem if nodes with fixed IP addresses are moved from one location to another. Although a wireless LAN provides mobility support with roaming services, true mobility for large IP networks can only be realized if the IP addresses are assigned dynamically. This is because IP addresses are location dependent and therefore need to be changed to reflect the different locations of a mobile node. Hence, the problem of mobility in IP networks lies with the way IP addresses are structured, with or without wireless connectivity. Dynamic allocation of IP addresses is usually applied to mobile nodes and not to wireless access points since the access points occupy static (fixed) locations.
The dynamic host configuration protocol (DHCP) is one method of configuring IP addresses dynamically regardless of location. A dynamically assigned IPaddress is known as an active lease. The active lease usually has an expiration date, which allows automatic reallocation of IP addresses that are no longer in use. Thus, DHCP relieves the administrative burden of managing IP addresses in addition to providing mobile IP addresses. When DHCP is implemented on a wired IP network, a mobile client is able to connect to the network in different locations (e.g., in different subnets). This is achieved by physically disconnecting the network cable from a fixed outlet or socket and reconnecting at the new site. Hence, ongoing connections will have to be broken when a client on a wired network moves to a new location. However, when DHCP is applied to wireless LANs, IP connections can be maintained (and applications can continue to run) even as a mobile client changes location. This removes the need to log in and out of the network. Thus, wireless LANs with mobile IP addresses can provide continuous and location independent access to Internet services.
Chapter 3: Wireless LAN Implementation3.5.8 Load balancing
Load balancing allows wireless LANs to serve greater loads more efficiently. Each access point can monitor the traffic load within its coverage area and then try to balance the number of nodes serviced according to the traffic load in adjacent access points. To achieve this, access points must exchange traffic load information through the backbone network. Most load balancing methods do not depend on signal strength as this may complicate the roaming algorithm. Typically, roaming has priority over load balancing since a mobile node must first be able to connect to an access point with reasonable signal quality/ strength before load balancing can be performed.
3.5.9 Securing wireless access
The free-space wireless link is more susceptible to eavesdropping, fraud, and unauthorized transmission than its wired counterpart. Being an open medium with no precise bounds makes it impractical to apply physical security like in wired networks. Nevertheless, several alternative security mechanisms can be used to prevent unauthorized access of data transmitted over a wireless LAN. These are:
- Encrypting all data transmitted via the wireless link;
- Closing the network to all nodes that have not been programmed with the correct network identification;
- Restricting access within a wireless LAN by listing only those nodes that are allowed to transmit data;
- Implementing passwords in network operating systems.
Portable wireless LAN devices rely on limited battery power to conduct communications over a wireless link that is prone to error bursts due to fading and other propagation impairments. As current battery research does not predict a substantial change in the available energy in a consumer battery, it is crucial that wireless mobile devices are designed to be efficient in energy usage. Minimizing energy usage is a significant constraint since it impacts design at all levels of network control. There has been substantial research in energy-efficient hardware (e.g., low power electronics, processor sleep-time, and powerefficient modulation) for mobile communications. However, due to fundamental physical limitations, progress towards further efficiency will become mostly a software-level issue. In wireless LANs, the software protocol can be designed to allow an idle network device to turn off its receiver most of the time, thereby saving considerable amounts...
Meet the Author
Benny Bing is with the Department of Electrical and Computer Engineering at the University of Maryland. He has worked for Singapore Telecom, Hewlett Packard, and AT&T Global Information Solutions, and received his M. Eng. from Nanyang Technological University in Singapore. He served as a member of the international advisory committee of the IEEE International Conference on ATM and has been guest editor of IEEE Communications Magazine.
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