24-03-2012, 03:08 PM
Wireless Network
Ad-Hoc Wireless Networking_updated.doc (Size: 368 KB / Downloads: 26)
Ad-Hoc Mode in Wireless Networking
On wireless computer networks, ad-hoc mode is a method for wireless devices to directly communicate with each other. Operating in ad-hoc mode allows all wireless devices within range of each other to discover and communicate in peer-to-peer fashion without involving central access points (including those built in to broadband wireless routers).
To set up an ad-hoc wireless network, each wireless adapter must be configured for ad-hoc mode versus the alternative infrastructure mode. In addition, all wireless adapters on the ad-hoc network must use the same SSID and the same channel number.
An ad-hoc network tends to feature a small group of devices all in very close proximity to each other. Performance suffers as the number of devices grows, and a large ad-hoc network quickly becomes difficult to manage. Ad-hoc networks cannot bridge to wired LANs or to the Internet without installing a special-purpose gateway.
Ad hoc networks make sense when needing to build a small, all-wireless LAN quickly and spend the minimum amount of money on equipment. Ad hoc networks also work well as a temporary fallback mechanism if normally-available infrastructure mode gear (access points or routers) stop functioning.
Infrastructure mode in wireless networking
Infrastructure mode wireless networking bridges (joins) a wireless network to a wired Ethernet network. Infrastructure mode wireless also supports central connection points for WLAN clients.
A wireless access point (AP) is required for infrastructure mode wireless networking. To join the WLAN, the AP and all wireless clients must be configured to use the same SSID. The AP is then cabled to the wired network to allow wireless clients access to, for example, Internet connections or printers. Additional APs can be added to the WLAN to increase the reach of the infrastructure and support any number of wireless clients.
Compared to the alternative, ad-hoc wireless networks, infrastructure mode networks offer the advantage of scalability, centralized security management and improved reach. The disadvantage of infrastructure wireless networks is simply the additional cost to purchase AP hardware.
Ad hoc Network
Ad hoc networks, which are also called mesh networks, are defined by the manner in which the network nodes are organized to provide pathways for data to be routed from the user to and from the desired destination. Actually, the two names ascribed to these networks provide considerable insight. Ad hoc has two definitions—the first can be either “impromptu” or “using what is on hand,” while the other is “for one specific purpose.” For example, members of an ad hoc committee (studying a specific issue) might discover that they are attending the same event and decide to have an ad hoc (impromptu) meeting.
Ad hoc networks follow both definitions, as well. They are formed as they are needed (impromptu), using resources on hand, and are configured to handle exactly what is needed by each user—a series of “one specific purpose” tasks.
Routing Protocols
Routing protocols between any pair of nodes within an ad hoc network can be difficult because the nodes can move randomly and can also join or leave the network. This means that an optimal route at a certain time may not work seconds later. Discussed below are three categories that existing ad-hoc network routing protocols fall into:
1. Table Driven Protocols
2. On Demand Protocols
3. Hybrid Protocols