18-03-2011, 06:32 PM
|
| M.Arsalan Qureshi | | Join Date: Oct 2008 Location: Garden Town, Multan Cantt
Posts: 616
Program / Discipline: BSTS Class Roll Number: 09-31 | |
Connecting LANs, Backbone Networks, and Virtual LANs Connecting LANs, Backbone Networks, and Virtual LANs * The IEEE 802.11 standard for wireless LANs defines two services: basic service set (BSS) and extended service set (ESS). An ESS consists of two or more BSSs; each BSS must have an access point (AP). * The physical layer methods used by wireless LANs include frequency-hopping spread spectrum (FHSS), direct sequence spread spectrum (DSSS), orthogonal frequency-division multiplexing (OFDM), and high-rate direct sequence spread spectrum (HR-DSSS). * FHSS is a signal generation method in which repeated sequences of carrier frequencies are used for protection against hackers. * One bit is replaced by a chip code in DSSS. * OFDM specifies that one source must use all the channels of the bandwidth. * HR-DSSS is DSSS with an encoding method called complementary code keying (CCK). * The wireless LAN access method is CSMA/CA. * The network allocation vector (NAV) is a timer for collision avoidance. * The MAC layer frame has nine fields. The addressing mechanism can include up to four addresses. * Wireless LANs use management frames, control frames, and data frames. * Bluetooth is a wireless LAN technology that connects devices (called gadgets) in a small area. * A Bluetooth network is called a piconet. Multiple piconets form a network called a scatternet. * The Bluetooth radio layer performs functions similar to those in the Internet model's physcial layer. * The Bluetooth baseband layer performs functions similar to those in the Internet model's MAC sublayer. * A Bluetooth network consists of one master device and up to seven slave devices. * A Bluetooth frame consists of data as well as hopping and control mechanisms. A fram is one, three, or five slots in length with each slot equal to 625 µs.
__________________ |