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.
