关于进一步加强预应力混凝土管桩推荐.pptVIP

* * Connection Establishment * * Piconets and Scatternets Two or more Bluetooth units that share a FH channel form a piconet. At most 1 master and 7 slaves can be in one piconet Any unit can become a master, but by definition the paging unit that establishes the piconet is the master The master identity and clock specify the channel parameters All devices in a piconet are synchronized to the same FH sequence Up to 10 piconets can co-exist with overlapping coverage areas and form a scatternet A unit can be a master in one piconet and a slave in another, or slave in several piconets * * Power Management Frequency-hopping mechanism provides synchronization between master-slaves therefore no dummy packets have to be exchaged A receiver can quickly decide whether a packet is present or not, by the access code and the header and sleep for the rest of the slot Power-save modes: HOLD mode, where no communication is possible for a specified hold time SNIFF mode, where the slave listens only to some slots (depends on the application) PARK mode, where the slave listens to the master’s beacon at large intervals to re-synchronize, does not have a MAC address and does not participate in the traffic * * Modes of operation * * Security As radio signals can be easily intercepted, Bluetooth devices have built-in security to prevent eavesdropping or falsifying the origin of messages (spoofing) The main security features are: a challenge-response routine – for authentication stream cipher – for encryption session key generation – session keys can be exchanged during a connection * * Competing Technologies Infrared Data Association (IrDA) vs Bluetooth IEEE 802.11b vs Bluetooth * * IrDA vs Bluetooth Wireless Standard IrDA already proven standard (50 million units) Bluetooth still in development Data Transfers IrDA up to 4Mbps; 16Mbps( under development) Bluetooth 1Mbps(max) 721Kbps(average) Range IrDA – 3 feet Bluetooth - 30 feet (or more) Line of Sight Required for IrDA, can be adv